摘要:

21 Organometallic Chemistry of Monometallic Species By P.K. BAKER Department of Chemistry University of Wales Bangor Gwynedd LL57 2UW UK 1 Introduction Important reviews have appeared on monometallic organo transition-metal complexes containing carbon monoxide as a Q donor,' tcne tcnq and related polynitrile n acceptors,' and water3 as a ligand. Reviews on TiCp carboxylates and related cornplexe~,~ ZrI'Cp and Hf'"Cp compounds with Si Ge Sn N P As Sb 0,S Se Ts. or transition-metal centred anionic ligand~,~ palladium@) and platinum(I1) five-coordinate alkene complexes,6 and metallocyclobutane complexes of the Group sight transition metals7 have appeared. Reviews concerning transition metals in the chemistry of vinylcyclopropanes* and the activation of carbon-fluorine bonds' have been published.Reviews have also been published on the patterns of stoichiometric and catalytic reactions of organozirconium and related complexes,1o recent advances in the chemistry and applications of high oxidation state alkylidene complexes,' 'the uses of irontricarbonyl lactone complexes in organic synthesis,' 'and sulfoxides and stereochemical control in organometallic chemistry.' How orientations of alkene alkyne and alkylidene ligands reveal n-bonding features in tetrahedral transition- metal complexes has also been reviewed.14 2 Ti Zr and Hf The synthesis and X-ray crystal structure of the first tris(naphtha1ene) complex [Zr(y4-naphthalene),]' -,which is also the first structurally characterized homoleptic naphthalene metalate have been described.I5 The preparations of the first isolable F.Aubke and C. Wang Coord. Chem. Rev. 1994 137,483. 'W. Kaim and M. Moscherosch Coord. Chem. Rev. 1994 129 157. U. Koelle Coord. Chem. Rev. 1994 1351136 623. Y. Dang Coord. Chem. Rev. 1994 1351136 93. E. Hey-Hawkins Chem. Rev. 1994 94 1661. 'V.G. Albano G. Natile and A. Panuzi Coord. Chem. Rev. 1994 133 67. -P. W. Jennings and L. L. Johnson Chem. Rev. 1994 94 2241. R.I. Khusnutdinov and U.M. Dzhemilev J. Organomet. Chem. 1994 471 1. J. L. Kiplinger T. G. Richmond and C. E. Osterberg Chem. Rev. 1994 94 373. E. Negishi and T Takahashi Acc. Chem. Res. 1994 27 124. R. R. Schrock Pure Appl. Chem. 1994 66 1447. '' S.V. Ley Pure Appl. Chem. 1994 66 1415.l3 S. L. Griffiths C. F. Marcos S. Perrio S. P. Saberi S. E. Thomas G. J. Tustin and A. T. Wierzchleyski Pure Appl. Chem. 1994 66 1565. l4 V.C. Gibson Angew. Chem. lnt. Ed. Engl. 1994,33 1565. M. Jang and J. E. Ellis Angew. Chem. Int. Ed. Engl. 1994 33 1973. 38 1 382 P. K. Baker terminal carbonyl complexes of zirconium (~v) [Zr(CO)(q 3-C ,H 5)Cp;] [BPh,] (crys- tallographically characterized)' and [Zr (CO)(q -COMe)(q-C R 5)] [BMe(C6F5)3] (R = H Me) which has been characterized by X-ray crystallography for the '0-outside' and methyl i~omer,'~ have been reported. A series of catalytically active base-free zirconium methyl and benzyl complexes has been prepared including the zwitterionic compound [ZrMe{ 1 ,3-C5H3(SiMe3),) ,(p-Me)B(C,F,),] which has been crystallographically characterized.' Reaction of cytostatically active titanocene dichloride with a-amino acids gives the first titanium@) a-amino acid complexes [Ti(a-amino acid),Cp,]Cl, of which the a-2-methylalanine example was crystallo- graphically characterized.' The newly prepared ansa-bridged complexes [ZrClCp{ (CH,),C(q5-C5H,)(q2-c9H6))] [ZrC1Cp{Me,C(q5-C5H,)(q3-and C13H8))] show unusual modes of attachment of the indenyl or fluorenyl moieties.20 The first quantitative and stereoselective synthesis of rac-metallocenes such as (1) [M = Zr Y = NPh C5H (both crystallographically characterized); M = Hf Y = NPh] have been described." Treatment of [Zr(py)(q2-Me,SiC,SiMe,)Cp2J with Bu'C,C,Bu' gives the smallest possible cyclic cumulene (2) which has been crystallographically characterized., The preparation and molecular structure of the unusual zirconocene complex (3) containing two alkynes have been reported.23 Reaction of [ZrCl,Cp*] with [Li(tmeda)],[tmm] (tmm = trimethylenemethane) gives the distorted y4-bonded trimethylenemethane complex (4),," whereas reaction of [ZrCI,Cp;] with [Li(tmeda)] ,[tmm] affords the q3-bonded trimethylenemethane complex (S).' 3 V Nb and Ta The first stable mononuclear tantalum(o) carbonyl compound [Ta(CO),(dppe)] has been prepared.26 The a-agostic n-ethyl and n-propyl compounds [NbCl(p-H- CHR)(q2-PhC,R')Tp'] (R = Me Et; R' = Me Et Pr") undergo thermolytic exchange l6 D.M. Antonelli E. B. Tjaden and J. M. Stryker Organometallics 1994 13 763.l7 Z. Guo D. C. Swenson A. S. Guram and R. F. Jordan Organometallics 1994 13 766. M. Bochmann S. J. Lancaster M. B. Hursthouse and K. M. A. Malik Organometallics 1994 13 2235. l9 T. M. Klapotke H. Kopf,I. C. Tornieporth-Oetting,and P. S. White,Angew. Chem. Int. Ed. Engl. 1994,33 1518. 2o G. M. Diamond M. L. H. Green P. Mountford N. A. Popham and A. N. Chernega J. Chem. Soc. Chem. Commun. 1994 103. 21 W.A. Herrmann M. J. A. Morawietz and T. Priermeier Angew. Chem. Int. Ed. Engl. 1994 33 1946. 22 U. Rosenthal A. Ohff W. Baumann R. Kempe A. Tillack and V. V. Burlakov Angew. Chem. Int. Ed. Engl. 1994 33 1605. 23 B.P. Warner W. M. Davis and S. L. Buchwald J. Am. Chem. SOC.,1994 116 5471. 24 G.C. Bazan G. Rodriguez and B.P. Cleary J. Am. Chem. SOC. 1994 116 2177.25 G.E. Herberich C. Kreuder and U. Englert Angew. Chem. Int. Ed. Engl. 1994 33 2465. 26 M.D. Koeslag and M. C. Baird Organometallics 1994 13 11. Organometallic Chemistry of Monometallic Species !$Me (3) (4) of the Nb and the alkyne-bonded alkyl groups to afford [NbC1R'(q2-PhC,CH,R)Tp'] via the unprecedented metathesis of metalkarbon and carbon-carbon bonds.27 The sequential removal of chloride ions from [NbCl,Cp] using SbC1 in acetonitrile yields a series of novel cationic niobium(v) complexes including the 'double' [SbCl,] -salt [NbCl(NCMe),Cp]3+[Nb(NCMe)6Cp]4+[SbCl,],.7NCMe, which has been crystallographically characterized.28 Reaction of [V(NAr)(PMe,),Cp] [Ar = 2,6-C,H,(CHMe,),] with Ph,P=CHPh gives the crystallographically characterized complex [V(=CHPh)(NAr)(PMe,)Cp] which is the first vanadium(v) alkylidene complex to be rep~rted.~' The synthesis molecular structure and reactions with water and methanol of the cationic ketinimine complex (6)have been described.,' Treatment of [MH(CO)Cp;] (M = Nb Ta) with 0 affords the metal formato complexes [M(O)(q'-O,CH)Cp;] apparently via the CO complexes [MH(q2-C0,)Cp;].31 The first thermally stable Group 5 dihydrogen complex [Ta(q2-H,)(CO)Cp,] [BF,] has been prepared.4 Cr Mo and W The preparation and isolation of the crystallographically characterized complex [Cr(q2-H2)(C0),(PPr'),] which has the shortest ligated H-H bond length have been 27 M. Etienne F. Biasotto and R. Mathieu J. Chem. SOC. Chem. Commun. 1994 1661. 28 G.R. Willey M. L. Butcher T.J. Woodman and M. G. B. Drew J. Chem. SOC. Chem. Commun. 1994 2721. 29 J.-K.F. Buijink J.H. Teuben H. Kooijman and A.L. Spek Organometallics 1994 13 2922. 30 A. Antiiiolo M. Fajardo R. Gil-Sanz C. Lopez-Mardomingo A. Otero A. Atmani M. M. Kubicki S. El Krami Y. Mugnier and Y. Mourad Organometallics 1994 13 1200. 31 P.-F. Fu A. K. Fazlur-Rahman and K. M. Nicholas Organometallics 1994 13 413. 32 S. Sabo-Etienne B. Chaudret H. Abou el Makarim J.-C. Barthelat J.-P. Daudey C. Moi'se and J.-C. Leblanc J. Am. Chem. Soc. 1994 116,9335. 384 P. K. Baker described., Reaction of [Mo(CO){R,P(CH,),PR,},] (R = Et CH,Ph Ph) with SiH,R’R” gives a series of y2-silane complexes ~~s-[Mo(CO){R,P(CH,)~PR~}~(~~-HSiHR‘R”)] which has been crystallographically characterized for R = Et R’ = H R” = Ph., The synthesis and crystallographic characterization of the complex- stabilized alkynyl [Cr(CO),(CENCGCPh)] and cyclobutenyl (7) complexes have been reported.35 Treatment of [M{=C(OEt)CH2Li}(CO),1 (M = Cr W) with PCl(NPr’,) affords the P-H functionalized ylide-carbene complexes (8) (crystallo-graphically characterized for the chromium case) via transient (a-(phosphino)alkyl} carbene complexes.36 The electrochemical reduction of trans-[WCl(CN)(dppe),] in the presence of phenol yields the crystallographically characterized complex trans-[WCl(CNH,)(dppe),] which when oxidized chemically or electrochemically gives the crystallographically characterized paramagnetic cation trans-[WCl(CNH,)(dppe),] [BF,].The X-ray results indicate that the CNH group at both the 18 and 17-electron tungsten centres is best described as an iminomethylenium (=C=NHl) ion.37 Reaction of [WC1{N(CH,CH2NSiMe,),)1 with Li[CH,R] (R = Me Pr SiMe, But) or K[CH,Ph] at room temperature affords the alkylidyne complexes [W=CR{N(CH,CH,NSiMe,),)I via spontaneous loss of H from the tungsten(1v) alkyl complexes [W (CH,R){ N(CH,CH,NSiMe,),}] .38 (CO)&l< Pt-NP* HH The preparation and molecular structure of the first 2H-1-aza-Zphosphirene complex (9) have been de~cribed.,~ Photolysis of the cisisomer of (10)yields trans-(lo) which is the first example of a metallo-crown ether in which the a,@-bis(phosphine) polyether ligand is trans ~oordinated.~’ Treatment of [Se(a-C,Me,),] with [M(CO),(thf)] (M = Cr W) yields the crystallographically characterized complexes [M(CO),(Se,(a-C,Me,),}] providing the first examples of selenide to diselenide 33 G.J. Kubas J. E. Nelson J. C. Bryan J. Eckert L. Wisniewski and K. Zilm Inorg. Chem. 1994,33,2954. 34 X.-L. Luo G. J. Kubas J.C. Bryan C. J. Burns and C. J. Unkefer J. Am. Chem. SOC.,1994,116 10312. 35 R. Kunz and W. P. Fehlhammer Angew. Chem. Int. Ed. Engl. 1994 33 330. 36 R. Streubel M. Hobbold J. Jeske and P.G. Jones J. Chem. Soc. Chem. Commun. 1994 2457. 37 D. L. Hughes S. K. Ibrahim H. Moh’d Ali and C. J. Pickett J. Chem. Soc. Chem. Commun. 1994,425. 38 K.-Y. Shih K. Totland S.W. Seidel and R. R. Schrock J. Am. Chem. Soc. 1994 116 12 103. 39 R. Streubel J. Jeske P. G. Jones and R.Herbst-Irmer Angew. Chem. Int. Ed. Engl. 1994 33 80. 40 G. M. Gray and C.H. Duffey Organometallics 1994 13 1542. Organometallic Chemistry of Monometallic Species 385 reduction within the coordination sphere of a transition metal and the first crystallographically characterized complexes to contain a terminal diselenide ligand.4' The synthesis and molecular structures of the anionic complexes [Na(2,2,2-crypt)] [MOS~,(CO),],~~[K(2,2,2-~rypt)],[CrP,(CO),].en~~and [K(2,2,2-crypt)13 [CrSb7(C0),]43 have been reported. Reaction of [W(CO),(PPr',),] with half a mole of RSSR (R = Me Ph p-tolyl CH,Ph) or I gives the stable radicals [W(SR)(CO),(PPrj),] or [WI(CO)3(PPr\)]2] respectively; the latter has been crystallographically ~haracterized.~~ Treatment of [WI,(=CHPh)(CO)(PMe,),] with CS and PPh gives the crystallographically characterized q2-phenylalkynyl complex [WI,(C0)(PMe,),(q2-PhC2SH)], which reacts with LiBu" and isocyanides to give the stable q2-thioketenyl complexes [WI(C0)(CNR)(PMe,),(q2-PhC,S)] (R = But 2,6-C,H3Me,) (crystallographically characterized for R = 2,6-C6H3Me2).45 Reaction of [W(CO),(NCMe)Tp'][BF,] (generated in situ) with NH or NH,Bu" gives the neutral complexes (11) (R = H Bu") by the amine-induced coupling of carbonyl and nitrile ligands; protonation of (11) at the acyl oxygen atom yields the cationic metallocycle hydroxycarbene complexes [W=C(OHbN(R)-C(Me)=N (H) (CO),Tp'][BF,] (R = H Bu") of which the n-butyl example was crystallographically ~haracterized.~~ Protonation of [WMe(CO)(q2-MeC,Ph)Tp'] in the presence of ketones (acetone 2-butanone acetophenone 3,3-dimethyl-2-butanone) or aldehydes (benzaldehyde trimethylacetaldehyde) gives the q'-ketone or q'-aldehyde products [W(CO)(q1-OCRR')(q2-MeC2Ph)Tp'] + ;further reaction with K[HBBui] yields the neutral alkoxide complexes [W(OCHRR')(CO)(q'-MeC,Ph)Tp']which was crystal- lographically characterized for R = H R' = Variable temperature 'H 13C and 31PNMR spectroscopy demonstrates that the 1 6-electron q3-2-met hall yl complex [MoH (q,-C4H7 )(dppe- IC~ P)(dppe-~P)] rapidly interconverts intramolecularly into the 18-electron q4-trimethylenemethane complex [M~H,(q~-C(CH,),}(dppe-k-~P)(dppe-~~P)] .48 Treatment of the cyclopropylcarbyne complexes [MoCrCCRCH,CH,)(P(OMe),),Cp] (R = H D Me) with HCl affords the diene complexes [MoCI(P(OMe),)(q4-CH,=CRCH=CH2)Cp], of which one of the methyl isomers has been crystallographically ~haracterized.~~ Condensation of 41 C.M.Bates C. P. Morley and M. Di Vaira J. Chem. Soc. Chem. Commun. 1994 2621 42 U. Bolle and W. Tremel J. Chem. SOC. Chem. Commun. 1994 217. 43 S. Charles B. W. Eichhorn A. L. Rheingold and S.G. Bott J. Am. Chem. Soc. 1994 116 8077. 44 R. F. Lang T. D. Ju G. Kiss C. D. Hoff J. C. Bryan and G.J. Kubas J. Am. Chern. Soc. 1994,116,7917. 45 T.-Y. Lee and A. Mayr J. Am. Chem. SOC.,1994 116 10 300. 46 S.G. Feng P.S. White and J. L. Templeton Organometallics 1994 13 1214. 41 J.L. Caldarelli L. E. Wagner P.S. White and J. L. Templeton J. Am. Chem. Soc.1994 116 2878. 48 R. A. Henderson and K. E. Oglieve J. Chem. Soc. Dalton Trans. 1994 767. 49 K. B. Kingsbury J. D. Carter L. McElwee-White R. L. Ostrander and A. L. Rheingold Organometallics 1994 13 1635. 386 P. K. Baker molybdenum vapour with the phosphaalkyne PGCBu' gives the crystallographically characterized complex tris(q4-2,4-di-t-butyl-l,3-diphosphacyclobutadiene)Mo(o).50 Reaction of [Mo(CO),(NCMe),(q5-C9H7)][BF4] with an excess of PECBu' yields the unusual q3-ligated 1,3-diphosphacyclobutadiene molybdenum complex [Mo (CO ) { P-q,-(Bu')CPC (Bu')PFBF ,} (q5-C9H7)] which has been characterized by X-ray ~rystallography.~ The first spin triplet ground state 16-electron complexes [MoClL,Cp*] (L = tertiary phosphine) have been prepared and preliminary studies of their reactivity have also been made.52 The stepwise hydrolysis of a terminal nitrosyl ligand has been achieved by reaction of [W(CH,SiMe,)(NCMe),(NO)Cp*][BF,] with one equivalent of H20 to give the crystallographically characterized complex [W(CH,SiMe,)(0)(q2-NH,0)Cp*][BF4] ;the latter reacts with one more equivalent of H20 to yield [W(CH,SiMe,)(O),Cp*] and [NH,0H][BF4].53 The synthesis of the first ansa-molybdenocene and tungstenocene complexes have been described including the X-ray crystallographically characterized complex [MOM~~(O(S~M~~C,H~),}].~~ Treatment of [MoBr(CO)(PR,)(q7-C7H7)](R = Me Ph) with a but-3-yn-l-ol/[NH4] [PF,] mixture in methanol gives the first examples of stable cycloheptatrienylmolyb- denum carbene complexes [Mo(CCH ,CH2CH ,O )(CO)(PR,)(q7-C 7H 7)] [PFJ.The reaction of [Cr(CO),(q7-C7H7)][BF4] with Ph,P(CH,),PPh (n = 1,2 and 4)at low temperature yields two new series of complexes the 7-exo ring adducts (12) (for n = 1,2) and the phosphine-linked binuclear species [{Cr(CO),(q6-C7H7)} 2{ 7,7'-exo-Ph,P(CH2)4PPh,}][BF,]2 which has been crystallographically ~haracterized.~ + 5 Mn Tc and Re Reaction of the cyclometalated complex [ReBr(CO),{=C(NHPr')(NHC ,H4)}] with I affords [ReI(CO),(=C(NHPri)(NHC6H41-2)}] which when reacted with NHEt, induces the intramolecular activation of a C-H bond to yield [Re(CO),{q2- F.G.N.Cloke K. R. Flower P. B. Hitchcock and J. F. Nixon J. Chem. SOC. Chem. Commun. 1994,489. 51 P. B. Hitchcock M. J. Maah J. F. Nixon and M.Green J. Organornet. Chem. 1994 466,153. 52 F. Abugideiri D.W. Keogh and R. Poli J. Chem. Soc. Chem. Commun. 1994 2317. 53 P. Legzdins S.J. Rettig and S. F. Sayers J. Am. Chem. SOC. 1994 116 12 105. 54 T. Mise M. Maeda T. Nakajima K. Kobayashi I. Shimizu Y. Yamamoto and Y. Wakatsuki J. Organomet. Chem. 1994 473 155. " R. W. Grime and M. W. Whiteley J. Chem. Soc. Dalton Trans. 1994 1671. 56 D.A. Brown J. Burns W.K. Glass D. Cunningham T. Higgins P. McArdle and M.M. Salama Organometallics 1994 13 2662. Organometallic Chemistry of Monometallic Species 387 C(NHPri)(NHC6H,I-2))]. This complex and I give [ReI(CO),(C(NHPr') (NHC6H,I,-2,6)}] via reopening of the Re-C CJ bond.57 The preparation molecular structure and reactivity of the rhenium oxovinylaikylidene complex synper-[ReO{=C(H)CH=CPh,}{OC(CF,),Me},(thf)]have been rep~rted.~' The coor- dinated acetone of [Mn(CO),(Bu'N=CHCH=NBu') (OCMe,)][ClO,] undergoes intramolecular addition to the coordinated diazabutadiene to give fac-[Mn(CO) {Bu'CN=CHCH(CH,COMe)N(H)But}][C104].Deprotonation of fuc-[Mn(CO) {Bu'CN=CHCH(CH,COMe)N(H)But}][C104]with KOH yields the enolate com- plex fac-[Mn(CO),{Bu'N=CHCH(CH=C{O}Me)N(H)Bu'}] which reacts further with CNBu' to give the crystallographically characterized C2.2.13 bicyclic complex ~~~-[M~(CO),{B~'N=CHCH(C{=CN(H)B~L)COM~)N(H)BU*}].~~ A general method for obtaining new types of diphosphines involves a series of deprotona- tion/halogenation reactions with [Mn(CO),(dppm)][ClO,] to give [Mn(Co),((PPh,),CH}I [Mn(CO)4{ (PPh,),CHX}I[X,I (x = Br 117 [Mn(CO),(PPh,),CX)] and [Mn(CO),( (PPh,),CBr,)][Br,].The molecular struc- ture of [Mn(CO),{ fPPh,)CI)]CH,Cl has also been determined.60 The preparation and molecular structures of [Tc(=C=CHPh)Cl(dppe),] and [Tc(ZCCH,Bu')Cl(dppe),][BPh,] the first examples of technetium carbene or carbyne complexes have been reported.61 The synthesis and molecular and electronic structures of the unusual anionic 0x0 bis(but-2-yne) complex [Na(crypt)][ReO(q2- MeC,Me),] and related compounds have been described.62 Reaction of [Mn(CO)L,Cp] [L = dmpe dmpp dmpm (PMe,),] with SiPh,H,- gives the oxidative-addition products [MnH(SiPh,H -,)L,Cp] which has been crystallographically characterized for n = 2 L = dm~e.~, The addition cyclo- addition and metathesis reactions of the vinylidene complexes [M(=C=C(H)R}(CO),Cp] (M = Mn Re) and the cationic carbyne complexes [Mn(-CCH,R)(CO),Cp] have been described.A wide range of products was + observed from these reactions including (13) which has been crystallographically characteri~ed.~ + Reaction of [Mn(-CPh)(CO),Cp] with R,NC,NR (R = Me Et) yields the cyclopropenyl cations [C,(NR,),Ph] +,whereas the reaction with MeC,NR (R = Me Et) affords the novel q4-carbene complexes (14) (R = Me) and (15) (R = Et).65 The enantioselective preparation of organosulfur complexes by the [2,3] sigmatropic rearrangements of ylides of diallyl and dipropargyl sulfonium salts of rhenium including the crystallographically characterized complex (S,S)-[Re(NO)(PPh,)(SCHRR')Cp] (R = CH=CH, R' = CH,CH=CH,) have been + reported.66 Reaction of [Re(NO)(PPh,)(ClCH,Cl)Cp] with thiophenes gives 57 K.-L.Lu H.-H. Lee C.-M. Wang and Y.-S. Wen Organometallics 1994 13 593. 58 B. T. Flatt R. H. Grubbs R. L. Blanski J. C. Calabrese and J. Feldrnan Organometallics 1994 13 2728. 59 F. J. Garcia Alonso V. Riera M. Vivanco S. Garcia-Granda and A. Gutierrez Rodriguez Organornetallics 1994 13 3209. 6o J. Ruiz R. Arauz V. Riera M. Vivanco S. Garcia-Granda and A. Menendez-Velazquez Organometallics 1994,13 4162. 61 A. K. Burrell J. C. Bryan and G.J. Kubas Organometallics 1994 13 1067. 62 T. R. Cundari R. R. Conry E. Spaltenstein S. C. Critchlow K. A. Hall S. K. Tahmassebi and J. M. Mayer Organometallics 1994 13 322.63 J. Sun R. S. Lu R. Bau and G.K. Yang Organometallics 1994 13 1317. 64 M. R. Terry L. A. Mercando C. Kelley,G. L. Geoffroy P. Nornbel N. Lugan R. Mathieu R. L. Ostrander B. E. Owens-Walterrnire and A. L. Rheingold Organometallics 1994 13 843. 65 H. Fisher and C. Troll J. Chem. Soc. Chem. Commun. 1994 457. 66 P. C. Cagle A.M. Arif and J.A. Gladysz J. Am. Chem. SOC. 1994 116 3655. 388 P. K. Baker I-VH&* .ph]+ -l.l"YNPi C NPr' 0 Me L the stable S-coordinated thiophene complexes [Re(NO)(PPh,){q'-(S)-Th)] + (Th = thiophene 2,5-dimethylthiophene benzo[b]thiophene and 2-methylbenzoCb1- thiophene). Bases abstract a proton from C-2 of the q'-S-coordinated thiophenes to yield neutral 2-thienyl and 2-benzothienyl complexes; the reaction of the 2,5- dimethylthiophene complex with base gives the 3-(2,5-dimethylthienyl) complex uia proton abstraction at the C-3 atom.67 6 Fe Ru and 0s The preparation molecular structure and reactions of the carbon dioxide complex [Fe(q'-CO,)(depe),] have been described.68 Complexes of monodentate hy-droxylamine hydrazine and diazine ligands namely [MX(CO),(q'-NH20H)(PPh,),][S0,CF3] (M = Ru 0s; X = C1 Br) [MX(CO),(q'-NH,NH,)(PPh,),][SO,CF,] (M = Ru 0s; X = Cl Br) and [MX(CO),(q'-NH=NH)(PPh,),][SO,CF,] (M = Ru 0s; X = C1 Br) respectively have been synthesized; [OSB~(CO),(~~-L)(PP~~),][SO~CF~] (L = NH,NH, NH=NH) rep-resent the first structurally characterized complexes containing q'-bonded NH,NH and HN=NH ligand~.~~ The reaction of [OsHCI(CO)(PPr\),] with 1-phenyl-2-propyn- 1-01 gives a mixture of products from which [OsCI (=CHCH=CHPh)(CO)(PPr\),] and the heterocycle (16) were isolated and crystallographically ~haracterized.~' Treatment of [RuH,(PMe,),] with PhCHO at -20 "C gives the crystallographically characterized oxaruthenocycle complex (17) which is hydrogen-bonded to benzyl alcoh01.~' Photolysis of cis-[FeH,(dmpe),] in the presence of simple thiophenes affords insertion products of the Fe into both C-H and C-S bonds; the molecular structure of [Fk(SCMeCHCHCH)(dmpe),] suggests that the ring is best described as a localized diene rather than a delocalized 'ferrathiaben- ~ene'.~' Reaction of [Ru(CO),(dppe)] with NO,C,H3-2-CF,-4-Cl gives the crystal- lographically characterized complex [Ru(CO),(dppe)(q2-ONC6H3-2-CF,-4-Cl)] which contains a n-bonded nitr~soarene.~~ The activation of terminal alkynes using cis-[RuCl (dppe),] results either in monoalkynyl complexes uia a vinylidene or bis(alkyny1) ruthenium complexes which are the essential precursors of trans-67 M.J. Robertson C. J. White and R. J. Angelici J. Am. Chem. Soc. 1994 116 5190. " S. Komiya M. Akita N. Kasuga M. Hirano and A. Fukuoka J. Chem. SOC.,Chem. Commun. 1994,1115. 69 T.-Y. Cheng A. Ponce A. L. Rheingold and G. L. Hillhouse Angew. Chem. Int. Ed. Engl. 1994,33,657. 70 M.A. Esteruelas F. J. Lahoz E. Oiiate L.A. Oro and B. Zeier Organometallics 1994 13 1662. " F. Ozawa I. Yamagami and A. Yamamoto J. Organomet. Chem. 1994,473 265. 72 I. E. Buys L. D. Field T. W. Hambley and A.E. D. McQueen J. Chem. SOC.,Chem. Commun. 1994,557. 73 S. J. Skoog J. P. Campbell and W. L. Gladfelter Organometallics 1994 13 4137. Organometallic Chemistry of Monometallic Species [Ru(C=CR)(NH,)(dppe),][PF,] and [Ru(C=CPh)(=C=C=CPh,)(dppe),] [PF,] derivative^.^^ Hydrolysis of the chloro(2-pyrrolyl) carbene complex [RuC1,(=CC1(2-pyrrolyl))(CO)(PPh3),]is followed by rearrangement to give [R~Cl(a-2-pyrrolyl)(CO),(PPh~)~].~~ Several carbyne(dich1oro) and carbyne(di-ch1oro)hydrido osmium complexes have been prepared from alkyne precursors including the crystallographically characterized complex (18).76 Ph CI 0 The preparation and molecular structure of the novel dinitrosyl complex [Fe(PPh3)(q2-tcne)(N0),] have been described.77 A series of [Fe(CO),(acac)] compounds with electron donor C-Ssubstituents (OMe OCOR NR,) have been resolved via oxazolidine or imine derivatives or through incorporation of a homochiral dialkylamino auxiliary.The absolute configurations of the complexes have been confirmed by X-ray cry~tallography.~~ The novel coupling of [Fe(C0),(7-azaben-zonorbornadiene)] with cyclohexene occurs both thermally and photochemically to give the crystallographically characterized complex (19); C-C bond formation from the exo face of 7-azabenzonorbornadiene is accompanied by the generation of [Fe(CO),(q4-cyclohexadiene)] syn to the new C-C bond.79 The first example of the selective reaction of a diastereoisomeric mixture of [Fe(CO),(2-isobornoxy-5-methyl-cyclohexadienylium)][PF,] with achiral KCdimethylmalonate] gives the highly enantiomerically enriched diene complex (20) (84% ee).80 74 D.Touchard C. Morice V. Cadierno P. Haquette L. Toupet and P. H. Dixneuf J. Chem. SOC. Chem. Commun. 1994 859. 75 M.M. P. Ng W. R. Roper and L. J. Wright Organometallics 1994 13 2563. 76 B. Weber P. Steinert 8.Windmuller J. Wolf and H. Werner J. Chem. Soc. Chem. Commun. 1994,2595. 77 L. Li G. D. Enright and K. F. Preston Organometallics 1994 13 4686. '' J. A. S. Howell A. G. Bell P.J. O'Leary P. McArdle D. Cunningham G. R. Stephenson and M. Hastings Organometallics 1994 13 1806. 79 C.-H. Sun N.-C. Shang L.-S. Liou and J.-C. Wang J. Organomet. Chem. 1994 481 179. C. W. Ong and R. H. Hsu Organometallics 1994 13 3952. 390 P.K. Baker To" Me CH(C02Me)2 Reaction of [FeH(CO),(q-C5Ph,Ar)] (Ar = Ph p-tol) with the trityl radical CPh, gives the 17-electron complexes [Fe(CO),(q-C,Ph,Ar)] uia hydrogen atom abstrac- tion.81 The preparation and molecular structures of [RuI{ (R)-(binap)}Cp] [bi- nap = 2,2'-bis(dipheny1phosphino)-1,l'-binaphthyl] and [Ru{ (R)-(binap))Cp] [CF,SO,] have been described. The latter is of particular interest since it contains the unprecedented tridentate mode of attachment of a binap ligand by q2-bonding of one of the naphthyl rings as well as both phosphorus atoms.82 The stoichiometric activation of eth-l-ynyl-l-cyclohexanolby [RuCl(PPh,),(q5-ind)] in the presence of Na[PF,] gives the crystallographically characterized complex (21) which contains a new spirobicyclic system obtained by an unprecedented coupling process.83 Deprotona- tion of [Ru{=C=C(Ph)CH,CN}(PPh,),Cp]I with [NBuilF affords the neutral crystallographically characterized cyclopropenyl complex (22) which reacts with H + or [CPh,] to regenerate the vinylidene complex.84 The first silylene complexes not + stabilized by heteroatom n donation to silicon [Ru(=SiR,)(PMe,),Cp*][B(C,F,),I (R = Me Ph) have been prepared and the methyl example has been characterized by X-ray cry~tallography.~~ Treatment of [RuMe(PPh,),Cp] with Me,SiHSiMe,OMe yields the first donor-stabilized bis(sily1ene) ruthenium complex (23) which has been crystallographically characterized.86 The preparation and molecular structure of the six-coordinate intermediate-spin iron@) complex [Fe(o-O=CMe,)(dppe)Cp*] [CF,SO,] which shows unexpected paramagnetic behaviour have been described.87 Reaction of [RuBr(q4-C,H40)Cp] with Br gives the novel crystallographically characterized q3-allyl complex [RuBr,(q3-C,H,OBr)Cp].Reaction of [RuBr(q4- C,H ,)Cp] with 3-bromocyclopent-4-ene- l-one affords the crystallographically char- acterized cyclopentenoyl complex [RuBr,(y3-C,H,0)Cp] which reacts further in the presence of NEt to give the cyclopentadienone complex [RUB~(~~-C,H,O)C~].~~ Treatment of [RuCl(q4-nbd)Cp*] with Ag[BF,] in ethanol gives [Ru(q4-nbd)Cp*] [BF,] which undergoes a skeletal rearrangement of the attached norbornadiene via C- 1-C-2 bond cleavage to yield a 6-methylfulvene complex [RuCp*(q6-*' I. Kuksis and M.C. Baird Organometallics 1994 13 1551.82 D.D. Pathak H. Adams N. A. Bailey P. J. King and C. White J. Organomet. Chem. 1994 479 237. 83 V. Cadierno M. P. Gamasa J. Gimeno E. Lastra J. Borge and S. Garcia-Granda Organornetallics 1994 13 145. 84 P.-C. Ting Y.-C. Lin M.-C. Cheng and Y. Wang Organometallics 1994 13 2150. 85 S.K. Grumbine T. D. Tilley F. P. Arnold and A. L. Rheingold J. Am. Chem. Soc. 1994 116 5495. 86 H. Tobita H. Wada K. Ueno and H. Ogino Organometallics 1994 13 2545. '' P. Hamon L. Toupet J.-R. Hamon and C. Lapinte J. Chem. Soc. Chem. Commun. 1994 931. " K. Kirchner K. Mereiter and R. Schmid J. Chem. SOC., Chem. Commun. 1994 161. Organometallic Chemistry of Monometallic Species 391 Ph3P' C,H,CHCH,)][BF,]; the last can be prepared directly from [RuCl(y4-nbd)Cp*] and AgCBF,] in CH2C1,.89 The first stable silacyclopentadienyl complex [RuHCp*(yS- Me,C,SiSi(SiMe,),}][BPh,] which has been crystallographically characterized and can be described as a protonated metallocene has been synthesized.The complex [RuHCp*{ q5-Me,C,SiSi(SiMe,),}][BPh4] can be deprotonated with (thf),Li[Si(SiMe,),] to yield the silacyclopentadienyl ruthenocene [RuCp*(qS-Me,C,SiSi(SiMe,),}] .90 The first ring-tilted highly strained [2]ruthenocenophane containing only an ethylene bridge across the RuCp unit has been prepared and crystallographically characterized; it undergoes thermal ring-opening polymerization to give poly(r~thenocenylethylene).~~ The synthesis and molecular structure of the unusual q5-monophospholyl complex [RuCp*(yS-2,5-Bu:C,H,P)] have been described .9 The preparation molecular structure (for arene = C&k6) and C-H activation of [RuH,(SiMe,),(q6-arene)] (arene = C&6 p-cumene C6Me6) have been rep~rted.~ The metal atom synthesis and X-ray crystal structure of the unusual iron@) complex [FeH2(SiCl3),(y6-C6H5Me)] been de~cribed.~ Treatment of [RuC1,L(g6-have C,Me,R,)] (R = H Me; L = PMe, PPh,) with HC=CC(H)(OH)(C,H,(NMe,)-p) in the presence of Na[PF6] gives the oxametallocyclic complexes [Ru(CH=C(C,H,(NMe2)-p)CHO)L(y6-C,Me,R,)I[PF6] (crystallographically characterized for R = H L = PPh,) via an unprecedented 1,2-migration of the dimethylaminophenyl substit~ent.~~ Condensation of Ru or 0s atoms with mixtures of C,F6 and a second arene at -196 "C affords the novel complexes [M(q4-C6F6)(y6- arene)] (M = Ru or 0s; arene = C6H6 C6H4Me2-1,3 or C6H3Me3-1,3,5) crystallo- graphically characterized for M = Ru arene = C6H,Me3-1,3,5.96 7 Co Rh and Ir Reaction of CoCl and NiC1,with two equivalents of LiR [RF = 2,4,6-tris(tri-fluoromethy1)phenyll gives [Co(RF),] and [Ni(R,),] respectively the first homoleptic 89 H.Suzuki T. Kakigano H. Fukui M. Tanaka Y. Moro-oka J. Oryanomet. Chem. 1994,473 295. '"W. P. Freeman T. D. Tilley and A. L. Rheingold J. Am. Chem. SOC. 1994 116 8428. 9' J. M. Nelson A.J. Lough and 1. Manners Angew. Chem. lnt. Ed. Engl. 1994 33 989. " D. Carmichael L. Ricard and F. Mathey J. Chem. Soc. Chem. Commun. 1994 1167. 93 P. I. Djurovich P. J. Carroll and D.H. Berry Oryanometallirs 1994 13 2551.94 V. S. Asirvatham Z. Yao and K. J. Klabunde J. Am. Chem. Soc. 1994 116 5493. 95 D. Pilette S. Moreau H. Le Bozec P. H.Dixneuf J. F. Corrigan and A. J. Carty. J. Chem. Soc. Chem. Commun. 1994,409. 96 A. Martin A.G. Orpen A. J. Seeley and P.L. Timms J. Chem. SOC. Dalton Trans. 1994 2251. 392 P. K. Baker transition-metal complexes containing o-bonded R ligand~.~~ Several substituted- pyridine cobalt bis(dimethy1glyoxime) buta-l,3-diene complexes with unusual struc- tures such as (24) and their Diels-Alder reactions with a variety of dienophiles have ON' 'NOH BU' Me Me been reported.98 Irradiation of trans-[RhCl(CO)(PMe,),] in benzene/thf (1:3 v/v) at 230 K gives three main products [RhHCl(Ph)(CO)(PMe,),] (two stereoisomers) and trans-[RhPh(CO)(PMe,),] all of which revert into tr~ns-[RhCl(CO)(PMe,)~] when the reaction mixture is allowed to warm to room temperat~re.~' The unusual activation of two equivalents of C,H at 333 K by [IrH(CH=CH,)(q2-C,H,)Tp'] gives [IrPh,Tp'] which reacts with N2to afford the dinitrogen complexes [IrPh (N2)Tp'] and [(IrPh,Tp' )(p-N,)] which has been crystallographically charac- terized.O0 Two key intermediates in the rhodium-catalysed carbonylation of ethene [RhHI,(CO),] -and [Rh(COEt)I,(CO),] -,have been characterized at low tempera- ture.lo' The preparation and X-ray crystal structure of the first isonitrilate transition- metal complex [K(~~~)][CO{CN(~,~-C,H,M~,))~] have been reported.lo2 Treat- ment of [IrCl(CO)(PPh,),] with NSF gives the first thiazyldifluoride complex [1rFC1(NSF2)(CO)(PPh,),1 which has been crystallographically characteri~ed."~ Reaction of [{IrCl(q2-C2H,),),] with Pr;PCH,CO,Me gives trans-[IrCl(q2- C,H4)(Pr~PCH,CO2Me-~-P),] which reacts with CO to afford trans-[1rC1(C0)(Pr~PCH2C0,Me-~P),] and with HC,R (R = Ph C0,Me) to yield [I~H(C~CR)C~(P~~PCH,CO,M~-KP)(P~~PCH~CO~M~-K~P,O)].When heated these o-alkynyls give the vinylidene complexes trans-[IrCl(=C=CHR)(Pr~PCH,CO,Me-lcP),] which react with Al,O,/H,O to afford [I~(=C=CHR)(P~~PCH,CO,M~-KP)(P~~PCH,CO,-K~P,O)] via cleavage of the Me-0 bond of one of the phosphino ester ligands.'04 The first structurally characterized example of a transition-metal complex with an 0-bonded methyl sulfito ligand [Ir(CO){OS(O)OMe) (SO,)(PPh,),].O.Stoluene has been described.' O5 Reaction of [Ir(triphos)(q4-C,H,)]x (x = BPh, PF,) with benzo[b]thiophene (BT)gives the unprecedented complex [Ir(triphos)(q3-C,C,S-C,H,S)]X in which the 97 M.Belay and F. T. Edelmann J. Organomet. Chem. 1994,479 C21. YX M. W. Wright T. L. Smalley Jr. M. E. Welker and A. L. Rheingold J. Am. Chem. SOC.,1994,116,6777. 99 S. E. Boyd L. D. Field and M.G. Partridge J. Am. Chem. Soc. 1994 116 9492. 100 E. Cutierrez A. Monge M. C. Nicasio M. L. Poveda and E. Carmona J.Am. Chem. SOC.,1994,116,791. 101 D. C. Roe R. E. Sheridan and E.E. Bunel J. Am. Chem. SOC.,1994 116 1163. 102 P. A. Leach S.J. Ceib J. A. Corella 11 G. F. Warnock and N.J. Cooper J. Am. Chem. Soc. 1994 116 8566. 103 P.G. Watson E.Lork and R. Mews J. Chem. Soc. Chem. Commun. 1994 1069. 104 P. Steinert and H. Werner Organometallics 1994 13 2677. 105 S. L. Randall C. A. Miller T. S. Janik M. R. Churchill and J.D. Atwood Organometallics 1994,13,141. Organometallic Chemistry of Monometallic Species BT ligand is attached to the iridium through the S atom and a C=C of the thiophene ring. Mild thermolysis of this complex yields the iridabenzothiabenzene complexes [Tr(triphos)(q2-C,S-C,H,S)]Y which has been crystallographically characterized (Y = BPh ).' O6 Treatment of crystalline [IrH2(triphos)(y2-C2H4)][BPh4]with ethyne (4 atm) at 343 K for 3 h gives ethene but-2-ene and five different mononuclear organometallic products including (25),which is the catalytic precursor when a similar reaction is carried out at 373 K.'07 The preparation and reactivity of the unsupported (y3-oxaallyl) complexes [Rh(PR3)2{q3-CH2C(0)R')](R = Et Ph; R' = But Ph) crystallographically characterized for R = Ph R' = But have been reported."" The synthesis and molecular structure of the chiral bidentate P,N-ligand complex [Rh( (2-( lS,2S,5R)-( -)menthoxydiphenylphosphino}pyridine)(~4-cod)][ClO,] have been described.' O9 The preparation and X-ray crystal structure of [Rh(C-CPh)(PPh,),(y4-nbd)] which initiates the living polymerization of phenyl- alkynes have been reported."' Reaction of [RhHPh(PMe,)Cp*] with 1.5 equivalents of biphenylene rapidly affords [RhH(a-biphenylenyl)(PMe,)Cp*] where C-H activation occurs at the r-position.Heating this complex gives the C-C inserted product (26) which has been crystallographically characterized.' '' The synthesis molecular structure and reac- tions of the nitrosyl complex [Ir(NO)(q2-C2H4)Cp*][BF4] have been (25) (26) Heating (27) gives the cyclobutadiene complex [Rh(q4-C4MeBu\)Cp*] oia a hydrogen shift and ring-closure pathway.113 Treatment of [Co(q4-4-~inylcyclopentene)Cp*] with HBF4-OMe2 yields the ethylcyclopentenyl complex (28) in which the electron- deficient metal centre is stabilized by a three-centre two-electron (agostic) interaction.Complex (28) easily undergoes disrotatory 'inwards' ring opening to give [Co{ q-C,H6(syn-Et-5)}Cp*][BF4] which contains an acyclic Sethylpentadienyl 1igand.I l4 Reaction of [RhCp?][PF,] with excess KOH and Me1 in dme for two days at 60 "C affords the first decaisopropylmetallocene [Rh(y-C5Pr\),][PF6] by forming twenty C-C bonds.' The chemical and electrochemical formation of the hydride-forming C.Bianchini A. Meli M. Peruzzini F. Vizza S. Moneti V. Herrera and R. A. Sanchez-Delgado 1.Am. Chem. Soc. 1994 116,4370. lo' C. Bianchini M. Graziani J. Kaspar A. Meli and F. Vizza Organometallics 1994 13 1165. lo' G.A. Slough R. Hayashi J. R. Ashbaugh S. L. Shamblin and A. M. Aukamp Organometallics 1994,13 890. lo9 C. G. Arena F. Nicolo D. Drommi G. Bruno and F. Faraone J. Chem. Soc. Chem. Commun. 1994,2251. 'lo Y. Kishimoto P. Eckerle T. Miyatake T. Ikariya and R. Noyori J. Am. Chem. Soc. 1994,116 12 131. C. Perthuisot and W.D. Jones J. Am. Chem. Soc. 1994 116 3647. 'I2 R.J. Batchelor F. W. B. Einstein N. D. Lowe B. A. Palm X. Yan and D. Sutton Organometallics 1994 13 2041. R. P. Hughes A. S. Kowalski and B.T. Donovan J. Organomet. Chem. 1994,472 C18. l4 J. C. Nicholls and J. L. Spencer Organometallics 1994 13 1781. *ls D. Buchholz and D. Astruc Angew. Chem. Int. Ed. Engl. 1994 33 1637. 394 P.K. Baker But But I catalytic intermediates [M(bipy)Cp*] (M = Rh Ir) and [M(bipy)(r'-arene)] (M =Ru 0s; arene = C6H6 C6Me6 p-MeC,H,Pr') have been reported."' The preparation and reactions of the novel rhodium(x) piano-stool complexes (29) (X =CH, 0),crystallographically characterized for X = 0,have been de~cribed."~ 8 Ni Pd and Pt The first carbon dioxide palladium(0) complex [Pd(PMePh,),(y2-C0,)J has been prepared.' Several novel o-acetylide complexes of platinum(I1) have been syn- thesized of which (30)has been crystallographically characterized."' The thermolytic rearrangement of cis-[Pt(CH,SiMe,),L,] (L =PMe, PEt, PMe,Ph PMePh, PPh,) results in an unusual migratory isomerization to give the asymmetric organoplatinum(x1) complexes cis-[PtMe(CH,SiMe,CH,SiMe,)L,];a detailed mech- anistic study of this rearrangement has been made.'20 The first examples of the successive insertion of CO and strained alkenes have been observed for [PdRX(Ar- bian)] (X =C1 Br I) and [PdR(NCMe)(Ar-bian)][SO,CF,I {Ar-bian = bis(ary1imino)acenaphthene; Ar =p-MeOC6H4 p-MeC,H, o,o'-Pr:C,H,} giving new products of the type [Pd{ CH( R')CH( R')C( O)CH( R')CH( R')C( O)R)X(Ar- bian)].I2' The reaction of [Pd(CNBu'),] with bis(disilany1)methane derivatives activates two Si-Si bonds and gives cyclic bis(silyl)Pd(CNBu') complexes one of which (3l) has been crystallographically characterized.122 A series of A2-oxazolines has been prepared from cationic platinum(x1) nitrile complexes; the molecular structure of (32) is also re~0rted.l~~ Treatment of equimolar amounts of PR,(C,CI,) (R =Et Ph) [Ni(q4-cod),] and L [L = PMe,Ph PEt, P(CH,Ph),] gives three types of organometallic product namely the phosphonickelocycles [Ni{ C6C14(P R ,)-2}J 116 W.Kaim R. Reinhardt and M. Sieger Inorg. Chem. 1994 33 4453. 117 E.T. Singewald C. A. Mirkin A. D. Levy and C. L. Stern Angew. Chem. lnt. Ed. Engl. 1994,33,2473. 118 M. Sakamoto I. Shimizu and A. Yamamoto Organometallics 1994 13 407.119 F. Diederich R. Faust V. Gramlich and P. Seiler J. Chem. SOC. Chem. Commun. 1994 2045. 120 B. C. Ankianiec V. Christou D. T. Hardy S. K. Thomson and G. B. Young J. Am. Chem. SOC. 1994,116 9963. 121 R. van Asselt E. E. C. G. Gielens R. E. Rulke K. Vrieze and C. J. Elsevier J. Am. Chem. SOC. 1994 116 977. 122 M. Suginome H. Oike and Y. Ito Organometallics 1994 13 4148. 123 R.A. Michelin M. Mozzon P. Berin R. Bertani F. Benetollo G. Bombieri and R.J. Angelici Organometallics 1994 13 1341. Organometallic Chemistry of Monometallic Species (crystallographically characterized for R = Et) [NiCl{C6C14(PR ,)-2}L] and [NiCI{C,CI,(PR ,)-2}L2] (crystallographically characterized for R = Ph L = PEt,). However when one equivalent of a bidentate phosphine L-L [L-L = Ph,P(CH,),PPh,] is used in place of L the unusual five-coordinate complexes [NiCI{C,CI,(PR ,)-2}{ Ph,P(CH,),PPh,)] (n = 2,3) and the bis(monodentate) dppm complex [NiCI{C6C1,(PP h2),-2)(q1-dppm),] were ~btained.',~ The preparation molecular structure (R = Me) and properties of the first octahedral diorganonickel(1v) complexes (33) (R = Me Bu') have been described.'25 The synthesis and X-ray crystal structures of the 14-electron bis(carbene) complexes (34) (M = Ni Pt) have been reported.'26 The preparation and molecular structure of the first donor-free bis(si1ylene) complex of nickel [Ni{ Si(Bu'NCH= CHNBu')),(CO,)] have been des~ribed.'~~ The preparation X-ray crystal structure and chemistry of the first pure mono(a1kyne) complex of nickel [Ni{q2-HO(CH,),CC~CC(CH,),OH},] have been reported; hydrogen bonding dictates the structure of this complex.12* The first examples of quantitative allene 1,l-dimethylal- lene and tetramethylallene migratory insertion reactions into alkyl and acyl palladium compounds of bidentate and tridentate nitrogen donors have been described; the structure of [Pd(bipy)(q3-2-acetyl-1,1,3,3-tetramethylallyl)][CF3S03] and the prep- aration of an unusual ql-allyl palladium complex with a terpy ligand have also been reported.' 29 The reactions of q3-oxatrimethylenemethane platinum complexes with lZ4 M.Font-Bardia J. Gonzalez-Platas G. Muller D. Panyella M. Rocamora and X. Solans J. Chem. SOC. Dalton Trans. 1994 3075. H.-F. Klein A.Bickelhaupt T. Jung and G. Cordier Oryanometallics 1994 13 2557. A. J. Arduengo 111 S. F. Gamper J.C. Calabrese and F. Davidson J. Am. Chem. Soc. 1994 116,4391. M. Denk R.K. Hayashi and R. West J. Chem. Soc. Chem. Commun. 1994 33. D. Walther A. Schmidt T. Klettke W. Imhof and H. Gorls Angew. Chem. Int. Ed. Engl. 1994,33 1373. R. E. Riilke D. Kliphuis,C. J. Elsevier,J. Fraanje K.Goubitz P. W.N. M. van Leeuwen and K. Vrieze,J. Chem. SOC. Chem. Commun. 1994 1817. 396 P. K. Baker selected nucleophiles provide the first examples of nucleophilic substitution of the central carbon of an ally1 group via a platinocyclobutane intermediate.' 30 Treatment of [Pt(PPhJ2(q3-CH2CCPh)][CF,SO3] with Na[CH(CO,Me),] yields the first platinum trimet h ylenemet hane complex [Pt(PPh3)2 {q3-CH,C(C{CO,Me} ,)CHPh}] which has the trimethylenemethane ligand q3-bonded to the ~1atinum.l~~ with ethyne The reaction of [N~{~'-Bu',P(CH,)PBU',)(~~-C~H~)~] at low temperature gives [Ni{q'-Bu',P(CH,)PBu',}(q6-c6H6)] the first example of a nickel(o) complex with an arene coordinated as a six-electron donor.32 I3O K. Ohe H. Matsuda T. Morimoto S. Ogoshi N. Chatani and S. Murai J. Am. Chem. SOC.,1994 116 4125. 13' V. Plantevin P. W. Blosser J.C. Gallucci and A. Wojcicki Organometallics 1994 13 3651. T. Nickel R. Goddard C. Kruger and K.-R. Porschke Angew. Chem. Int. Ed. Engl. 1994 33 879.

ISSN:0260-1818    

DOI:10.1039/IC9949100381

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

22 Organometallic Chemistry of Bi- and Polynuclear Complexes By G. HOGARTH Department of Chemistry University College London London WCl OAJ 1 Introduction This report follows in much the same vein as last year’s contribution. No attempt will be made to present a comprehensive review of the literature since this is documented elsewhere.’ Instead the most significant publications and areas of interest will be highlighted. Special topics covered this year include allenyl complexes compounds in which metal centres are linked together imido complexes and those with related n-donor groups and the metal-mediated synthesis of sulfur-containing macrocycles. 2 Theoretical and Physical Studies In a publication entitled ‘Is there a direct iron-iron bond in [Fe,(CO),]?’ Mealli and coworkers give details of a reinvestigation of this question by means of ab initio calculations.While the situation is quite complicated there appears to be a small direct attraction between the two iron centres which however is hidden by a relatively large effective iron-iron repulsion.2 These results accord with earlier studies which also concluded that the net direct metal-metal interaction is anti-bonding in nature. Fenske-Hall calculations have been used to describe the rhenium-rhenium interac- tions in both high- and low-valent doubly bonded dirhenium complexes. Thus for d2-d2 [(Re(OH),(=CH)),] the electronic configuration is best described as a2n2 while for d6-d6 [{Re(CO),Cp),] 027t4626*27c*2 is an accurate de~cription.~ In somewhat related work ab initio Hartee-Fock calculations on triply bonded [V,(p-dmp),] (dmp = dimethoxyphenyl) reveal that the metal-metal interaction comprises 6-,n- and &components; the electronic configuration is best considered as 02n2d2 and not 02n4as previously ass~rned.~ The bonding in the prototypical high-nuclearity arene clusters [RUs(co),2(c6H6)(,Us-c)]and [RU6(CO) l(c6H6)2(&j-c)] has been investigated using extended Huckel calculations attention being focused on the relationship between the apical ($) and facial (p3)bonding modes of the arene.Most interestingly G. Hogarth ‘Organometallic Chemistry’ Specialist Periodical Reports Vol 23 Chapter 8 p 171. ’J. Reinhold E. Hunstock and C. Mealli New J. Chem. 1994 18 465. T. A. Barckholtz B.E. Bursten G. P. Niccolai and C. P. Casey J. Oryanomet. Chem. 1994,478 153. C.N. Poumbga M. Benard and I. Hyla-Kryspin J. Am. Chem. SOC. 1994 116 8259. 397 398 G. Hogarth the calculations reveal that while the apical isomers are the most stable the local benzene-ruthenium interaction is stronger in the facial isomers.' The effect of temperature on the solid-state structure of [Fe,(CO),,] has been investigated by analysing crystallographic data at 100 160 250 and 300K. As the temperature is decreased the asymmetrically bridging carbonyl ligands become progressively more symmetric the bridged iron-iron vector shortens and at the lowest temperature approximate C, symmetry is observed. These changes are associated with a decrease in atomic motions which allow the atoms within the same molecule to move closer together while the decrease in molecular motion also increases the interpenetration of molecules within the crystal.6 Correlation of geometry with the stretching frequency of metal-bound carbonyls has been attempted for a series of carbonyl clusters.Somewhat surprisingly the positions of the terminal carbonyls are quite independent of cluster geometry. However there is more variation in the lower frequency absorptions associated with the bridging carbonyl~.~ Eisenberg and coworkers have successfully correlated the force constants associated with the metal-metal bond (obtained from Raman spectroscopy) with internuclear separation for a number of binuclear rhodium complexes and have predicted the latter in complexes for which crystallographic data are not available.8 From the results of solid-state NMR spectroscopic studies on tetranuclear [Ru,(,u-H),(CO) ,] it is concluded that either the tetrahedral metal core rotates as a whole or the hydride ligands move over its surface through a series of concerted jumps.' The 70-electron cluster [(1r(,~~-S)Cp},]~ (1)is prepared upon addition of + bis(trimethylsily1)sulfide to [TrCI,Cp*] followed by chromatography on an ion-exchange column.The structure consists of a distorted cubane framework with one short Ir(rv)-Ir(1v) bond (2.764A) four long Ir(Iv)-Ir(III) contacts (av. 3.5 A) and one long Ir(III)-Ir(m) vector (3.683A). Interestingly at higher temperatures all four cyclopentadienyl ligands become equivalent by a fluxional process attributed to the migration of the iridium-iridium bond around the cluster;" the free energy of activation is estimated at 57 kJ mol- Flash photolysis of [{Fe(CO)(p-CO)Cp),] at 98 K in 3-methylpentane initially results in carbonyl loss yielding the triply bridged complex [Fez@-CO),Cp,] .However further irradiation leads to loss of a second carbonyl to afford [{Fe(CO)Cp),] (2) postulated as the first complex to contain an unsupported iron-iron triple bond. In order to understand the nature of the latter in more detail Fenske-Hall calculations have been carried out which support both the proposed C structure and the presence of an iron-iron triple bond." Photolysis of the datively bonded heterobimetallic complex [(CO),(PMe,)Os + W(CO),] results in heterolytic rather than homolytic cleavage of the metal-metal bond.I2 D.Braga P. J. Dyson F. Grepioni B. F.G. Johnson and M. J. Calhorda Inorg. Chem. 1994,33 3218. D. Braga F. Grepconi L. J. Farrugia and B. FG. Johnson J. Chem. SOC.,Dalton Trans. 1994 2911 ' S. F. A. Kettle E. Diana R. Rosetti P. L. Stranghellini R. D. Pergola and L. Garlaschelli Inorg. Chem. Acta. 1994 227 241. ' P.D. Harvey F. Shafiq and R. Eisenberg Inorg. Chem. 1994,33 3424. ' S. Aime R. Gobetto A. Orlandi C.J. Groombridge G.E. Hawkes M.D. Mantle and K.D. Sales Organometallics 1994 13 2375. lo A. Venturelli and T.B. Rauchfuss J. Am. Chem. SOC.,1994 116 4824. F.A. Kvietok and B.E. Bursten J. Am. Chem. SOC.,1994 116,9807. J.L. Male H.B. Davis R.K.Pomeroy and D.R. Tyler J. Am. Chem. SOC.,1994 116 9353. Organometallic Chemistry of Bi- and Polynuclear Complexes 12+ OC\ Fe Fe 3 Multiple Bonds Two publications detail the synthesis and reactivity of quadruply bonded chromium (11) complexes. The chloro-bridged dimer [{ Cr(p-Cl)Cp*},] is an excellent precursor for the synthesis of alkyl and aryl substituted complexes. Thus addition of organolithium reagents affords [(Cr(p-R)Cp*),] (R = Me Et Bu CH,SiMe, or Ph) all of which have a short chromiumshromium contact low magnetic moments and attenuated reactivity properties consistent with the presence of a strong metal-metal bond. Reaction of the diethyl complex with benzene results in carbon-hydrogen bond activation and the formation of the mixed alkyl-aryl compound [Cr,(p-Et)(p-Ph)Cp;].The dimethyl analogue is oxidized to give the non metal-metal bonded 0x0-bridged chromium(v) complex [Cr,Me,(O),(p-O)CpS] while hydrogenation affords the 48-electron cubane cluster [(Cr(p,-H)Cp”)),] (Cp” = C,Me4Et).I3 Girolami and coworkers give details of the preparation of [Cr,(CH,SiMe,),(p- CH,SiMe3),12-(3) which is proposed to have a ‘bent’ chromiumshromium bond (based on the relative geometries of the substituents) bridged by two agostic alkyl moieties.14 The triply bonded dimolybdenum complex [{ Mo(CO),(y5-cyclo-Bu\C,H,P)},] containing 2,5-di-butyl phospholyl ligands has been prepared while reactivity studies reveal that it bears a close likeness to the analogous cyclopentadienyl complex. Chisholm et al.have synthesized a number of unbridged tungsten-tungsten triply bonded complexes containing the di-t-butyl acetylacetenato ligand for example [(WR(0’Pr)(Bu\a~ac)}~] (R = Ph Et).I6 Two publications give details of the synthesis17 and electrochemistry’ of the doubly bonded phosphido-bridged diiron complexes [Fe,(CO),(p-PBu\)(p-PR,)] (R = Ph Cy) and [Fe,(CO),(p-PBu\)(p- PCy,)(p-dppm)] (4). The former show two well-defined one-electron reduction processes and the EPR spectra of the radical anions have been recorded.18 The unsaturated phosphido-bridged diruthenium complex [Ru (p-H)(CO),(PBu\H),(p-PBu:)l is one of the products of the reaction of triruthenium dodecacarbonyl with the secondary phosphine PBu\H. It reacts with carbon monoxide to give the saturated bis(phosphid0) derivative [Ru2(p-H)(CO),(PBu\H)(p-PBu‘,)l a process which is reversed upon addition of more of the l3 R.A. Heintz R. L. Ostrander A. L. Rheingold and K. H. Theopold J. Am. Chem. Soc. 1994 116 11 387. l4 P. M. Morse M. D. Spencer S.R. Wilson and G. S. Girolami Organometalh 1994 13 1646. ‘’ D. Carmichael L. Ricard and F. Mathey J. Chem. SOC.,Chem. Commun. 1994 2459. l6 M.H. Chisholm E. F. Putilina K. Folting and W. E. Streib J. Cluster Sci. 1994 5 67. B. Walther H. Hartung S. Bambirra A. Krug and H.-C. Bottcher Organometnllics 1994 13 172. l8 J.G. M. Van der Linden J. Heck B. Walther and H.-C. Bottcher Inorg. Chem. Acta. 1994 217 29. 400 G. Hoyarth (3) R = SiMe3 I -3 (5) (7) secondary phosphine.” Addition of the Grignard reagent Mg(CH,SiMe,) to [(Ru(p,-Cl)Cp*},] yields a second complex containing a ruthenium-ruthenium double bond namely [Ru,(SiMe,)(p-CH,)(p-Cl)Cpz] (5),the reaction of which with trifluoroacetic acid is temperature dependent.Hence at low temperatures trimethyl- silane is eliminated to yield [Ru2(p-CH2)(p-C1)(p-O2CCF,)Cp~] room (6); at temperature the reaction takes a different course affording [Ru (p-CHSiMe,)(p- Cl)(p-O,CCF,)Cp~] (7) a result of carbon-silicon bond formation.,O Reaction of [(Ru(p,-Cl)Cp*},] with enones and enals results in the formation of unsaturated alkyne-bridged complexes [Ru,(p-CO)(p-RC,R’)Cp;] (R = H R’ = Me Et; R = R’ = Me),,’ while Knox and coworkers have shown that the analogous cyclopentadienyl complexes [Ru,(p-CO)(p-RC,R)Cp,] (R = Ph CF,) are good precursors to cluster complexes.22 With [Ru(C0),(q2-C,H,)] trinuclear results as a mixture of two isomers, [RU~(CO),(~-CO)(~,-CO)(~,-RC~R)C~~] differing in terms of the metal to which the alkyne is n-bound which are interconverted in solution at higher temperatures.Reaction with dicobalt octacarbonyl yields tetranuclear [Ru,Co,(CO),(p3-CO)(p4-PhC2Ph)Cp2]. The doubly bonded dicobalt complex [{Co(CO),L),] (L = C,Me,CH,CH,CH=CH,) reacts readily with the phosphaalkyne PECBu’ to give [CO~(~-CO)(~-~~-~~-~~-PCBU~C(O))L], where car- bon monoxide and the phosphaalkyne are coupled at the binuclear centre., 4 Organic Ligands Addition of diiron nonacarbonyl to the fluorinated ketene (CF,),C=C=O affords the l9 H.-C.Bottcher G. Rheinwald H. Stoeckli-Evans G. Suss-Fink and B. Walther J. Organomet. Chem. 1994,469 163. 2n W. Lin S. R. Wilson and G.S. Girolami Organometallics 1994 13 2309. W. Trakarnpruk A.M. Arif and R.D. Ernst Organometallics 1994 13 2423. 22 K. J. Adams J. J. Barker J. P. H. Charmant C. Canter G. Klatt S. A. R. Knox A. G. Orpen and S. Ruile J. Chem. SOC. Dalton Trans. 1994 477. 23 R. M. Matos J. F. Nixon and J. Okuda Inorg. Chem. Acta. 1994 222 13. Organometallic Chemistry of Bi- and Polynuclear Complexes 401 alkylidene complex [Fe,(CO),{ p-C(CF3),}] which contains only terminal carbonyl ligands as does the PPh substituted derivative., Chaudret and coworkers have prepared the highly reactive mononuclear fragment [RuCp*] in situ via the addition of CF,SO,H to [(Ru(p-OMe)Cp*},].It reacts with the solvent in which it is generated. Thus in dichloromethane methylidyne clusters [Ru3(p-C13)(p3-CH)Cpj] and + [R~,(p-Cl),(p-C0)(p~-CH)Cpj]~ + result while in chlorocyclohexane the chloroal- kylidyne derivative of the latter is formed.,’ A further methylidyne cluster [Mo,(CO),(p,-CH)Cp,] results from the photochemically induced reduction of one of the carbonyls in [{Mo(CO),Cp},] upon reaction with the silane SiHMe,Ph.26 Reactions of the ethylene-bridged diosmium complex [Os,(CO),(p-C,H,)] with activated alkynes results in cycloreversion affording dimetallacyclobutenes [Os (CO) (p-RC=CR)] . ’ Addition of bis (diet hy1amino)acetylene to [(M(CO),Cp},] (M = Mo W) at high temperatures leads to the formation of the alkyne complexes [M,(CO),(p-RC2R)Cp,] (R = NEt,) (8).Crystallographic data reveal however that rather than the anticipated dimetallatetrahedrane-type struc-ture the complexes contain the unexpected 1,2-dimetallacyclodicarbeneunit as the central core., Rauchfuss and coworkers have reported details of the photochemical reaction of [Fe,(CO),(p-S,)] with buckminsterfullerene; FAB mass spectrometry shows a range of products C6o[Fe,(Co)6(p-s,)] (n = 1-6) in which the disulfur units link the diiron centre to the carbon frame~ork.,~ Photolysis of the alkylidene complex [Fe,(CO),(p-CO)(p-CHBu)Cp,] results in dehydrogenation affording the vinyl alkylidene [Fe,(CO)(p-CO)(p-HCCH=CHEt)Cp,] in which the carbon-carbon double bond is metal bound;30 reaction of allylbromide with [R~,(CO),~(p-dppm)] affords [Ru2(C0),(p-C3HS)(p-Br)(p-dppm)] as a result of oxidative addition of the carbon-bromine bond to the metal centre.31 P The cyclopropenyl complex [Ru3(p3-CO)(p3-cycEo-C3H,Me)Cp~] (9) is isolated from the reaction of [{Ru(p3-Cl)Cp*},] with trans-3-methyl-2-butenal.Crystallo-graphic studies reveal that the cyclopropenyl ligand sits on a face of the trimetallic 24 M. Wiederhold and U. Behrens J. Organornet Chem. 1994 476 101. 25 D. Rondon J. Delbeau X.-D. He S. Sabo-Etienne and B. Chaudret J. Chern. SOC. Dalton Trans. 1994 1895. 26 M. Akita K. Noda and Y. Moro-oka Organometallics 1994 13 4145. M. R. Burke F. Seils and J. Takats Organometallics 1994 13 1445. 28 J. Heck K.-A.Kriebisch W. Massa and S. Wocadlo J. Organornet. Chern. 1994 482 81. 29 M. D. Westmeyer C. P. Galloway and T. B. Rauchfuss Inorg. Chem. 1994 33 4615. ’O C. P. Casey and G. P. Niccolai Organornetallics 1994 13 2527. ’’ M. I. Bruce P. A. Humphrey R. J. Surynt and E. R.T. Tiekink Aust. J. Chem. 1994 47 477. 402 G. Hogarth centre adopting a relative staggered arrangement.,' Protonation of fulvalene-bridged alkyne complexes [Mo,(CO),(p-RC,CR,OMe)(p-Fv)] (Fv = H,CSCsH,) results in loss of methanol and the formation of stable fluxional carbenium complexes [Mo2(CO),(p-q2,q3-RC=CCR',)(p-Fv)] + .32 In a similar manner the metal-stabil- ized dicarbenium ions [Mo,(CO),(~-H,CC=CH,)C~,]~ + (10) and [Co,(CO),(p- dppm),(p-H,CC-CCH,)]2 result from the addition of two equivalents of tetraf- + luoroboric acid to the respective dipropargylalcohol c~mplexes.~~~~~ H2C' \ /CH2+ Molecular orbital calculations on the crystallographically characterized dimolyb- denum complex reveal that the positive charge is transferred to the metal centre; both complexes undergo double addition of donor ligands such as amines phosphines thiols and pyridine to the methylene centres.Addition of cyclopentadiene to the triruthenium hydride [RU~(,U-H)~(~~-H),C~:] leads to the formation of the metalla- cyclopentadiene complex [Ru,(~~-CM~=CHCH=CH)(~-H)~C~:] as a result of an unprecedented C(sp2)-C(sp3) bond cleavage of the cyclic diene.3s Heating [{IrH,Cp*),] in neat thiophene results in a double sulfur-carbon bond cleavage reaction and the formation of [Ir,(p-S)(p-H,C=CHCH=CH,)Cp?], the extruded sulfur being captured by the metal centre.When the reaction was carried out using thiophene-d4 a ,H product was formed with deuterium scrambled over all positions of the bridging butadiene ligand. The latter can easily be removed upon carbonylation giving [Ir,(CO),(p-S)Cp;]. However the sulfur is firmly bound to the binuclear centre.36 Demetallation of trinuclear [Ru3(CO),(p3-C,,H,,)] by Me3N0 affords the binuclear paracyclophane complex [RU,(C0)6(p-r3,r3-C,,H16)] the organic ligand being bound to the metal centre by two enyl interaction^.^' Johnson and coworkers also report that abstraction of H- from the cyclohexadienyl ligand in [OS,(CO)&~- q5-cyclo-C6H6Ph)]-(1 1) by [CPh,][BF,] affords carbene [oS3(co)9(~3-r',~2,~2- C6H5Ph)] (12) and ketone [OS3(CO)9(p3-q1,q2,r2-0=CC6HsPh)] (13) complexes; the latter is probably formed via carbonyl coupling with the carbene ligand in the former.38 Two independent groups give details of the reaction of 1,2,4,5-tetrabromodurene 32 H.El Amouri Y. Besace J. Vaissermann G. Jaouen and M. J. McGlinchey Organometallics 1994 13 4426. 33 M. D. McClain M. S. Hay M. D. Curtis and J. W. Kampf Organometallics 1994 13 4377. 34 S.C. Bennett M.A. Phipps and M.J. Went J. Chem. SOC. Chem. Commun. 1994 225. 35 H. Suzuki Y. Takaya T. Takemori and M. Tanaka J. Am. Chem. Soc. 1994 116 10779. 36 W.D. Jones and R. M. Chin J. Am. Chem. SOC. 1994 116 198. 31 A. J. Blake P. J. Dyson B. F.G.Johnson and C. M. Martin J. Chem. Soc. Chem. Commun. 1994 1471. 3R A. J. Edwards M. A. Gallop B. F. G. Johnson J. U. Kohler J. Lewis and P. R. Raithby Angew. Chem. Int. Ed. Engl. 1994 33 1093. Organometallic Chemistry of Bi-and Polynuclear Complexes with [Fe2(Co),12-and [Fe,(CO),] .39940 In the first instance formation of [{Fe,(CO),},{p-(CH,)4C6H2)] (14) is postulated in which diiron centres are linked via o-interactions with the methylene groups on the aryl ring. In the second a quite different product [Fe3(C0)9{p-(CH,)4C6H2]] (15) results; a diiron hexacarbonyl fragment is linked in a bis(ally1) fashion and an iron tricarbonyl moiety is bound in an exocyclic diene-type manner. Ph G Ph + (14) (15) 5 Allenyl Complexes The chemistry of the allenyl ligand when bound to bi- and trinuclear centres has been the focus of four publications in 1994.Carty and coworkers report that the diruthenium and diosmium allenyl complexes [M,(Co),(p-PhC=C=CH,)(p-PPh,)] formed from the selective attack of diazomethane at the a-carbon of the acetylide complexes [M,(Co),(p-C~CPh)(p-PPh,)] are in fact bound to the second metal centre via the C,-C double bond and not C,-C as previously Addition CNBu' to the ruthenium complex (16) results in regiospecific attack at C yielding [Ru,(CO),{p- q1,~'-P~C=C(CNBU')CH,](~-PP~,)],~~ while thermolysis in the presence of dppm affords [R~,(CO)~{p-q~,r~,yl~,r~-Ph~PC(O)C(Ph)CCH~}(p-dppm)] (17) a result of coupling of the allenyl fragment carbon monoxide and the phosphido m~iety.~' Wojcicki and coworkers give details of the synthesis of trinuclear allenyl complexes from the mononuclear precursor [Ru(CO),(CH,C=CPh)Cp].Reaction with tri- ruthenium dodecacarbonyl then affords [Ru3(C0),(p3-q1 ,q2,q2-PhC=C=CH,)Cp] while with iron carbonyls analogous mixed iron-ruthenium complexes are pre- 39 F. R. Alam K. A. Azam S.E. Kabir and S.S. Ullah Indian J. Chem. Sect. A 1994 33,420. 40 L. Girard A. Decken A. Blecking and M.J. McGlinchey J. Am. Chem. SOC.,1994 116 6427. 41 N. Carleton,J. F. Corrigan S. Doherty R. Pixner Y. Sun N. J. Taylor and A. J. Carty Organometdics 1994,13,4179. 42 S. M. Breckenridge,A. J. Carty M. A. Pellinghelli,A. Tiripicchio and E. Sappa,J. Organomet. Chem. 1994 471 211. 404 G. Hogarth pared.43 In a somewhat different approach the triosmium allenyl complex [Os (CO),(p-H)(p,-Me,SiC=C=CH,)I is prepared upon thermolysis of [Os,(CO),(p-CO)(p,-Me,SiC2Me)] proton loss from the methyl group of the alkyne affording the new allenyl ligand., 6 Metal-mediated Transformations of Organic Ligands Several interesting isomerizations of organic ligands have been reported.The flyover carbene complex [Co2(p-q3,q2-C3H3CH=CHMe)Cp2] (18) rearranges to [Co2(p- q3,q2-MeC3H2CH=CH2)Cp2] (19) via a metal-mediated 1,5-hydrogen shift,45 while the kinetic product of the addition of [co2(co)g] to [MoCl(q2-MeC=CPh),Cp] namely [MoCo(CO),(p-PhC=CMeCPh=CMe)Cp] rearranges to the ther-modynamically more stable isomer [MoCo(CO),(p-MeC=CPhCPh=CMe)Cp] upon therm~lysis.~~ Insertion of dimethylacetylene dicarboxylate into [Fe,(CO),(p-H)(p-CO)(p-PPh,)(p-dppm)] affords the cis product [Fe,(CO),(p-RC=CRH)(p-PPh)(p-dppm)] (20)(R = C0,Me).This rearranges to the trans isomer (21) upon photolysis a process which is reversed when left at room temperature. Interestingly thermolysis of either isomer results in the irreversible formation of a third metallacyclic isomer [Fe2(CO),(q2-RC=CHC(OMe)=O)(p-PPh2)(p-dppm)] (22) which also has a trans arrangement of substituents on the vinyl moiety.47 Stoichiometric alkyne metathesis has been achieved at a tetranuclear centre. Thus heating the alkyne-alkylidyne complex [Os3W(CO),,(p3-CMe)(p3-tolC=CMe)Cp] (to1 = p-MeC,H,) affords the dimetallaallyl complex [Os,W(CO),(p,-tol-CCMeCMe)Cp] as a result of carbon-carbon bond formation.However loss of a second carbonyl gives the new alkyne-alkylidyne complex [Os3W(CO)g(p3-Ctol)(p3- MeC=CMe)Cp].48 Closely related to the latter thermolysis of [Os,W(CO),,(p,- tolCCtolCto1)Cpl at 50 "C also results in carbonsarbon bond cleavage to afford the butterfly cluster [Os W(CO),(p,-Ctol)(p,-tolC=Ctol)Cp] (23). At slightly higher temperatures (55 "C),however a second very slow cleavage reaction occurs to give the tris(alky1idyne) complex [Os,W(CO)g(p,-Ctol)3cp] (24) which again has a butterfly 43 C. E. Shuchart A. Wojcicki M. Calligaris P. Faleschini and G. Nardin Organometallics 1994 13 1999. 44 A. A. Koridze N. M. Astakhova P.V. Petrovskii F. M. Dolgushin A. I. Yanovsky and Yu. T. Struchkov J. Organomet.Chem. 1994 481 247. 45 J. A. King Jr. and K. P. C. Vollhardt J. Organomet. Chem. 1994 470 207. 46 W. Hirpo M. D. Curtis and J. W. Karnpf Organometallics 1994 13 3360. 47 G. Hogarth and M.H. Lavender J. Chem. SOC.,Dalton Trans. 1994 3389. 48 M.T. Kuo D.-K. Hwang C.-S. Lin Y. Chi S.-M. Peng and G.-H. Lee Organometallics 1994,13,2142. Organometallic Chemistry of Bi-and Polynuclear Complexes H H H R To1 structure; two alkylidyne ligands cap triangular faces while the third bridges wing-tip osmium atoms and a tungsten in a hinge site.49 Loss of carbon monoxide from the mononuclear cyclopropenyl complex [Ir(CO),(q3-C,Bu\)] initially gives [Ir,(CO),(q3-C3Bu~),(p-CO)].Loss of another carbonyl results in formation of [Ir,(CO),(~2-C3Bu\)(p-q2,~3-C3Bu\)], in which both rings are ruptured.Quite remarkably however carbonylation of the latter results in reformation of the mononuclear tricarbonyl complex.50 One-electron oxidation of [Mo,(p-C,Me,)Cp,] gives the radical cation which on the basis of geometric changes upon electron loss is postulated to contain a three-electron metal-alkene interaction. Upon further oxidation proton loss gives [Mo,(p-C,Me,CH,)Cp,] which contains + a molybdenum-molybdenum double bond. 51 A number of interesting carbon-carbon bond formation processes has been 49 J. T. Park B. W. Woo J.-H. Chung S.C. Shim J.-H. Lee S.4. Lim and I.-H. Suh Organometallics 1994 13 3384. 50 R. P. Hughes D. S. Tucker and A. L. Rheingold Organometallics 1994 13 4664. 51 N.G. Connelly B.Metz and A.G. Orpen J. Chem. Soc. Chem. Commun. 1994 2109. 406 G. Hogarth reported. Reaction of ethoxyacetylene EtOC-CH with [Fe,(CO),(p-CO)(p-SR)] -affords the vinyl carbene complexes [Fe2(Co),(p-EtCo=CHc(Co2R'))(p-SR)] (25) (R' = Me Ph) after quenching with benzoyl or acetyl chloride.' Allene couples readily to carbon monoxide and to itself at the diiron centre. Hence photolysis of [Fe,(CO),(p-CO)(p-dppm)] and allene affords [Fe,(CO),(p-H,CCCH,)(p-dppm)l 7 [Fe2(C0)5 {p-c(0)c(cH2)2} (p-dppm)l (26) and [1Fe2(C0)4(p-(H,C),CC(CH,),}(p-dppm)] ;in the reaction with [Fe,(CO),(p-PPh,)(p-CH,PPh,)] it couples with the phosphido bridge to give [Fe,(CO),(p-Ph,PC(CH,),}(p-CH,PPh,)] (27).53 Protonation of the unsaturated vinylidene complex [Re,(CO),{p-C=CHC(Me)=CH,}Cp,] (28) affords the alkylidyne compound [Re,(CO),(p- CCH=CMe2)Cp2]+ which in turn reacts with methyllithium to yield the new saturated vinylidene [Re,(CO),(p-C=CHBu')Cp,] resulting from regioselective attack at the y-~arbon.~ The nature of the reaction of primary alkynes with [Ru,(p-Cl)(p-SPr'),Cp,*l'is strongly dependent upon the substituent.Thus with HCrCCR,OH water is lost to afford [Ru,(=C=C=CR,)(p-Cl)(p-SPr'),Cp~]* while with phenyl ethyne coupling occurs to give the carbene complex [Ru2(p- SP~'),(~-P~C=C(C~C~O-~,~~~~,)C)C~~] + (29) during which a proton is transferr- ed from a phenyl ring to the carbon it is bound to." Both carbonyl and isonitrile insertion into a (r-TCvinyl ligand is observed at a triruthenium centre.Thus reaction of [Ru,(CO),(p-CO),(p-PhC=CHPh)(p,-PhNR)](R = C,H,N) with PPh and PhCH,NEC affords [Ru3(CO),(PPh3),(p-0=CPhC=CHPh)(p3-PhNR)]and [Ru3(C0),(p-CO),{p-(PhCH2)N=CPhC=CHPh)),-PhNR)] re~pectively.~~ The coupling of both phospha- and arsabenzenes has been achieved at the triosmium centre. Reaction of [Os,(p-H),(CO),,] with the 2-trimethylsilyl substituted rings initially affords [Os,(p-H),(CO),(p,-ql ,q2-cyclo-EC,H,R)] (30) (E = P As; R = SiMe,) while further reaction results in a [4 + 21 Diels-Alder coupling of the rings yielding [Os3(p-H)(C0)9(p-q',~2-E,C,,H7R,)] (31).57 7 Linking Metal Centres A large number of publications has appeared this year concerning the synthesis and 52 D. Seyferth J. B. Hoke J. C. Dewan P. Hofmann and M. Schellbach Organometallics 1994 13 3452.53 S. A. R. Knox D. A.V. Morton A.G. Orpen and M. L. Turner Inorg. Chim. Acta. 1994 220 201. 54 C. P. Casey Y. Ha and D. R. Powell J. Am. Chem. SOC. 1994 116 3424. " H. Matauzaka Y. Takagi and M. Hidai Organometallics 1994 13 13. 56 P. Nombel N. Lugan F. Mulla and G. Lavigne Organometallics 1994 13 4673. '' A. J. Arce A. J. Deeming Y. De Sanctis A. M. Garcia J. Manzur and E. Spodine Organometallics 1994 13 3381. Organometallic Chemistry of Bi-and Polynuclear Complexes 407 properties of compounds in which metal centres (not directly bonded to one another) are linked by bidentate ligands. Such ligands may or may not be unsaturated the former potentially allowing strong communication between the metal centres.The electroactive ligand dppf has been used to link triiron-bis(su1fido) and tricobalt- ethylidyne centres in [{ Fe3(co)8(p3-S)2) ,(p-dppf)] 58359 and [{ c03(c0)8(p3-CMe)} (p-dppf)I6' respectively; a moderate electronic interaction has been found in the latter. Diphosphines with saturated backbones have been used to link Fe3Au fragments reaction of [Fe,(CO) ,I2-with [Au,Cl,(p-L-L)] (L-L = dppm dppe) affording [{Fe,Au(CO) i}2(p-L-L)]2- ;the diphosphine links the butterfly clusters through coordination to the wing-tip gold centres.61 Somewhat related is the complex [{Fe,(CO),(p,-PMe)} 2(p3,p3-PA~P)] (32) in -which a gold atom links the two triiron centres via coordination to the capping phosphide moieties.62 Tricobalt centres have also been linked by alkylidyne groups.Thus both [{c03(CO),} 2(p3,P3-CCH=CHC)I and C(c03 (CO) } 2 (p37P3-CC6H4C)I (33 )60 have been prepared the latter showing strong communication between the metal centres via the aryl ring. Related to these is [{CO,(CO),}~(~~,~,-CS~M~~OS~M~,C)] where the link consists of a siloxane moiety.64 Shriver and coworkers have reported a very novel example in which triiron centres are linked by a C ligand. Reaction of the ketenylidene complex [Fe3(CO),(p3- C=C=0)l2 -with triflic anhydride yields [{Fe3(CO),)2(p,,p,-C~CC~C)]2-, the 58 Z.-G. Fang Y.S. Wen K. L. R. Wong S.-C. Ng L.K. Liu and T.S.A. Hor J. Cluster Sci. 1994,5 327. 59 Z.-G. Fang P. M. N. Low S.-C. Ng and T. S. A. Hor J. Organomet. Chem. 1994,483 17. S. Onaka M. Otsuka A. Mizuno S.Takugi K. Sako and M. Otomo Chem. Lett. 1994 45. 61 0.Rossell M. Seco R. Riena M. Font-Bardia and X. Solans Organometallics 1994 13 2127. 62 M.T. Bautista P.S. White and C.K. Schauer J. Am. Chem. SOC. 1994 116 2143. 63 M. Akita M. Terada N. Ishii H. Hirakawa and Y. Moro-oka J. Organomet. Chem. 1994 473 175. 64 J. Borgdorff N. W. Duffy B.H. Robinson and J. Simpson Inorg. Chim. Acta. 1994 224 73. 408 G. Hogarth (32) Fe = Fe(C0)3 (33) co = Co(C0)3 2+ (34) (35) tetracarbon unit consisting of two linked acetylide moieties being formed by oxygen ab~traction.~’ Binuclear centres carrying alkyne ligands have been linked by the substituent on the alkyne. Reaction of [Co,(CO),] with Me,SiC-CSiMe,H affords the siloxane- bridged complex [{C~,(CO)~(p-Me,SiC~)}~(p-Me~Si-~-si~e,)],~~ which has been crystallographically characterized while reduction of alkyne complexes [Mo~(C~)~(~-HC~CCH=CHR)C~,] (R = H Me) by sodium amalgam affords [(Mo~(CO),(~-HC,)},(~-CH~CHRCHRCH~)] as a result of carbon-carbon bond f~rmation.~~ While the last two examples may be considered as diyne complexes novel tetrayne dicobalt complexes [{ Co,(CO),(p-dppm)(p-RC,)} ,(p-C_CC=C)] can be synthesized by oxidative coupling of [Co (CO),(p-dppm)(p-RC,C~CH)] or by .* lithiation and subsequent coupling of [Co (CO ), (p-dppm)(p-RC,CH=CHCl)] Other symmetrically coupled products include [{ Rh,(p-CH2)2Cp~},(p-S,)]2 (34) + in which the dirhodium centres are linked by a rectangular S unit69 and [(Fe2(CO),(p-CO)Cp,}2{p-C=N(CH,),N=C}] (n = 2,3) which act as bidentate chelating agents via the nitrogen atoms towards a range of Lewis acidic metal halides.70 In [{Co,(CO) ,}{p-Al(thf),} {Co,(CO) 0]] tri- and tetracobalt moieties are linked by a quasi-octahedral aluminium centre being bound through the oxygens of triply bridging ~arbonyls;~~ in [{Rh,(p-RC=CHR)Cp,},(p-cyclo-C,H,Me)] (35) 6s D.M. Norton C. L. Stern and D.F. Shriver Inorg. Chem. 1994 33 2701. 66 R. Ruffolo A. Decken L. Girard H. K. Gupta M. A. Brook and M. J. McGlinchey Organometallics 1994 13 4328. h7 J. F. Capon S. Cornen N. Le Berre-Cosquer R. Pichon R. Kergoat and P. L’Haridon J. Organomet. Chem. 1994 470 137. 68 J. Lewis M. S. Khan M. R. A. Al-Mandhary and P. R. Raithby J. Organomet. Chem. 1994 484 161.6y K. Isobe Y. Ozawa A. Vazquezde de Miguel T.-W. Zhu K.-M. Zao T. Nishioka T. Ogura and T. Kitagawa Angew. Chem. Int. Ed. Engl. 1994 33 1882. ’O S. Schroelkamp W. Sperber D. Lentz and W. P. Fehlhammer Chem. Ber. 1994 127 621. ’’ J. J. Schneider U. Denninger and C. Kriiger 2.Nuturforsch. TeiI B. Chern. Sci. 1994 49 1549. Organometallic Chemistry of Bi- and Polynuclear Complexes 409 (R = CF,) equivalent dirhodium centres are linked by the asymmetric pentadienyl ligand both being bound in a 0-.n vinyl fashion.72 8 0x0 and Imido Complexes A whole range of bi- and trinuclear imido complexes has been prepared by simple metathesis reactions of chloroimido complexes such as [MCl,(NR),] (M = Mo W),73,74 [MCl,(NR)Cp] (M = Nb Ta),73 [NbCl(NR)Cp,],73 and [ReCI(NR),]74 with the carbonyl anions [M(CO),Cp]-(M = Mo W) [Fe(CO),Cp]- [Mn(CO),] - and [Co(CO),] -.For example addition of [Mo(CO),Cp] to [ReCl(NBu') affords binuclear [(NBU'),R~MO(CO),C~],~~ while reaction of two equivalents of the same anion with [MoCl,(NBu'),] gives trinuclear [Cp(CO),MoMo(NBu'),Mo(CO),Cp].74 The same workers also report that one- electron reduction of [MCl,(NBu')Cp] (M = Nb Ta) or [NbCl(NBu')Cp,] affords spin-spin coupled d'-d' imido-bridged binuclear complexes [{ MCl(p-NBu')Cp) ,] and [(Nb(p-NBu')Cp,} 2] respectively.7 While the bis(su1fido) complex [{ Mo(NBu')(p-S)Cp},] has the expected trans- planar core geometry,76 the related fluorinated imido complex [{ MoO(p-NC,F,)Cp') ,]quite unexpectedly possesses a cis-puckered central core previously only observed for the analogous tetraoxo species.77 The sulfido complex displays some interesting reactivity.Addition of AgOTf affords a one-dimensional polymer in which dimolybdenum units are linked by repeating SAg,S rings while iodine gives the crystallographically characterized charge-transfer adduct [MO(NBU')(~-SI,)C~],.~~ Bergman and coworkers have reported the synthesis of the diiridium imido complexes [Ir2(PR,Me)(p-NR')Cp;] (R = Ph R' = But; R = Me R' = Ph),78 and also heterobimetallic [Cp,Zr(p-NBu')IrCp*] (36).79The latter is highly reactive undergoing addition of both polar (NH OH SH) and non-polar (H, SiH CH) bonds across the metal-metal vector. A very unusual transformation occurs upon addition of diethylphosphine oxidative addition of the phosphorus-hydrogen bond being fol- lowed by insertion of the phosphido moiety into the imido ligand to yield [Cp,Zr(p- Bu'NPEt,)IrHCp*] (37).79 Reaction of [{ReO(p-O)Cp*),] with [W(CO),(CGCPh)Cp] at 100"C affords the bridged acetylide complex [Cp*Re(O)(p-C=CPh)W(CO),Cp] (38) which reacts further with oxygen at 100°C to give the isomer [Cp*Re(CO)(p-CO)(p-C-CPh)W(O)Cp] (39) as a result of intermetal 0x0 transfer.When the reaction was carried out with 170-labelled oxygen the label was incorporated suggesting that a peroxo complex may be an intermediate in the transformation.80 Publications from three different groups are concerned with mixed os-mium-tungsten 0x0-containing clusters. Hydrogenation of [Os,W(CO) (p3-72 R.S.Dickson M. J. Liddell B. W. Skelton and A.H. White Aust. J. Chem. 1994 47 1613. 73 J. Sundermeyer and D. Runge Angew. Chern. Int. Ed. Engl. 1994 33 1255. 74 J. Sundermeyer D. Runge and J.S. Field Angew. Chem. Int. Ed. Engl. 1994 33 678. 75 S. Simone and J. Sundermeyer J. Organomet. Chem. 1994 472 127. 76 J. Allshouse R. C. Haltiwanger V. Allured and M. Rakowski Du Bois Inorg. Chem. 1994 33 2505. 77 J. Fawcett J. H. Holloway E. G. Hope D. R. Russell G. C. Saunders and M. J. Atherton J. Organomet. Chem. 1994 464 C20. 78 D. A. Dobbs and R. G. Bergman Organometallics 1994 13,4594. 79 A.M. Baranger and R.G. Bergman J. Am. Chem. Soc. 1994 116 3822. N.3. Lai W.-C. Tu Y. Chi S.-M. Peng and G.-H. Lee Organometallics 1994 13 4652. 410 G. Hogarth Ctol)Cp] results in reduction of a carbonyl ligand and formation of [Os,W(p- H)(CO),(~-O)(~-CH~O~)C~],~~ while thermolysis of [Os,W(CO) {p3-q2-C(O)CH,tol}Cp] affords [Os,W(CO),(p-O)(p3-CCH,tol)Cp],again by car-bon-xygen bond cleavage.82 The latter shows an extensive reactivity centring around the alkylidyne moiety while the 0x0 ligand acts as an innocent spectator.82 A further example of the formation of an oxide upon carbon-oxygen bond cleavage is found in the synthesis of square-based pyramidal [Os,W,(p-H)(CO),(p-O)(p3-CMe)Cp2] and trigonal bipyramidal [Os,W(CO) ,,(p-O)(p3-CMe)Cp] when [Os (p-H)(CO),{p-O=CCH,W(CO),Cp}] is pyr~lysed.~~ In the Os,W complex the 0x0 ligand asymmetrically bridges a tungsten-osmium vector lying closer to the former.Dissolution in dichloromethane however leads to the isolation of isomeric [Os,W(CO) ,(p,-O)(p,-CMe)Cp] in which the 0x0 ligand is three-coordinate and a metal-metal bond is cleaved.Surprisingly heating the latter at 190"C in the solid state regenerates the initial isomer.83 Puddephatt and coworkers give details of the reactivity of [Pt,(p-dppm),(p,- ReO,)]' addition of neutral (CO) and charged (Cl- Br- I-) two-electron donor ligands occurring to the triplatinum face on the cluster.84 Two 0x0-capped tri- ruthenium arene clusters namely [Ru3(p-H),(p-X)(p3-0)(q6-arene),] '(X = H Cl) contain closed (X = H) and open (X = C1) trinuclear centre^.^' 9 Oxygen-and Sulfurcontaining Macrocycles Went and coworkers have used a dicobalt framework in order to prepare oxygen86 and containing macrocycles with carbon-carbon triple bonds.For example protonation of [Co,(CO),(p-dppm)(p-HOCHRC-CCHROH)I results in the forma- J. T. Park J.-H. Chung H.-K. Kim W. K. Yoon I.-H. Suh and J.-H. Lee Bull. Korean Chem. SOC.,1994 15 599. 82 J.T. Park Y. Chi J. R. Shapley M. R. Churchill and J. W. Ziller Organometallics 1994 13 813. 83 J.-H. Gong D.-K. Hwang C.-W. Tsay Y. Chi S.-M. Peng and G.-H. Lee Organometallics 1994,13 1720. 84 J. Xiao L. Hao R. J. Puddephatt L. Manojlovic-Muir K. W. Muir and A. A. Torabi J. Chem. SOC.,Chem. Commun. 1994 2221. *' G. Meister G. Rheinwald H. Stoeckli-Evans and G. Suss-Fink J. Chem. Soc. Dalton Trans. 1994,3215. 86 S.C. Bennett J.C. Jeffery and M.J. Went J. Chem. SOC.,Dalton Trans. 1994 3171. F.G.Mohmand K. Thiele and M. J. Went J. Organomet. Chem. 1994 471 241. Organometallic Chemistry of Bi- and Polynuclear Complexes 411 tion of metal-stabilized dicarbenium complexes which react further with diols HO(CH,),OH (n = 4-6) to give tetraoxacyclodiyne complexes [Co,(CO),(p- dppm){p-C-CCHRO(CH,),OCHR)I, in which the dicobalt centres are incorpor- ated into the macrocycle. A similar synthetic methodology has been used to prepare the sulfur-containing complexes [Co,(CO),{p-C,(CH,SCH2CH~),S]](40) and [CO,(CO),(~-C~CCH,S~~~~~~~~~~~~~~)]~ which lose the metal fragment(s) upon addition of Me,NO to afford the free macrocycles 1,4,7-trithiacycloundec-9-yne and 1,4,7,12,15,18-hexathiacyclodocosa-9,20-diyne respectively. Adams et al. report that thermolysis of 1,5,9-trithiacyclododecane(12-S-3) with pentanuclear [Ru,(CO),,(p5-C)] initially results in the formation of [RU,(CO)~~(~~- C)(p-q1-12-S-3)] in which only a single sulfur atom is metal bound.However under more forcing conditions further carbonyl loss gives [Ru,(CO) (p5-C)(p-q3-12-S-3)] in which all three sulfurs are coordinated to the cluster.88 The same workers also give details of the ring-opening oligomerization reactions of thietane (4-S- 1).89 The previously reported complex [Re3(p-H)3(CO),,(p-4-S-l)]reacts with an excess of thietane resulting in ring-opening and oligomerization to give [Re,@-H),(CO),,{p- S(CH,),},] (n = 4,5,7). Treatment with pyridines release the free macrocycles 12-S-4 16-S-4 and 24-S-6 respectively. The crystal structures of [{(q5-C,H,SCH2CH,)},SFePd]2+ (41)and an acetonitrile adduct have been reported in which the 1,l'-disubstituted ferrocene fragment is part of the macrocycle the palladium being bound within." 1*+ 10 Medium and High Nuclearity Clusters Thermolysis of [Ru5(CO),,(p5-C)] with cyclopentadiene gives [Ru,(CO),,(p,- C)CP,],~~ while reaction of the related dianion [RU~(CO),,(~,-C)]~-with [Pd(a~etone),(q~-C,Ph,)]~ + results in both oxidation of the cluster and transfer of the organic ligand to yield [Ru,(CO) ,(p5-C)(q4-C,Ph,)].The cyclobutadiene ring is bound to one basal ruthenium of the square-based pyramidal cluster.92 Thermolysis of [Ru,(CO),,] with the cyclic phosphine P,Buk affords a number of phosphinidene clusters including [RU~(C~)~,(~~-PBU')~(~~-PBU~)~, [Ru,(CO),,(p,-PBu'),(p4- 88 R.D.Adams S. B. Falloon and K. T. McBride Organometallics 1994 13 4870. 89 R.D. Adams and S. B. Falloon J. Am. Chem. SOC. 1994 116 10540. 90 M. Sato K. Suzuki H. Asano M. Sekino Y. Kawata Y. Habata and S. Akabori J. Organomet. Chem. 1994,470 263. 91 A. J. Blake P. J. Dyson R. C. Gash B. F.G. Johnson and P. Trickey J. Chem. SOC.,Dalton Trans. 1994 1105. 92 P. J. Bailey A. J. Blake P. J. Dyson S. L. Ingham and B. F. G. Johnson J. Chem. SOC.,Chem. Commun. 1994,2233. 412 G. Hogarth PBu'),] and [Ru9(p-H),(CO),,](p3-PBu'),(p7-P)].The last contains an interstitial phosphide resulting from phosphorussarbon bond cleavage.93 Reaction of dicobalt octacarbonyl with Na,Te and [PPh,]Cl in methanol under solvothermal conditions affords [Co 1(Co),,(p4-Te)5(p6-Te)2]2 which has D,, -symmetry and consists of an elongated pentagonal prismatic array of cobalt atoms with a single cobalt in the centre.Each of the five square faces is capped by tellurium the remaining two telluriums capping the pentagonal faces while also being bound to the interstitial cobalt.94 Vacuum pyrolysis of [Os,(CO),,(NCMe),] at 260 "C affords the largest osmium carbonyl clusters yet isolated namely [os17(co)36]2- and [OS,,(CO),,]~-. The former consists of a trigonal pyramidal core of fourteen osmium atoms with a further three capping; the latter has a cubic close packed arrangement of metal centres and is the first example of a totally symmetrical array of metal atoms of this nuclear it^.^^ The hex-3-yne complex [Pt2Ru,(CO),,(p,-EtC,Et),(p,-EtC2Et)] has been pre- pared and crystallographically characterized.It consists of an Ru,Pt dodecahedron capped by the remaining two ruthenium atoms. Interestingly the complex does not obey the polyhedral electron skeletal pair theory but its structure can be rationalized in terms of the 18-electron rule.96 The nonanuclear cluster [Ru6Pt3(p-H)(p3-H)(CO),,(p3-PhC,Ph)] prepared from diphenylacetylene and [Ru,Pt,(p-H),(p,- H)(CO),,],97 is shown to be an effective catalyst for the hydrogenation of the acetylene to (2)-~tilbene.~' At higher temperatures however the catalyst is transformed into new species with low catalytic ability as a result of further alkyne addition to the cluster.98 A further mixed-metal nonanuclear cluster namely [Ru,Rh,(CO),,(p,-B)(p7-B)] -(42),is located from the reaction of [Ru,(CO),(BH,)]- with [(RhCl(CO),f,].It has a complex structure based on a trigonal prismatic Ru,Rh unit with an open-triangular array of the three further metal centres capping a square face.99 The twelve-atom cluster [Pd,RU,(CO),2(p-CO),(p3-co)6]2 consists of a trigonally distorted octa- -hedron of palladium atoms capped by ruthenium centres.'" [Pd,Mn,(CO),,(p,-q2,q2,q2-cyclo-PC,Ph2H2),] (43) has a highly unusual structure based on an 'I' shaped array of metal centres. The 2,5-diphenylphospholyl ligand bridges the palladium atoms through phosphorus while coordinating to the manganese in a diene-like fashion."' Several larger heterometallic clusters include coinage metals.Reaction of [OS,(CO),,]~-with [Au,Cl,(p-L-L)] [L-L = Ph,P(CH,),PPh, n = 1,2,4] in the presence of TlPF affords [Os,(CO),,(p-Au,(p-L-L)}] which consists of a bicapped octahedron of osmium atoms; one gold atom is in a capping site while the second bridges a metal-metal edge.lo2 The triiron-gold cluster [Fe,(CO),{p3-93 E. Charalambous L. Heuer B. F. G. Johnson J. Lewis W.-S. Li M. McPartlin and A. D. Massey J. Organomet. Chern. 1994 468 C9. 94 R. Seidel R. Kliss S. Weissgraber and G. Henkel J. Chem. SOC. Chem. Commun. 1994 2791. '' B. F. G. Johnson J. Lewis M. McPartlin H. R. Powell P. R. Raithby and W.T. Wong J. Chem. SOC. Dalton Truns. 1994 521. 9b R. D. Adams T.S. Barnard Z. Li W. Wu and J. Yamamoto J. Cluster Sci. 1994 5 551.97 R. D. Adams T. S. Barnard 2.Li W. Wu and J. Yamamoto Organometallics 1994 13 2357. 98 R. D. Adams T.S. Barnard Z. Li W. Wu and J. Yamamoto J. Am. Chem. SOC. 1994 116 9103 99 J. A. Galsworthy C. E. Housecroft and A. L. Rheingold J. Chem. SOC. Dalton Trans. 1994 2359. loo E. Brivio A. Ceriotti R. D. Pergola L. Garlashelli F. Demartin M. Manassero M. Sansoni P. Zanello and F. Laschi J. Chem. Soc. Dalton Trans. 1994 3237. lo' L. Brunet F. Mercier L. Richard and F. Mathey Angew. Chem. Int. Ed. Engl. 1994 33 142. Io2 Z. Akhter S. I. Ingham J. Lewis and P. R. Raithby J. Orgunomet. Chem. 1994,474 165. Organometallic Chemistry of Bi-and Polynuclear Complexes 2-{Au(PPh,)),)] has a square-planar arrangement of gold centres'03 while related + + cobalt clusters [Co(CO),{Au(PPh,)),] and [Co(CO),{Au(PPh,),)]+ consist re- spectively of a bicapped trigonal bypyramid of metal atoms with the cobalt in an equatorial site and a fragment of an icosahedron formed by the gold atoms with the cobalt in the centre.lo4 In a novel reaction addition of [Ni6(CO),,]2- to [AuCI(PPh,)] leads to complete loss of phosphine.The products [Ni12AU6(CO),2(p-CO)12]2-, is best considered as containing a gold octahedron with alternate faces capped in a trigonal prismatic fashion by four Ni,(CO) moieties.lo5 Of the two novel silver-containing clusters [Ag4{p- Fe(C0),},I4-(44)and [Ag5(p-Fe(CO)4),(p3-Fe(CO)4}2]3-(45),the smaller con- sists of a square-planar array of silvers with all four edges bridged by iron carbonyl moieties while the larger comprises a bow-tie arrangement of the coinage metal atoms with iron tetracarbonyl units bridging both ends the top and the bottom.lo6 (44) Fe = Fe(C0)4 (45) Fe = Fe(C0)4 I1 Assorted Complexes Reaction of Cp*H with [OSH2Br6] yields [(OsBr,Cp*},] which provides a conveni-ent entry into diosmium chemistry.For example reduction with lithium aluminium hydride affords the tetrahydro-bridged complex [{ OS(~-H),C~*),].~~~ The diiron mesityl complex [{ Fe(mes)(p-mes)},] exhibits some interesting reactivity. Thus CNBu' inserts into both bridging and terminal sites to give the homoleptic iminoacyl complex [(Fe(~2-mesC=NBu')(p-mesC=NBu')),l while insertion of CNPh occurs only into the bridging sites."' Reduction of [Mn2(p-H)2(C0)6(p-dppm)]by sodium D.L. Sunick P. S. White and C.K. Schauer Angew. Chem. Int. Ed. Enyl. 1994 33 75. Io4 M. Holzer J. Straehle G. Baum and D. Fenske Z. Anorg. AUg. Chem. 1994 620 192. lo' A. J. Whoolery Johnson B. Spencer and L. F. Dahl Inorg. Chem. Acta. 1994 227 269. V. G. Albano F. Azzaroni M. C. Iapalucci G. Longoni M. Monari S. Mulley D. M. Proserpio and A. Sironi Inorg. Chem. 1994 33 5320. lo' C. L. Gross S. R. Wilson and G.S. Girolami J. Am. Chem. SOC.,1994 116 10294. 414 G. Hogarth amalgam affords the dianion [Mn,(CO)6(p-dppm)]2- which displays an extensive chemistry. Acid chlorides afford acyl complexes while oxidation by two equivalents of ferrocenium ion in the presence of primary alkynes affords side-bound vinylidene complexes [Mn2(CO)6(p-q1 ,q2-C=CHR)(p-dppm)] .log Silylene diiron complexes [Fe,(CO),(p-Simes,)]' lo and [Fe,(CO),(p-CO)(p-SiBu'X)Cp,] (X = C1 Br I),' '' have been prepared one of the latter (X = I) reacting with strong Lewis bases"' to give donor-stabilized cationic p-silylyne complexes [Fe,(CO),(p-CO)(p-%But-base)Cp,]+.The diruthenium bis(sily1ene) complex [{ Ru(p-H)(p-SiPh,)Cp*}J reacts with acetylene to give [Ru,(p-H),(p-Ph,SiCH=CHSiPPh,)CpT] (46),which when hydro- genated at 80 "C yields the agostic silyl complex [Ru,H(p-SiPh,H)(p-Ph,SiCH=CH,)Cp;] (47) as a result of silicon-carbon bond cleavage.' l2 The nature of the substituent on the bridging thiolate ligands in [Mo,(CO)(CN)(p-SR),Cp,l -has a profound effect upon the site of methylation being directed at the lone pair on sulfur with electron-releasing substituents and to the cyanide with electron-withdrawing groups.' ' Oxidation of the bridging sulfido ligand in [Re,X,(CS)(CO)(p-S)(p-X)(p-dppm),] + by an NOPF6/02 mixture affords a bridging sulfur dioxide complex stable one- and two-electron reduction products of which have also been prepared.' l4 Two publications give details of ring-opening reactions of thiophenes.Addition of thiophene itself to [{W(OBu') 3} ,] affords [W ,(OBu'),(p-OBu')(q'-C 5H 3S)(p-q2,ql-CCH,CH=CHS)] in which one ring (which has lost a hydrogen) is a-bound through carbon while the second is opened and bridges the ditungsten centre.'I5 Deeming and coworkers have reported on reactions of 2,2'-bithiophene and 2,2',5',2"-trithiophene by Group 8 metal carbonyls.Thus oxidative addition of carbon-hydrogen bonds to the triosmium centre occurs with [Os3(CO),,(NCMe),]. Sulfur-carbon bond cleav- age is however not noted. In contrast reactions with [RU~(CO)~,] or [Fe,(CO),] yield ferrole complexes [M,(Co),(p-HC=CHCH=cR)] (48)(R = thiophene bi- thiophene) as a result of a double carbon-sulfur bond cleavage and extrusion of the latter. In the case of iron an intermediate product [Fe,(CO),(p-q2,q'-A. Klose E. Solari C. Floriani A. Chiesi-Villa C. Rizzoli and N. Re J. Am. Chem. Soc. 1994,116,9123. lo9 X.-Y. Liu V. Riera and M. A. Ruiz Organometallics 1994 13 2925. H. Tobita I. Shinagawa S. Ohnuki M. Abe H. Izumi and H. Ogino J. Organomet. Chem. 1994,473,187. Y. Kawano H. Tobita M. Shimoi and H.Ogino .I.Am. Chem. Soc. 1994 116 8575. T. Takao H. Suzuki and M. Tanaka Organometallics 1994 13 2554. M.-L. Absasq F.Y. Petillin and J. Talarmin J. Chem. Soc. Chem. Commun. 1994 2191. l4 K. J. Kolodsick P.W. Schrier and R. A. Walton Polyhedron 1994 13 457. M. H. Chisholm S.T. Haubrich J. D. Martin and W. E. Streib,.I. Chem. Soc. Chem. Comrnun. 1994,683. 415 Organometallic Chemistry of Bi-and Polynuclear Complexes SCH=CHCHCR)] (49),is also observed; ring-opening has occurred but the sulfur has not been extruded.' ' The tetramethylfulvene-bridged diiron complex [Fe,(CO),(p-q2,q5-cH,CsMe4)] (50)reacts with carbon disulfide to give the dithiocarboxylato complex [Fe,(CO),(p,- S2CCH,CsMe,)] (51) resulting from insertion into the iron-methylene bond.' l7 Photolysis of [Co(CO),Cp] leads to the isolation of a third isomeric form of [(Co(p-CO)Cp),] containing only doubly bridging carbonyls as opposed to previous- ly prepared isomers which have terminal or triply bridging ligands.' l8 Heating the methylene complex [Co,Ir(p-CO),(p-CH,)Cp,Cp*] at 120"C results in carbonyl loss and oxidative addition of a carbon-hydrogen bond yielding [Co,Ir (p-H)(&-Co)(p3- CH)Cp,Cp*] ;the transformation is reversed upon carbonylation." Crystallographi-cally characterized [Re3(p-H),(CO)9(p3-FBF3)]2is a rare example of the tetra- -fluoroborate anion capping a metal triangle through a single fluorine atom.'20 The mechanism of carbonyl substitution in the butterfly clusters [MO,CO,(CO),-~L,(~~-S)~(~~-S)C~!J (n = 1,2; L = PR,) has been studied in some detail.The process is associative and involves formation of an adduct in a pre-equilibrium step; the incoming ligand binds to a wing-tip cobalt centre and the sulfido moiety sitting in the butterfly cage becomes three-coordinate.'21 Reaction of other butterfly clusters [Ru,(CO),~(~~-PR)] (R = Ph NPr') with Ph,P(O)C-CBu' affords the tetrahedral complexes [Ru,(CO),(p-CO)(p3-C,Bu')(p3-Ph,POPR)] re-sulting from a novel phosphorus-oxygen bond formation process.' ,* Thermolysis of [Os,(p-H)(CO),,Cp*] at 50 "C results in simple carbonyl loss and metal-metal bond formation. However further heating above 90°C leads to the stepwise car-bon-hydrogen bond cleavage of two of the methyl groups on the cyclopentadienyl A.J. Arce P.Arrojo Y. De Sanctis M. Marquez and A.J. Deeming J.Organomet. Chem. 1994,479,159. H. Hashimoto H. Tobita and H. Ogino Organometallics 1994 13 1055. M. P. Robben W.E. Geiger and A. L. Rheingold Inorg. Chem. 1994 33 5615. l9 F. H. Forsterling and C. E. Barnes Organometallics 1994 13 3770. C. S. Yang H.C. Hornig F. L. Liao and C. P. Cheng J. Chem. SOC. Chem. Commun. 1994 1657. 121 0.J. Curnow J. W. Kampf M. D. Curtis J.-K. Shen and F. Basolo J. Am. Chem. Soc. 1994,116,224. lZ2 J. F. Corrigan N. J. Taylor and A. J. Carty J. Chem. SOC. Chem. Commun. 1994 1769. 416 G. Hogarth moiety giving [Os4(p-H),(CO),,(p-q1,q5-C5Me4CH2)] (52) and [Os4(p-H)3(C0)9{p3-q1,ql ,q5-C5Me,(CH,),}] respecti~ely.'~~ Ru .Ru Polymeric films with the formula [{ Ru(CO),(bipy)},] (53) formed upon elec- trochemical reduction of [Ru(CO),(bipy),],+ are believed to contain chains of ruthenium atoms.' 24 lZ3 W.Wang H. B. Davis F. W. B. Einstein and R. K. Pomeroy Orgunometullics 1994 13 5113. lZ4 S. Chardon-Noblat M.-N. Collomb-Dunand-Sauthier A. Deronzier R. Ziessel and D. Zsoldes Inorg. Chem. 1994 33 4410.

ISSN:0260-1818    

DOI:10.1039/IC9949100397

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

23 New Compounds and Structures P. LIGHTFOOT School of Chemistry University of St Andrews St Andrews Fife KY16 9ST UK 1 Introduction The aim of this review is to present an overview of the developments in new compounds and structures of interest to the solid state chemistry community in 1994. The field is currently too vast to provide a comprehensive treatment in a review of this size. Instead the content has been limited to new inorganic extended lattice structures and concentrates on new structural types. Hence new phases adopting well-known structure types or simple variants of these are not included. Even then the content is necessarily somewhat subjective and the article seeks to give a flavour of the current directions in inorganic solid state chemistry and include the most interesting new structures across the whole field.The particular area of cuprate chemistry relevant to high T materials is not dealt with as this is covered in another chapter. The organization of the review is via periodic classification-transition metal oxides other metal oxides non-metal oxides and non-oxides. 2 Overview Solid state inorganic chemistry is a flourishing field with the search for technologically important materials becoming ever keener. The imagination and skill of the synthetic chemist is becoming more evident in the materials area with new methods based on soft chemistry becoming as prevalent as the traditional high-temperature routes to new materials. It is particularly apparent that the use of hydrothermal and related methods although still little explored and understood will provide a rich source of fascinating new solid state chemistry and potentially useful materials in the future.Additionally the area of composite inorganic-organic frameworks is becoming more widely explored. 3 Transition Metal Oxides First Row Transition Metal Oxides.-A new polymorph of TiO, TiO,(R) having a ramsdellite-like structure has been synthesized by topotactic oxidation of Lie,,TiO in acidic solution.' A soft-chemical route has also been used to prepare a hybrid layer/tunnel intergrowth structure M6+6Ti16035+6,2 (M = K Rb; -0.7 < 6 < 0.5) J. Akimoto Y. Gotoh Y. Oosawa N. Nonose T. Kumagai and K. Aoki J.Solid State Chem. 1994,113,27. T. Sasaki M. Watanabe Y. Fujiki and Y.Khami Chem. Muter. 1994,6 1749. 417 418 P. Lightfoot 0La a Figure 1 The structure ofLa,Ti,A " -5% (Reproduced by permission f;om J. Solid State Chem. 1994 111 52) comprised of layer-type Ti80Lfg units and tunnel-type Ti,O:; units stacked in an alternating manner. The new reduced titanate Ba2Ti,30,23 has been shown to adopt a close-packed structure related to BaTi'O ,,with additional Ti atoms occupying face-sharing octahedral sites giving a short Ti-Ti distance as in the hexagonal perovskite structure. The structure of a complex mixed oxide of Ti La3Ti,Al1503 (Figure l) has been solved ab initio from combined X-ray and neutron-powder diffraction data4 and represents the most complex structure to have been determined this way to date.A new 24-layer oxide Ba8V702 (Figure 2) has been prepared.' It represents the first vanadium oxide in which both VOZ- and VOZ-coordinations and the coexistence and ordering of all three common oxidation states of vanadium (+3 +4 and +5) are observed. Bi1.7V80166 represents the first example of a hollandite-type J. Akimoto Y. Gotoh M. Sohma K. Kawaguchi and Y. Oosawa J. Solid State Chem. 1994 113 384. R.E. Morris J.J. Owen J.K. Stalick and A.K. Cheetham J. Solid State Chern. 1994 111 52. G. Liu and J.E. Greedan J. Solid State Chem. 1994 108 371. F. Abraham and 0.Mentre J. Solid State Chem. 1994 109 127. New Compounds and Structures Figure 2 The structure of Ba,V,O, (Reproduced by permission from J. Solid State Chem.1994 108 371) compound having bismuth in the large tunnels. Bi is coordinated by a very flat square pyramid of oxygen atoms from the V80, framework. A new Mn"' oxide BaMn,O,(OH) has been prepared hydr~thermally.~ The structure consists of ribbons composed of four parallel chains of edge-sharing MnO octahedra. One out of two Mn atoms is missing from the inner chains the corner-sharing oxygens from these chains being replaced by Ba. Several interesting new nickel oxides have been studied. YSr,Ni,O is a stoichiomet- ric oxide of Ni' having a structure related to that of Sr,CuO in which 1/3 of the bridging oxygen atoms are missing from chains of apex-linked Ni-0 square planes. On the contrary the Yb-Sr-Ni-0 system has no K,NiF,-related phases.Instead YbSr,NiO has a structure related to that of K,PtC1,.9 The phase previously reported as Sr,Ni,O, has been shown" to be the mixed valent Sr,Ni,O,. This material adopts ' 0.Tamada H. Paulus H. Fuess N. Yamamoto and S. Muranaka J. Solid State Chem. 1994 108 112. M. James and J.P. Attfield J. Chem. Soc. Chem. Commun. 1994 1185. M. James and J.P. Attfield J. Mater. Chem. 1994 4 575. lo F. Abraham S. Minaud and C. Renard J. Mater. Chem. 1994 4 1763. 420 P. Lightfoot a trigonal structure with three independent face-sharing sites-suggesting partitioned Ni" in octahedral and Ni" in trigonal prismatic coordination. The compound Sr,NiPtO,' also contains trigonal prismatic Ni" in a one-dimensional structure related to that of Sr,PtO,. Stoichiometric BaNi,~,,O,, again shows partitioning of mixed valence Ni.Three octahedral sites in the hexagonal perovskite-related structure are occupied" by Ni" N?" and Ni".Finally Li,Ni,TaO has a novel rock-salt superstructure with Ta ordered and Li/Ni partially ordered over octahedral sites. l3 The Li site disorder is static and does not yield significant Li+ ion conductivity. Cuprates containing discrete planar CuO sheets have continued to be widely studied in relation to superconductivity and are discussed elsewhere in this Volume (in the chapter entitled 'Conducting Solids Covering Ionic and Electronic Conductors'). One example of a related structure is the mixed copper-cobalt phase Eu,~,Ba,~,Co,Cu30 2,14 which adopts a new structure comprising a 1 1 intergrowth of '112' and '1 23' elements.A new three-dimensional oxygen-deficient copper perovskite La,BaYCu,O, (Figure 3) has been ~repared.'~ It is related to the well-known La,BaCu,O, by insertion of extended layer-like '123' areas in the three-dimensional network caused by incorporation of the smaller Y ion. + A new series of magnetic cuprates RCu,O (R = La Nd Sm and Eu) has been reported.' The Cu-0 network consists of a three-dimensional array of corner-shared CuO square planes with a Cu-0-Cu angle of -115".A complex new series of tubular bismuth cuprates has been prepared by Li-doping of (Bi +xSr2 -,CuO +&-(Sr8-,,Cu6016+z). Models have been proposed for various members on the basis of detailed HREM data.17 Heavier Transition Metal Oxides.-A complex mixed oxide of Zr and Nb Li29Zr9Nb3040,has been identified and shown to have a rock-salt-related superstruc- ture18 in which 5% of the oxygen sites are vacant in an ordered manner.Li and Zr/Nb order on the cation sub-lattice with Li adopting four- five- and six-coordination. Several new reduced niobates have been prepared. Nb18P,~,05 is a slightly reduced form of Nb,PO, and is isostructural with it.19 It adopts a block structure with 3 x 3 Re0,-type slabs connected in chains leading to semiconducting behaviour in this direction. Rbl~,,NbloOl (Figure 4) has three discrete Nb sites." The reduced Nb is sited in octahedral [Nb,O,,]O clusters while NbV occurs in both octahedral and tetrahedral sites. A related compound is Rb,A1,Nb3s0,,,21 again having three types of Nb site-octahedral [Nb,O,,]O clusters isolated NbO octahedra and Nb,O clusters of face-sharing octahedra.T.N. Nguyen D. M. Giaquinta and H.-C. zur Loye Chem. Muter. 1994 6 1642. J. A. Campa E. Gutierrez-Puebla M. A. Monge I. Rasines and C. Ruiz-Valero J. Solid State Chem. 1994 108 230. l3 J.G. Fletcher G. C. Mather A. R. West M. Castellanos and M. P. Gutierrez J. Muter. Chem. 1994,4 1303. l4 L. Barbey B. Domenges N. Nguyen and B. Raveau J. Solid State Chem. 1994 111 238. l5 R. J. Cava H. W. Zandbergen R. B. Van Dover J. J. Krajewski T. Siegrist W. F. Peck jr. R. S. Roth and R. J. Felder J. Solid State Chem. 1994 109 345. l6 S.W. Keller V.A. Carlson D. Sandford F. Stenzel A. M. Stacy G.H. Kwei and M. Alario-Franco,J.Am. Chem. Soc. 1994 116 8070. li G. Van Tendeloo B. Domenges M. T. Caldes M. Hervicu and B. Raveau J. Solid State Chem. 1994,112 161. P. Lightfoot J.B. Thomson F. J. Little and P.G. Bruce J. Muter. Chem. 1994 4 167. l9 J. Xu S.C. Chen K. V. Ramanujachary and M. Greeblatt Inorg. Chem. 1994 33 267. " N. Kumada N. Kinomura R. Wang and A. W. Sleight Muter Res. Bull. 1994 29 41. '' M.J. Geselbracht and A.M. Stacy J. Solid State Chem. 1994 110 1. New Compounds and Structures 421 Ba eY La CU06 cuos cuo4 octahedion pyramid square Figure 3 Idealized structure of La,BaYCu,O, (Reproduced by permission from J. Solid State Chern. 1994 109 345) A new reduced Ruddlesden-Popper related phase Rb,LaNb20,,22 has been prepared by a novel soft-chemical route-reaction of RbLaNb207 with Rb vapour at 250°C.The structure of Li,NaTa,O, has been derived from powder diffraction data., It is related to the tetragonal tungsten bronze structure with Ta in octahedra and pentagonal bipyramids and Na occupying the pentagonal channels. Molybdate chemistry has remained a very active area. Two fully oxidized compounds NaY(MoO,) and Na,Y(MoO,), have been shown to have structures related to that of scheelite., The latter phase has Na partially occupying the tetrahedral sites in an ordered arrangement with Mo. The reduced phase (Mo,Nb),,O, has a block structure composed of 3 x 4 blocks interconnected through MOO tetrahedra.25 K,.,,Ba,~,,Mo,,O, (Figure 5) has been shown to be the n = 5 member of the metal-metal bonded oligomer series M,-xM04n+206n+4 containing Mo, clusters consisting of five trans edge-shared Mo octahedra26 with all octahedral edges bridged by 0 atoms.Similarly Ba3Mo,,02,27 represents the n = 4 oligomer. A prominent feature of these structures is the pronounced short-long-short arrangement of apical-apical Mo bond distances. 22 A. R. Armstrong and P. A. Anderson Inory. Chem. 1994 33 4366. 23 J. Grins L. Banos D. C. Sinclair and A. R. West J. Muter. Chem. 1994 4 445. 24 N.J. Stedman A.K. Cheetham and P.D. Battle J. Muter. Chem. 1994 4 707. 25 S.C. Chen and M. Greenblatt J. Solid State Chem. 1994 108 366. 26 G. L. Schimek and R. E. McCarley J. Solid State Chem. 1994 113 345. ’’ G. L. Schimek D.A. Nagaki and R.E. McCarley Znorg. Chem. 1994,33 1259.422 P. Lightfoot Rb Nb06 octahedra Nb04 tetrahedra Figure 4 Crystal structure ofRb,,,,Nb,,O, (Reproduced by permission from Mater. Res. Bull. 1994 29 41) The structures of two new layered molybdates have been derived from powder diffraction data. Mo03.1/2H20 has isolated layers formed by double rows of edge- sharing octahedra linked through corner-sharing octahedra.28 (NMe,)Mo -,O has a different arrangement of the MOO octahedra than any of the known molybdenum oxides.29 Two new tungstates have been prepared and characterized.,’ La,W,O, can be considered a distorted superstructure of scheelite with 1/3 of the A sites vacant. The compound LaFeW,O, (Figure 6) has a layer structure consisting of two distinct layers; the first has WO tetrahedra and La in eight-coordination whereas the second has both Fe and W in edge-sharing octahedra.The subvalent oxide Ag,SiO has been shown to contain both isolated Ag’ ions and Ag clusters suggesting a better formulation as [Ag614+ (Ag+),(SiO:-)2.31 4 Other Oxides Metal Oxides.-Bismuth oxide chemistry has remained active due to its relevance in the high T field. Somewhat surprisingly in this respect new structural details are still being elucidated in the ‘simplest’ systems. Bi,BaO,. has been shown to adopt a perovskite-related structure with Bi and Ba randomly occupying the B sites.32 High ionic conductivity is observed on the anion sub-lattice. CaBi20 has been shown to adopt a sheet structure with four-coordinated Bi polyhedra distorted to accommodate ” P.Benard L. Seguin D. Louer and M. Figlarz J. Solid State Chem. 1994 108 170. ” J. Guo P. Zavalij and M. S. Whittingham Chem. Muter. 1994 6 357. 30 M. Gartner D. Abeln A. Pring M. Wilde and A. Reller J. Solid State Chem. 1994 111 128. 31 C. Linke and M. Jansen Inorg. Chem. 1994,33 2614. 32 C. Michel C. Pelloquin M. Hervieu B. Raveau F. Abbattista and M. Vallino J. Solid State Chem. 1994 109 122. New Compounds and Structures Figure 5 The structure ofK,,,,Ba,,,,Mo,,O, (Reproduced by permission from J. Solid State Chem. 1994 113 345) the lone pair.33 A new oxyhydroxide La0,26Bi0,7400H has been shown to be the first example of a PbFC1-related structure with complete substitution of OH on the C1 site.34 Sb,WO has been reported to be the first pure Sb analogue of the Aurivillius series of bismuth oxides.35 A new gallate Na,Ti,-,Ga,+,0,,,36 has been studied as a potential Na' ion conductor.The structure shows sodium ions residing in one- dimensional tunnels of octagonal cross-section. Phosphates.-Phosphate chemistry continues to be one of the most active areas of exploratory solid state chemistry. Many new structure types have been reported this year synthesized either hydrothermally or by solid-state reaction. Raveau and co-workers have continued to be prominent in the development of transition metal phosphate chemistry by solid-state means. The new reduced titanium phase K0.,8TiP20,37 has been shown to contain corner-linked TiO and P207groups 33 I. Natali Sora W. Wong-Ng Q.Huang R. S. Roth C. J. Rawn B. P. Burton and A. Santoro J. Solid Stute Chem. 1994 109 251. 34 N. Kumada N. Kinomura S. Kodialam and A. W. Sleight Muter. Res. Bull. 1994 29 497. 35 A. Castro P. Millan R. Enjalbert E. Snoeck and J. Galy Muter. Res. Bull. 1994 29 871. 36 Y. Michiue and M. Watanabe Solid Stute lonics 1994 70/71 186. 37 A. Leclaire J. Chardon M. M. Borel and B. Raveau J. Solid Stute Chem. 1994 109 83. 424 P. Lightfoot C Figure 6 Schematic diagram of the structure of LaFeW,O, (Reproduced by permission from J. Solid State Chem. 1994 111 128) forming tunnels; of the two independent K sites one is partially occupied suggesting a possibly wide range ofnon-stoichiometry .Several new vanadium phosphates have also been prepared-Cd,V,(P0,),,38 CdV,0(P0,),,39 Pb2V,VO(P0,),,40 and Cd,VP0,41 contain vanadium in oxidation states 11 111 III-IV and v respectively.Two new niobium phosphates show relationships to well known oxide structures; RbNb,P0842is derived from the hexagonal tungsten bronze structure via an ordered substitution of PO tetrahedra for NbO octahedra whilst Rb3NbsP,0,,43 is related to pyrochlore. The same group have also reported several molybdenum phosphates. Layer structures are obtained for B~Mo,O,(PO,)~,~~ derived from cube-like Mo,O:+ units and KMO,P,O,,,~~ derived from sheets of alternating vertex-linked MOO,and PO polyhedra joined by unusual trigonal bipyramidal MOO groups. Tunnel structures are obtained for R~,O,(MOO),(PO,),,~~ which is derived from the 38 S.Boudin A. Grandin M. M. Borel A. Leclaire and B. Raveau J. Solid State Chem. 1994 110 43. 39 S. Boudin A. Grandin M. M. Borel A. Leclaire and B. Raveau J. Solid State Chem. 1994 111 380. 'O A. Leclaire J. Chardon A. Grandin M. M. Borel and B. Raveau J. Solid State Chem. 1994 108 291. 41 S. Boudin A. Grandin A. Leclaire M. M. Borel and B. Raveau J. Solid State Chem. 1994 111 365. 42 A. Leclaire M. M. Borel A. Grandin and B. Raveau J. Solid State Chem. 1994 110 256. 43 A. Leclaire M. M. Borel J. Chardon and B. Raveau J. Solid State Chem. 1994 111 26. ''M.M. Borel J. Chardon A. Leclaire A. Grandin and B. Raveau J. Solid State Chem. 1994 112 317. 45 A. Guesdon M. M. Borel A. Leclaire A. Grandin and B. Raveau J. Solid State Chem. 1994 109 145. 46 M. M. Borel A.Leclaire A. Guesdon A. Grandin and B. Raveau J. Solid State Chem. 1994 112 15. New Compounds and Structures Figure 7 Portion of the crystal structure of Cs,Mo,O,(PO,),.H,O (Reproduced by permission from J. Solid State Chern. 1994 111 315) previously known K,O(MoO),(PO,) by a 180" rotation of adjacent layers and CS6M070,(P04),.H20,47 which has large 'butterfly-shaped' tunnels from which water can be reversibly de-intercalated. (Figure 7). Other new phosphates prepared by solid-state techniques include CaYP70,0,48 the first characterized n = 5 member of the ultraphosphate series [P,+ ,03*+ J- U(U0,)(P04),49 which has discrete Uv' and U" sites in PaC1,-type chains and P-BaV,(P,O,) having a complex intersecting tunnel structure. O Hydrothermal methods have been used by many groups to prepare new phosphates.Ferey and colleagues have extended their series of oxyfluorinated phosphates to include several new gallium phase^^',^^ as well as materials based on vanadium and iron. Ga16(P04)14(HPO)2(OH),F7.[H,N(CH2)6NH3],.6H,0 has been shown to contain 16-membered ring channels and is the first phase to include both bonding and encapsulated F-(Figure 8). [V,P04F12 -[C2N,H,,]2 53 and Fe3 +Fe2 fF,(HP0,),.ethylenediamine.2H2054 + represent the first reported fluorinated vanadium and iron phosphates respectively. Two further microporous gallium phosphates are Ga3P30,,0H.H3CNH,CH3,55 isotypic with AlP04-21 and Ga3(P0,),F3P.C,Hl,N (Figure 9),56 containing bell-shaped channels of approximate dimensions 7 x 9 A.Reduced and mixed valence 47 A. Guesdon M. M. Borel A. Leclaire A. Grandin and B. Raveau J. Solid State Chem. 1994 111 315. 4R A. Hamady and T. Jouini J. Solid Stute Chem. 1994 111 443. 49 P. Benard D. Louer N. Dacheux V. Brandel and M. Genet Chem. Muter. 1994 6 1049. S.-J. Hwu R.1. Carroll and D. L. Serra J. Solid State Chem. 1994 110 290. 51 T. Loiseau R. Retoux P. Lacorre and G. Ferey J. Solid State Chem. 1994 111 427. 52 T. Loiseau and G. Ferey J. Solid State Chem. 1994 111 403. 53 D. Riou and G. Ferey J. Solid Stute Chem. 1994 111 422. 54 M. Cavallec D. Riou and G. Ferey J. Solid State Chem. 1994 112 441. 55 T. Loiseau D. Riou M. Licheron and G. Ferey J. Solid State Chem. 1994 111 397. '' X. Yin and L.F. Nazar J. Chem. Soc. Chem. Commun.1994 2349. 426 P. Lightfoot Figure 8 Theframework structure of Gal6(P04)14(HP04),(OH),F,.[H,N(CH2),NH3]4.6H,0 (Reproduced by permission from J. Solid State Chem. 1994 111,403) Figure 9 Framework structure ofGa3(P04),F,P.C4H14Nz (Reproduced from J. Chem. SOC. Chem. Commun. 1994 2349) New Compounds and Structures A10 PO 0. Co No Figure 10 Two views of the layer structure o{ (Al,P,O 6)3 -[NH,(CH,),NH,] (C,H oNH2)f + (Reproduced from J. Chem. Soc. Chem. Commun. 1994 565) vanadium phosphates have been further explored. Cs[(V,03)(HP0,),(H,0)] 57 has a one-dimensional (-V'v-O-Vv-O-) chain of corner-sharing octahedra. Two new layered V" compounds have been shown to be based on distorted and defected VOPO layers,58 whilst V,P,O,,(H,O),.H,N(CH,),NH is a mixed valence microporous phase having ten-membered ovoid channels.59 The potassium vanadium phosphates K,(VO)(V,03)(P0,),(HP04)and K3(VO)(HV,0,)(P04),(HP0,) are isostructural and differ only in the addition of an extra hydrogen atom into nearly iden tical frameworks.6o " R.C. Haushalter Z. Wang M. E. Thompson J. Zubieta and C. J. O'Connor J. Solid Stute Chem. 1994 109 259. '' V. Soghomonian R. C. Haushalter Q. Chen and J. Zubieta Inorg. Chem. 1994,33 1700. 59 T. Loiseau and G. Ferey J. Solid State Chem. 1994 111 416. 6o J.T. Vaughey W.T.A. Harrison and A. J. Jacobson J. Solid Stute Chem. 1994 110 305. 428 P. Lightfoot Figure 11 The structure of [C,H,NH] +[CoGa2P,OI2]-(Reproduced from J. Chem. Sac. Chem.Commun. 1994 2453) A new layered aluminophosphate,61 (Al,P4016)3-[NH,(CH2)sNH,]2+ (CsHloNH2)+ has been prepared using 1,5-diaminopentane as the initial template molecule (Figure 10). Cyclization of part of the template to give piperidinium and partioning of the two resultant species into different voids circular and elliptical within the layers is a unique example of a reactive template in hydrothermal synthesis. Two new microporous cobalt-containing phosphates have been reported; COPO,.O.~C~H~~N,~~ is the first reported open framework structure with a 1 1M :P ratio having the transition metal exclusively occupying tetrahedral sites whilst [C,H,NH] +[CoGa,P,O 12] -(Figure 1 1) is the first heteroatom-substituted micro- porous gallium ph~sphate.~~ The zinc phosphate Zn4(P04)3(H20)(C,HsNH,)64 is unusual in having a M :P ratio greater than unity leading to direct Zn-0-Zn linkages.In the search for ever more complex framework structures K[Ni(H,0),A1,(P04),] is the first reported example of an octahedral/trigonal bipyramidal/tetrahedral framework Des-pite the abundance of work on AlPO’s and GaPO’s very little work has been reported 61 R. H. Jones A. M. Chippindale S. Natarajan and J. M. Thomas J. Chem.SOC.,Chem. Commun. 1994,565. 62 J. Chen R. H. Jones S. Natarajan M. B. Hursthouse,andJ. M. Thomas Angew. Chem.,Int. Ed. Engl. 1994 33 639. 63 A.M. Chippindale and R.I. Walton J. Chem. SOC. Chem. Commun. 1994 2453. 64 T. Song M. B. Hursthouse J. Chen J. Xu K. M. A. Malik R. H. Jones R. Xu and J. M.Thomas Adv. Muter. 1994 6 679. 65 L. M. Meyer and R.C. Haushalter Chem. Mater. 1994 6 349. New Compounds and Structures 429 on the heavier B-metal phosphates; Cs[In2(P0,)(HP0,)2(H,0),]66 is one of the few indium phosphates so far characterized. An unusual layered zirconium phosphate Zr(P0,)F(OSMe,),67 has the axial sites of the metal octahedra occupied by a fluoride ion and the oxygen of a solvent dimethyl sulfoxide molecule. Mg,[Be,(PO,) (OH)]-.6H,068 contains a new one-dimensional polymeric chiral beryllophosphate anion. Two other new non-centrosymmetric structures are the new titanyl phases Rb,Ti302(P0,),(HPO)2 and Rb3Ti,0(P,07)(P0,)3,69 however the short ‘titanyl’ Ti=O bond characteristic of the non-linear optical KTP (KTiOPO,) materials is barely apparent in these compounds and they show poor non-linear response.Other phosphorus-containing oxides i.e. phosphites and organophosphonates are beginning to be explored with reports of a new one-dimensional phosphite VO(H2P02),.2H2070 and two-dimensional phosphites CO(H,PO,),.~H,O~~ being studied. The latter series is capable of reversible topotactic water de-intercalation and also pyridine intercalation. Organophosphonates include the layered com-pounds (C2H 5NH3 )2 Cv303(H20)(PhP03)41 and c(c2 5 )4N1[(vo)3 (OH)(H20) (C,H5P03)3].H,0,73 and the 3-D framework ~?-CU(CH,PO,).~~ Other Oxyanion Derivatives.-Two reduced vanadium arsenates having 1-D chain structures have been reported,75 and two isostructural framework vanadium ar-senates A(VO),(AsO,) (A = Ba or Sr)76 have been described.A new berylloarsenate Be,(A~0,),.2H,0,~~ has been shown to contain bridged tetrahedral 3-rings. In the search for new non-linear optical materials two new early transition metal arsenates N~N~,AsO,~~ have been reported. A new mixed orthovana- and CS~T~,AS,O~,,~~ date-pyrovanadate series MBa2V301 or MBa,V,PO,, with M = Bi In or Ln has been discovered.” A model has been proposed for the structure of the new microporous titanosilicate ETS-10 using a combination of methods.81 The structure contains twelve-membered rings built from SiO tetrahedra and TiO octahedra and displays a considerable degree of disorder. A second porous titanosilicate is Na2Ti,03Si04.2H,0.82 With a view to understanding the mechanism of formation of the new mesoporous silicate materials (M41S) the structures of some heteronetwork clathrates of approximate compositions [NPhMe,],[Si,O (OH),] .38.7H20 and [NPhCH,Me3],02,].53.6H20 have been studied.83 The structure of a new mesopor- 66 S.S. Dhingra and R.C. Haushalter J. Solid State Chem. 1994 112 96. 67 D. M. Poojary B. Zhang and A. Clearfield J. Chem. SOC. Dalton Trans. 1994 2453. 6R C. Rob1 and V. Gobner 1.Chem. SOC.,Chem. Commun. 1994 2345. 69 W.T. A. Harrison T. E. Gier J.C. Calabrese and G. D. Stucky J. Solid State Chem. 1994 111 257. ’O A. Le Bail M.D. Marcos and P.Amoros Inorg. Chem. 1994 33 2607. M.D. Marcos P. Amoros D. Beltran and A. Beltran Inorg. Chem. 1994 33 1220. 72 M.I. Khan Y.-S. Lee C. J. O’Connor R.C. Haushalter and J.Zubieta Inorg. Chem. 1994 33 3855. 73 M.I. Khan Y.-S. Lee C.J. O’Connor R.C. Haushalter and J. Zubieta Chem. Mater. 1994 6 721. 74 J. Le Bideau C. Payen P. Palvadeau and B. Bujoli Inorg. Chem. 1994,33 4885. 75 R. C. Haushalter Z. Wang L. M. Meyer S. S. Dhingra M. E. Thompson and J. Zubieta Chem. Mater. 1994 6 1463. 7h S.-L. Wang and C.-Y. Cheng J. Solid State Chem. 1994 109 277. 77 W.T.A. Harrison T. M. Nenoff T. E. Gier and G.D. Stucky J. Solid State Chem. 1994 111 224. 78 W.T.A. Harrison C.S. Liang T. M. Nenoff and G. D. Stucky J. Solid State Chem. 1994 113 367. 79 K.-H. Lii J. Chem. Soc. Dalton Trans. 1994 2289. 8o J. Huang Q. Gu and A. W. Sleight J. Solid State Chem. 1994 110 226. M. W. Anderson 0.Terasaki T. Ohsuna A. Philippou S. P. MacKay A.Ferreira J. Rocha and S. Lidin Nature 1994 367 347. D. M. Poojary R.A. Cahill and A. Clearfield Chem. Mater. 1994 6 2364. ’’ J. Emmer and M. Wiehcke J. Chem. SOC.,Chem. Commun. 1994 2079. 430 P. Lightfoot ous aluminosilicate MCM-21 shows many unique and interesting features. This material has two independent pore systems both accessed by ten-ring openings one consisting of sinusoidal channels and the other large twelve-ring supercages of inner height 18.2 Three new condensed framework silicates BaVSi207,85 B~,SC,(S~O,),,~~ and Li,Ca,Si,O 3,87 have also been reported. A distorted phar- macosiderite analogue Na,H,(H,PO,),[(GeO)(GeO,),l .4H2Og8has been shown to contain both anions and cations as included species; both can be easily exchanged for a variety of other ions.Keszler et al. have prepared several new borate structure types the most notable being the huge 'STACK' family of stoichiometry A,M' M2(B0,),,89 of which over 150members are reported for large A cations and smaller +2 + 3 or +4 M M' cations. When M' = M2 are larger trivalent cations a new layered structure type is ob~erved.~' Powder diffraction data for the solid solution Ba,Y -xEu,(B03) has revealed the maximum size of M that the structure can tolerate. Three new beryllium borates and a zinc borate have been prepared and characterized for their interest as optical materials; Lil,Be5B(B03)g,91 BaBe,(B0,)292 and NaBe2B0,F,93 and Ba,Zn(B0,),.94 Several new selenites have been reported; Ga(HSeO,)(Se,O,).l .07H,0g5 is unusual in that it contains alternating anionic and cationic layers.Another layered phase is NH,(V02)3(Se0,)2,96 which has VO octahedra in a hexagonal tungsten bronze-like arrangement with the octahedra being 'capped' by SeOi-groups. A new mixed valent manganese selenite Mni1Mn~iO(Se0,),,97 has three crystallographicaily distinct MnO octahedra. Final- ly a new tellurate Na,Te,0g,98 has been reported. 5 Halides Chalcogenides etc. Oxyhalides Oxychalcogenides &.-Two new oxybromides M,Cu,O,Br (M = Sr Ba) have been reported." They are composed of planar cU30 sheets related to the CuO sheets in superconductors by the 'filling-in' of every alternate vacant square site with Cu intergrown with fluorite-type M,Br layers. A new tin oxyfluoride Sn,OF,,lOO has been prepared by hydrolysis of SnF,.The structure includes Sn" in four discrete crystallographic sites. The compound Sm,Ta,Cl,O lo' has been shown to consist of layers of Ta octahedral dimers alternating with layers of Sm face-capped trigonal prismatic dimers. BiCuOS and the isostructural selenides (MO)(CuSe) 84 M. E. Leonowicz J.A. Lawton S.L. Lawton and M. K. Rubin Science 1994 264 1910. 85 G. Liu and J. E. Greedan J. Solid State Chem. 1994 108 267. 86 L.-H. Wang L. F. Schneemeyer R. J. Cava and T. Siegrist J. Solid State Chem. 1994 113 211. '' M. E. Villafuerte-Castrejon A. Dago and R. Pomes J. Solid State Chem. 1994 112 438. " T. M. Nenoff W.T.A. Harrison and G.D. Stucky Chem. Muter. 1994,6 525. 89 K. I. Schaffers,P. D. Thompson T. A. Alekel 111 J.R. Cox and D.A. Keszler Chem. Muter. 1994,6,2014. 90 J. R. Cox D.A. Keszler and J. Huang Chem. Muter. 1994 6 2008. 91 J.L. Luce K. 1. Schaffers and D.A. Keszler Inorg. Chem. 1994 33 2453. 92 K.I. Schaffers and D.A. Keszler Inorg. Chem. 1994 33 1201. 93 L. Mei Y. Wang and C. Chen Muter. Res. Bull. 1994 29 81. 94 R. W. Smith and L. J. Koliha Muter. Res. Bull. 1994 29 1203. 95 R. E. Morris and A. K. Cheetham Chem. Muter. 1994 6 67. 96 J. T. Vaughey W. T. A. Harrison L. L. Dussack and A. J. Jacobson Inorg. Chem. 1994 33 4370. 97 M. Wildner J. Solid State Chem. 1994 113 252. 98 S. L. Tagg J.C. Huffman and J. W. Zwanziger Chem. Muter. 1994 6 1884. 99 W.J. Zhu F. Wu Y.Z. Huang C. Dong H. Chen and Z.X. Zhao Muter. Res. Bull. 1994 29 219. loo I. Abrahams S.J. Clark J. D. Donaldson Z.I. Khan and J.T. Southern J. Chem. Soo. Dalton Truns. 1994 2581. lo' G. Guo M. Wang J. Chen J. Huang and Q. Zhang J. Solid State Chem. 1994 113 434. New Compounds and Structures 431 (M = Bi Nd Gd Dy)lo2 have layered structures composed of alternating fluorite (BiO) units and tetrahedral (CuX) units. The MCuOSe (M = La Sm Y) analogues have also been reported.'03 An interesting new oxysulfide Ba,Ti,Sl,0,'04 may be considered as the first member of the family (BaO),(BaTiS,) formed by rearrange- ment of the infinite-chain BaTiS structure into a layered structure by inclusion of BaO. The oxynitride Na,W0,N'05 has been shown to adopt a wurtzite-like structure related to the low-temperature polymorph of Li,PO,. Three new oxyarsenide U,CU,ASO,'~~ structure types B~,M~,AS,O,'~~ and A,Zn,As,O (A = Ba Srj,lo8 have been reported.The latter is unusual in containing zinc in square planar coordination to oxygen. Sulfides.-Many new sulfide structures have been reported. An interesting new synthetic approach has been the use of supercritical amine solvents in the preparation of new phases in single crystal form. Kolis and co-workers have prepared several new frameworklog and low-dimensional' lo structures by this method. More 'traditional' soft-chemical routes have also been used. Thus hydrothermal techniques have been used to prepare post-transition metal sulfides such as Sn,S,.(NMe,),.H,O (Figure 12),," Cs,Sn5S,,.2H,0,112 Sn5S,0,[HNMe,],,"3 [MeNH,],Sb,S, (Figure 13),ll4 and [Me,N],Ge,S,,.' l5 Many new framework and layered topologies have been discovered and it is clear that this is a rich source of new materials for future work.Soft chemical methods have been used to prepare the new binary sulfide Re$ ,' by topotactic oxidative deintercalation of Na,Re,S ,. The structure consists of Re$ octahedral clusters linked into chains via S-S bridges. The first 'self-misfit' layer compound (Nb -,La,S)NbS, has been prepared and characterized.' l7 The com- pound differs from the normal misfit-layer type 'LaNbS,' by a 45" rotation of the 'NbS' subsystem. Other mixed metal sulfides reported include the AMTeS series"8 (A = K Rb Cs; M = Cu Ag) containing the new trigonal pyramidal polychalcogenide anion TeSi -and two antimony sulfides containing polysulfide anions Cs,Sb,S and CsSbS,.' Selenides and Tellurides.-Cs,M,(P,Se j5 (M = Sb Bi) contain P,Se:- anions in three unique bonding modes leading to a staircase layered framework featuring weak 102 A.M.Kusainova P.S. Berdonosov L.G. Akselrud L.N. Kholodkovskaya V. A. Dolgikh and B. A. Popovkin J. Solid State Chem. 1994 112 189. 103 W.J. Zhu Y.Z. Huang C. Dong and Z.X. Zhao Mater. Res. Bull. 1994 29 143. in4 A.C. Sutorik and M.G. Kanatzidis Chem. Mater. 1994 6 1700. 105 S. H. Elder F. J. DiSalvo J. B. Parise J. A. Hriljac and J. W. Richardson J.Solid Stute Chem. 1994,108 73. 106 S.L. Brock H. Hope and S. M. Kauzlarich Inorg. Chem. 1994 33 405. 107 D. Kaczorowski M. Potel and H. Noel J. Solid State Chem. 1994 112 228. 108 S. L. Brock and S.M. Kauzlarich Inorg. Chem. 1994 33 2491. 109 P.T. Wood W.T. Pennington and J.W. Kolis Inorg. Chem. 1994 33 1556. 110 J. E. Jerome P. T. Wood W. T. Pennington and J. W. Kolis Inorg. Chem. 1994 33 1733. 111 J. B. Parise Y. KO J. Rijssenbeek D. M. Nellis K. Tan and S. Koch J.Chem.SOC.,Chem. Commun. 1994 527. 112 Y. KO C.L. Cahill and J.B. Parise J. Chem. SOC.,Chem. Commun. 1994 527. 113 J. B. Parise and Y. KO Chem. Muter. 1994 6 718. 114 X. Wang and F. Liebau J. Solid State Chem. 1994 111 385. 115 J.Y. Pivan 0. Achak M. Louer and D. Louer Chem. Mater. 1994 6 827. 116 A. Nemudry and R. Schollhorn J. Chem. Soc. Chem. Commun. 1994 2617. 1 I7 R. Roesky A. Meerschaut A. van der Lee and J. Rouxel Muter. Res. Bull. 1994 29 1149. 118 X. Zhang and M.G.Kanatzidis J. Am. Chem. Soc. 1994 116 1890. 119 T.J. McCarthy and M.G. Kanatzidis Inorg. Chem. 1994 33 1205. 432 P. Lightfoot Figure 12 Crystal structure of Sn,S,.(NMe,),.H,O (Reproduced from J. Chem. Soc. Chem. Commun. 1994 527) Figure 13 The structure of [Me,NH,],Sb,S, (Reproduced by permission from J. Solid State Chem. 1994 111 385) M-M interactions.12' Two unusual fluorochalcogenides BaCuFQ (Q = S Se) have been reported. They have tetragonal layered structures and may be viewed as intergrowths of fluorite-type [Ba,F,] and anti-fluorite-type [CU,Q,].'~' Exploratory lZo T.J. McCarthy T. Hogan C. R. Kannewurf and M.G. Kanatzidis Chern. Muter. 1994 6,1072. lZ1 W.J. Zhu Y.Z. Huang F. Wu C. Dong H.Chen and Z.X. Zhao Muter. Res. Bull. 1994 29 505.New Compounds and Structures 433 telluride chemistry has been very productive. Electrochemical methods have been used to synthesize several new one-dimensional materials containing tetraalkyl ammonium cations.' 22-1 24. Solid-state methods have also produced interesting new chain corn pound^.'^^^'^^ Two modulated structures in the series MA,Te (M = Nb Ta;A = Si Ge) have been st~died;'~~,'~~ TaSi,,,,,Te has an incommensurate superstructure which can be considered as a succession of commensurate domains of TaSi,,,Te and TaSi,,,Te structures. N~,F~CU,~,,T~,~~~ contains Nb,Fe,Cu,Te units stacked together to produce chains with one-dimensional extended metal-metal bonds. Halides.-The major effort has been in metal halide cluster chemistry by Corbett and co-~orkers.'~~ Extended lattice compounds have also been studied.An interesting new series of metallic tin halides has been re~0rted.I~' These materials have layered structures related to the Ruddlesden-Popper phases but differ in having quaternary ammonium cations between perovskite-like tin halide sheets (see for example Figure 14). Variable chain length alkyl groups in the cation allow a great deal of tunability of the conducting properties. another example of combined 'molecular' and 'extended lattice' solid state chemistry is in the stabilization of NbI monomers in the layered structure of Nb,S,I, (Figure 15).13' Gd,I,Mn13 contains distorted double chains of Gd,Mn edge-sharing octahedra. The isostructural series MMnZrF (M = T1 Rb NH, K) is unusual in containing seven-coordinated Mn2 in alternating edge-shared + pentagonal bipyramids with Zr4 + linked together to form a three-dimensional framework.Nitrides &..-New synthetic routes to nitrides are receiving increasing attention due to their potentially interesting structure and properties. LiWN,', has been prepared by the reaction of Li2W0 and NH at elevated temperature. The compound is metallic and is isostructural with LiMoN, having a layered structure with trigonal prismatic W5+. The identification of the subnitrides Na,,Ba,N and Ag,,Ca,N previously reported as Ag,Ca, containing discrete Ba,N octahedra suggest that subnitride chemistry may be more common than expected.', A new quaternary nitride Li3Ba2NbN,,l3 has also been reported; Nb is tetrahedrally coordinated by N.An exciting development has been the discovery of superconductivity above 20 K in the borocarbides LnNi,B,C. The compound LuNi2B2C has been shown to adopt a 122 C. J. Warren S.S. Dhingra R.C. Haushalter and A. B. Bocarsly J. Solid State Chem. 1994 112 340. 123 C. J. Warren R.C. Haushalter and A.B. Bocarsly Chem. Mater. 1994 6 780. 124 S.S. Dhingra C. J. Warren R.C. Haushalter and A. B. Bocarsly Chem. Muter. 1994 6 2382. J. A. Cody and J.A. Iberts Inorg. Chem. 1994 33 2713. 126 S.S. Dhingra and R.C. Haushalter Chem. Mater. 1994 6 2376. 12' A. van der Lee M. Evain L. Monconduit R. Brec and V. Petricek Inorg. Chem. 1994 33 3032. 12' M. Evain A. van der Lee L. Monconduit and V. Petricek Chem.Mater. 1994 6 1776. 129 J. Li F. McCulley M. J. Dioszeghy S. C. Chen K.V. Ramanujachary and M. Greenblatt Inorg. Chem. 1994 33 2109. 130 D. B. Mitzi C. A. Feild W.T.A. Harrison and A.M. Guloy Nature 1994 369 467. 13' G.J. Miller and J. Lin Angew. Chem. Int. Ed. Engl. 1994 33 334. 132 M. Ebihara J. D. Martin and J. D. Corbett Inorg. Chem. 1994 33 2079. 133 M. El-Ghozzi D. Avignant and M. Guillot J. Solid State Chem. 1994 108 51. 134 P. Subramanya Herle M. S. Hegde N.Y. Vasanthacharya J. Gopalakrishnan and G.N. Subanna J. Solid State Chem. 1994 112 208. 13' G.F. Snyder and A. Simon Angew. Chem. Int. Ed. Engl. 1994,33 689. X. Z. Chen and H. A. Eick J. Solid State Chem. 1994 113 362. 434 P . Lighgoot Figure 14 Schematic crystal structure of (C,H,NH3)2(CH3NH3),Sn3110 (Reproduced by permission from Nature 1994 369 467) variant of the ThCr,Si structure-type with additional carbon in the Lu plane.13' LuNiBC is derived from LuNi,B,C by adding another Lu-C layer (Figure 16).Gd,B3C2 adopts another new structure type related to that of YBC by incorporation of extra non-metal linking zigzag carbon-branched boron chains.' 38 Finally U,RuSi3 has been prepared and found to have an ordered AlB structure with Ru and Si ordered over a two-dimensional s~b-lattice.'~~ 13' T. Siegrist H. W. Zandbergen R. J. Cava J. J. Krajewski and W. F. Peck Jr. Nature 1994 367 254. lJs F. Wiitkar J.-F. Halet J.-Y. Saillard P. Rogl and J. Bauer Znorg. Chem. 1994 33 1297. lJ9 R. Pottgen P. Gravereau B. Darriet B. Chevalier E.Hickey and J. Etourneau J. Muter. Chem. 1994,4 463. New Compounds and Structures Figure 15 Structure of Nb,S21, (Reproduced by permission from Angew. Chem. Znt. Ed. Engl. 1994 33 334) Figure 16 Crystal structures of LuNi,B,C and LuNiBC (Reproduced by permission from Nature 1994 367 254)

ISSN:0260-1818    

DOI:10.1039/IC9949100417

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

24 Magnetism By A. HARRISON and A.S. WILLS Department of Chemistry University of Edinburgh The King's Buildings West Mains Road Edinburgh EH9 3JJ UK 1 Introduction It is difficult to pick one or two principal achievements of the past year in a field as broad as magnetism one scientist's key discovery may be treated with indifference by another particularly where there are distinct pure and applied camps. However one achievement that may interest all parties is the discovery of dramatic magnetoresistive effects in mixed metal oxides of the form La -,M,MnO (where M is a divalent ion such as Ca" Sr" or Ba" x is typically 1/3 and z is approximately 3). We describe the background to this problem in Section 4of the review together with recent results and conjecture about the origin of the effect.Elsewhere progress has been more steady. 'Nanostructures' is a buzz word at present and in the context of magnetism concerns fine particles or ultra-thin films and multilayers; Section 5 of the review is devoted to this topic. Section 6 concerns ionic solids classified according to their structural and hence generally their magnetic exchange anisotropy as one- or two- or three- dimensional. As in previous years there are several strong undercurrents that sweep through these divisions frustrated magnets continue to fascinate experimentalists and theorists alike,' with most interest focused at present on the most frustrated 2D case the Kagome lattice; in three dimensions there are interesting developments in pyrochlores and garnets.One-dimensional structures continue to provide model materials to test simple theories of cooperative magnetic behaviour as well as physical properties unique to one dimension. Haldane's Conjecture that there is a fundamental difference in the spin structure and excitations of integer and half-integer spins in antiferromagnetic chains still motivates much of this work. Finally in Section 7 we treat magnets that are best described as molecular ranging from discrete clusters used to test our understanding of the interdependence of structure electronic properties and magnetism to extended molecular materials where the primary goal is to make an organic ferromagnet that is a solid that contains no metal ions but which has a spontaneous magnetization.The record value of T for this type of material is still very small (1.48K) which reflects the inherent weakness of ferromagnetic exchange in non-metallic materials and also the difficulty of arranging the restricted bridging geometry of superexchange bridges between the magnetic building blocks in three A. P. Ramirez Ann. Rev. Mater. Sci. 1994,24,453. 437 A. Harrison and A.S. Wills dimensions. A more promising class of compound for spontaneous magnetization at ambient temperatures and pressures is mixed metal salts for which record values of T are of the order of 250K. We will deliberately neglect most of the work devoted to magnetism in elemental and alloyed metals because this is mainly couched in terms accessible to physicists rather than chemists.However we will draw the reader’s attention to key issues reviews and books in this field throughout the review. It will be apparent from the start that a sizeable minority of the references are to work published in 1993;this mainly reflects the time lag in getting hold of papers and letters in time for the previous review. Throughout the review we shall try to use a standard form and units for the isotropic exchange constant J for the coupling between a spin Si and its neighbour Sj such that the Hamiltonian H for the interaction is H = -C Si.Sj <ij> Where the sum is taken over all exchange pairs. The magnitude of J will be expressed in Kelvin as J/kB where kB is Boltzmann’s constant. 2 Conferences Books and Reviews The principal meeting in 1994 for those interested in magnetism and magnetic materials was the terannual International Conference on Magnetism held in Warsaw the proceedings for this event will be published in 1995 and covered in the following volume of this report.Smaller meetings were held either on more restricted aspects of magnetism or organized at a national level. There were several meetings for various aspects of applied magnetism covering soft magnetic materials,2 magnetic re~ording,~ and magnetic technology in general.4 The annual meeting for North American magneticians is the Magnetism and Magnetic Materials (MMM) conference whose proceedings were published jointly with those for INTERMAG.’ European meetings included that for condensed matter physicists which covered a broad range of physical magnetic phenomena,6 and the annual meeting on magnetic materials and applied magneti~rn.~ There have also been conferences on subjects which are intimately connected with magnetism.The proceedings of the annual Conference on Low Temperature Physics present new devices for measurement of magnetic properties at low temperatures;2 a large proportion of the contributions were concerned with a variety of SQUID-based magnetometers most of which were based on high-T ceramics. The International Conference on Strongly Correlated Electron Systems was concerned with many different types of materials-heavy fermionic systems such as ‘Proceedings ofthe International Conference on Soft Magnetic Materials’ ed. A. J. Freeman J.Magn. Magn. Mat. 1993 133. ‘The Magnetic Recording Conference 1993’ ed. E. S. Murdock IEEE Transactions on Magnetics 1993,-30. ‘Thirteenth International Conference on Magnetic Technology’ ed. D. E. Lobb IEEE Trunsuctions on Magnetics 1993 30. ‘Sixth Joint Magnetism and Magnetic Materials-International Magnetics (MMM-Intermag) Conference’ ed. A. Chaiken R. E. Fontana J. D. Lavers J. E. Monson and J. L. Nix IEEE Transactions on Magnetics 1994 30. ‘14th General Conference of the Condensed Matter Division of the European Physical Society’ ed. J. L. de Segovia F. Flores and F. Garcia-Moliner Physica Scripta 1994 T55. ‘Proceedings of the 5th European Magnetic Materials and Applications Conference (EMMA ’93)’ ed. P. Vojtanik and A. Zentko IEEE Transaction on Magnetics 1993 30.Mugnetism 439 UPt, UPd,Al, and URu2Si, and both ‘conventional’ and high-T superconduc- tors-and in all cases magnetic measurements provide a useful experimental handle for their electronic properties.8 Finally a symposium on ‘Frontiers in High Magnetic Fields’ dealt not only with the problems associated with producing high magnetic fields but also with the interpretation of data taken in such an environment and a description of some of the problems in the band structure and transport properties of materials that have been elucidated through measurements of properties such as magnetoresistance.’ Smaller meeting or rather workshops are sponsored annually by NATO :this year’s crop include meetings entitled ‘Applied Magnetism’ (covering a wide range of topics on magnetic recording separation magnetoresistance magneto-optical and microwave devices and hard and soft magnetic materials) lo ‘Nanomagnetism’ (concerned with thin films small particles clusters and nanocrystalline materials and magnetostriction in amorphous alloys)” and ‘Magnetism and Structure in Systems of Reduced Dimension’ (primarily dealing with magnetic thin films and multilayers).l2 We will refer to more specialized reviews throughout the review. Kahn has produced an excellent book on magnetism in molecular materials which also provides a useful introduction to the theoretical basis of magnetism with an emphasis on mechanisms of superexchange.’ Ionic materials-and in particular ferrites-have been treated in a new book on magnetic ceramics dealing with the preparation properties and app1i~ations.l~ Yet more applied aspects of magnetism have been covered in recent works on permanent magnetic materials,’ magneto-optic recording,’ and magnetic recording techniques in general.3 Experimental Methods The most dramatic developments in the characterization of magnetic materials have probably been in microscopy techniques in the past few years. The development of magnetic analogues to atomic force’ and scanning tunnelling microscopes provides a means of imaging magnetized surfaces with a resolution of the order of 50nm and progress in the development of hardware’ and theory” is steady and applications are numerous extending from the manufacturing of magnetic devices2 to palaeomag- ‘Proceedings of the International Conference on Strongly Correlated Electron Systems’ ed.R. P. Guertin Z. Fisk M. B. Maple and L. J. Sham Physica B 1993 199 & 200. ‘Proceedingsof the Todai International Symposium on ‘Frontiers in High Magnetic Fields” ed.M. Miura Physica B 1993 201. lo ‘Applied Magnetism’ ed. R. Gerber C. D. Wright and G. Asti NATO AS1 Series E Applied Sciences Vol. 253 1994; Kluwer Academic Publishers Dordrecht The Netherlands. ‘Nanomagnetism’ ed. A. Hernando NATO AS1 Series E Applied Sciences Vol. 247 1993; Kluwer Academic Publishers Dordrecht The Netherlands. l2 ‘Magnetism and structure in systems of reduced dimension’ ed. R.F. C. Farrow B. Dieny M. Donath A. Fert and B. D. Hermsmeier NATO AS1 Series B Physics Vol.131 1993; Plenum Press New York. I3 0.Kahn ‘Molecular Magnetism’ VCH Germany 1993. l4 R. Valenzuela ‘Magnetic Ceramics’ CUP Cambridge 1994. P. Campbell ‘Permanent Magnetic Materials and their Applications’ CUP Cambridge 1994. l6 M. Mansuripur ‘The Physical Principles of Magneto-Optical Recording’ CUP Cambridge 1994. l7 H. N. Bertram ‘Theory of Magnetic Recording’ CUP Cambridge 1994. A. DiCarlo M. R. Scheinfein and R. V. Chamberlin Proc. SPIE-Znt. Soc. Opt. Eng 1993 1855 187. l9 E. R. Burke R. D. Gomez A. A. Adly,and I. D. Mayergoyz Proc.SPIE-Znt. SOC.Opt.Eng. 1993,1855,166. ” P.B. Fischer M.S. Wei and S.Y. Chou J. Vuc. Sci. Techno!.,B 1993 11 2570. 21 A Kikukawa S. Hosaka Y. Honda and H. Koyanagi J. Vac. Sci. Trchnol. A 1993 11 3092. 22 G.Persch C. Born H. Engelmann K. Koehler and B. Utesch Scanning 1993 15 283. 440 A. Harrison and A.S. Wills neti~m.~~ Other forms of magnetic microprobes are based on magnetoresistive sensors24 and a near-field optical microscope in conjunction with the magneto-optic Kerr effect providing a resolution of the order of 10nm.25 Over the past 30 years SQUID magnetometers have provided the most sensitive means of probing changes in magnetization and look set to become adopted in medical imaging of the brain and heart in the emerging fields of magnetoencephalography and magnetocardiology . The challenge is to produce yet more sensitive devices with higher signal-to-noise ratios that operate at yet higher temperatures and a successful response to this challenge may be provided by high-T SQUIDS constructed from films of YBa2Cu307-x.The films are grown epitaxially by laser deposition or sputtering in 0, producing oriented stoichiometric crystals either individually or as multilayers with insulating materials. Integrated devices of exceptional sensitivity may then be produced by patterning the material by ph~tolithography.*~-~~ The importance of neutron scattering in the characterization of magnetic materials was underlined by the award of the 1994 Nobel Prize for Physics to Bertram N. Brockhouse and Clifford G. Shull for their pioneering work developing and applying neutron scattering to a variety of problems in condensed matter science.30 One of the outstanding legacies of this work is the triple-axis spectrometer the most powerful tool for investigating spin-wave dispersion in solids and the best method of determining exchange interactions in solids that diffract.The contributions made by neutron and X-ray scattering3' to many aspects of the study of magnetic materials has been reviewed:32 neutrons still have a unique role to play in determining the dispersion of magnetic excitations and hence exchange constants as well as the most versatile method of determining static spin correlations in powders,33 topographic imaging,34 probing magnetic m~ltilayers,~~ depth profiling,36 and characterizing surfaces.37 While these techniques are familiar and widely used the application of magnetic X-ray scattering remains a more specialized field applied mainly to actinide elements and compounds providing high-resolution studies of the static structure and critical ~cattering;~**~~ where the sample contains elements that scatter resonantly the technique is unrivalled in its ability to study small or weakly scattering samples with elemental and site sensitivity and with suitable polarization of the beam may also separate spin and orbital components of the moment.40 X-Ray 23 J.Maddox Nature 1994 371 739. 24 C. A. Thompson R. W. Cross and A.B. Kos Ret.. Sci.Inst. 1994 65 383. 25 T.J. Silva and S. Schultz Proc. SPIE-lnt. Soc. Opt. Eng. 1993 1865 180. 26 J. Clarke Nature 1994 372 501. 27 D. Koelle A. H. Miklich R. Ludwig E. Dantaker D.T. Nemeth and J. Clarke Appl. Phys. Lett. 1993,63 2271. 28 D. Grundler H.David R.Eckart and 0.Doessel ibid. 1993 63 2700. 29 R. Leoni P. Carelli M. G. Castellano D. Peschiaroli C. Berger A. Gabutti S. Janos and K. Pretzl,J. Low. Temp. Phys. 1993 93 503. S. W. Lovesey Physics World 1994 November 54. 31 C. Vettier J. Magn. Magn. Mat. 1994 129 59. 32 C. Vettier Physica B 1993 192 1. 33 J. Rodriguez-Carvajal ibid. 1993 192 55. 34 J. Baruchel ibid. 1993 192 79. 3s P. Mangin C. Dufour and B. Rodmacq ibid. 1993 192 122. '' G. P. Felcher ibid. 1993 192 137. 37 H. Dosch ibid. 1993 192 163. 38 S. Langridge W.G. Stirling G. H. Lander and J. Rebizant Phys. Rev. B 1994 49 12010. 39 S. Langridge W. G. Stirling G.H. Lander and J. Rebizant ihid. 1994 49 12022. 40 G. H. Lander Physica B 1993 186188 664. Mag net ism 441 magnetic circular dichroism is being adopted as a useful probe of local magnetism thanks to the development of instruments at central synchrotron facilitie~:~~ the technique involves measuring the difference between the X-ray absorption spectrum of ferro- or ferri-magnetic material taken with a left -then right-circularly polarized beam.The synchrotron source allows the experimenter to select an absorption edge of a particular orbital of a particular element and assess the contribution of the spin and orbital momenta to the overall moment. 4 Giant Magnetoresistance and Beyond A material whose electrical resistance changes in response to a magnetic field is said to show magnetoresistance (MR).42 While all materials show this effect as a conse- quence of the Lorentz force exerted by a magnetic field on moving electrons it is usually negligible.However certain magnetic alloys may show a significant MR if they contain magnetic atoms because the magnetic field may control the alignment of the moments on these atoms which in turn influences the scattering of conduction electrons. Permalloy an alloy of nickel and iron is a good example of such a material and is used in reading heads for magnetic hard discs; in the 80%Ni-20%Fe type Permalloy the resistance increases by about 3% in high applied fields. In 1988 a dramatic reduction in resistance in specially constructed composite films of Fe and Cr was observed when a magnetic field was applied and the magnitude of the effect inspired the name given to the phenomenon-giant magnetoresistance (GMR).Since then GMR has been observed in many such metallic composites or magnetic rnultilayers as well as granular alloys comprising ferromagnetic nanoparticles embedded in a non-magnetic phase.43 What unites these materials is not only the magnitude of the effect (ranging typically from 5 to 50% and reaching as high as 150%) but also the fact that it is negative (i.e. the resistance decreases as field increases) and it is independent of field orientation. The structure of the materials may be engineered so that the coupling between magnetically-oriented sheets or particles is sufficiently weak for their relative polarizations to be manipulated with the external magnetic field. This has inspired considerable activity in refining the methods of constructing such materials as well as modelling theories of magnetotransport and interfacial magnetism an important factor in determining the ease of reorientation.More recently dramatic developments have been seen in films and bulk phases of metal oxides related to the perovskite LaMn03.44-48 Bulk phases and thin films of La,-,M,MnO (where M is a divalent ion such as Ca Sr Ba Pb or Cd x is approximately 0.33 and z is approximately 3.0) show MR which may be up to 100,000% depending on composition and crystallinity this extraordinary effect calls 41 C. Giles C. Malgrange J. Goulon F. de Bergevin C. Vettier E. Dartyge A. Fontaine C. Giorgetti and S. Pizzini J. Appl. Cryst. 1994 27 232. 42 P. M. Levy in ‘Solid State Physics’ ed.H. Ehrenreich and D. Turnbull Academic Press San Diego,1994 Vol. 47 p.p. 367. 43 J. S. Jiang J. Q. Xiao and C. L. Chien in ‘Magnetism and structure in systems of reduced dimension’ ed. R. G.C. Farrow B. Dieny M. Donath A. Fert and B.D. Hermsmeier Plenum Press New York 1993 NATO AS1 Series B Physics 131 1993 p.p. 381. 44 K. Chahara T. Ohno M. Kasai and Y. Kozono Appl. Phys. Lett. 1993,63 1990. 45 S. Jin M. McCormack T. H. Tiefel and R. Ramesh J. Appl. Phys. 1994 76 6929. 46 S. Jin T. H. Tiefel M. McCormack R. A. Fastnacht R. Ramesh and L. H. Chen Science 1994,264,413. 47 R. von Helmolt J. Wecker B. Hotzapfel. L. Schultz and K. Samwer Phys. Rev. Lett. 1993 71 2331. 48 R. von Helmolt J. Wecker K. Samwer L. Haupt and K. Barner J. Appl. Phys. 1994 76 8925.A. Harrison and A.S. Wills for a more emphatic name than giant magnetoresistance and has been dubbed colossal magnetoresistance (CMR). The parent compound LaMnO is an antiferromagnetic insulator with a distorted perovskite structure. On doping with divalent ions some Mn"' is converted into Mn" and charge carriers are introduced to produce ametallic phase. Exchange between Mn"' and Mn" is ferromagnetic being a classic example of Zener's double exchange. If two nearest-neighbour manganese ions are in oxidation state 111 the valence electrons fill the three t, orbitals and one eg orbital singly and strong Hund coupling and on-site Coulomb repulsion conspire to produce localized antiferromagnetically coupled spins. If one ion is oxidized to Mn" through the removal ofan e electron the electron in the eg orbital of a neighbouring Mn"' ion may hop to the Mn" ion and the most favourable way for this to happen is with the spins on these Mn ions oriented in aparallel fashion [Figure l(a)].The overall spin structure changes from an antiferromagnetic array through canted and spiral states to a metallic ferromagnetic state as x,the proportion of divalent ions increases. At the same time the crystal structure changes from tetragonal monoclinic or rhombohedra1 to cubic depending on composition. The resistance and magnetization change with temperature in the manner depicted in Figure l(b) for a sample of La,~,,Ca,~,,MnO prepared as a 10008 film the peak of the resistivity corresponds to the rapid build-up of ferromagnetic correlations as the sample is cooled through T and the spin-disorder scattering is most significant.As the sample is cooled further and the fluctuations become less significant so the resistivity falls. This is consistent with a model of charge transport in which the spin associated with a conduction electron induces a local distortion of the spin lattice and carries this distortion with it as it moves. The dependence of resistivity p on temperature follows a lnp -T-law at temperatures very much smaller than T, suggesting variable-range hopping of spin polarons. If spin-disorder scattering controls MR the peak in this quantity should lie close to the peak in resistance; indeed for a sample of given composition a correlation between the two is found though the maximum in MR is generally on the low-temperature side of the peak in resistance which indicates that there is more to the mechanism of CMR than is currently understood.CMR is very sensitive to almost any feature of the structure and composition imaginable in addition to a dependence on the type and concentration of divalent ions decreasing the oxygen content degrades the MR and the degree of crystallinity also has an influence. The highest CMR effects have been observed in La-Ca-Mn-0 epitaxial films prepared by laser ablation followed by annealing and the epitaxial nature of the growth is believed to be crucial to the perf~rmance.~~ There is much to be done in this field in preparing and characterizing new materials and striving to achieve consistency as well as trying to develop theories that explain the observed phenomena more fully.5 Nanostructured Magnetic Materials Methods of preparing and characterizing solids in which one or more dimension is controlled to be of the order of nanometers or microns have progressed greatly over the past decade and the fruits of this success are enjoyed by many sections of the science and technology community. In this section we consider the impact of such work in the field of magnetism particularly in the study of fine magnetic particles. In last year's Annual Report on Magnetism we drew attention to the considerable Magnetism 443 La-Ca-Mn-0 Film 125000 l-? v 2 30 $ 100000 n 200r 75000 20 ;E W ~ 50000 Q w 10 25000 -0 0 Figure 1 (a)Electron exchange between Mn"' and Mn" leading to ferromagnetic correlations; (b) dependence of magnetization (M),resistivity (p)and MR(AR/R,) in afilm ofLa,,,,Ca,,,,MnO time and effort spent preparing and studying magnetic materials which are in the form of fine particles.The technological importance of such materials is obvious being a central part of the recording industry and forming the basis of ferrofluids. They are also of interest to the fundamental scientist providing a link between magnets in the form of discrete clusters and extended solids49*50 as well as useful models to test our understanding of structure-property relations; they may also possess properties 49 D. Gatteschi A. Caneschi L.Pardi and R. Sessoli Science 1994 265 1054. 50 I. M. L. Billas A. Chatelain and W. A. Deheer ibid. 1994 265 1682. 444 A. Harrison and A.S. Wills unique to their size such as quantum mechanical tunnelling between domain spin states’ ’ and modified band structures and cooperative magnetic proper tie^.'^,'^ For all of these reasons there has been considerable effort expended in preparing fine particles with a controlled size and shape and the great number of individual papers review^,^^-'^ and tracts of conference^^-^,^,'^,' ’ bears witness to this. The lion’s share of the work on fine particles has been on maghemite (y-Fe203) and related iron compounds (such as FeOOH) because they and their derivatives constitute the bulk of materials used in the recording industry.Much of this is an extension of mature work on the relation between the preparative conditions and particle size and shape centring on new methods of preparing acicular particles and also new methods of making small particles-that is of the order of 10nm diameter. The shape of particles is commonly controlled albeit in a rather indirect way by growth of the metal oxide particles by forced hydrolysis in the presence of certain chemicals that promote growth in certain directions relative to others; the reason why such chemicals are effective is not clear though it is believed that the constituent molecules are adsorbed on parts of the surface to promote or inhibit further gro~th.’~,~~ Shape may also be controlled by biomimetic routes using natural or synthetic hollow fibres as matrixes for the growth of fibrous magnetite.59 The size of magnetic particles may be controlled by growing the particles in a restricted environment by ensuring that particle formation is very rapid or through the use of naturally occurring small particles.The restricted environment may be in the form of fine droplets of solution of a precursor of the magnetic material dispersed in a gas to form an aerosol. Rapid pyrolysis then deposits the solid held in each droplet and if care is taken to reduce aggregation of the particles formed this may lead to chemically pure particles with typical diameters of the order of tens of nanometers. The technique has the advantage of being relatively cheap and applicable to a wide range of materials such as ferrites;60 one disadvantage is that the rapid growth process is likely to produce particles with a high density of structural defects which may degrade the performance of the particles in recording applications.61 A similar approach is used in an all-liquid medium where the precursors to the magnetic particles are contained in fine droplets suspended as an emulsion in a second liquid.62 This microemulsion method has been used to prepare barium ferrite (BaFe,,O,,); the ferrite precursors were precipitated as carbonates suspended in aqueous droplets typically 5-25 nm diameter and when they were filtered off and calcined produced ferrite particles 5-15 nm in diameter.” J. I. Arnaudas A. Del Moral and C. de la Fuente in ‘Nanomagnetism’ ed.A. Hernando Kluwer Academic Publishers Dordrecht The Netherlands 1993 Vol. 247. NATO AS1 Series E Applied Sciences 247. ’2 A. Vega L. C. Balbas J. Dorantes-Davila and G. M. Pastor Nunostruct. Muter. 1993 3 359. ’3 P. Alvarado J. Dorantes-Davila and H. Dreysse ibid. 1993 3 331. 54 Q. A. Pankhurst and R. J. Pollard J. Phys. Cond. Mutt. 1993 5 8487. ” B. Barbara A. Marchand and L.C. Sampaio in reference 43 p. 359. ’6 S. Schultz and D. R. Smith reference 43 p. 377. ” T. B. Byeon J. Y. Lee D. Y. Kim J. G. Sohn H. Lee and K. H. Han Tuehan Kurnsok Hukhoechi 1993,31 632. ” X. Gu P. Wu Y. Zhang and X. Yuan Huudong Yejin Xueyuun Xuebuo 1993,9 39. ’9 C.W. Lawton and C.S. Shields Mut. Res. SOC.Symp. Proc. 1993 292 107. 6o M. V. Cabanas J.M. Gonzales-Calbet and M. Vallet-Regi J. Muter. Res. 1994 9 712. 61 M. P. Morales C. de Julian J. M. Gonzales and C. J. Serna ibid. 1994 9 135. 62 V. Pillai P. Kumar M. S. Multani and D. 0.Shah Colloids Surf A 1993 80 69. Magnetism 445 Once formed fine particles may be transmuted into other sorts of particles. One common strategy is simply to coat the fine particles in a second material combining the desirable properties of both materials-the shape of the core material and the high coercivity of the coating. For example fine acicular particles of FeOOH were coated with barium ions then sintered with microwaves to produce BaFe,,0,,;63 Co-Fe fine particles were produced by adding acicular fine particles of FeOOH to a solution of Fe(NO,) and Co(NO3)3 to produce a coat of cobalt ferrite and the metal alloy was then produced by reducing under hydrogen.64 Another useful surface modification of fine magnetic particles is to coat them with silica and thereby produce particles with the colloidal stability and well-characterized surface chemistry of silica.65 One interesting modification of such particles involves setting them in poly(pyrro1e) to produce a conducting polymeric nanocomposite with superparamagnetic properties.66 The small size of the particles alters their properties in several ways.Ordering temperature and saturation magnetization are obviously influenced by the increase in the ratio of surface to bulk atoms as the size decreases though care must be taken to ensure that the morphology of the particles is not also changed as the size changes because this influences the cooperative properties.In metallic particles changes in band structure with size may also have a great effect on cooperative effects.67 Finally the ease with which the magnetization of a fine particle or grain in an alloy may be reversed is also dependent on size and shape. The relaxation of the remanent magnetization of each particle may be envisaged as a classical process involving a thermally activated transition between wells whose depth may be described in the classical terms used to describe energy barriers in superparamagnetism. Evidence is emerging that the transition between different magnetization states may involve quantum mechanical t~nnelling.~~,~~ The phenomenon is found both for clusters containing 103-104 spins and domain walls of up to 10" spins in thin films and bulk magnets.Quantum mechanical tunnelling is observed on a mesoscopic scale in the random-anisotropy amorphous magnet (Gd -xTbx),Cu; the magnetic viscosity depends on temperature in a linear fashion with a non-zero intercept at T= 0 indicating that remanent magnetization may relax even at absolute zero.51 The majority of fine magnetic particles are put into magnetic devices the most important of which are recording media. A medium such as magnetic tape is complex and the properties of the individual fine particles it contains are only one factor contributing to its performance binders anti-wear and anti-static agents as well as the way in the particles behave in this cocktail of materials are also critical.The physical properties of dispersed magnetic media suspended in a viscous medium are still poorly understood depending on strong short-range interactions between colloidal particles and long-range magnetostatic forces.7o 63 M. Fujita N. Hiratsuka T. LJeda K. Sugiyama and K. Yamada IEEE Trans. Magn. 1993 29 2129. 64 K. Tagawa N. Utuno. H. Umehara and A. Tasaki Jpn. J. Appl. Phys. Part I 1994 33 1320. 65 A. P. Philipse M. P. B. van Bruggen and C. Pathmamanoharan Lanymuir 1994 10 92. 66 M.D. Butterworth S. P. Armes and A. W. Simpson J. Chem. Soc. Chem. Commun. 1994 2129. 61 A. Vega L. C. Balbas J. Dorantes-Davila and G.M. Pastor Nanostruct. Mater 1993 3 359. 68 P.C. E. Stamp E. M. Chudnovsky and B.Barbara Int. J. Mod. Phys. 1992 6 1355. 69 B. Barbara J.E. Wegrowe L.C. Sampain J. P. Nozieres M. Uehara M. Novak C. Paulsen and J. L. Tholence Phys. Scr. 1993 T49. 7" R. W. Chantrell and K. O'Grady in 'Applied Magnetism' ed. R. Gerber C.D. Wright and G. Asti Kluwer Academic Publishers Dordrecht The Netherlands 1994 Vol. 253 p. 113. 446 A. Harrison and A. S. Wills Most of the work on thin films7’ and multilayered material^^^-^^ concerns metals and is directed at producing magnetic recording media operating in a conventional inductive fashion through the Kerr effect or as magnetoresistors as described in Section 4. There are still many technological problems to overcome fine control may be exerted over the thickness and crystallinity of the growing film using molecular beam epitaxy but this technique is very expensive and not suitable for bulk fabrication.Electrochemical ferrite plating appears to offer a versatile low-temperature route from solutions to oxide films,75 as do sol-gel methods,76 but the most exciting recent development has been in laser ablation which allows stoichiometric transport of refractory materials from bulk to thin-film phases of controlled thickness.77 Although the technique is not yet widely used and suffers from the reputation that it is expensive and restricted to specialists it could soon shed this stigma and provide a powerful alternative to MBE methods. While the preparation and study of films built from elemental and alloyed metallic elements is most important and provides exciting theoretical challenges the growth of films and multilayers of oxides and other metal compounds is closer to the interests of the readership of this review.In the past review we reported work on MnTe films grown on a GaAs substrate by MBE the bulk phase has the NiAs structure but when strained through epitaxial growth on this substrate adopts the zinc blende structure. Strain may be also imposed by growing as thin multilayers with non-magnetic semiconduct- ing spacers such as CdTe.78 The FCC structure of this form of MnTe represents a highly frustrated 3D lattice and this in combination with the variable degree of strain allows us to tune the balance of exchange interactions and hence alter the nature of the ordered spin structures leading to new incommensurate magnetic structures.When the CdTe spacers between layers is very small and comparable to the range of Mn-Mn exchange interactions there is clear evidence for interlayer coupling. 6 Ionic Solids One-dimensional Materials.-The major themes in one-dimensional magnetism have not changed significantly since last year. The intense study of S = 1 antiferromagnetic chains in the past decade has not only provided evidence in favour of Haldane’s Conjecture but also led to a reassessment of our understanding of the behaviour of spin chains in general. In order for us to say that certain aspects of the behaviour of integer-spin antiferromagnetic chains are ‘non-classical’ it is first necessary to be certain what is meant by ‘classical’ and it is becoming clear that it is necessary to go beyond harmonic one-magnon processes to treat the dispersion of magnetic excitations at the level necessary to do so.Haldane’s Conjecture and Quantum Ground States. Y,BaNiO is emerging as a model material to further test Haldane’s Conjecture and the theoretical work that has 71 R. Allenspach J. Magn. Magn. Mat. 1994 129 160. 72 J.P. Renard J. Mat. Sci. Technol. 1993 9 1. 73 P.J. Grundy D. Greig and E.W. Hill Endeavour 1993 17 154. 74 J. Freeland D. Keavney D. Storm and J.C. Walker Mater. Res. SOC.Symp. Proc. 1993 313 541. l5 M. Abe and T. Itoh Proc. Electrochem. SOC. 1993,93 379. 76 E. M. Wong H. Zheng J. D. Mackenzie and T. Tsuchiya Mat. Res. SOC.Symp. Proc. 1993 313 351. 77 D.B. Chrisey P.Lubitz K. S. Grabowski and C. M. Cotell J. Appl. Phys. 1994 75 1676. ” T. M. Giebultowiza H. Luo N. Samarth J.K. Furdyna V. Nunez J. J. Rhyne W. Faschinger G. Springholtz G. Bauer and H. Sitter Physica B 1994 163 168. Mag netism 447 followed it. This material is a charge-transfer insulator containing antiferromagneti- cally coupled chains of Ni" (S = l) and the ground state appears to be quantum disordered. The properties of strongly-correlated electronic systems with enhanced quantum fluctuations is of course also of great interest to those working on high-Tc superconductors and this material of lower dimension offers a good opportunity to explore a broader range of this class of magnet because theoretical work has a firmer footing in 1D compared with 2-and 3-D.It may also be doped with similar sorts of defects to the defects that disrupt the magnetic fluctuations in layered cuprates substitution of Zn" for Ni" simply severs the chains while exchange of off-chain Yrl' ions with Ca" injects holes into the 2p orbitals of oxygen atoms in the NiO It has been proposed that the spin S = 1 in a Haldane chain is best regarded as comprising two S = 1/2 entities and experimental evidence has been put forward in recent years that when such a chain is severed in NENP ([~i(~,~,~,),(~~,)]~i~~) the two new ends each have S = 1/2 defects associated with them. Careful study of the specific heat of Y,BaNi -,Zn,O indicates that this is not the case,,' and that the new chain ends behave as S = 1 entities as would be expected on more conventional grounds.The discrepancy between the two results is difficult to resolve one suggestion is that the data for NENP relate to paramagnetic defects introduced by structural disorder. Introduction of holes to the chain has a dramatic effect on the magnetic fluctuations changing the host material from a gapped spin liquid to a quantum antiferromagnet with sub-gap states which were described as modes associated with the modified superexchange produced by the holes;79 the identity of the holes was determined by a study of the polarization of 0 K-edge and Ni L-edge X-ray spectra. Though NENP provides the most intensely studied Haldane model material and has been under the spotlight as such for the past decade it still has puzzling aspects.One phenomenon that has only recently been rationalized is the nature of the sharp TR absorption peak observed in an applied magnetic field. This mode has been attributed to an excitation across the field-shifted singlet-triplet gap but it violates the wavevector selection rule and it does not vanish when the splitting is sufficiently large to bridge the gap. It is argued that the staggered form of the chain backbone introduces low-symmetry crystal fields that produce an internal staggered field when an external field is applied and prevents the gap from closing when the critical field is reached.*' S = 1 may also be introduced in the form of VI" an example being in AgVP,S,. The material has recently been produced in the form of single crystals suitable for oriented magnetic susceptibility measurements and both parallel and perpendicular compo- nents of the susceptibility relative to the chain axis have been shown to fall rapidly in the vicinity of 50 K confirming the singlet ground state character below that temperature., Inelastic neutron scattering measurements on the isostructural Cr"' compound AgCrP,S have been performed to clarify the quantum-classical crossover that is expected as the spin on the magnetic ion increases.Both S = 1/2 and S = 1 chains are expected to show quite different quantum phenomena on account of the fundamental difference between integer and half-integer spin chains. The exchange 79 J. F. DiTusa S.-W.Cheong J.-H. Park G.Aeppli C. Broholm and C.T. Chen Phys. Rev.Lett. 1994,73 1857. A. P. Ramirez S.-W. Cheong and M. L. Kaplan ibid. 1994 72 3108. " P.P. Mitra and B.I. Halperin ibid. 1994 72 912. " T. Asano Y. Ajiro M. Mekata H. Yamazaki N. Hosoito T. Shinjo and H. Kikuchi Solid Stute Commun. 1994 90,125. 448 A. Harrison and A.S. Wills constant derived from the spin-wave dispersion in AgCrP,S6 appears to behave in a very similar way to that for a S = 1/2 chain with marked non-classical character the spin-wave velocity is much greater than the classical value derived from magnetic susceptibility data the constant of proportionality being .n/2.83 Spin-Peierls Transition in CuGe03. Interest in antiferromagnetic chains is not confined to those containing S = 1 the recent discovery of a spin-Peierls transition in the inorganic compound CuGeO has led to renewed interest in S = 1/2 Heisenberg antiferromagnetic chains.The expertize developed for growing large single crystals of ceramic superconductors has been turned to producing crystals suitable for elastic and inelastic neutron scattering measurements. The magnetic susceptibility of CuGeO plummets to a very small value at 14K indicating the formation of a singlet ground state. High-field ESR and magnetization measurements provided the first evidence of Zeeman splitting of a spin-Peierls gap,84 while the structural dimerization of Cu ions in the spin-Peierls state has been proved by the observation of superlattice reflections of half-integer indices in both neutron- and X-ray diffraction pattern^.^^,^^ In contrast refinement of powder neutron diffraction data taken well above and below 14K showed no improvement when allowed to refine with a unit cell in which dimerization was allowed;87 magnetic susceptibility data taken at 10 K fitted well to a linear chain model with alternating exchange and provided an estimate of the mean exchange constant (88 K) and the ratio between the weaker and stronger in-chain exchange constants of 0.69.Magnetic Ladders. Another type of material that has been used to study quantum ground states and provide a link between such phenomena in 1D and in 2D have been magnetic ladder compounds with the structure depicted schematically in Figure 2(a). The theoretical understanding of this well-defined model is good and may elucidate the behaviour of purely 1-and 2-D relatives.88 An experimental realization of such a model was recently recognized in the form of (VO),P,O which has the arrangement of S = 1/2 VIV ions depicted in Figure 2(b).The uprights of the ladder are provided by exchange interactions J II and the rungs by exchange interactions J ,and both J II and J are approximately 96K. An alternative description of the relative strengths of magnetic exchange in the ladder is as an alternating chain model with exchange constants J = 136K and J = 95 K derived from magnetic susceptibility measure- ments. To discriminate between these possibilities the spin-wave excitation spectrum of a powder sample has been measured-single crystals of sufficient size being unavail- able-and shown to be consistent with singlet-triplet excitations in the spin ladder model confirming it as the first example of this class of material.89 The range of the spectrometer in Q and cc) allowed part of the one-magnon dispersion curves to be mapped out and determined the gap to be 47K at Q = 0.813k1 very close to 83 H.Mutka C. Payen and P. Molinie Europhys. Lett, 1993 21 623. 84 T. M. Brill J. P. Boucher J. Voiron G. Dhalenne A. Revcolevschi and J. P. Renard Phys. Rev. Lett. 1994 73 1545. 85 J. P. Pouget L. P. Regnault M. Ain B. Hennion J. P. Renard P. Veillet G. Dhalenne and A. Revcolevschi ihid.,1994 72 4037. K. Hirota D. E. Cox J. E. Lorenzo G. Shirane J. M. Tranquada M. Hase K. Uchinokura H. Kojima Y. Shibuya and I. Tanaka ibid. 1994 73 736. M.A.Green M. Kurmoo J. Stalick and P. Day J. Chem. Soc. Chem. Commun. 1994 1995. 88 T. Barnes and J. Riera Phys. Rev. B 1994 50 6817. 8y R.S. Eccleston T. Barnes J. Brody and J. W. Johnson Phys. Rev. Lett. 1994 73 2626. Magnetism 449 v P J J* Figure 2 (a) Schematic lay-out of a spin-ladder lattice showing exchange between atoms on the uprights and in the rungs; (b) arrangement of S = 112 V'" ions and exchange bridges provided by oxygen atoms in the spin ladder compound (VO)2P,0 theoretical predictions.88 An alternative model spin ladder compound is emerging in the form of SrCu,O which is a member of a series of compounds of general formula Sr,-in which sheets of Cu, and Sr,- stack alternately along the c-axis of the orthorhombic cells.The CU,+~O,, sheets may be derived from regular CuO, sheets by shearing in the manner depicted in Figure 3 and producing a pattern of strips that approximate to ladders as far as the likely relative strength of exchange interactions is concerned. One might envisage a gradual crossover from 1D to 2D as n increases. SrCu,O corresponds to the two-leg ladder while Sr,Cu,O corresponds to a three-leg ladder that is the rungs join three rather than two uprights. The magnetic susceptibility of the two-leg compound indicates excitations from a non-magnetic ground state while the three-leg compound appears to have a gapless ground state and these measurements are supported by 63Cu NMR spin lattice relaxation measurements. O ABX3 Hexagonal Perovskites. CsNiC1 is one of the most frequently-studied one- dimensional magnets providing the first model with which Haldane's Conjecture was tested and more recently a critical study of the validity of linear spin-wave models to describe the coherent spin excitations.Inelastic neutron scattering measurements indicate that the introduction of two-magnon excitations not only predicts distinct scattering processes in the two-magnon continuum but also modifies the energies and intensities of one-magnon processes to agree better with experiment .91 Thus it is possible to rationalize the structure factor for the scattering of neutrons from CsNiC1 9" M. Azuma Z. Hiroi M. Takano K. Ishida and Y. Kitaoka ibid. 1994 73 3463. 91 T. Ohyama and S. Hiroyuki J. Phys. SOC.Jpn. 1993 62 3277.A. Harrison and A.S. Wills Figure 3 Cu-0 coordination polyhedra in sheets of Cu,O in the compounds (a) SrCu,O and (b) Sr,Cu,O,. The solid circles are Cu" ions and 0'-ions lie at the vertices of the squares providing strongest exchange bridges when the Cu-0-Cu bridge has an angle of 180". These interactions are depicted by the bold solid lines and adopt 2-leg and 3-leg ladder lattices in the sheared structures of (a) and (bj respectively without recourse to more exotic spin structures and excitations. Most of the recent work on CsNiCl concerns its three-dimensional magnetism antiferromagnetic interchain exchange on the triangular lattice perpendicular to the chain axis leads to frustrated spin structures and complex phase diagrams that may be used to test theories of multicritical phenomena.The H-T phase diagram has been further elucidated by ultrasonic measurements to reveal further features as the direction of the magnetic field H is rotated relative to the crystal axes9' The ordering of moments in the triangular plaquettes of the ab plane may be regarded as possessing a further degree of freedom not observed in the ferromagnetic counterpart that is the handedness or chirality of the spins as we trace a line around the plaquette. This has been proposed to alter the magnet's universality class and therefore the critical exponents associated with various quantities measured close to the ordering transitions and this has been verified in specific heat measurement^.^^ Other ABX hexagonal perovskites have come in for scrutiny for a variety of reasons.The S = 5/2 easy-axis Heisenberg antiferromagnet CsMnI has been used in a comparison between quantum and classical 1D antiferromagnets CsMnI being regarded as a high-spin magnet and therefore essentially classical while CsNiC1 is both of lower and integer spin and therefore subject to Haldane's Conjecture. Deviations from the predictions of linear spin-wave theory observed in CsNiC1 may therefore not " Y. Trudeau M. L. Plumer M. Poirier and A. Caille Phys. Rev. B 1993 48 12 805. y3 D. Beckmann J. Wosnitza H. von Loehneysen and D. Visser Phys. Rev. Lett. 1993 71 2829. Magnet ism 451 be explained in terms of the frustration introduced by interchain exchange.94 Detailed studies have also been carried out on CsMnI to characterize the structures and excitations of the different ordered phases better.95 RbMnBr approximates to a hexagonal perovskite but a small lattice distortion not only produces an enlarged magnetic unit cell but also commensurate and incommensurate magnetic structures with unusual multicritical phen~mena.~~.~~ CsFeX (X = Cl Br) has been studied as a singlet ground state magnet rather than because of the low-dimensionality or interchain fr~stration~~-though these are both relevant in providing a full description of the spin excitations.These materials appear to provide fertile ground for the development of theories of spin-correlations particularly in induced-moment systems and experiments are facilitated by the experimentalists' ability to produce large high-quality single crystals for inelastic neutron s~attering.~~,~~,'~~ Miscellaneous 1D Magnets.MnAsO,.H,O contains chains of antiferromagnetically coupled chains of corner-sharing MnO octahedra. The coupling within these chains may be switched to ferromagnetic when reacted with solid LiNO, inducing a topotactic ion-exchange reaction to produce LiMnAsO,(OH)."' Both compounds order antiferromagnetically with TN= 24 and 30K for the parent compound and lithiated salt respectively but neutron diffraction measurements on deuterated derivatives confirm the intrachain correlations. The insulating compounds Ba,MnX (X = S,Se and Te) have a chain-like structure of tetrahedrally coordinated Mn" ions linked by single atoms of X in non-linear bridges of 1 17-120°.'02 Magnetic susceptibility data were fitted successfully to the standard Bonner-Fisher model for the Heisenberg antiferromagnetic chain producing Curie-Weiss constants that became less antiferromagnetic as the mass of X increased and this was rationalized either through the increase in superexchange pathlength or the reduction in bridging angle as the mass of X increased-both effects leading to a marked decrease in the superexchange constant.Vanadium compounds are enjoying renewed attention of late because of the catalytic activity of many Vv compounds and also the varied low-dimensional structures that can be produced through imaginative coupling of vanadium ions through oxoanions. For example framework compounds containing V-0 octahedra linked through their vertices to P-0 tetrahedra may be produced with different structures by altering the oxidation state of the vanadium ions and the degree of protonation of the phosphate groups.One recent addition to this set of compounds is the mixed-valence V'v,v vanadium hydrogen phosphate Cs[(V,O,)(HPO,),(H,O)] which contains chains of corner-sharing octahedra (-V'v-O-Vv-O-).103 These chains are bound through 94 M.Enderle K. Kakurai K. N. Clausen,T. Inami H. Tanaka and M. Steiner Europhys. Lett. 1994,25,717. 9s T. Inami K. Kakurai H. Tanaka M. Enderle and M. Steiner J. Phys. Soc. Jpn. 1994 63 1530. 96 L. Heller M. F. Collins Y. S. Yang and B. Collier Phys. Reu. B 1994 49 1104. 97 T. Kato T. Ishii Y. Ajiro T. Asano and S.Kawano J. Phys. Soc. Jpn. 1993 62 3384. 98 N. Suzuki in 'Recent Adv. Magn. Trans. Met. Compds' ed. A. Kotani and N. Suzuki World Scientific Singapore 1993 p. 291. 99 P.A. Lindgard and B. Schmid Phys. Rev. B 1993 48 13 636. loo W.M. Liu and B.L. Zhou Z. Phys. B 1994 93 395. lo' M. Aranda J. P. Attfield S. Bruque and R. B. von Dreele J. Chem. Soc. Chem. Commun. 1994 155. lo' M. A. Greaney K. V. Ramanujachary Z. Teweldemedhin and M. Greenblatt J. Solid State Chem. 1993 107 554. R. C. Haushalter Z. Wang M.E. Thompson J. Zubieta and C. J. O'Conner ihid. 1994 109 259. A. Harrison and A.S. Wills tridentate (HP04)2 -ions to produce a three-dimensional network. Magnetic susceptibility data indicate that the material obeys the Curie-Weiss law with 6 = -1OK while at low temperatures there is complex antiferromagnetic behaviour that has yet to be unravelled.V-0 octahedra linked through P-0 tetrahedra are also found in the chain-like material (NH4)VOP04,'04though of course all the vanadium ions are now in the oxidation state IV and S = 1/2. Magnetic susceptibility measurements taken over the range 25-300 K could be fitted to a Curie-Weiss law with 6 = -4.7K but at lower temperatures the susceptibility passes through a broad maximum (5 K) and could not be fitted very well to the Bonner-Fisher model. Possible reasons for this are the poor one-dimensional character and the uncertainty about whether electrons are localized or not. Two-dimensional Materials.-Work on layered magnets has been dominated over the past eight years by the need to understand the mechanism of high-temperature superconductivity in layered cuprates; it still is.However the number of papers on the subject has fallen as other bandwagons have rolled by and all but the hard-core practitioners have leapt aboard. The related subject of low-moment frustrated antiferromagnetism also continues to attract a substantial following and the strongest pull is provided at present by the most frustrated simple two-dimensional case the Kagome lattice. Layered Cuprates and Nickelates. There are several important issues involved in the work on layered cuprates. A better understanding of the magnetic properties of these materials is tied to an understanding of their extraordinary electronic properties; in addition these materials provide remarkably good examples of S = 1/2 square Heisenberg antiferromagnets which in turn are important model materials for a better understanding of low-spin and low-dimensional magnetism.Let us start with the simplest member of this class of materials (at least in terms of the chemical formula) the hole-doped superconductor La,Cu04 + The magnetic transition between the paramagnetic and ordered antiferromagnetic state has long been the subject of controversy neutron magnetic Bragg scattering perturbed angular correlation and nuclear quadrupole resonance (NQR) experiments indicate that the transition has a smooth second-order form while Mossbauer and muon spin rotation measurements reveal that the two-sublattice magnetization has a discontinuous onset.Recent zero-field 39La NQR measurements on nearly-stoichiometric single-crystal samples of LazCu04+ which were prepared with a very low level of structural defects revealed the transition at TN to be sharp but continuous indicating that the phase transition is second-order with a transition to 3D behaviour very close to TN,or a remarkably small critical exponent of the sub-lattice magnetization b( <0.1).'05 The discrepancies between the results of different earlier measurements were attributed to the different degrees of inhomogeneity of the samples less homogenous samples show a range of ordering transitions and therefore appear to show a smooth transition. Pure La,CuO has a small Dzyaloshinskii-Moriya interaction that results from the orthorhombic distortion and produces a sharp peak in the magnetic susceptibility at TN in the presence of a small magnetic field applied perpendicular to the CuO planes.R. C. Haushalter Q. Chen V. Soghomonian J. Zubieta and C.J. O'Connor ihid 1994 108 128. D. E. MacLaughlin J. P. Vithayathil H. B. Brom J. C.J. M. de Rooy P. C. Hammel P. C. Canfield A. P. Reyes 2. Fisk J.D. Thompson and S.-W. Cheong Phys. Rev. Lett. 1994 72 760. Magnetism 453 Measurement of this magnetization then produces a measure of the two-sublattice antiferromagnetic susceptibility and estimates of the inter- and intra-plane magnetic exchange.lo6 The data are comparable to the results of neutron scattering studies of the sub-lattice magnetization in terms of the information they provide about the static magnetic correlation length though ofcourse they may only be interpreted in detail now that a considerable amount is already known about this compound.This work illustrates one of the fundamental problems in using such materials as model magnets their properties are exceptionally sensitive to non-stoichiometry and crystal quality; further the strength of the in-plane magnetic exchange and the significant number of small perturbations to the simple Hamiltonian for a nearest-neighbour square Heisenberg antiferromagnet has lead to difficulties in measuring and interpreting magnetic data and provided the impetus for a search for other model compounds. One material that has emerged from this study is the layered cuprate Sr,CuO,Cl,.It enjoys the following advantages over La,CuO and related materials as a model material the structure is rigorously tetragonal down to at least lOK leading to a simpler Hamiltonian and reducing the nearest-neighbour inter-plane exchange to two or three orders of magnitude below the magnitude of the XY anisotropy; further it is very difficult to dope the material with electrons or holes reducing the concentration of inadvertent defects. Recent neutron-scattering measurements of the dependence of the spin-spin correlation length on temperature provided a very good test of the success of recent developments in theories of quantum magnetism to model static and dynamic properties of low-moment low-dimensional antiferrornagnets.' O7 The results were combined with the outcome of Monte Carlo simulations and spanned a wide range of temperature that corresponds to correlation lengths ranging from 1 to 200 lattice constants.This extensive data set corresponded accurately with the predictions of a model that had no adjustable parameters and which was an adaption of the pioneering work of Chakravarty Halperin and Nelson expanded into the renormalized classical region. It might be expected that when the correlation length becomes particularly large and the temperature approaches TNvery closely a crossover from 2D Heisenberg to 2D XY behaviour will be seen but this set of measurements did not reveal such a change. Much of the work on L~,CUO,+~ YBa,Cu,O, and related materials has treated deviations from the simple Hamiltonian for the nearest-neighbour S = 1/2 Heisenberg antiferromagnet as parameters to be determined by experiment without too much concern for their microscopic origin.Closer consideration of the microscopic origin of these terms reveals some fascinating problems the relative orientations of moments within and between planes indicate a breaking of the XY rotationally invariant symmetry. This appears at odds with what one would expect for the single-ion anisotropy for S = 1/2 i.e. no effect. The relative orientations of moments in adjacent planes had previously been explained by the spin-wave quantum zero-point energy which favours a collinear spin array; however careful consideration of the energies involved indicate that this is too small to be compatible with experiment.One rationalization of this observation is based on a modified Hamiltonian for the tetragonal phase of the form T. Thio and A. Aharony ibid. 1994 73 894. '07 M. Greven R. J. Birgeneau Y. Endoh M. A. Kastner B. Keimer M. Matsuda G. Shirane and T. R. Thurston ibid. 1994 72 1096. A. Harrison and A.S. Wills where the directions 11 I,and z are defined as parallel and perpendicular to the direction ij within the plane and perpendicular to the plane respectively. Thus in addition to the easy-plane anisotropy quantified by AJ = (J + Jl,)/2-J, there is an in-plane anisotropy 6J = JII-J that is present even in a tetragonal crystal provided that both spin-orbit coupling and Coulomb exchange are present."' A classical sum of the exchange energy gives the mean-field rotationally invariant energy that we would expect for a tetragonal magnet but if the spin-wave energy is calculated and modes allowed to interact the in-plane spin-wave mode at q = 0 acquires a gap and the spins experience an anisotropy that favours a particular direction in the lattice.The anisotropic part of the exchange between spins in adjacent planes also leads to a net exchange field favouring certain inter-plane alignments. A consideration of these and dipolar interactions has lead to a rationalization of the spin structures of various Ln,CuO compounds (where Ln is La Pr or Nd for example) as well as YBa,Cu,O,.' O9 The drive to understand the behaviour of high temperature superconductors has also provoked interest in related layered transition metal oxides most notably materials derived from La,NiO,.Such materials provide another point of view with which to test our understanding of S = 1/2 systems and in contrast to the cuprates the nickelate compounds remain insulating over a wide range of composition. The pure compound is predicted by band structure calculations based on a local spin density approximation to be a diamagnetic metal; when Coulomb interactions between Ni 3d electrons are introduced the ground state involves doped holes which form small polarons in an antiferromagnetic background and this is supported by experiments on La -,Sr,NiO +h which reveal not only the polarons but incommensurate magnetic correlations and a structural modulation that varies with x.In contrast La2Ni04+d shows an invariant antiferromagnetic structure below TNas 6 is increased from 0 to 0.11 though TNdoes change ranging from 335 to 50 K over the same compositional range. However at high degrees of non-stoichiometry (6 = 0.125) TNis considerably higher (1 10K) and the magnetic structure becomes incommensurate:' the interstitial oxygen atoms produce a modulation in Ni-0 bond lengths leading to charged domain walls that form antiphase boundaries between antiferromagnetic domains. Neutron scattering measurements on a single crystal of this material show that holes and spins order at the same temperature and that the incommensurability is strongly tempera- ture dependent. However the wavevector of the ordering does not vary continuously with temperature but rather locks into a rational fraction of the lattice wavevectors and the sequence of fractions forms a Devil's staircase.Kagornk Antiferrornagnets. Much of the work on Kagome antiferromagnets in 1994has been theoretical. The paucity of suitable model materials (some would argue that suitable model materials are absent) combined with the simplicity of the model has lead to extensive simulations of this and related lattices. An eye-catching illustration of the difference between the Kagomk lattice and non-frustrated lattices was provided by a simulation of the time-evolution of spin fluctuations. When a moment is perturbed from its equilibrium position in the square lattice it vibrates as a harmonic oscillator lo8 T.Yildirim A. B. Harris 0.Entin-Wohlman and A. Aharony ibid. 1994 73 2919. T. Yildirim A. B. Harris 0.Entin-Wohlman and A. Aharony ibid. 1994 72 3715. J. M. Tranquada D.J. Buttrey V. Sachan and J. E. Lorenzo ibid. 1995 73 1003. Magnetism 455 while the Kagome lattice in both the q = 0 and 43 x 43 spin arrays shows at least two characteristic time-scales and after a couple of well-defined initial excursions the spin fluctuations appear quite irregular. The q = 0 state is much more stable with respect to small excitations while the 43 x J3 structure soon loses its memory of the initial configuration.' The one material that has been demonstrated to show some resemblance to a Kagome antiferromagnet is the Cr"' garnet SrCr,Ga -.O ,,(SCGO(n)).Cr"' ions are surrounded by weakly distorted oxygen octahedra to form alternating triangular and Kagome planes but these planes are never completely occupied and even in the most favourable case site occupation of the Kagomtt lattice is only 90%-(9 -x)/9 of the Cr"' sites are occupied by Ga ions. Intraplane coupling is known to be antiferromag- netic and very strong with a high-temperature Curie-Weiss parameter 8 of approxi- mately -400K. As the site occupancy x is raised above the percolation threshold (p -6.0) a spin-glass-like cusp is seen in the susceptibility at Tg-2-5 K,increasing in temperature as x increases and at temperatures well below T neutron scattering measurements on a sample with x = 7.1 indicate that 80% of the spectral weight of the scattering was inelastic.Recent pSR measurements of the magnetic fluctuations in a sample with x = 8.0 show that the spin fluctuations on Cr'"s1ow down as the sample is cooled toward the susceptibility cusp of approximately 3.5 K but the fluctuations persist at temperatures as low as 100mK without any static order setting in."' It is argued that this is consistent with a spin-liquid ground state at T = 0 K with a small number of unpaired spins migrating in a sea of singlet pairs. Careful ac and dc magnetic susceptibility measurements on samples with x = 8 confirm that the spin state below Tg has some spin-glass character but that it is not conventional.'13 As Ga ions are replaced by Fe"' ions to produce SrCr,Ga,-2,Fe,01 9 the magnetic freezing temperature is found to increase and the magnetic interaction between planes is believed to increase and a sample with y = 1.5 now appears to show conventional spin-glass behaviour below Tg.Miscellaneous 20 Magnets. A series of layered Mn" alkylphosphonates MnC,H,,+ ,PO3.H,O (n = 1-4) have been prepared as part of a program of research on new ways of obtaining solids with a spontaneous magnetization.l14 Common strategies to devise new materials with spontaneous magnetization-a highly desirable but relatively rare form of matter-generally rest on attempting to couple equal moments ferromagnetically or unequal moments antiferromagnetically (i.e. to produce aferrimagnet). A third strategy is to try to engineer a canted antiferromagnetic ground state as proposed many years ago by Moriya for materials with non-equivalent magnetic ions in certain low-symmetry space groups.Such is the case in this set of alkylphosphonates with a magnetic anomally at about 15K as the length of the alkyl chain is increased the ordering temperature alternates weakly with odd and even n and the canting angle increases steadily indicating a sensitive dependence on subtle changes in crystal structure. Ni ions may be linked through azido ions to produce a 'I' A. Keren ihid. 1994 72 3254. 'Iz Y. J. Uemura A. Keren K. Kojima L. P. Le G. M. Luke W. D. Wu Y. Ajiro,T. Asano Y. Kuriyama M. Mekata H. Kikuchi and K. Kakurai ihid. 1994 73 3306. 'I3 B. Martinez A. Labarta R. Rodriguez-Sola and X. Obradors Phys. Rev. B 1994 50 15 779.'lo S.G. Carling P. Day D. Visser and R. K. Kremer J. Solid State Chem. 1993 106 111. 456 A. Harrison and A.S. Wills regular 2D polymeric solid of p(1,1-N3),Ni2 units in (C,Hl,N8Ni),."5 Although the principal exchange within the sheets appears to be antiferromagnetic magnetization measurements indicate that spin canting occurs at about 55K to produce weak ferromagnetism a remarkably high three-dimensional ordering temperature in view of the large distance between sheets. Magnetic susceptibility measurements on a series of layered ferrimagnetic oxalates of general formula (XR4)Fe11Fe"'(C,0,) (X = N P; R = n-propyl n-butyl phenyl) reveal an unusual response :the tetrabutylammonium salt shows a remarkable negatiue magnetization when it is cooled in a 100G field below 45 K." No explanation was offered for this phenomenon though it was noted that the only other compound that is known to behave in a similar manner is LiVO, which is also insulating and shows a spontaneous magnetization at low temperature.Three-dimensional Materials.-The vast majority of magnetic materials that are technologically significant are essentially three-dimensional that is there is no striking structural anisotropy . Work on ferrimagnetic mixed-metal oxides continues to thrive producing new synthetic routes to ferrites and garnets and more sophisticated methods of interpreting their collective magnetic properties. From a fundamental viewpoint most of the interest in 3D materials derives from a small group of frustrated materials exemplified by pyrochlores such as CsNiCrF and the garnet Gd,Ga,O 12 which we describe in some detail below.Framework compounds in which magnetic ions interact through relatively large bridging units such as oxoanions are being investigated as new cooperative magnets. Na,Fe,(PO,) is one such material having a structure related to the 'Nasicon' family of fast-ion conductors.' The phenomenon of GMR and stronger effects discovered recently in doped oxides based on LaMnO is probably the most remarkable development in structurally isotropic materials and this has been discussed in Section 4. Frustrated Magnets. Rare earth pyrochlores such as Tb,Mo,O are composed of vertex-sharing tetrahedra of the magnetic ions and despite having no positional disorder show spin-glass properties.The compound CsNiCrF also has the pyro- chlore structure and is a member of the series of compounds CsXYF where the magnetic ions X" (X = Fe Ni and Mn) and YII1(Y = Fe Cr and V) are randomly distributed over the vertices of the tetrahedra. It is to be expected therefore that any magnetic correlations are very short in range and detailed analysis of the diffuse magnetic scattering of neutrons from a single crystal Of CSNiCrF indicates their extent to be limited to single tetrahedra in which the spins are predominantly oriented parallel or antiparallel to a single direction and have a net antiferromagnetic exchange field. l1 These data differ from those taken on other members of the series notably CsMnFeF and CsNiFeF which show non-collinear short-range order.The single-ion anisotropy should be comparable in the three different materials leading to similar tendencies to order uniaxially. The origin of the difference is proposed to lie in the different tendencies of the materials to show order by disorder entropy favours the ground state with the greatest number of low-energy excitations which is the collinear case and this J. Ribas M. Monfort X. Solans and M. Drillon Inorg. Chem. 1994 33 742. C. Mathoniere S. G. Carling D. Yusheng and P. Day J. Chem. Soc. Chem. Commun. 1994 1551. C. Greaves P. R. Slater M. Slaski and C. M. Muirhead Physica B 1994 194196 199. M. J. Harris M. P. Zinkin Z. Tun B.M. Wanklyn and I. P. Swainson Phys. Rev. Lett. 1994,73 189. Magnetism 457 appears to dominate frustrated exchange energy and single ion anisotropy for CsNiCrF,.The garnet Gd3Ga,0, (GGG) is another compound in which long-range antiferromagnetic order is suppressed by a degree of frustration Figure 4 illustrates the structure in which the Gd ions sit at the vertices of two interpenetrating triangular sub-lattices within the garnet structure. The moment on Gd is large (S = 7/2) and the single-ion anisotropy is very small (less than 0.04 K). At first sight the compound is not a promising candidate for research into frustrated magnetism exchange is weak (OWeiss EZ-2K) so any magnetic correlations only become significant at very low temperatures. However GGG is prepared for magnetic bubble memories as high- quality high-purity single crystals and its magnetic properties are already understood in considerable depth.At low temperatures the magnetic phase diagram shows a curious re-entrant antiferromagnetic phase as a field of the order of 1 T is applied. Specific heat and magnetic susceptibility measurements have been used to map out this phase diagram in greater detail' (Figure 4(b)). Similar magnetic phase diagrams have been seen in other materials but in general their origin is found in single-ion effects the field induces a transition from a singlet to a magnetic doublet state rather than raising the Zeeman energy of the moments above the local exchange field. The critical exponent a of the specific heat at the boundary of the antiferromagnetic phase in a field of 1T is less than zero which indicates either a disordered Ising system or a Heisenberg system.The latter is unlikely despite the insignificant single-ion anisotropy because dipole-dipole interactions are comparable in magnitude to the exchange forces and lead to uniaxial anisotropy; the authors plumped instead for an interpretation of their data based on Ising spins in a random environment. While the king character is uncontroversial it is less obvious that there is appreciable randomness in the structure. The crystal growth process leads to a site disorder over the Ga and Gd sub-lattices of the order of 1% which means that 1 atom in 10 in any linear dimension is misplaced and it is argued that this is sufficient to introduce the disorder required. 7 Molecular Solids The driving forces in the study of magnetism in molecular solids are many but two stand out first there is the still-elusive goal of producing a molecular solid with a bulk magnetization at ambient temperatures and pressures; second there is the desire to understand better the mechanism of superexchange and discrete molecules provide many geometries and compositions of exchange bridges and hence many different model compounds with which to test advances in theory.The basis of exchange within and between molecular units has been thoroughly treated in Kahn's recent booki3 and an extensive review by Miller and Epstein lays out the various strategies used to try to arrange ferro- or ferri-magnetic arrays of moments;12' the latter work charts the progress of T in molecular magnets over the past forty years comparing it favourably with T, the transition temperature for superconductivity.The material responsible for the dramatic leap in recent years is the amorphous material [V(TCNE),] .y(CH2C1,) (TCNE = tetracyanoethene) with T -400 K which is above its decomposition temperature. Despite the excitement 'Iy P. Schiffer A. P. Ramirez D.A. Huse and A. J. Valentino ibid. 1994 73 2500. I2O J.S. Miller and A. J. Epstein Angew. Chem. Inf. Ed. Engl. 1994 33 385. A. Harrison and A.S. Wills -PM 0.0 0.2 0.4 0.6 0.8 Temperature (K) (b) Figure 4 (a)Disposition of magnetic moments in the garnet Gd,Ga,O,,(GGG). The arrangement of magnetic moments in the unit cell has been projected onto the xy axis and their heights are denoted in units of a/8 where a is the cell constant.The arrows represent the orientation of moments in the antiferromagnetic phase; (b)magnetic phase diagram of GGG depicting the antiferromagnetic (AFM),and paramagnetic (PM)phases as well as transition lines for spin- glass-like (SG) freezing observed in magnetic susceptibility measurements and short-range ordering (SRO)transitions observed with magnetic susceptibility and heat capacity measurements Magnetism 459 0. I Figure 5 Nitronyl nitroxide radical building blocks used to construct molecular ferrornagnets (a) NPNN (p-nitrophenyl nitronyl nitroxide) and (b) N,N'-dioxy-1,3,5,7-tetramethyl-2,6-dia-zaadamantane generated by this material it still defies detailed characterization the task of unravelling the mechanism of exchange and the local spin order is complicated not only by the amorphous structure but also by its extreme insolubility and its extreme sensitivity towards attack by air and water.It is not even certain what the oxidation state of 'V'I' nor the spin state of TCNE is though most workers favour the description [V"(TCNE),].O.S(CH,Cl,), with S = 3/2 on V" and S = 1/2 on TCNE' -,coupled ferromagnetically to produce S = 5/2. There have been preliminary investigations of the suitability of this material for lightweight magnetic shielding but these indicate that the permeability is too modest to be practical.12' More manageable materials in terms of preparation and characterization are the other class of molecular magnet that has inspired considerable activity of late nitronyl nitroxide radicals of the type depicted in Figure 5(a); these have not yet produced Tcin excess of a few Kelvin and we consider them below.Research on spin-crossover compounds is not as widely conducted as in the past though new compounds continue to be reported. Traditionally high-spin (HS)/low- spin (LS) crossovers have been caused by an external perturbation such as a variation in temperature or pressure. A combined effect of temperature and pressure changes is required to produce a cross over in [Fe(bt),(NCS),] 122 (bt = 2,2'-bi-2-thiazoline). At atmospheric pressure there is a temperature-induced first-order spin-state transiton at T = 181.9K (for increasing temperatures) and Tc= 172.3K (for decreasing tempera- tures).The resulting hysteresis is characterized by a width of ATc = 7.1 K. The application of pressure produces no noticeable change to the transition temperatures within the range 0.001-1.90 kbar. However at 1.9 kbar the hysteresis width decreases significantly to ATc = 5.7 K. Spin crossover may also be induced by light.123 A quantitative light-induced crossover may to be driven in the solid Fe"(stpy),(NCS) by irradiating the sample in the spin-allowed d-d or metal-ligand charge-transfer absorption bands of the stable LS species. This occurs at temperatures below 40K much lower than required for a thermally induced crossover. Under these conditions the metastable HS state can be trapped. In this example the 'light-induced excited spin-state trapping' is based on cis-trans photoisomerizable ligand where ligand photoisomerization changes the spin state of the metal ion and is reversible.This year sees a number of reviews covering diverse topics in molecular magnetism. 12' B. G. Morin C. Hahm J. S. Miller and A. J. Epstein J. Appl. Phys. 1994 75 5782. E. Koenig G. Ritter H. Gruensteudel J. Dengler and J. Nelson Inorg. Chem. 1994,33. 837. lZ3 C. Roux J. Zarembowitch B. Gallois T. Granier and R. Claude ibid. 1994 33 2273. 460 A. Harrison and A.S. Wills These include the following the synthesis and properties of molecular ferromagnets and ferromagnetic superconductors using organometallic or metal-organic free radical building blocks;' 24 structure and magnetism of Cu" dimers with di-p-chloride bridges;125 triangular d2-d'-d' mixed valence clusters;'26 the probing of biological metal clusters using the dipolar interactions between cluster and intrinsic or extrinsic paramagnet^.'^^ The ever expanding area of high nuclearity spin clusters (HNSC) has also been extensively reviewed including aspects of spin frustration superparamag- netism and the problems associated with understanding the magnetic susceptibility of the systems.128 We return to examples of such clusters below.Dimers Trimers and Discrete Clusters.-Not surprisingly the majority of magnetic dimers studied in 1994 were homonuclear Cu" species although mixed dimers of CU" with other first-row transition metals or lanthanides constitutes a growth area.Continuing the format of previous years the dimers have been divided according to the metals ions involved and we have noted where possible the type of magnetic interactions as follows Viv (AF),129Viv (F),13' Cry (AF),132 MniV (~~),133,134 (~~)135-137 ~~Il-~~lll ~~111 138 2 7 CO (AF,F),139 Ni! (F) 140*141 Ni! (AF),14' CU',,'~~ Cu! (AF),143-'52 CU"-V'~ (F),'53 Cu"-Mn" (AF),154 Cu"-Fe"' (AF),'" Cu"-M" (M = Mn Fe Co) (AF),156 Cu"-Ln"' (Ln = Eu Gd Tb Dy Ho 124 P. Cheng and D. Liao Daxue Huaxue 1993 8 1. 12' J. Mrozinski Conf. Coord. Chem. 1993 14 227. J. J. Borras-Almenar E. Coronado and B. S. Tsukerblat Chem. Phys. 1993 177 1. 12' B. J. Hales Methods Enzymol. 1993 227 384. C. D. Delfs D. Galteschi and L. Pardi Comments Inorg. Chem.1993 15 27. lZ9 S. Ma J. Shi D. Liao Z. Jiang S. Yan and G. Wang Polyhedron 1993 12 2359. S. Mitsubori T. Ishida T. Nogami and H. Iwamura Chem. Lett. 1994 2 285. M. Nakahanada K. Ino and S. Kaizaki J. Chem. Soc. Dalton Trans. 1993 24 3681. 13' P. A. Goodson J. Glerup D. J. Hodgson K. Michelsen and U. Rychlewska Inorg. Chem. 1994,33,359. 133 K. R. Reddy M.V. Rajasekharan S. Padhye F. Dahan and J. R. Tuchagues Inorg. Chem. 1994,33,428. 134 J.B. Vincent H.L. Tsai A.G. Blackman S. Wang P.D.W. Boyd K. Folting J.C. Kuffman E.B. Lobkovsky D.N. Hendrickson and G. Christou J. Am. Chem. Soc. 1993 115 12353. 13' P. N. Turowski W.H. Armstrong S. Liu S. N. Brown and S. J. Lippard Inorg. Chem. 1994 33 636. 136 R. M. Buchanan R. J. O'Brien J.F. Richardson and J.-M.Latour Inorg. Chim. Acta 1993 214 33. 13' A. Elmali Y. Elerman I. Svoboda H. Fuess K. Griesar and W. Haase Z. Naturforsch Teil B Chem. Sci. 1994 49 3. 13* Y. Maeda Y. Tanigawa N. Matsumoto H. Oshio M. Suzuki and Y. Takashima Bull. Chem. Soc. Jpn. 1994 67 125. 139 S. Ma D. Liao Z. Jiang S. Yan F.Xue and G. Wang Synth. React. Inorg. Met.-Org. Chem. 1994,24,137. Y. Aratake M. Ohbta H. Sakiyama M. Takokoro N. Matsumoto and H. Okawa Inorg. Chim. Acta 1993 212 183. 14' R. Vicente A. Escuer J. Ribas X. Solans and M. Font-Bardia Inorg. Chem. 1993 32 6117. 14' K. K. Nanda R. Das L. K. Thompson K. Venkatsubramanian P. Paul and K. Nag ibid. 1994,33,1188. 143 L. Chen L.K. Thompson and J.B. Bridson Inorg. Chim. Acta 1993 214 67. 144 S.S. Tandon L. Chen L. K. Thompson and J.N.Bridson Inorg. Chem. 1994,33 490. 145 G. De Munno J. A. Real M. Julve and M. C. Munoz Inorg. Chim. Acta 1993 211 227. 146 Y. Nakao M. Yamashita T. Itoh W. Mori S. Suzuki and T. Sakurai Bull. Chem. Soc.Jpn. 1994,67,260. 147 C. E. Xanthopoulos M. P. Sigalas G.A. Katsoulos C. A. Tsipis A. Terzis and A. Hountas Inorg. Chim. Acta 1993 214 153. 14* S. 1. Levchenkov V. A. Kogan and V.V. Lukov Zh. Neorg. Khim. 1993 38 1992. 149 S. Emori and K. Todoko Bull Chem. Soc. Jpn. 1993 66 3513. '" C. J. Harding V. McKee J. Nelson and Q. Lu J. Chem. Soc. Chem. Commun. 1993 23 1768. P. Bergerat 0.Kahn P. Legoll M. Drillon and M. Guillot Inorg. Chem. 1994 33 2049. 152 P. M. Slangen P. J. van Koningsbruggen K. Goubitz J. G. Haasnot and J. Reedijk ibid 1994,33 1121.R. Cortes M. K. Urtiaga L. Lezama M.I. Arriortua and T. Rojo ibid 1994 33 829. R. Ruiz F. Lloret M. Julve J. Faus M.C. Munoz and X. Solans Inorg. Chim. Acta 1993 213 261. Is' S.C. Lee and R.H. Holm J. Am. Chem. Soc. 1993 115 11 789. Z. Yu R. Tao X. Zhou D. Jin and D. Liao Polyhedron 1994 13 951. 14' Magnetism 461 Er),ls7 Re (P),"' and Ln'," (Ln = Gd Tb Ho Er).lS9 A remarkable 'giant' antiferromagnetic interaction has been observed through the bihydroxide bridge (H30,).160 The very short 0-0 distance 2.41-2.54 A is consistent with a strong hydrogen bond made by a central proton surrounded by two hydroxide groups [HO-H-OH]-. This bridging has been investigated in a Cu! complex [Cu2(bpym)2(H302)(H20)2](C104)3. The system is diamagnetic at room tempera- ture compatible with very strong AF coupling between Cu" ions J > 1500K and indicating the remarkably efficient exchange pathway between Cu" ions through H30,.Calculations show that for the Cu-0-0 angle of 119.3' both s and p contributions are important. There have been interesting developments in the area of small metal clusters. M tetramers have been constructed from a variety of transition metals M (M = Co Cr),16' Fey (F),'62 Fe:' (AF),'63 and Cuy (AF).'64p168 The effects of vibronic interactions on the magnetic moment of tetrahedral mixed-valent clusters have been examined the~retically'~~ by modification of the Anderson-Hasegawa Hamiltonian by including the interaction of the electronic states with nontotally symmetric combina- tions of the local ligand vibrations.Experimental realizations of such systems include Fe"'-Fe; (AF),162 Cuy-M" (M = Mn Co Ni).170 As clusters increase in size the task of working out the magnetic structures and excitations and interpreting measurements such as the magnetic susceptibility increases rapidly in complexity. Thus hexanuclear clusters such as CUE(AF),' Fe'Q' (F),' 72 and Fe'," (AF)'73 may have a variety of nuclear structures and many significant exchange pathways producing in some cases a multitude of low-lying spin states. Only if several assumptions are made about the relative strengths of exchange pathways may susceptibility data be interpreted in a detailed manner. Clusters with nuclearities as high as 12 may also be synthesized an example being Mn,20,2(02CR)16(H20)4 (R = Ph Me).174 The Ph-derivative of the Mni'Mn'," complex has a peffof -12pB per Mn, unit at 320K compared with the spin-only '" Y.Li Z. Jiang S. Ma X. Li D. Liao S. Yan and G. Wang Polyhedron 1994 13 475. 158 M.T. Costello P. W. Schrier P. E. Fanwick and R. A. Walton lnorg. Chim. Acta 1993 212 157. 159 X. Li Z. Jiang D. Liao S. Yan Y. Li and G. Wang Polyhedron 1994 13 99. 160 G. De Munno D. Viterbo A. Caneschi F. Lloret and M. Julve Inorg. Chem. 1994 33 1585. 161 C. J. Gomez-Garcia,J. J. Borras-Almenar E. Coronado P. Delhaes C. Garrigou-Lagrange and L. C. W. Baker Synth. Met. 1993 56 2023. K. L. Taft A. Caneschi L. E. Pence C. D. Delfs G. C. Papaefthymiou and S.J. Lippard J. Am. Chem. Soc. 1993 115 11 753. P.Chaudhuri M. Winter P. Fleischhauer W. Haase U. Floerke and H.-J. Haupt Inorg. Chim. Acta. 1993 212 241. 164 B. Chiari 0.Piovesana T. Tarantelli and P. F. Zanazzi Inory. Chem. 1993 32 4834. G. D. Fallon B. Moubaraki K. S. Murray A.M. van den Bergen and B.O. West Polyhedron 1993 12 1989. S. Teipel K. Griesar W. Haase and B. Krebs Inorg. Chem. 1994 33 456. 167 R. Costa A. Garcia R. Sanchez J. Ribas X. Solans and V. Rodriguez Polyhedron 1993 12 2691. Y. Zhang L. K. Thompson M. Bubenik and J.N.Bridson J. Chem.Soc. Chem. Commun. 1993,18,1375. A. J. Marks and K. Prassides Chem. Phys. 1993 179 93. "O Z. Liu D. Liao Z. Jiang S. Yan and G. Wang Synth. React. Inorg. Met.-Org. Chem. 1993 23 1117. 171 G. J. A. A. Koolhaas Anthony A. W. L. Driessen P. J. van Koningsbruggen J.Raedijk and A. L. Spek J. Chem. SOC.,Dalton Trans. 1993 24 3803. A. Cornia D. Gatteschi and K. Hegetschweiler Inorg. Chem. 1994 33 1559. 173 C.A. Christmas H.L. Tsai L. Pardi J. M. Kesselman P.K. Gantzel R.K. Chadha D. Gatteschi D. F. Harvey and D.N. Hendrickson J. Am. Chem. Soc. 1993 115 12483. R. Sessoli H. L. Tsai A. R. Schake S. Wang J. B. Vincent K. Folting D. Gatteschi and G. Christou J. Am. Chem. Soc. 1993 115 1804. 462 A. Harrison and A. S. Wills moment of 15.87 pB,indicating the presence of appreciable antiferromagnetic interac- tions at this temperature. The increase in moment for both the Me- and Ph- derivatives [( 1) and (2) respectively] upon cooling below approximately 20 K reflects some ferromagnetic coupling.The nonsolvated (2) appears to have an S = 9 ground state while (1) has a S = 10ground state in zero applied field. However the application of a magnetic field to (2) causes the ground state to become the M = -10 component of the S = 10 state. The presence of an imaginary component of the ac susceptibility suggests that there are magnetic relaxation effects in zero applied field. The origin of this relaxation is not clear. Either these molecules are large enough to exhibit relaxation effects individually or there are as yet uncharacterized intermolecular interactions. One of the most striking forms of molecular magnet in recent years are the ring-shaped complexes [Fe(OMe),(0,CCH2C1)],,'75 and [Ni,,(O,CMe), (chp) ,(H,O),(THF),] 76 (chp is the anion of 6-chloro-3-pyridone); the dodecanuc- lear nickel complex is depicted in Figure 6 which shows the two nickel ions of the asymmetric unit bound in an alternating pattern around the rim of the ring and bridged through two ,u,-oxygen atoms provided by the chp molecules.In both cases the magnetic core of the molecule may be regarded as a ring of M202 units but while the Fe"' compound showed antiferromagnetic coupling (with J -15K) the Ni" com- pound was ferromagnetically coupled (with J -4 K). The low-lying spin states of the Fe"' compound were revealed by measuring the magnetization at 0.6 K in high applied magnetic fields as the field was increased the magnetization increased in discrete evenly-spaced steps as successive Zeeman states became the ground state.Above 50 K the temperature dependence of the magnetic susceptibility is typical of a Heisenberg chain of antiferromagnetically coupled S = 5/2 ions with a nearest-neighbour coupling constant of J = 15K. Theoretically then the number of magnetic ions in the ring increases the reduced susceptibility converges indicating that the magnetic properties of the 10 ring can be reasonably well modelled by an 8-spin ring. Numerical solution of the Heisenberg-Dirac-van Vleck spin Hamiltonian for a ring of 8 Fe"' ions gave J = 15K with g = 0. Extended Molecular Solids.-Most of the materials screened or studied as potential organic ferromagnets are nitronyl compounds. The discovery of bulk ferromagnetism at T = 0.65 K in the j crystal phase of p-nitrophenyl nitronyl nitroxide [j-NPNN Figure 5(a)] was followed in 1993 by the record T to date for a solid that contains no metal ions T = 1.48 & 0.02 K for N-N'-dioxy-l,3,5,7-tetramethyl-2,6-diazaadaman-tane [Figure 5(b)].Work continues on both materials and simple derivatives. Detailed MO calculations have attempted to throw light on the difference between j-NPNN and the antiferromagnetic y phase177 and the density ofunpaired electron spin has been mapped out using polarized neutron diffraction measurements supported by ab initio MO calculations:178not surprisingly most of the unpaired spin density is found on the 175 K. L. Taft C. D. Delfs G. C. Papaefthymiou S. Foner D. Gatteschi and J. S. Lippard ibid. 1994 116 823. 17' A. J. Blake C. M. Grant S. Parsons J. M. Rawson and R.E. P. Winpenny J. Chem.Sac. Chem. Commun. 1994,2363. 177 M. Okumura W. Mori and K. Yamaguchi Chem. Phys. Lett. 1994 219 36. A. Zheludev V. Barone M. Bonnet B. Delley,A. Grand E. Ressouche P. Rey R. Subra and J. Schweizer J. Am. Chem. Soc. 1994 116 2019. Magnetism 463 Figure 6 Disposition of Ni" ions bound through a variety of oxygen atoms in the dodecanuclear CNi 2'(H2(chp)l21(OzCMe)21 16(THF)6i two NO groups and negative density sits on the bridging sp2 carbon atom with little delocalization onto the phenyl group. Replacement of p-nitrophenyl in NPNN by different groups produces both ferro- and anti-ferromagnetically coupled molecules depending on the substituent :' 79 3-quinolyl shows bulk ferromagnetism at low temperatures (T,-0.2 K);'80,18' N-alkylpyridinium derivatives of a-NPNN show enhanced intramolecular ferromag- netic interactions for certain alkyl groups and in the case of the methyl derivatives the solid is composed of dimers of the radical cation which are themselves bound in a triangular lattice.The intradimer interactions are ferromagnetic while the weaker interdimer interactions are antiferromagnetic so the magnet as a whole behaves as a frustrated triangular antiferromagnet with S = 1. NPNN has also been complexed with a variety of first-row transition metal ions to produce large clusters182 and extended chain^:'^^"^^ the compound [Cu(hfac),] [NITnPr(3-NTT)I2 (where hfac = hexafluoroacetylacetonate and NITR is NPNN with p-nitrophenyl replaced by some functional group R) contains clusters of sewn 179 K.Awaga T. Inabe T. Nakamura M. Matsumoto and Y. Maruyama Mol. Cryst. Liq. Cryst. Sci. Techno[.,Sect. A 1993 232 69. 180 T. Sugano M. Tamura T. Goto R. Kato M. Kinoshita Y. Sakai Y. Ohashi M. Kurmoo and P. Day ibid. 1993 232 61. 181 F. L. Pratt R. Valladares J. Caulfield L. Deckers J. Singleton A. J. Fisher W. Hayes M. Kurmoo P. Day et al. Synth. Met. 1993 61 171. 182 A. Caneschi L. David F. Ferraro D. Gatteschi and A.C. Fabretti Inorg. Chim. Acta 1994 217 7. 183 D. Luneau G. Risoan P. Rey A. Grand A. Caneschi D. Gatteschi and J. Lauguer Inorg. Chem. 1993 32 5616. 184 A. Caneschi D. Gatteschi and A. le Lirzin J. Chem. Muter. 1994 4 319. A. Harrison and A. S. Wills spins coupled predominantly through very strong antiferromagnetic interactions;ls2 Mn(hfac),NTT(p-MNE,].0.25HCC13 contains chains of Mn" ions bridged by nitronyl nitroxide to produce a ferrimagnetic chain of S = 1/2 and S = 5/2;3D ferrimagnetic order sets in below about 5 K.' 84 Ferrimagnetic chains are most commonly constructed out of antiferromagnetically coupled S = 5/2 and S = 1/2 units because all things being equal this gives rise to the highest saturation magnetization; however the most common source of S = 1/2 is not NPNN but Cu" and the most recent addition to the well-stocked stable of CuMn 1D ferrimagnets is MnCu(opda)(H,O),.DMSO [opba = o-phenylenebis(oxamato)] .Is5 In order for a 1D ferrimagnet to show bulk spontaneous magnetization the interchain exchange must be ferromagnetic and this is hard to arrange and while success was found using NPNN derivatives as the interchain links the opda salt shows antiferromagnetic interchain coupling leading to TN-5K.However a weak external magnetic field induced a transition to a ferromagnetic state so this magnet is best regarded as a metamagnet built from ferromagnetic chains. More promising is NH,Ni(mnt),.H,O (where mnt = maleonitrile dithiolate) which appears to contain antiferromagnetically- coupled localized moments at room temperature but on cooling below about 100K undergoes an abrupt transition to a state with ferromagnetic correlations.' 86 Finally a series of chain-like MnCu compounds have been reported that contain Mn"' rather than Mn". The species [Mn"'Cu"(L),(acetato)(H,0)2] (L = 1,2-cyclo-hexa-nedioneoximato) is a bulk ferromagnet with T = 9 K when M is Mn while relatives with L = dimethylglyoximato are metamagnetic when M is Mn and antiferromagnetic when M is Fe.' 87 The ferromagnetic interaction between Mn"' and Cu" arises from the strict orthogonality of the dny,d,, and d, orbitals on Mn"' (d4)(d, -yz is empty) and an electron in the d, -y2 orbital on Cu" if both ions are considered to lie in the xy plane; the extra electron on Fe"' then sits on a d,2-y2 orbital giving rise to dominant antiferromagnetic exchange.PM[V0(hfa~),]'~~ (PM = pyrimidine) is a new molecular ferromagnet intra- molecular exchange between S = 1/2 spins on VO' through the pyrimidine bridge [Figure 7(a)] is reinforced by weak intercluster coupling to produce bulk ferromag- netism below T -0.14 K.The TEMPO derivative 4-benzylideneamino-2,2,6,6-tetramethylpiperidin-1 -oxyl (TEMPO is 2,2,6,6-tetramethylpiperidin-1-oxyl) crystal- lizes with a layered arrangement of the organic radicals which appear to interact ferromagnetically producing spontaneous magnetization at T -0.18 K."' Strong ferromagnetic interactions between rn-phenylenebis(galvinoxy1)biradical molecules have been inferred from magnetic susceptibility measurements which reveal a broad anomally centred at 72 K.'" The compound 9-[a-(9H-fluoren-9-ylidene)-4-chloro-benzyll-9H-fluoren-9-yl contains two fluoren-9-yl and one chlorophenyl moiety arranged in the propellor shape depicted in Figure 7(b) these then pack in the crystal H.O.Stumof Y. Pei L. Ouahab F. Le Berre E. Codjovi and 0.Kahn fnory. Chem. 1993,32 5687. It(' M. L. Allan J. H. F. Martens A.T. Coomber R. H. Friend I. Marsden E. A. Marseglia A. E. Underhill and A. Charlton Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A. 1993 229 147. la' F. LLoret R. Ruiz B. Cervera I. Castro M. Julve J. Faus J. A. Real F. Sapina Y. Journaux J. C. Colin and M. Verdaguer J. Chem. Soc. Chem. Commun. 1994 2615. S. Mitsubori T. Ishida T. Nogami H. Iwamura N. Takeda and M. Ishikawa Chem. Lett. 1994 685. T. Nogami K. Tomioka,T. Ishida H. Yoshikawa M. Yasui F. Iwasaki H. Iwamura N. Takeda and M. Ishikawa ibid. 1994 29. loo K. Mukai T. Tamaki S. Kawasaki and S.Nagaoka Mol. Cryst. Liq. Cryst. Sci. Technol.. Sect. A 1993 233 1. Magnetism 465 Figure 7 (a) Exchange pathway between S = 1/2 spins on VO' through the pyrimidine bridge in PM[VO(hfac),] ; (b) the propellor-shaped magnetic building block in 9-[~-(9H-fluoren-9- ylidene)-4-chlorobenzylj-9H-fluoren-9-yl so that exchange between these moieties is dominant along one axis and susceptibility data may best be fitted to a standard expression for a Heisenberg chain.The exchange is unremarkable in terms of its sign (it is antiferromagnetic) but it appears to be remarkably large leading to a Nee1 temperature of 3.25 K for the solid-the highest yet observed for a collection of organic radicals.'" Charge-transfer salts may also contain organic radicals with significant intermolecu- lar magnetic interactions. (BEDT-TTF)(TCNQ) (BEDT-TTF) = bis(ethy1enedithio)tetrathiafulvalene and TCNQ = tetracyanoquinodimethane) is composed of BEDT-TTF sheets and TCNQ columns and shows significant magnetic order within the BEDT-TTF sheets below 35 K followed by antiferromagnetic order at TN= 3.0 f0.1 K in the TCNQ columns.'92 Crystallization of BEDT-TTF with [PMo,,04,14-produces the localized moment 1D S = 1/2 antiferromagnet (BEDT- TTF),[PMo ,04,] C, and other fullerenes continue to contribute to the literature on magnetochemis- try but more because fullerenes continue to be trendy than because they have much inherent magnetic importance; the majority of publications are more concerned with what magnetism has to say about the electronic structure of these molecules.'94~195 The discovery of spontaneous magnetization in TDAE-C, (where TDAE is tetra- kis(dimethy1amino)ethylene) a couple of years ago has not been followed up by much work since an exception being the study of the dependence of the Curie temperature on 19' N.Azuma T. Ozawa and J. Yamauchi J. Chem. Soc. Perkin Trans. 2 1994 203. 19' Y. Iwasa K. Mizuhashi T. Koda Y. Tokura and G. Saito Phys. Rev. B 1994 49 3580. Iy3 C. Bellito M. Bonamico and G. Staulo Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A 1993 232 155. 194 R. Tycko J. Phys. Chem. Solids 1993 54 1712. lyS D.N. Sheng Z.Y. Weng C.S. Ting and J.M. Dong Phys. Rev. B,1994 49 4279. A. Harrison and A. S. Wills the preparation conditions:' 96 non-stoichiometric derivatives appear to have anomal- ously high ordering temperatures with portions of the sample showing T -24K.One area that is progressing is that of encapsulated fullerenes. It has been the aim of many workers in this field to 'shrinkwrap' a variety of metal ions inside a fullerene thus providing fascinating opportunities for electronically optically or magnetically active materials. While C, and other small fullerenes are difficult to fill in this manner nanotubes concentric tubes of carbon with diameters of the order of nanometers may be filled with elemental metals and metal corn pound^.'^^ Mossbauer and magnetiz- ation measurements on nanotubes containing fine particles of iron or iron carbide show anomalously high coercivities a property attributed to the small particle size;' 98 the future in this field looks promising and we anticipate much more activity to report next year.19' D. Mihailovic K. Lutar A. Hassanien P. Cevc and P. Venturini Solid State Commun. 1994 89 209. S. C. Tsang Y. K. Chen P. J.F. Harris and M. L.H. Green Nature 1994 372 159. 19' H. Onodera K. Sumiyama K. Suzuki A. Kasuya Y. Nishina Y. Saito T. Yoshikawa and M. Okuda Jpn. J. Appl. Phys. Part 2 1994 33 L24.

ISSN:0260-1818    

DOI:10.1039/IC9949100437

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

25 Conducting Solids Covering Ionic and Electronic Conductors By P. R. SLATER School of Chemistry University of Birmingham Edgbaston Birmingham B 15 2TT UK 1 Introduction There have been a number of significant advances in 1994 particularly in the area of superconductivity. Research into intermetallic superconductors has been revived with the discovery of new quaternary boro-carbide and -nitride alloys showing Tc’sas high as 23 K (equalling the longstanding record for an intermetallic held by Nb,Ge). In the area of oxide superconductors several recent results have indicated the importance of flat CuO planes to obtain the maximum T with an apparent correlation between the distortion of these planes and the lowering of T,. A similar correlation involving Ni,B layers which appear to be a common feature in these phases also appears to exist in the intermetallic boro-carbides and -nitrides.The field of ionic conductivity continues to be dominated by research into new materials for solid oxide fuel cells and rechargeable Li battery applications with the latter area attracting the most interest as in previous years. A review on fullerene chemistry appears elsewhere in this volume. 2 High Temperature Oxide Superconductors Hg Cuprate Superconductors.-A considerable amount of effort has been expended in the area of Hg cuprate superconductors since they represent the phases with the highest superconducting transition temperatures T,. A problem with these materials has been the difficulty in synthesizing pure bulk samples and a considerable amount of work has been concerned with this dilemma with many subtle modifications of experimental conditions.Due to lack of space and the fact that even now the synthesis methods are far from perfect these studies are not included in this review. The problems associated with growing single crystals of HgBa,Ca,- 1C~n02n+ using a solid media high pressure technique have been overcome by using a gas-phase high pressure technique.’.2 The former method was limited to several hundred milligrams with no free space to grow single crystals. The use of an Ar gas atmosphere with a partial pressure of0 leaves free space for single crystal growth and allows large sample volumes (as large as several cm’). Using this method single crystals of Pb doped J.Karpinski,H. Schwer,I. Mangelschots K. Conder A. Morawski T. Lada and A. Paszewin Nature 1994 371,661. J. Karpinski H. Schwer I. Mangelschots K. Conder A. Morawski T. Lada and A. Paszewin Physica C 1994 234 10. 467 468 P. R. Slater HgBa,Ca,Cu,O,,+ (Hg-1234) of size up to 0.5 x 0.5 x 0.05mm3 with a high T onset of 129K have been prepared. Single crystals of the infinite layer compound CaCuO, without Sr doping have also been grown. Thin films of Hg,Ba,CalCU,06+ (Hg-1212) on a SrTiO substrate have been prepared by laser ablation starting with sintered pellets of target composition H~,B~,C~,CU,~,+,,~ or separate targets of HgO and Ba,Ca,Cu,05 The as-grown films were amorphous due to the necessity of using low substrate temperatures (< 250 "C) to incorporate Hg into the film.Annealing in a quartz tube with a Hg-1212 bulk sample was necessary in order to obtain a crystalline film. The resulting crystalline Hg-1212 films showed preferential orientation perpendicular to the (100) SrTiO substrate with superconducting transitions as high as 124 K. Gao et al. have re-examined the pressure dependence of T in the HgBa,Ca,-,Cu,02 + + system up to higher pressure^.^ They observed record Tc'sof 118K (n = l) 154 K (n = 2) and 164 K (n = 3). Moreover the partial substitution of Pb for Hg in HgBa,Ca,Cu,O,+ (Hg-1223) was found to suppress the pressure induced T enhancement suggesting that Hg plays an important role in these +, compounds. The effect ofpressure on the structure of HgBa,Ca,- 1Cun02n+2 (n = 1 2,3) has been examined by Hunter et al.using neutron diffraction. The compressibility along the c axis is nearly the same for all three compounds and is up to two times larger than that along the a axis. For n = 1 and 2 the Cu-0 apical bond distance showed the largest compressibility while for n = 3 it was the Hg-0 bond distance. A neutron diffraction study of the five Cu layer phase HgBa2Ca4Cu5OI2+ (Hg-1245) has been performed at room temperature and at 10K by Huang et aL7 As in other members ofthe homologous series all the CuO planes were found to be almost coplanar i.e. there is insignificant or no 'buckling' of the CuO planes. There was no evidence for the substitution of Hg by Cu or the presence of extra oxygen atoms associated with such a substitution.Hur et al. have reported enhancements in the critical current density and stability in air or 0 at high temperatures (> 400 "C) by partial substitution of Hg by TI in HgBa,Ca,- 1C~,02n+2+6 (n = 2,3) with similar T values being ~btained.~.~ The synthesis of phases containing double Hg layers has been demonstrated this year. The occurrence of double Hg layers had been identified during HREM studies of HgBa,Ca,-1C~n02n+ suggesting that it might be possible to synthesize bulk phases containing these double layers as observed in the related TI-containing system.lo Radaelli et al. have performed such a synthesis by a high temperature high oxygen pressure route (18 kbar 1000"C).ll As in the case of the single layer phase HgBa,YcU,O +, the prototype Ca-free double Hg layer material S.Miyashita H. Higuna and F. Uchikawa Jpn. J. Appl. Phys. Lett. 1994 33 L931. C. C. Tsuei A. Gupta G. Trafas and D. Mitzi Science 1994 263 1259. L. Gao Y. Y. Xue F. Chen Q. Xiong R. L. Meng D. Ramirez C. W. Chu J. H. Eggert and H. K. Mao Phys. Rev. B 1994 50 4260. ' B. A. Hunter J. D. Jorgensen J. L. Wagner P. G. Radaelli D. G. Hinks H. Shaked R. L. Hitterman and R.B. Von Dreele Physica C 1994 221 1. ' Q. Huang 0.Chmaissem J. J. Capponi C. Chaillout M. Marezo J. L. Tholence and A. Santoro Physica C 1994 227 1. N.H. Hur N. H. Kim K. W. Lee K. H. Yook Y. K. Park and J. C. Park Physica C 1994 234 19. N. H. Hur N. H. Kim K. W. Lee Y. K. Park and J. C. Park Physicu C 1994 231,4. lo G.Van Tendeloo C. Chaillout J. J. Capponi M. Marezio and E. V. Antipov Physica C 1994 223,219. P. G. Radaelli M. Marezio M. Perroux S. de Brion J. L. Tholence Q. Huang and A. Santoro Science 1994 265 380. Conducting Solids Covering Ionic and Electronic Conductors 469 Hg,Ba,YCu,O -6 is non superconducting but superconductivity can be induced by Ca doping for Y with a maximum T of -45 K. Rietveld refinement of powder neutron diffraction data confirmed the general features similar to Bi- and T1-2212 but revealed some differences. In particular the oxygen site in the Hg bilayer (O* Figure 1) is partially (20 to 25%) vacant. This means that some of the Hg atoms lose one of the neighbouring oxygen atoms along the z axis. Therefore they no longer have an apically compressed octahedral coordination but rather a pyramidal coordination with only one short Hg-0 bond along the z axis and three or four in-plane bonds.In addition the CuO planes are buckled (Cu-01-Cu 'buckling' angle is 168.8') making the Cu environment similar to YBa,Cu,O, unlike the single Hg layer compounds. It is interesting to note the low T and significant buckling of the CuO planes which is not observed for the higher T single Hg layer phase suggesting a possible correlation between these two features. Bryntse has reported a double layer phase containing a mixture of T1 and Hg in the double layer.' A phase of composition Hgo~,,7T1,,333Ba,CaCu208+, was prepared with a T of 100K which is 12K lower than for the corresponding TI-2212 phase.A three Cu layer phase of composition HgO,,T1,,,Ba,Ca,Cu,O,,~, with a T of 130K has also been reported.' The limits of Sr substitution for Ba have been examined in HgBa,CuO,+ by Subramanian and Whangbo.' Single phase HgBa -xSrxC~04+s has been achieved for 0 Ix I0.7 with T decreasing with increasing x such that superconductivity is lost when x > 0.5. These results together with conclusions from band structure calculations indicate that the hole source in this compound is the excess oxygen content (6) which is reduced by Sr substitution due to a reduction in the cell size. In order to stabilize the Ba-free compounds the partial replacement of Hg by other elements is required. The stabilization of HgSr,CuO,+ has been achieved by partial substitution of Mo for Hg with a maximum T of 78 K for 15% Mo substitution for Hg.I5 This represents the highest T for a Ba-free Hg-1201 phase and since high pressure oxygenation was found to reduce T,the samples were considered to be either optimally doped or overdoped.Cr substitution for Hg has also been achieved with a maximum T of 58 K for Hgo,,Cro~3Sr,Cu0,+6.'6 The attempted substitution ofCr on the Cu sites resulted in large impurities indicating that Cr prefers the Hg site. Mo substitution in Ba- free Hg-1212 has also been demonstrated with Tc'sin the region of loOK.' Re is also reported to stabilize Sr-based Hg compounds but it is tentatively assumed that it substitutes for the Cu site rather than the Hg site. Stabilization by Ce substitution i.e.Hg0,,Ce0~,Sr3~,M,Cu2~,0,~, (M = Ca Ce Nd) has also been demonstrated with a maximum T of 62 K for Hgo~,Ceo,,Sr,,,Cao~,Ndo~2Ceo,lCu2,1-0 As in the case of Pr substitution reported last year a superstructure resulting from cationic ordering between Ce and Hg (plus Cu) was observed. The Ca and Nd homogeneity range was very narrow and no Hg-1212 phase was observed when M = Ce. The stabilization of Ba-free Hg-1223 has however not yet been achieved. l2 1. Bryntse Physicu C 1994 226 184. l3 F. Goutenoire A. Maignan G.Van Tendeloo C. Martin C. Michel M. Hervieu and B. Raveau Solid State Cotnmun. 1994 90,47. l4 M.A. Subramanian and M.-H. Whangbo J. Solid State Chem. 1994 109 410. l5 K. K. Singh V. Kirtikar A. P. B. Sinha and D. E. Morris Physica C. 1994 231 9.J. Shimoyama S. Hahakura K. Kitazawa K. Yamafuji and K. Kishio Physica C 1994 224 1. l7 S. Hahakura J. Shimoyama 0.Shiino and K. Kishio Physica C 1994 233 1. A. Maignan M. Hervieu C. Martin C. Michel and B. Raveau Physica C 1994 232 15. 470 P. R. Slater Figure 1 The structure ofHg,Ba,YCu,O A 1 1 intergrowth of Hg-1201 and La,Cu04 has been synthesized by Huve et ~1.'~ The phase HgBa,La,Cu,O,,, is superconducting with a T of 53K (after Ar annealing) and represents the first member of the series [HgBa,CuO +,Irn b2CuO4In. Choy et al. have succeeded in intercalating mercury halides between the two BiO layers in Bi,Sr,CaCu,O which has been previously reported to intercalate halides.,' The intercalation compounds (HgX,),~,Bi,Sr2CaCu,0 (X = Br I) retain superconductivity although with a slightly reduced T (71 K for X = Br 68 K for X = I compared to 76K for the starting material) despite the large expansion along the c axis (7.2A).Superconductors Containing 0xyanions.-Cuprate systems have been shown in the past few years to exhibit a remarkable flexibility for the incorporation of C02 3 -groups l9 M. Huve C. Martin G. Van Tendeloo A. Maignan C. Michel M. Hervieu and B. Raveau Solid State Commun. 1994 90,37. 'O J.-H. Choy N.-G. Park S.-J. Hwang D.-H. Kim and N.H. Hur J. Am. Chem. Soc. 1994 116 11 564. Conducting Solids Covering Ionic and Electronic Conductors 471 as well as other oxyanions. A significant amount of further work has been performed in this area with the synthesis of several new intergrowth phases and other systems.Ono et al. have observed a new oxycarbonate phase Bi,(Bi,Sr,Ca),Ca(Cu,C),C,O, which contains a mixture of octahedral and square pyramidal Cu in some multiphase Bi-Sr-Ca-Cu-C-0 samples formed at high pressure (2 GPa).,’ Since they were unable to prepare the oxycarbonate as a major phase (and it was only detected in 3 out of 25 samples examined) the superconducting properties were not measured. The structure consists of alternating layers of half Bi,Sr,Cu,C,O,, CaCuO, and half Bi2Sr6Cu3C201 6. They also observed another oxycarbonate containing no Bi i.e. (Sr,Ca),,Cu +,C4 -x024 which consists of intergrowths of infinite layer SrCuO and Sr,CuO,CO type lamellae. Pelloquin et al. have prepared the third member (n = 3) of the oxycarbonate series (Bi -,P~,S~,CUO,)(S~,CUO~CO~)~ (0 5 x 2 0.25),, which had previously been seen as a defect in lower n members.This corresponds to an intergrowth of triple Sr,CuO,CO oxycarbonate layers and a single 2201 layer. The structure is modulated as with all bismuth cuprates and oxycarbonates. The T (x= 0)is 34 K compared with 30 K (n = 1) and 40 K (n = 2) and in contrast to the first two members T is not raised by Pb doping (x > 0). Thus T appears to go through a maximum as n increases although the metastable character of this phase due to the high stability of Sr,CuO,CO and the lower n members means that it is difficult to optimize the T,. Stage I iodine intercalation has been successfully achieved into the oxycarbonate B~,S~,CU,CO,O,.~~ The semiconducting underdoped host material became super- conducting with a T of 23 K after intercalation which is explained by hole doping from the intercalated iodine atoms into the CuO sheets.A new oxycarbonate Pbo~7Hg,,,Sr4Cu,C0,07 has been reported by Martin et The phase which consists of an intergrowth of the two non-superconducting compounds Sr,CuO,CO and Pb,~,Hg,,,Sr,CuO was superconducting after anneal- ing in a reducing atmosphere with a T of 70K. Uehara et al. have reported the oxycarbonate HgBa,Sr,O,+,Cu,(CO,) with a T of 66K.25 As in the case of the related T1-containing oxycarbonate T1Ba,Sr,Cu,07(C0,) reported last year the structure can be related to HgBa,CuO,+ with a periodic replacement of COi- for HgO along the (110) direction.The similar oxycarbonate Hg,~,Pbo~,Sr,~,Ba,Cu2CO,O,-,has also been prepared with a maximum T of 68 K for x = 2.26A modulation along the (110) direction is observed which is attributed to an ordering between (Pb,Hg)O and carbonate groups with the degree of ordering depending on among other factors the local CO content. The compound Bi,~,Hg,,,Sr,Cu,CO,O -,,consisting of an intergrowth of 1201 Bi,~,Hg,,,Sr,CuO,+ and Sr,CuO,CO, has been prepared with a T of 17K.27This phase exhibits large possibilities for non-stoichiometry such as partial substitution of Sr for (Bi Hg) and a shearing mechanism along c that leads to longitudinal ” A. Ono S. Horiuchi and M. Tsutsumi Physicu C 1994 226 360. ’‘ D. Pelloquin M. Hervieu A. Maignan C. Michel M.T. Caldes and B. Raveau Physicu C 1994,232,75. 23 Y. Muraoka H. Nameki M. Kikuchi S. Awaji N. Kobayashi and Y. Syono Physicu C 1994,233,209. 24 C. Martin M. Hervieu M. Huve C. Michel A. Maignan G. Van Tendeloo and B. Raveau Physicu C 1994 222 19. z5 M. Uehara S. Sahoda H. Nakata J. Akimitsu and Y. Matsui Physicu C 1994 222 27. 26 M. Huve G. Van Tendeloo M. Hervieu A. Maignan and B. Raveau Physicu C 1994 231 15. *’ D. Pelloquin M. Hervieu C. Michel A. Maignan and B. Raveau Physicu C 1994 227 215. 472 P. R. Slater intergrowths of 1201 and oxycarbonate which dramatically changes the local composition. Amamoto et a!. have prepared a new insulating oxyborate Nd,Sr,Cu,O,(BO,) consisting of alternate stacking of (Nd,Sr),CuO,BO and N~S~,CU,O,BO,.~~ The high room temperature resistance (> 2 MQ cm) is attributed to the Cu oxidation state of 2+ and the consequent absence of holes.Single crystals (2 x 2 x 2mm3) of the parent oxycarbonate (Ba -xSrx)2Cu1.102,2 +,(CO,),. have been prepared for the first time by means of the abnormal grain growth of ceramic samples.29 Although they show some voids and do not exhibit a perfect shielding effect the crystals are superconducting with an onset of T of 32K. Oxyanion substitutions in Y(Ba/Sr),Cu,O related systems have attracted further study. A structural study of the system (Cu,C)(Sr,Ca),(Y,Ca,Sr)Cu,O has been performed by Miyazaki et aL3’ As-prepared samples were semiconducting but superconductivity was induced by annealing at 1000°C in an oxygen pressure of 4 MPa.The structural study and wet chemical analysis suggested that hole doping is caused during high pressure oxygen annealing by the release of some Cog- groups and by the consequent introduction of oxygen atoms into the vacant apical oxygen site where the C0:- group has been lost. Ono and Horiuchi have synthesized superconducting samples of the Ba-free 1212 oxycarbonate phases (Cu,C)Sr,(Y,Ca)Cu,O for the first time by using high pressure ~ynthesis.~’ The Tc’sof the Ca-containing phases are -80 K regardless of considerable variations in Ca and C contents while the T is -45K for the Ca-free phase. The incorporation of the oxyanions SeOi-and Te0;-into YSr,Cu,O,- and (Y/Ce),Sr,Cu,O,- has been attempted., No evidence for the substitution of Te was found whereas Se substitution was successful (highest purity samples for 50% Se substitution of the ‘chain’ Cu sites) with superconductivity (T = 45 K) being observed in YSr,Cu,,,Se,.,O,- by Ca doping for Y.XPS measurements indicated that Se enters the structure as Se4+ as opposed to Se6+ and remains in the lower oxidation state even after annealing under high oxygen pressure. Superconductivity (T = 15-20K) has been observed in (Y/Ce),Sr,-,Ba,Cu,O,~ phases doped with BO;- SO:- PO:-on the ‘chain’ Cu sites after annealing under high oxygen pressure.33 Neutron diffraction studies showed significant (4-9%) vacancies in the (Y/Ce),O fluorite block which are filled after oxygen annealing. New phases La,~,Ce,~,Ba,Cu,BO,- and Nd,~,Ce,~,BaSrCu,BO with complete BO layers were also reported.Hiroi et a/.have observed a new metallic oxycarbonate Sr8Cu7COl in high pressure synthesis studies of the Sr-Cu-C-0 system.34 The structure consists of an oxygen deficient perovskite where 1/8 of the Cu are replaced by Cot- so as to form a 242a x 242a x c unit cell. The lack of superconductivity can be attributed to the fact that there are no intact CuO planes. ” Y. Amamoto H. Yamane T. Oku Y. Miyazaki and T. Hirai Physicu C 1994 227 245. 29 H. Shibata K. Kinoshita and T. Yamada Physica C 1994,232 181. 3” Y. Miyazaki H. Yamane T. Kajitani N. Kobayashi K. Hiraga Y. Morii S. Funahashi and T. Hirai Physica C 1994 230 89. 31 A. Ono and S. Horiuchi Jpn. J. Appl. Phys. 1994 33 L1149. 32 P. R. Slater C. Greaves M.Slaski E. Z. Kurmaev St. Uhlenbrock and M. Neumann Physica C 1994,231 109. 33 P. R. Slater C. Greaves and M. Slaski Physicu C 1994 235-240 741. 34 Z. Hiroi K. Yamaura M. Azuma and M. Takano Physica C 1994 235240 1005. Conducting Solids Covering Ionic and Electronic Conductors 473 High pressure synthesis techniques have resulted in a new series of oxycarbonate superconductors although the exact compositions of these phases remains somewhat controversial. In March 1994 Ihara et al. reported superconductivity with T > 117K in the system Ag -,Cu,Ba,Ca,- 1C~n02n+3-6.35 Their idea was to form similar phases to the Hg series with non-toxic Ag in place of Hg. The synthesis was performed at high temperatures and high pressures (5 GPa at 1100 "C for 1-3 hours) using a Ba2Can-1C~,0 precursor (n = 3 4 5) and Ag,O or Ago.XRD data showed the presence of major phases ascribed to Ag-1223 Ag-1234 and Ag-1245 with the T for Ag-1234 being 117 K and lower Tc'sbeing observed for the other two phases. EDX of platelike Ag-1234 crystals indicated that the content of Ag varied with the Cu content in a wide range of xfrom 0.25-1.0 demonstrating a mixing of Ag and Cu. These phases were observed to be more stable to atmospheric degradation than the corresponding Hg or T1 phases. Similar phases were subsequently reported by the same group but without the presence of Ag i.e. Cu -.Ba2Can- 1C~n02n+4-6.36 A superconducting sample containing mainly Cu-1234 phase gave a T of 116.4 K. A deficiency in Cu (x-0.4) was determined from an XRD analysis of a single crystal.(3-1223 and 1245 phases were also synthesized showing lower Tc's. Jin et al. also succeeded in synthesizing similar superconducting multiphasic samples in the Ba-Ca-Cu-0 sys- HREM confirmed structures similar to the type found in analogous single layer Hg or TI systems and showed the presence of intergrowths of other n members (up to n = 6),as are also observed for the related Hg and T1 system^.^' However some controversy has arisen over the exact nature of these superconducting phases. In particular as to whether the Ag-containing samples actually contain Ag in the superconducting phase. Wu et al. have examined the Ag-Ba-Ca-Cu-0 system and found no evidence by EDX analysis for Ag in the perovskite related phase.However samples which had Ag in the starting matrix were found to show a sharper superconducting transition and a larger Meissner signal suggesting that Ag20 could act as a reaction enhancer in the formation of the Cu-l2(n -1)n phases.39 Kawashima et al. also examined this system and found by chemical and structural analysis that no Ag was present but instead the phases contained carbon suggesting they were oxy~arbonates.~' The presence of CO; -was later confirmed by EELS investigations by Alario-Franco et aL4' Two members of the homologous series were (Cuo,5Co~5)Ba,Ca,~,Cu,0,,+3isolated with n = 3 (T = 67K) and n = 4 (T = 117 K). Electron microscopy indicated that Cu and C are in both cases located alternately along the a axis of the subcells resulting in superstructures with dimensions 2a x b x 2c.Most of the Ag was found to be present as Ag metal suggesting that Ag,O worked only to increase the oxygen pressure. The cell parameters were similar to those observed by Ihara et al. in their Ag-free samples suggesting that these samples are also 35 H. Thara K. Tokiwa H. Ozawa M. Hirabayashi H. Matuhata A. Negishi and Y.S. Song Jpn. J. Appl. Phys. 1994 33 L300. 36 H. Ihara K. Tokiwa H. Ozawa M. Hirabayashi A. Negishi H. Matuhata and Y. S. Song Jpn. J. Appl. Phys. 1994 33 L503. 37 C.-Q. Jin S. Adachi X.-J. Wu H. Yamauchi and S. Tanaka Physica C 1994 223 238. 38 X.-J. Wu S. Adachi C.-Q. Jin H. Yamauchi and S. Tanaka Physica C 1994 223 243. 39 X.-J. Wu C.-Q. Jin S. Adachi and H. Yamauchi Physica C 1994 224 175.40 T. Kawashima Y. Matsui and E. Takayama-Muromachi Physica C 1994 224 69. 41 M. A. Alario-Franco P. Bordet J.-J. Capponi C. Chaillout J. Chenavas T. Fournier M. Marezio B. Souletie A. Sulpice J.-L. Tholence C.Colliex R. Argoud J. L. Baldonedo M. F.Gorius and M. Perroux Physica C 1994 231 103. 474 P. R. Slater oxycarbonates. a conclusion supported by the observed Cu deficiency. An interesting point however is that the n = 4samples of Jin et al. and the Ag-containing samples of Ihara et al. have a larger c axis than those of Kawashima et al. (18.30A and 18.1 1 A compared to 17.93 A) suggesting that if COi- is also present for the former two cases then it is present in a lower concentration i.e. the phases are non-stoichiometric (Cu -xC,)Ba2Ca,- ,CU,O~,+~.The question as to why the Tc’sof all samples are so similar remains unanswered. Shimakawa et al. have determined the structure of the n = 4 phase by neutron diffra~tion,~ and observed a composition of (Cuo~,,Co~3,)Ba,Ca3Cu401 The structure has average tetragonal symmetry and is similar to the (Hg T1)-containing cuprate analogues. The structure has two types of inequivalent CuO planes square planar (inner) and square pyramidal (outer). The inner two CuO planes are less ‘buckled’ than the outer two. An unusual feature of these oxycarbonates is that the T,for the n = 4 phase is greater than the T,for the n = 3 phase. It is also unusual that such a high T is observed for such a distorted structure (the Cu-0 apical distance for the outer plane Cu atoms is different depending on whether Cu or C is present).One possible explanation proposed by the authors is that even though the presence of CO; -degrades superconductivity for the two outer CuO layers the two inner CuO layers support superconductivity with a high T,. Kawashima et al. have since discovered a new series of similar oxycarbonates containing two (Cu,C) layers instead of one the ideal composition being (Cuo~,Co~5)2Ba3Ca,-,Cu,0,,-5.43Then = 4(T -113K)andn = 5 (T,near 1lOK) phases were prepared in bulk and in addition an intermediate phase in which n = 4 and n = 5 slabs were stacked alternately was found from electron micro~copy.~~ As before the Cu and C were found to be located alternately along the a axis of the subcell resulting in a doubling of the cell along a.The n = 3 phase has also been prepared with a T of 91 K.,’ In this phase a slightly different ordering between Cu and C was observed by electron microscopy resulting in a superlattice 2a x b x 2c with a doubling along the c direction as well as the a direction. Similar oxycarbonate superconductors have been obtained in the Sr-based systems Ca-Sr-Cu-C-0 by Yamaura et A single phase sample (T -92K) has been obtained from a nominal composition (Cao~,Sro~7)3Cu2Co~7s0,, by heating in the presence of KClO oxidizer at 1200°C and 6GPa for 30 minutes. A supercell a x 4a x 2c most probably a result of the ordering of C vacancies (the sample is 25% C deficient) along the b axis was observed. No superconductivity was detected when the KClO oxidizer was not added.Equivalent systems with partial BO; -substitution for C0:-have also been reported by Uehara et al. i.e. Sr2(Ca,Sr),~,Cu,(C03),~,(B0,),0, (n = 1 x = 0.3 T = 50K; n = 2 x = 0.45 T = 105 K; n = 3 x = 0.6 T = 115K).47Samples without B0;- sometimes showed superconducting properties but with very low volume fraction ( < 1 YO),thus indicating that BOZ-was acting as a hole dopant. 42 Y. Shimakawa J.D. Jorgensen D.G. Hinks H. Shaked R. L. Hitterman F. Izumi T. Kawashima E. Takayama-Muromachi and T. Kamiyama Phys. Rev. B 1994 50 16008. 43 T. Kawashima Y. Matsui and E. Takayama-Muromachi Physica C 1994 227,95. 44 Y. Matsui T. Kawashima and E. Takayama-Muromachi Physica C 1994 235240 166. 45 T.Kawashima Y. Matsui and E. Takayama-Muromachi Physica C 1994 233 143. 46 K. Yamaura Z. Hiroi and M. Takano Physica C 1994,229 183. 47 M. Uehara M. Uoshima S. Ishiyama H. Nakata J. Akimitsu Y. Matsui T. Arima Y. Tokura and N. Mori Physica C 1994 229 310. Conducting Solids Covering Ionic and Electronic Conductors 475 The Main Superconducting Families and Related Phases.-Superconducting tetragonal Sr,CuO synthesized at high temperatures and high pressures has attracted further interest. The T of this phase has been raised from 70 K to 94 K by annealing in a N atm~sphere.~~ There was no sign of any weight loss during the annealing treatment and so the change in T is presumed to be due to a readjustment of the oxygen positions to achieve an optimum doping level.A study of the synthesis conditions of Sr,CuO + by Laffez et al. has shown the presence of two crystallographic domains (a -3.76 c -12.54A and a -3.79 c -12.46A) of the fundamental tetragonal structure.49 The first phase is formed if a small amount of oxidizer (KClO,) is added while the latter is formed for higher amounts of oxidizer. The Tc’sof 5 1K and 80 K have been assigned to these phases respectively. For the latter phase a new superlattice 5a/,/2 x 5a/,/2 x c was observed. Tetragonal Sr,CuO has also now been synthesized at low temperature (370 “C) in latm. 0 from the decomposition of the hydroxometallate precursor S~,CU(OH),.~~ Contrary to the phase prepared under high pressure this phase was not superconducting despite the fact that a similar supercell 4aJ2 x 4aJ2 x c was observed indicating that the material was structurally the same.Heating to 450 “C in 0 resulted in a conversion into the orthorhombic phase. Synthesis at moderately high pressure (50-3000 bar) also produced non-superconducting tetragonal Sr,CuO + with a similar 4J2a x 442a x c superstructure.’’ The structures of high pressure- moderate pressure- and ambient pressure-phases have been determined by neutron diffraction and shown to be the same with the latter having a slightly higher oxygen content.’ ’*’,Moreover in contrast to previous assumptions (see last years review) the structure does not appear to contain ‘intact’ 2D-CuO planes. The oxygen vacancies are located in these CuO planes and not in the Sr,O layers as previously thought and the exact origin of the superconductivity in these phases is not clear.One possible explanation is that oxygen clustering occurs thereby creating islands of superconduct- ing material with ‘intact’ CuO planes.’ Three very important results reported this year have been the observation of hole doped superconductivity in phases without apical oxygen atoms coordinated to the CuO planes. It had been previously thought that such apical oxygen atoms were necessary for hole doped superconductivity. Low temperature ( -200 “C) fluorination (by F gas) of Sr,CuO has been shown to insert fluorine atoms to give the oxyfluoride Sr,CuO,F with the La,Cu04 str~cture.’~ Superconductivity was observed after post synthesis reduction in N or H,/N to reduce the amount of interstitial fluorine (6) with a maximum T of 46K being recorded for 6 -0.3.The superconducting properties and Madelung energy calculations indicate that the fluorination results in O/F interchange to create electronically active CuO planes (Figure 2). Superconduc-tivity with a maximum T of 26K has been induced in Ca,CuO,Cl by partial substitution of Na for Ca under high oxygen pressure (900 “C,6 GPa 30 min~tes).’~ 48 P. D. Han L. Chang and D. A. Payne Physica C,1994 228 129. 49 P. Laffez X.J. Wu S. Adachi H. Yamauchi and N. Mori Physica C,1994 222 303. 50 J. F. Mitchell D. G. Hinks and J. L. Wagner Physica C,1994 227 279. 51 T. Ami M. K. Crawford,R. L. Harlow Z. G. Li T. Vogt Q.Zhu and D. E. Cox Physica C,1994,235-240 1003.52 Y. Shimakawa J.D. Jorgensen J. F. Mitchell B.A. Hunter H. Shaked D. G. Hinks R. L. Hitterman Z. Hiroi and M. Takano Physica C,1994 228 73. 53 M. Al-Mamouri C. Greaves P. P. Edwards and M. Slaski Nature 1994 369 382. 54 Z. Hiroi N. Kobayashi and M. Takano Nature 1994 371 139. 476 P.R. Slater 00 #F F* Sr cu Figure 2 The structure of(a) Sr,CuO and (b)Sr,CuO,F,, showing the idealized apical F(F)and interstitial F(F*) sites NaClO has been used both as a source of Na and to create an oxidizing atmosphere. The nature of the superconducting carriers has not yet been unequivocally assigned but the fact that a highly oxidative pressure was required for the appearance of superconductivity strongly suggests that the carriers are holes.No superconductivity was observed if KClO was used instead of NaClO, showing that Na is important. Hole doped superconductivity has been observed for the first time in a phase with the Nd,CuO structure. Tm,~,,Ca,~,,CuO, prepared at 1100"C under a pressure of 6GPa (using KClO to provide an oxidizing atmosphere) was shown to be superconducting with a T of -30K.55 Normally superconductivity can only be induced in Nd,CuO,-type phases by electron doping. This is related to the long Cu-0 bonds in the CuO planes which arises out of lattice mismatch between the CuO planes and the Nd,O block. The long Cu-0 bonds mean that it is difficult to introduce sufficient mobile holes in the CuO sheets and in fact favours the doping of electrons.In contrast the small size of Tm results in short Cu-0 bonds (1.916 A j such that hole doped superconductivity becomes possible. New methods are increasingly being required to prepare high temperature superconductors. This is particularly so for the phases containing Hg and T1 due to their high toxicity and volatility which causes safety problems under normal high temperature preparation conditions. An interesting paper by Chen et al. reports the preparation of multiphase T1-based cwprate superconductors by a hydrothermal method which avoid the problems of T1 ~olatility.'~ Mixtures of TlNO, BaO CuO 55 W. J. Zhu Y. S. Yao X. J. Zhou B. Yin C. Dong Y. Z. Huang and Z. X. Zhao Physica C 1994,230,385. 56 Q. W. Chen Y. T. Qian Z. Y. Chen K. B. Tang G. E. Zhou and Y.H. Zhang Physica C 1994,224,228. Conducting Solids Covering Ionic and Electronic Conductors 477 CaCO, and H,O (to convert TlNO into Tl,O,) were heated in a teflon vessel with H,O at 160 "C for 16 hours. The product showed the presence of small amounts of TI-2201 and 2212 phases as well as various impurities and exhibited superconductiv- ity with a T onset near 95 K. The amount of BaO and H,O was found to play a crucial role in the formation of superconducting phases. The partial substitution of fluorine for oxygen has been achieved in TlBa,CuO -6 using TlF as a source of fluorine.57 The parent phase is normally non-superconducting due to the high Cu oxidation state (close to Cu3+) and the effect of fluorination is to reduce the Cu oxidation state and consequently induce superconductivity.Single phase tetragonal T1Ba,CuO5-,-,F has been observed for 0.1 5 x I0.5 with supercon- ducting transitions as high as 75 K for x = 0.3. XPS measurements made to investigate the core-level electronic states for TlBa,Ca -xYxCu207-y (x = 0 0.1 0.8 1.O) have shown that the T1 core-level shifts towards the higher binding energy side implying that electrons donated by Y substitution do not only fill the Cu-0 hole states but are also partially transferred to the TI site which thus behaves as a charge reservoir., Sastry and West have developed a new synthetic route to phase pure Pb-free Bi 2233.59 The synthesis involves the reaction (over 15-30 days) between the precursors Bi,CuO and (Sr,Ca),CuO,. In this way Bi-2233 with variable compositions can be prepared from stoichiometric compositions with variable Ca :Sr ratio and Bi :(Ca + Sr) ratios.An optimum T of 107K was obtained which was a lot less dependent on composition and heat treatment than for Bi-2201 and Bi-2212 phases. This method can also be used to form Pb-doped samples by starting with a (Bi ,Pb),CuO precursor. Iodine intercalation into semiconducting Bi,Sr,Y,,,Ca,~,Cu,O + has been shown to induce superconductivity (T,onset close to 76 K) indicating a transfer of holes from iodine atoms located in the BiO layers to the CuO sheets6' The fact that Bi,Sr,Y,,,Ca,,,Cu,O + does not become superconducting indicates that the hole transfer on iodine intercalation is only small. Iodine and bromine have been intercalated into the Bi-2222 phase to give X,Bi2Sr2(Gd,~82Ce,~,8)2~U2~~o (X = Br 0 Iy I0.2; X = I 0 < y I 1).62 Non-superconducting samples became superconducting (-20 K) after light bromination although there was no evidence from XRD that Br was intercalated between the two BiO layers.Normally high pressure oxygen annealing is required to induce superconductivity and such supercon- ducting samples were found to intercalate less iodine and become poorer superconduc- tors suggesting the presence of excess oxygen atoms between the BiO layers in these materials. Superconductivity has also been induced in Bi-2222 phases by the partial substitution of Pb for Bi without the need for high oxygen pressure annealing although the T was found to be increased by such annealing.63 Unlike conventional BCS superconductors the cuprate superconductors exhibit only a small oxygen isotope effect.Of this small effect Zeck et al. have determined that 57 M.A. Subramanian Mat. Res. Bull. 1994 29 119. 58 T. Suzuki M. Nagoshi Y. Fukuda S. Nakajima M. Kikuchi Y. Syono and M. Tachiki Supercond. Sci. Technol. 1994 7,817. 59 P.V. P.S.S. Sastry and A.R. West Physica C 1994 232 63. 6o P. V. P. S. S. Sastry and A. R. West J. Muter. Chem. 1994 4 647. 61 M.A. Subramanian J. Solid State Chem. 1994 110 193. 62 Y. Koike T. Hisaki K. Sasaki A. Fujiwara T. Noji and Y. Saito Physica C 1994 224 31. 63 H. B. Liu X. D. Chen X. P. Jiang D. E. Morris and A. P.B. Sinha Physica C 1994 220 265. P. R. Slater 80% of the total (positive) isotope effect is associated with the CuO planes., This suggests that theories of electron pairing in high temperature superconductors have to consider a phononic contribution in which the planar tilting or buckling modes in the CuO layers play an essential role.The compound PrBa,Cu,O has been synthesized for the first time by annealing at or 957°C under 5atm. 02,65 990°C under 50atm Ar/20O/00,.~~ No sign of superconductivity was observed but the compound is metallic in contrast to PrBa,Cu,O, which is semiconducting. An anomalous behaviour (non-linear above 6GPa) of the 147cm-' Cu(2) Raman mode corresponding to the z-motion of the CuO planes has been observed in YBa,Cu,O under pressure., The observed behaviour is similar to the variation of T with increasing pressure.In contrast YBa,Cu,O shows no non-linear behaviour in either the Raman mode or T,. There thus appears to be a correlation between the pressure-induced increases in T and the change in the frequency of the Cu(2) mode which the authors attribute to changes in the electronic state of the CuO planes as a result of charge carrier redistribution between Cu and 0 in the planes. Nakamura et al. have prepared c axis orientated superlattices of (La,A),CaCu,O -x (A = Sr Ca)/(La,Sr),CuO,- by laser ablation on a SrTiO substrate., Underdoped semiconducting La ~6Sro~,CaCu,0 -and overdoped metallic La .,Sr,.,CuO - form a superconducting (T onset = 25 K) superlattice if they are alternately stacked with four half unit cells of the former and ten half unit cells of the latter.Superconductivity at 60 K with a low volume fraction ( < 1YO) has been induced in the double Cu layer Ruddlesden-Popper phase La .,Srl ,,Cu,O, by synthesis at ambient pressure in the presence of KC10 oxidizer.69 Previously superconductivity could only be induced in these double layer cuprates by heating under high oxygen pressure. Guloy et al. have succeeded in preparing the three Cu-layer Ruddlesden-Popper phase La,Ca,Cu,O under high pressure.,' Although the phase exhibited metallic conduc- tivity doping to induce superconductivity could not be achieved due to its thermal instability making it very difficult to optimize the hole concentration. The effect of hydrostatic pressure on the structure of orthorhombic La -,Sr,CuO has been examined by Takahashi et aL7' Increasing the pressure causes the tilt angle of the CuO octahedra to decrease leading to a transition to a tetragonal structure and a small increase in T,.In the tetragonal phase the T was found to be independent of pressure. T thus appears to vary inversely with the tilt angle and is maximum for the tetragonal structure i.e.for flat and square CuO planes. This feature of the highest T for flat CuO planes seems to be common to superconducting cuprates cf. the Hg cuprates which have flat CuO planes and the highest T,. The synthesis of intergrowth structures reported widely for oxycarbonates is now 64 D. Zech H. Keller K. Conder E. Kaldis E. Liarokapis N. Poulakis and K. A. Muller Nature 1994,371 681. 65 Y.Yarnada S. Horii N. Yarnada Z. Guo Y. Kodarna K. Kawarnoto U. Mizutani and 1. Hirabayashi Physica C 1994 231 131. 66 N. Seiji S. Adachi and H. Yarnauchi Physica C 1994 227 377. " M. Kakihana H. Arashi M. Yashima M. Yoshimura L. Borjesson and M. Ka11 Physica C 1994,230,199. 68 K. Nakarnura H. Noburnasa K. Shirnizu and T. Kawai Physica C 1994 221 387. 69 R. Mahesh R. Vijayaraghavan and C.N.R. Rao Mat. Res. Bull. 1994 29 303. 'O A.M. Guloy B.A. Scott and R. A. Figat J. Solid State Chem. 1994 113 54. " H. Takahashi H. Shaked B. A. Hunter P. G. Radaelli R. L. Hitterrnan D.G. Hinks and J. D. Jorgensen Phys. Rev. B 1994 50 3221. Conducting Solids Covering Ionic and Electronic Conductors 479 being extended to other systems. Barbey et al. have prepared Eu2~,Ba,~,Cu3Co,012 which corresponds to the first (n = rn = 1) member of the intergrowth series [LnBa(Cu,C0)~0,],,[LnBa~(Cu,Co)~0,]~.~~ HREM has shown several intergrowth defects corresponding to the local formation of other (n,rn)members suggesting that it should be possible to prepare other members of the series.Li Rukang has reported the synthesis of two phases in the homologous series of fluorite block-containing compounds (BaTi0,),(Gd,Ce)3Cu,07 with rn = 2 and rn = These compounds are built up by alternative stacking of multiple perovskite layers CuO,planes and double fluorite layers. Semiconducting behaviour was observed down to 15K. A new semiconducting layered cuprate Gd,CaBa,Cu,Ti,O,, has been synthesized by Fukuoka et al.74 It is proposed that this phase is related to the previously reported Gd,Ba,Cu,Ti,O, compound but contains an extra rock-salt (Gd,Ca)O sheet inserted between the two TiO octahedra.The lack of superconductivity is attributed to the fact that the Cu oxidation state is only 2.0+. Ag addition to Pb,~,Cu,,,Sr,(Ln -,Ca,)Cu,O (R = Y Gd Dy Ho Er Tm) has been shown to enhance T by up to 15K above those of the corresponding Ag-free samples with the compounds containing the larger rare earths (lower initial T,) showing the greatest T enhancement (highest T = 78K. for Ag-doped Pb,~,Cu,~,Sr,Y,~,Ca,,5Cu207).75 EDX studies have indicated that a small amount of Ag enters the structure and it has also been suggested that Ag facilitates the incorporation of oxygen in the grains thus promoting the formation of the fully oxidized phase.The versatility of high pressure synthesis techniques has been further demonstrated by the synthesis of a new series of high temperature superconductors MSr,Ca,-1C~,02n+3 (M = Al Ga) isomorphous to the corresponding M = Hg TI At ambient pressure only the n = 2 phase can be formed provided Y is in place of Ca which corresponds to (A1,Ga)-doped YSr,Cu30 In order to form the Y-free phase the high pressure synthesis is required., For the Al-containing phases Tc’s of 110K and 83K were obtained for n = 4 and 5 re~pectively.~~ Significant intergrowths of phases with different values of n were observed in the n = 5 sample (values of up to n = 8 were present). EPMA measurements suggest deviations from the ideal composition with partial substitution of Cu for A1 and Sr for Ca.For the Ga-containing phases samples with n = 3 and n = 4 have been prepared with Tc’sof 70 K and 107 K re~pectively.,~ Non-cuprate Systems.-The search for superconductivity in non-cuprate systems has been the subject of further intense research with a number of reports of new superconducting materials. Superconductivity albeit at very low temperature (0.93K) has been observed in single crystals of Sr,RuO (grown by a floating zone method) with the La,Cu04 structure.79 This is only the second layered perovskite without Cu 72 L. Barbey B. Domenges N. Nguyen and B. Raveau J. Solid State Chern. 1994 111 238. l3 R. Li J. Mater. Chern. 1994 4 773. 74 A. Fukuoka S. Adachi T.Sugano X.-J. Wu and H. Yamauchi Physica C 1994 231 372. 75 H. B. Liu D. E. Morris X. P. Jiang and A. P. B. Sinha Physica C 1994 222 119. 76 M. Isobe Y. Matsui and E. Takayama-Muromachi Physicu C 1994 222 310. 77 M. Isobe T. Kawashima K. Kosuda Y. Matsui and E. Takayama-Muromachi Physica C 1994,234,120. 7R E. Takayama-Muromachi and M. Isobe Jpn. J. Appl. Phys. 1994 33 L1399. 79 Y. Maeno H. Hashimoto K. Yoshida S. Nishizaki T. Fujita J. G. Bednorz and F. Lichtenberg Nature 1994,372 532. 480 P. R. Slater to exhibit superconductivity [the first being Ba,-,K,Pb -yBiy04-8 (T = 14 K x =0.1 y = 0.15) reported last yeargo]. Gasparov et al. have observed evidence for superconductivity above 20K in multiphase samples of Ba,NbO,- prepared from Nb and BaO rapidly heated to -500OC in air O,/Ar,H, or under vacuum.g' When samples in the composition range 0.2 <x < 1 were prepared in air two superconducting transitions 18.6K and 9.3 K were observed with the 9.3 K transition apparently due to metallic Nb.For x = 0.5 a broader signal with a higher T onset (-22 K) was observed. Nakamura observed broad superconducting signals in the defect perovskite-type reduced niobates A,Nb,+,O (A = Ca Sr) (9.2K for 0 Ix I1.0 and 8.3 K for 1.2-1.5 I x I 5.0) covering almost the whole valence state of Nb from Nbl+ to Nb5+ in the Ca system and a somewhat narrower range in the Sr system.g2 The highest shielding effect was observed for starting mixtures having initial mean Nb valence between 1+ and 2 +. The authors argue that although Nb metal exhibits a similar T, the superconducting transitions are not due to this.Manivannan et al. have reported possible high temperature superconductivity at 70 K in an oxygen-deficient cubic perovskite of nominal composition BaPbo~,5Tlo~25Cuo~,0, -y (y = 0.854.89).83The phase was prepared by reaction at high temperature (137CL1420K) followed by quenching then annealing in 0 at 107Ck1120 K. Superconductivity was then observed after annealing in N at 770 K. No evidence was found for any other phases such as Tl,Ba,CuO which could account for this superconductivity. Further research into La2-xNi0,+8 (0 Ix 5 0.15; 6 >0,6 <0)has shown that the resistivity change at temperatures >600K is not due to a semiconductor to metal transition as previously thought.g4 Careful measurement of the sample weight in this temperature range shows that the oxide does not maintain constant composition but undergoes a clear oxygen loss acceleration at -600 K.Consequently the hole concentration is reduced and the resistivity increased. Taking this into account the observed resistivity upturn is not due to a 'transition' to a metallic state but is instead due to a normal non-stoichiometric effect. The two Ni layer Ruddlesden-Popper phase La,Ni,O has been prepared as a single phase for the first time by Zhang et al. using a method involving the co-decomposition of organic precursor^.^ The fully oxygen- ated phase (6 =0) obtained by annealing under high oxygen pressure is metallic and the phase becomes semiconducting as oxygen is removed.Alkaline earth (Ba Sr Ca)-doped samples have also been prepared.g6 Significant oxygen deficiencies are observed in samples as-prepared but these can be filled by annealing under high oxygen pressure. The room temperature resistivity of the as-prepared substituted samples decreases relative to La,Ni,O,,, and a semiconductor to metal transition occurs for La -xM,Ni,O,- (M = Ba Sr Ca) at x =0.075. All the samples annealed under high oxygen pressure show metallic behaviour. Thus contrary to La -.SrXNiO4 where metallic behaviour is only achieved for approximately 50% alkaline earth So M. Licheron and F. Gervais J. Alloys Compd 1993 195 77. " V.A. Gasparov G. K. Strukova and S.S. Khassanov JETP Lett. 1994 60 440. 82 A.Nakamura Jpn. J. Appl. Phys. 1994 33 L583. 83 V. Manivannan J. Gopalakrishnan and C. N. R. Rao J. Solid State Chem. 1994 109 205. 84 J. M. Bassat P. Odier and J. P. Loup J. Solid State Chem. 1994 110 124. 85 Z. Zhang M. Greenblatt and J. B. Goodenough J. Solid State Chem. 1994 108 402. 86 Z. Zhang and M. Greenblatt J. Solid State Chem. 1994 111 141. Conducting Solids Covering Ionic and Electronic Conductors 48 1 substitution La -xMxNi,O becomes metallic with only very small amounts (-4%) of substitution. Reduction of the La,CuO type phase YSr,Ni,O under H has been shown to give a stoichiometric Ni’ oxide YSr,Ni,O, with a Sr,CuO type structure in which 1/3 of the bridging oxygen atoms are missing from chains of apex linked Ni-0 square planar Measurements of the conductivity of this phase have been hampered by the presence of Ni metal in these samples.3 Other Electronic Conductors and Superconductors Intermetallic Systems.-As reported last year a weak superconducting signal at 12K was observed in a study of the Y-Ni-B intermetallic system.,’ This report and subsequent discoveries by Cava et al. in particular of phases with higher Tc’s have aroused considerable interest in these intermetallic superconductor systems which are prepared by standard arc-melting techniques. Continuing their studies into the nature of the superconducting phase in the Y-Ni-B system Nagarajan et al. found that adding small quantities of C dramatically enhanced the superconducting fraction thus indicating that the superconducting phase was a quaternary Y-Ni-B-C system.” A phase of composition YNi,BC,.was nominally single phase with a T onset of 12.5K. Cava et al. reported superconductivity at 23 K in the Y-Pd-B-C system in January 1994 which equals the highest Tcfor an intermetallic although the materials were not single phase.’ The best superconducting transitions were observed for the composi- tions YPd,B,C,., and Yl~2sPd4~sB4,2s which had been cooled on a C block. Electron microscopy on YPd,B,C samples (x = 0 superconducting fraction = 0.2%; x = 0.35 superconducting fraction = 1@-20%) has been performed by Zandbergen et al. to try to identify the superconducting phase.92 For the x = 0.35 sample six different phases were observed with only two phases in the other sample.The authors proposed that the superconducting character was due to a phase of composition YPd,BC. However the exact composition of this superconductor is somewhat controversial. Another group has suggested that the phase has composition YPd,B,C,93 and later work on the Th-Pd-B-C system has suggested a different comp~sition.~~ Superconductivity was then reported in single phase LnNi,B,C (Ln = Y Tm Er Ho Lu) with Tc’sup to 16.6 K (Ln = Lu).~’ Superconductivity was observed not only for the non-magnetic rare earth elements Lu and Y but also for the magnetic rare earth elements Tm Er and Ho although for the latter the T was suppressed indicating that thefelectrons are pair breaking. For other larger rare earth elements no superconduc- ” M. James and J.P. Attfield Chem. Commun. 1994 1185. M. James and J. P. Attfield Physica C 1994 235-240 751. 89 C. Mazumdar R. Nagarajan C. Godart L. C. Gupta M. Latroche S. K. Dhar C. Levy-Clement B. D. Padalia and R. Vijaaraghavan Solid State Commun. 1993 87 413. 90 R. Nagarajan C. Mazumdar Z. Hossain S. K. Dhar K. V. Gopalakrishnan L. C. Gupta C. Godart B. D. Padalia and R. Vijayaraghavan Phys. Rev. Lett. 1994 72 214. 91 R. J. Cava H. Takagi B. Batlogg H. W. Zandbergen J. J. Krajewski W. F. Peck Jr. R. B. Van Dover R. J. Felder T. Siegrist K. Mizuhashi J. 0.Lee H. Eisaki S. A. Carter and S. Uchida Nature 1994,367 146. 92 H. W. Zandbergen W. G. Sloof R. J. Cava J. J. Krajewski and W. F. Peck Jr. Physica C 1994,226,365. 93 C. L. Jia Y.-H. Xu M. Beyss F. Peter and K.Urban Physica C 1994 229 325. 94 H. W. Zandbergen T. J. Gortenmulder J. L. Sarrac J. C. Harrison M. C. de Andrade J. Hermann S. H. Han Z. Fisk M. B. Maple and R. J. Cava Physica C 1994 232 328. 95 R. J. Cava H. Takagi H. W. Zandbergen J. J. Krajewski W. F. Peck Jr. T. Siegrist B. Batlogg R. B. Van Dover R. J. Felder K. Mizuhashi J.O. Lee H. Eisaki and S. Uchida Nature 1994 367 252. 482 P. R. Slater Figure 3 The structure ofLuNi,B,C tivity was observed above 4.2 K. The superconductivity in the Y-Ni-B-C system observed by Nagarajan et al." has been attributed to a phase of similar composition. The crystal structure of LuNi,B,C has been determined by a single crystal X-ray diffraction study and is found to be tetragonal and a variant on the layered ThCr,Si type structure (Figure 3) with LuC NaC1-type layers alternating with Ni,B layers.The Ni,B layers contain a square planar Ni array sandwiched between the B planes.96 The Ni-Ni in-plane distances of 2.45 A are slightly shorter than those found in metallic Ni (2.50 A) suggesting strong metal-metal bonding. Another closely related non-superconducting phase LuNiBC has also been observed which is derived from LuNi,B,C by adding another LuC layer. Powder neutron diffraction data on YNi,B,C showed similar results to the single crystal X-ray diffraction study of LuN~,B,C.'~ There was no sign of B t)Ni disorder and all sites were fully occupied except for possibly the C site. HREM studies on superconducting LuNi,B,C and the related compound LuNiBC has shown the occurrence of intergrowths of the two structures together with planar defects." Such defects are however rare and are only dominant in batches prepared under unfavourable conditions.These intermetallics can 96 T. Siegrist H. W. Zandbergen R. J. Cava J.J. Krajewski and W. F. Peck Jr. Nature 1994 367 254. 97 B. C. Chakoumakos and M. Paranthaman Physicu C 1994 227 143. 98 H. W Zandbergen R. J. Cava J. J. Krajewski and W. F. Peck Jr. Physicu C 1994 224 6. Conducting Solids Covering Ionic and Electronic Conductors be viewed as an homologous series (LuC),(Ni,B,) (m= 1 LuNi,B,C; m = 2 LuNiBC). In unsuccessful efforts to introduce an extra LuC layer a new phase of composition Lu,NiBC was ~bserved.~' This phase has a layered structure with a sequence (Ni,-B-LuC-Lu-C,-Lu-LuC-B),.Superconductivity at around 15-16 K has also been observed in multiphase samples containing the metastable compound ScNi,B,C which is isostructural to LUN~,B,C.'~~ No superconductivity or ScNi,B,C was observed after annealing at 1050"C indicating that the phase is entropy-stabilized during the arc-melting process. The variation of crystallographic cell size with Ln radius in LnNi,B,C is anomalous showing a decrease in c (distance perpendicular to the layers) with increasing Ln size."' The anomaly results from the rigidity of the B-C bond and the conservation of Ni-B bond length such that the B-Ni-B bond angle accommodates the change in LnC layer size. It has been suggested that this change in bond angle which greatly changes the electronic states at the Fermi level is the origin superconductivity in LnNi,B,C with small Ln.For the larger Ln such as La the bond angle is strained (102")and so the Ni,B layers are somewhat buckled. This apparent correlation of decreasing T with increasing Ni,B layer buckling may be compared to the buckling observed in the cuprate superconductors since for these phases the maximum T,seems to occur for the smallest buckling (i.e.flat CuO planes). The effect of this contraction along the c axis and buckling of the Ni,B layers is also observed in the variation of T with pressure. Thus despite the fact that Lu is smaller than Y and that LuNi,B,C has a higher T than YNi,B,C the application of pressure is found to suppress Tc.Io2 Arisawa et a!.have prepared YNi,B,C thin films by magnetron sputtering.lo3 The as-deposited films were completely amorphous although the films could be crystallized very uniformly after annealing at 1050 "Cin a vacuum. The annealed films were highly c axis orientated and showed a T onset of -15 K. Tunnelling measurements of the superconductor energy gap in YNi,B,C were shown to be in good agreement with the BCS prediction indicating that the superconductor mechanism appears to be BCS type.lo4 Band structure calculations for LuNi,B,C indicate a density of states peak near the top of the nearly filled Ni (3d) bands with only modest B and C orbital admixt~re.'~~.'~~ There is also an appreciable amount of Lu (5d)character present which may account for the depression of T for magnetic rare earth elements.Despite the layer structure the band structure exhibits 3D character in contrast to the 2D character of the cuprate superconductors. For the non-superconductor LuNiBC the same band is present but the electron count is such that the Fermi level no longer falls in that band. Thus it may be possible to induce superconductivity by a suitable adjustment of the electron count by chemical substitution. The results suggest that these intermetallics represent a family of conventional (rather than high T,) supercon-ductors. 99 H. W. Zandbergen R. J. Cava J. J. Krajewski and W. F. Peck Jr. J. Solid State Chem. 1994 110 196. loo H. C. Ku C. C. Lai Y.B. You J. H. Shieh and W. Y. Guan Phys. Rev. B 1994 50 351. Io1 T. Siegrist R.J. Cava J. J. Krajewski and W. F. Peck Jr. J. Alloys Compd 1994 216 135. C. Murayama N. Mori H. Takagi H. Eisaki K. Mizuhashi S. Uchida and R. J. Cava Physica C 1994 235240 2545. S. Arisawa T. Hatano K. Hirata T. Mochiku H. Kitaguchi H. Fujii H. Kumakura K. Kadowaki K. Nakamura and K. Togano Appl. Phys. Lett. 1994 65 1299. T. Ekino H. Fujii M. Kosugi Y. Zenitani and J. Akimitsu Physica C 1994 235240 2529. lo' L.F. Mattheiss Phys. Rev. B 1994 49 13279. lo6 W. E. Pickett and D. J. Singh Phys. Rev. Lett. 1994 72 3702. 484 P. R. Slater Superconductivity in isostructural compounds LnPt,B,C containing Pt instead of Ni have also been reported although the phases could not be prepared single phase.lo7 T values of 10 K were observed for Ln = La Y and 6 K for Ln = Pr reflecting the influence of magnetic pair breaking.These materials can apparently accommodate some non-stoichiometry which leads to slightly different Tc's.The density of states for LaPt,B,C is approximately 1/4 that observed for LnNi,B,C suggesting that the lower T is at least in part due to a lower density of states at the Fermi level.lo8 Partial substitution of Au for Pt yielded greatly improved phase purity with no significant change in TC.lo9Phases with Ln = Nd Ce could also be prepared by means of this substitution but both phases were non-superconducting above 1.8 K. The phases LaIr,B,C and LaRh,B,C have also been prepared.' lo Although isostructural to LnNi,B,C and despite the fact that the density of states at the Fermi level (determined from magnetic susceptibility measurements) are comparable to those of the supercon- ducting materials of the same structure type neither of these phases exhibited superconductivity above 1.4K.The range of these intermetallics has been extended from the lanthanide elements to the actinides. While no superconductivity was observed in U-containing compounds superconductivity has been observed in Th-based borocarbides.' l1 For ThM,B,C superconducting transitions of 6 K (M = Ni) 6.5 K (M = Pt) and 14.5 K (M = Pd) have been observed the compounds being isostructural to LnNi,B,C. For M = Ni and Pt essentially single phase samples were observed while for M = Pd the samples were multiphasic. Bulk superconductivity at 21.5 K has also been observed in an as-yet undetermined Th-Pd-B-C quaternary phase (with excess B and Pd e.g.ThPd,B,C) which represents the highest T for a Th-based intermetallic phase. The pressure dependence of the 21 K phase was found to be small and negative. HREM studies ofthe 14.5K superconductor ThPd,B,C showed no intergrowths or planar defects. The through-focus reconstructed image indicated that the C position is fully occupied whereas no definite conclusion could be drawn on the precise occupancy of the B site.'12 It has been suggested from electron microscopy studies of several samples in the Th-Pd-B-C system that the 21 K superconductor is due to a phase of composition ThPd0,,,B4, exhibiting a cubic 4.2 A cell with a short-range ordered superstr~cture.~~ HREM indicates that this phase adopts a modified CaB structure in which the cubic face 1/2,1/2,0 which is vacant in CaB is partially occupied by Pd with the removal of some B atoms.The superstructure indicates short range clustering of the Pd atoms. The exact B composition is not known. EPMA indicates little C present and unlike the other intermetallic phases C is not necessary for the structure although the question of whether it is necessary for superconductivity still remains open. A similar cubic phase YPd,.,B,,, is also observed in the Y-Pd-B-C system and so the authors have lo' R. J. Cava B. Batlogg T. Siegrist J. J. Krajewski W. F. Peck Jr. S. Carter R. J. Felder H. Takagi and R.B. Van Dover Phys. Rev. B,1994 49 12 384. lo8 D. J. Singh Phys. Rev. B 1994 50 6486.lo' R. J. Cava B. Batlogg J. J. Krajewski W. F. Peck Jr. T. Siegrist R. M. Fleming S. Carter H. Takagi R.J. Felder R. B. Van Dover and L. W. Rupp Jr. Physica C 1994 226 170. 'lo R. J. Cava T. Siegrist B. Batlogg H. Takagi H. Eisaki S. A. Carter J. J. Krajewski and W. F. Peck Jr. Phys. Rev. B 1994 50 12966. J. L. Sarrao M. C. de Andrade J. Hermann S.H. Han Z. Fisk M. B. Maple and R. J. Cava Physica C 1994 229 65. 112 H. W. Zandbergen E. J. van Zwet J. C. Sarrac M. C. de Andrade J. Hermann S. H. Han Z. Fisk M. B. Maple and R. J. Cava Physica C 1994 229 29. Conducting Solids Covering ionic and Electronic Conductors Figure 4 The structure of La,Ni,B,N suggested that the 23 K superconductor in this system may be due to this phase rather than to phases of composition YPd,BC or YPd,B,C as previously suggested.In late 1994 the observation of superconductivity in these intermetallic systems was extended to boronitrides with a T of 12-13K being reported for a phase of composition La,Ni,B,N,. l1 A related non-superconducting phase LaNiBN was also prepared. The structure of La,Ni,B,N (Figure 4) is related to that of LuNi,B,C but consists of three rock-salt type LaN layers alternating with tetrahedral Ni2B2 layers an arrangement considerably more two-dimensional than in the superconducting borocarbides. LaNiBN has a related structure with two LaN layers stacked with Ni2B layers and isostructural with LuNiBC.lI4 The phases can be considered as members of a homologous series (LaN),(Ni,B,) with n = 2 (LaNiBN) or 3 (La,Ni,B,N,).Planar defects indicative of the existence of phases with larger n are possible with n = 4,5 and 6 defects being observed for La,Ni,B,N,. The discovery of superconductivity in R. J. Cava H. W. Zandbergen B. Batlogg H. Eisaki H. Takagi J. J. Krajewski W.F. Peck Jr. E. M. Gyorgy and S. Uchida Nature 1994 372 245. H. W. Zandbergen J. Jansen R. J. Cava J. J. Krajewski and W. F. Peck Jr. Nature 1994 372 759. 486 P. R. Slater La,Ni,B,N, with similar Ni,B tetrahedral layers to superconducting LuNi,B,C establishes Ni,B layers as important building blocks for high temperature supercon- ductivity in these intermetallics in much the same way as CuO layers are important to the cuprate high temperature superconductors. Lee et al.have reported superconductivity in the first Ni-based ternary silicide LaNiSi with a T of 1.2&1.26K and a structure which appears to be of the LaPtSi type.'15 Subsequently superconductivity was also reported in Lu,Ni,Si with a slightly higher T (-2 K)." Interestingly it is known that even small amounts of Ni suppress T in Lu,Fe,Si but superconductivity is observed in the structurally different Lu,Ni,Si which suggests that the crystal structure plays an important role in sustaining superconductivity in this compound. Organic Superconductors.-Schlueter et al. have reported two superconducting organic charge-transfer salts derived from the electron donor molecule bis(ethy1enedithio)tetrathiafulvalene (ET) the organometallic anion [Cu(CF,),] -and the neutral solvent molecule 171,2-trichloroethane (TCE).' '7*1' Superconductiv-ity at 4 K was observed in plate-like crystals of composition K,-(ET),Cu(CF,),TCE.A second superconducting phase suggested to be K -(ET),Cu(CF,),(TCE), with needle-like crystals was subsequently found with a higher T of 9 K. The change in T is thought to be due to a change from the disordered crystallographic structure of the anion in the K phase to an ordered structure in the K phase. Other Systems.-A new low temperature synthesis route to the superconducting Chevrel phase PbMo,S has been reported by Rabiller et al.'" The route involves heating a mixture of Mo$ and PbS metal precursor in H at 440 "C. The H allows excess S to be removed as a H,/H,S mixture and simultaneously prevents oxidation.By this method the reaction time is only 3 days compared to 3 weeks for the reaction of Mo,S and Pb powder. High pressure synthesis techniques have been used to synthesize hydrides and deuterides of alloys of the Group 4 metals Hf Zr with the Group 8 metal Ru.' 2o As expected from theoretical studies superconductivity was observed in these phases HfRuH(D),,. (T = 4.5 K) ZrRuH(D),,,-,~ (T,= 3 K). Single phase samples of TiRu hydride could not be obtained. A new halide Hg,As,Br has been synthesized by Shevelkov et ~1.'~' Unlike the related semiconducting phase Cd,As,Br this phase is metallic. The metallic character is attributed to an overlapping of occupied and vacant bands. '15 W. H. Lee F. A. Yang C. R. Shih and H. D. Yang Phys.Rev. B 1994 50 6523. '16 C. Mazumdar K. Ghosh S. Ramakrishnan R. Nagarajan L. C. Gupta G. Chandra B. D. Padalia and R. Vijayaraghavan Phys. Rev. B 1994 50,13 879. ''' J. A. Schlueter U. Geiser J. M. Williams H. H. Wang W.-K. Kwok J. A. Fendrich K. D. Carlson C. A. Achenbach J. D. Dudek D. Naumann T. Roy J. E. Schirber and W. R. Bayless Chem. Commun. 1994 1599. '18 J.A. Schlueter K. D. Carlson J. M. Williams U. Geiser H. H. Wang U. Welp W.-K. Kwok J. A. Fendrich J. D. Dudek,C. A. Achenbach P. M. Keane A. S. Komosa D. Naumann T. Roy J. E. Schirber and W.R. Bayless Physica C 1994 230 378. 'I9 P. Rabiller M. Rabiller-Baudry S. Even-Boudjada L. Burel,R. Chevrel M. Sergent M. Decroux J. Cors and J.L. Maufras Mater. Res. Bull. 1994 29 567. lZo V. E. Antonov E.L. Bokhenkov A. I. Latynin V. I. Rashupkin B. Dorner M. Baier and F. E. Wagner J. Alloys Cmpd. 1994 209 291. 12' A.V. Shevelkov E.V. Dikarev and B.A. Popovkin J. Solid State Chem. 1994 113 116. Conducting Solids Covering Ionic and Electronic Conductors 4 Ionic Conductors and Intercalation Compounds Li Ion Conductors.-Considerable interest has continued in the search for improved Li intercalation electrodes for rechargeable battery applications both in the modification of existing materials and the synthesis of new intercalation hosts. Two useful reviews on Li batteries have been written by Brandt (Historical development of secondary Li batteries)' 22 and Goodenough (Design considerations). 123 Manganese- and vanadium-oxides continue to attract considerable attention as intercalation hosts for use as cathode materials.Hwang et al. have prepared thin films of LiMn,O deposited by rf magnetron sputtering. 24 The as-deposited films were amorphous but a rapid thermal annealing process (above 650°C) in 0 led to crystallization into LiMn,O spinel. The LiMn,O thin film cathodes showed improved characteristics compared to films previously prepared by other techniques demonstrating good intercalation kinetics and promising cycling behaviour. About 0.8Li could be intercalated reversibly at a nearly constant potential and the films maintained more than 98% of their original capacity after more than 100 cycles. Gummow et a/. have succeeded in improving the rechargeable capacity of 4V Li,Mn20 (0 < x 5 1)spinel cathodes by doping with mono- or multi-valent cations + (e.g.Li ,Mg2+ ,Zn2+ ) or alternatively with additional oxygen to marginally increase the average Mn ion oxidation state above 3.5 + .12' The improved rechargeability (stable rechargeable capacities in excess of 100mAhg-' can be achieved) which is gained at the expense of capacity is attributed primarily to the suppression of the Jahn-Teller effect on deep discharge of the doped spinel electrodes.Furthermore for the doped cathodes complete Li removal cannot be achieved and the authors believe that the presence of this residual Li is also significant in enhancing the stability to repeated insertion/extraction of Li. Huang and Bruce have reported a new 3 V Li-Mn-0 cathode LiMn,O,. (A defect spinel with a higher average Mn oxidation state than the stoichiometric LiMn,O prepared at high temperatures) for Li batteries prepared by a new patented solution-based route which can be carried out in air unlike previous sol-gel processes.'26 The addition of C to the solution during preparation was found to yield a material with a significantly enhanced cycling performance-an enhancement of the discharge capacity of 50% on the 300th cycle for the cathode when C was added.The same workers has also reported the preparation of a very promising 4V Li-Mn-0 cathode by the same solution-based technique but with the product fired at 600 "C to give a composition close to LiMn,O,.' 27 Unlike the previous case the addition of C to this material during the solution synthesis had no effect on the cycling performance in the 4V region.The LiMn,O,. cathode when cycled on the 4 V plateau under the same conditions showed much poorer characteristics. Therefore despite the fact that these materials both have similar spinel structures their performance as cathodes for rechargeable Li batteries is markedly different. A problem associated with the use of LiMn,O as a cathode for Li polymer 122 K. Brandt Solid State lonics 1994 69 173. 123 J. B. Goodenough Solid State lonics 1994 69 184. 124 K.-H. Hwang S.-H. Lee and S.-K. Joo J. Electrochem. Soc. 1994 141 3296. 125 R.J. Gummow A. de Kock and M. M. Thackeray Solid State Ionics 1994 69 59. 126 H. Huang and P.G. Bruce J. Electrochem. Soc. 1994 141 L76. 12' H. Huang and P.G.Bruce J. Electrochem. Soc. 1994 141 L106. 488 P. R. Slater electrolyte batteries concerns the upper voltage plateau being above the stability threshold of polymer electrolytes such as poly(ethy1ene oxide) (PEO) and although the lower voltage plateau may be cycled it is only at the expense of decreased energy density and increased capacity fade. Doeff et al. have therefore reported the use of orthorhombic Na,MnO as a cathode for alkali metal polymer electrolyte batteries.',' This compound has a tunnel structure and reversibly intercalates up to 0.6 alkali metal (Li+/Na+) ions per Mn at moderate current densities corresponding to capacities of 160 to 180mAhg-'. Li/PEO/Na,.,Li,MnO cells in particular showed excellent capacity retention over 90 cycles at 0.1 mAcmP2.Ferg et al. have evaluated the properties of the spinel-type anodes Li,Mn,O,, Li,Ti,O,, and Li,Mn,O in Li ion 'rocking-chair' cells with the stabilized spinels Lil~03Mnl,9704 Li ions and LiZno,o,,Mn,~,,04 and layered LiCoO as ~ath0des.I~~ were shown to shuttle between the two transition metal hosts at reasonably high voltage with an accompanying change in the oxidation state of the transition metal cations so that Li ions do not reduce to the metallic state at the anode during charge thus helping to eliminate the safety problems associated with cells containing metallic Li Li-alloy and Li-C anodes. The cells with Li4Ti,01 anodes exhibited the best characteristics and are possible alternatives to Ni/Cd cells delivering comparable energy densities at approximately twice the voltage.Electrochemical insertion of Li into SrVO has been demonstrated.' 30 After the insertion of 0.1 Li to give Li,.,SrVO metallic conductivity was maintained and good reversibility of Li insertion/extraction was obtained. The authors therefore suggest the possibility of using SrVO as a cathode without any conductive additives in Li rechargeable batteries. Garcia-Alvarado and Tarascon have investigated the electrochemical intercalation of Li in Ag,V4O1 and Ag,V4O1 -,,.131 These com- pounds intercalate 7 and 5.7 Li ions respectively through a multiphase intercalation process. Ag,V,O, has been previously reported and has been successfully used as a positive electrode in primary Li cell power sources for biomedical devices.The results of this study demonstrate the potential for it to be used as a positive electrode in rechargeable Li cells. The intercalation/deintercalation reaction showed a small degree ofirreversibility due to some Ag displacement by Li and demonstrated by the presence of free Ag in the XRD patterns. Li insertion into p-Cu,V,O has been investigated by Eguchi et The single phase region of the lithiated fi-phase oxide Li,~-Cu,V,O is metastable at 0 < x < 0.5 and is smaller than in the corresponding a-phase oxide. Up to x = 2 Cu" was reduced preferentially to Cu' and Cu' and half of the Vv were reduced to Cuo and V" respectively for x > 2. Fey et al. have shown that the Li atoms in the inverse spinel LiNiVO can be electrochemically removed and reinserted in non-aqueous elec- trochemical cells at -4.8 V Versus metallic Li representing the highest voltage known for a Li intercalation reaction and suggesting a possible use as a cathode in Li ion cells to provide very high voltages.' 33 Isostructural LiCoVO also shows reversible Li 12' M.M.Doeff M.Y. Peng Y. Ma and L.C. De Jonghe J. Electrochem. Soc. 1994 141 L145. 129 E. Ferg R. J. Gummow A. de Kock and M. M. Thackeray J. Electrochem. SOC. 1994 141 L147. Y. J. Shan L. Chen Y. Inaguma M. Shikano M. Ttoh and T. Nakamura Solid State lonics 1994,70/71 429. 131 F. Garcia-Alvarado and J. M. Tarascon Solid State lonics 1994 73 247. 13' M. Eguchi I. Furusawa T. Miura and T. Kishi Solid State lonics 1994 68 159. 133 G.T.-K. Fey W. Li and J.R.Dahn J.Electrochem. Soc. 1994 141 2279. Conducting Solids Covering Ionic and Electronic Conductors 489 intercalation but only near 4.2 V uersus Li. in situ X-Ray diffraction demonstrates that this is an intercalation reaction (cell parameters contract on Li removal returning to the original value when Li is reinserted). The reason for the high voltage of the Li/LiNiVO cell is not understood and it is also unclear how the Li diffuses in and out of this compound because the tunnels which are present in normal spinels are absent in this inverse spinel. Nishijima et al. have deintercalated Li,FeN electrochemically to form Li -,FeN (0 Ix I1.O) with a decrease in resistivity with increasing Li deintercalation (x).'34 The extraction of Li occurs smoothly up to x = 1 .O with evidence for decomposition for x > 1.0.The Li/Li,FeN cell showed good reversibility with a high current density (500pA~m-~). Li,FeN appears to have ideal properties not only as a cathode for Li secondary batteries but also as an anode if combined with a cathode having high electrode potential relative to Li metal. The same authors have also reported similar studies of the cubic compound Li7MnN,.'35 Li deintercalation can be readily achieved electrochemically to give Li,-,MnN (0 I x I1.25) exhibiting good reversibility under high current density (1200pAcm-2). A good cycling performance with low potential to Li metal (-1.2V) suggests that it is a good candidate as an anode for 'rocking-chair' type Li secondary batteries.LiFeO with a layered ordered rock-salt structure of the a-NaFeO type has been obtained from NaFeO via Li +Na exchange in a eutectic melt of LiCl and LiN0,.136 The crystal structure strongly correlates with the temperature of the melt. The use of the pure halides with higher melting points results in the formation of a-LiFeO with a disordered rock-salt structure. LiMnO (ordered rock-salt structure) has also been obtained from NaMnO in molten LiI as well as by Li intercalation via molten LiI into the spinel LiMn,O,.LiFeO with the layered structure is isotypic with LiCoO and LiNiO, which are much studied intercalation cathode materials. In view of their high electronic conductivity (including reports of superconductivity at 50 K) and stability in reducing atmospheres the possibility of using the magnesium titanate spinels Mg -yTil (y =0.33 0.57) as electrode materials has been examined.'37 For y =0.33 Li insertion proceeds largely via a two phase equilibrium reaction with a maximum Li content of 0.37.For y =0.57 a different behaviour is exhibited with a minimum in the unit cell parameters and a marked drop in cell potential being observed at a Li content of -0.2. The authors have attributed the insertion reaction as a competitive process between two different mechanisms. For Li contents below 0.18 Li is inserted into the octahedral sites with associated movement of Mg from the tetrahedral to octahedral sites (a gradual composition driven spinel to rock-salt type change). For Li contents above 0.18 Li is inserted into empty octahedral sites without major rearrangement of the spinel lattice.Morales et al. have prepared the monophasic layered structure type Li -,(Ni,Co -y)l +,02 materials (0 Iy I0.4 and 0.8 Iy I 0.9) by the reaction of (NiyCol-y)304 (0 I y I 0.4) and Ni,Co -,O (0.8 I y I0.9) with LiOH at low temperatures (LT) (450 0C).'38 As in the case of the high temperature (HT) synthesized 134 M. Nishijima Y. Takeda N. Irnanishi 0.Yamarnoto and M. Takano J. Solid State Chem. 1994,113,205. 135 M. Nishijima N. Tadorkoro Y. Takeda N. Irnanishi and 0.Yamamoto J. Electrochem. SOC.,1994,141 2966. 13' B. Fuchs and S. Kemrnler-Sack Solid State lonics 1994 68 279. 13' J. T. S.Irvine S. Thiemann,G.Mather A. A. Finch and H. Tukarnoto Solid State lonics 1994,70/71,445.138 J. Mordles R. Stoyanova J. L. Tirado and E. Zhecheva J. Solid State Chem. 1994 113 182. 490 P.R. Slater analogues Co substitution for Ni stabilizes the Ni3+ ions and improves the two-dimensionality of the crystal structure. Acid treatment of both LT and HT oxides leads to a partial dissolution of the solid and to removal of Li and 'impurity' Co and/or Ni from the LiO layers of the trigonal framework. For Co-rich samples the ion extraction is accompanied by partial Li +/H + exchange especially for the LT samples. The best reversibility in the 4-3.2 V range for Li intercalation/deintercalation was found for the HT Ni-rich samples. New data (EPR of low spin Ni3+ magnetic susceptibility thermal analysis) for acid delithiation of Li,Ni -xO have been reported by Stoyanova and Zhecheva.13' It is shown that short range and long range cation order governs the behaviour of the oxides towards acids.For 0.6 < x < 0.9 where partial cation order occurs acids remove Li and impurity Ni ions from the LiO layers but do not attack Ni2 + and Ni3 + ,which are segregated in neighbouring (1 11)cubic planes. For x > 0.9 where long range cation order occurs the extraction of Li and impurity ions proceeds simultaneously with partial exchange between Li from the LiO layers and protons from the acid solution. The different chemical compositions of the acid-treated oxides are clearly demonstrated by their thermochemical properties up to 200 "C. For the partially layered oxides 0.6 < x < 0.9 reduction of the highly oxidized Ni ions and cation redistribution occurs within the initial structural framework whereas for the layered oxides (x > 0.9) dehydration processes also take place.Croce et a!. have reported a promising model system of a novel type of solid state Li 'rocking-chair' battery employing TiS as the negative Li sink electrode LiCoO as the Li source positive electrode and a highly conductive gel-type polymer membrane as the ele~trolyte.'~' Normally TiS is used as a cathode in conventional Li batteries but in this case it was used as the anode to accept Li ions from LiCoO during the charge process and to release them during the discharge process. The cell showed excellent charge- discharge efficiency over a prolonged number of cycles and the fact that the Li intercalation in Li,TiS may proceed beyond the well known x = 1 step to a second step extending to x = 2 means that there is a buffer against incidental overcharge and short circuiting thus improving the battery safety and reliability.Improvements to the properties of polymer electrolytes are continuing to be sought with the search for new improved polymeric hosts and means of improving the properties of existing hosts. A new host polymer poly(tetrahydrofurfry1 acrylate) (PTHFA) containing organic solvent moieties as a pendant group has been reported by Takebe and Shir~ta.'~' The idea of the research is based on the fact that some organic solvents such as THF dissolve inorganic salts dissociating them into ions; systems having such solvent moieties as a pendant group would be expected to enhance conductivity.PTHFA was found to be completely amorphous and compatible with LiCF,SO,. The PTHFA-LiCF,SO hybrid system has been shown to exhibit ionic conductivities of ca. lop6Scm-l at 100"C and the temperature dependence of the ionic conductivity was found to be in accord with that of the dielectric relaxation (which is thought to represent the segmental motion of the polymer) of the host polymer. Although the ionic conductivity of PTHFA-LiCF,SO was lower than PEO-salt systems it should be possible to enhance the conductivity by the addition of appropriate plasticizers. 139 R. Stoyanova and E. Zhecheva J. Solid State Chem. 1994 108 211. 140 F. Croce S. Passarini and B. Scrosati J.Electrochem. Soc. 1994 141 1405. Y. Takebe and Y. Shirota Solid State Ionics 1994 68 1. Conducting Solids Covering Ionic and Electronic Conductors 49 1 Improvements in the mechanical consistency of polyvinylether (PVE) based electrolytic membranes was obtained by introducing silyl groups suitable for cross-linking during the membrane processing into the ~ide-chains.'~~ The PVE membranes containing triethoxysilyl groups in the side-chains were synthesized and cross-linked during membrane processing in the presence of LiClO,. The electrolytic membranes had excellent stability and showed promising ionic conductivity approach- ing the value of lO-'Scm- ' at 25 "C. The introduction of siloxane bonds in the network because of its flexibility contributed to a low glass transition temperature without depressing the conductivity with respect to analogous PVE unfunctionalized systems.Lee et al. have synthesized a new type of plasticizer for Li polymer electrolytes a modified carbonate made by attaching three ethylene oxide units to the 4-position of ethylene ~arb0nate.l~~ Adding 50% of this plasticizer by weight of PEO to the PEO-LiCF,SO system yielded an ionic conductivity of 5 x Scm-' at 25 "C which is two orders of magnitude higher than that found for a PEO-LiCF,SO electrolyte without plasticizer and one order of magnitude higher than that found when using propylene carbonate as a plasticizer. This new plasticizer exhibits two outstanding properties compared to most existing plasticizers; (i) rather than creating a high conductivity pathway through the plasticizer itself it appears to increase the ionic conductivity throughout the entire complex system; (ii) it enhances ion pair dissociation which in turn improves the ionic conductivity.The search for high temperature polymer electrolytes with good thermal and oxidative stability at temperatures >250 "Chas continued. Based on previous findings that the individual incorporation of 2,5-diaminobenzene sulfonic acid (DABSA) and polysiloxane (PSX) with polyimides improved the ionic conductivity Bradshaw et al. have investigated the incorporation of both DABSA and PSX with polyimide creating the quaternary PMDA-ODA-PSX-DABSA (4:3 :0.6 :0.4) copolymer system with Li dopant LiCF,SO (PMDA = 1,2,4,5-benzenetetracarboxylic dianhydride; ODA = 4-aminophenyl ether).'44 This resulted in high ionic conductivity Scm-'at 250 "C which is almost two orders of magnitude higher than that of LiCF,SO doped PMDA-ODA-PSX copolymer and four orders of magnitude higher than that of LiCF,SO doped PMDA-ODA-DABSA copolymer.The large improve- ments are achieved by the combined effect of both fixed anionic groups which increases mobile cation concentration and PSX which introduced chain flexibility. Angell et al. have reported a new type of electrolyte for use in Li batteries.'45 The electrolyte is essentially a low temperature molten salt reduced to a rubbery condition by addition of a small amount of high molecular weight polymer. High molecular weight PPO (MW lo6) or PEO (MW lo5) was dissolved in a solvent (MeCN or acetone) and the salt mixture (LiClO,/LiNO or LiClO,/LiClO,) dissolved in this solution.The solvent was then removed by careful heating. The resulting electrolyte exhibits the best characteristics of 'superionic glass' and 'salt in polymer' electrolytes in a single material i.e. cationic conduction and rubbery compliances respectively. The 14' M. Andrei L. Marchese A. Roggero and P. Prosperi Solid State lonics 1994 72 140. 143 H. S. Lee X. Q. Yang J. McBreen Z. S. Xu T. A. Skotheim and Y. Okamoto J. Electrochem. Soc. 1994 141 886. 144 J. Bradshaw S. B. Tian and G. Xu Solid State lonirs 1994 73 147. 145 C.A. Angell J. Fan C. Liu Q. Lu E. Sanchez and K. Xu Solid State lonics 1994 69 343. 492 P.R.Slater material not only showed conductivity comparable with the conductivity of the best non-aqueous Li salt electrolyte solutions but could be made comparable to that of the lead acid electrolyte by moderate increases in temperature (e,g to 100"C). High Li ion conductivities (0> 10-4Scm-1 at room temperature) have been reported in solid solutions of A site deficient perovskites La,., -xLi3,Ti03 (-0.15 > x > -0.04)by the substitution mechanism La = 3Li.'46 The dome shaped composition dependence of conductivity indicates that the conduction mechanism involves the movement of Li ions through the A site vacancies. The conductivities of the corresponding Nd perovskite with smaller lattice parameters were low (2 x Scm-') and the smaller rare earth elements Sm Gd Ho Yb did not form a single phase perovskite.Dissanayake et al. have reported high ionic conductivity in the 'system Li,- 2xSxTi -xO (0 < x < 0.2) with the Li,TiO structure; this is the first report of high Li+ ion conduction in this family.'47 Previous attempts to dope Li,XO (X = Ge Ti) always yielded so called y (or LISICON) phases rather than Li,XO solid solutions. The conductivity was shown to increase with increasing x up to a maximum (bulk) value of 8.3 x lop6Scm-l (x= 0.2) at 27 "C with E = 0.51 eV. The enhancement in conductivity is mainly attributable to a decrease in the activation energy for conduction rather than the introduction of Li vacancies. The structures of the Li-containing nasicon-type phases ~i ~11~111 ~ -x(S04)3 -y(SeO,)y (M" = Mg Ni Zn; M"' = Al Cr) have been determined bq neutron diffra~ti0n.l~' Surprisingly the Li ions were found to occupy the large (8-10 coordinate) sites.However in these sites they are shifted off-centre to give four short Li-0 bonds arranged approximately tetrahedrally. Na Ion Conductors.-Nasicon related phases continue to attract interest. Large single crystals of the nasicon phase NaZr,(PO,) have been synthesized by hydrothermal crystallization in a F-containing medium.'49 The presence of F-ions substantially lowers the temperature of hydrothermal crystallization (150 "C compared to 250 "C) and leads to larger crystals (ca.50 pm x 50 pm compared to ca. 0.5pm x 0.5 pm). The structures of the Na-containing nasicon-type phases Na,M~M~'~,(SO,) -y(SeO,) (M" = Mg; M"' = Fe In) have been determined by powder neutron diffraction.' 50 A splitting of the octahedral Na site into two sites is seen due to a reduction in symmetry (compared to the nasicon system Na,+,Zr,Si,P,-,O,,) from R3c to R3 and for x = 0.5 Na and vacancies order along the hexagonal c direction.Data collected at different temperatures showed an apparent change in symmetry from rhombohedra1 to monoclinic in the temperature range 100"C-200 "C which correlates with the observed change in activation energy for conduction in this range. Such a change from high to low symmetry with increasing temperature is odd and it is suggested that the true structure at room temperature is also monoclinic but that it is only at temperatures greater than 100 "C that significant changes from the pseudorhombohed- ral cell is observed.Mentre et al. have investigated the nasicon-type solid solution H. Kawai and J. Kuwano J. Electrochem. SOC. 1994 141 L78. 147 M. A. K. L. Dissanayake H. H. Sumathipala and A. R. West J. Muter. Chem. 1994 4 1075. 14' P. R. Slater and C. Greaves J. Mater. Chem. 1994 4 1463. 149 W. Heizeng and P. Wenqin J. Alloys Compd 1994 209 L9. 150 P.R. Slater and C. Greaves J. Mater. Chem. 1994 4 1469. 14' Conducting Solids Covering Ionic and Electronic Conductors 493 Ca,_,Na2,Ti,(P04),.'S1 The space group changes from R3 (x I0.5) to R3c (x > 0.5).For CaTi,(PO,), Ca and vacancies order along the hexagonal c direction as observed also for Na,,,M','~,M~~,(SO,) -,,(SeO,) (x = 0.5).The conductivity of CaTi,(PO,) is slightly better than that of Na,Ti,(PO,) despite the higher valence of Ca2+ compared to Na'. This is explained by the half occupancy of the cavity sites in CaTi,(PO,) so that the ionic pathway is not loaded with Ca2+ cations leading to an easier Ca2+ ion mobility. Introduction of the faster Na' ions into the framework improves the ionic conductivity up to a maximum at x = 0.5. Crystalline and glassy samples of the phase Na,NbP,O ,have been investigated by Wang et al. using ac complex impedance and FTIR.ls2The ionic conductivity of the glassy phase (cr673K = 3.1 x lo- Scm-') was at least two orders of magnitude higher than that of the crystalline phase due to large differences in the structure of the two modifications and the random distribution of Na+ ions over the equipotential sites in the glass network.In addition to the major powder X-ray diffraction lines of the nasicon-type phase many other intense lines were observed and the ionic conductivity of the crystalline phase was significantly lower than that of other nasicon analogs. The authors therefore suggested that this phase is not of the nasicon-type but is likely to be a new compound. The conductivity of the phase Na,Nb,P,O, has also been measured (06733 = 8.4 x lo-' Scm-') and is slightly higher than crystalline Na4NbP30,,. A new sodium titanogallate Na,Ti,~,Ga,+,O, (x -0.8) has been obtained from studies of the Na,O-Ti0,-Ga,O system.' s3 The structure determined by single crystal X-ray diffraction contains one-dimensional channels of octagonal cross-section extending along the b axis in which the Na ions are located.A similar phase containing channels of hexagonal cross-section (Na,~,Ti,,,,Ga,,,,O,) has been reported previ- ously. Fourier analysis revealed that the distribution of Na ions in the channels was broadened along the channel axis suggesting that these channels may be promising one-dimensional conduction pathways for Na. A range of new Na ion conductors Na,M,(X207) (M = Al Ga Cr Fe; X = P As) have been synthesized by Masquelier et ~1."~ These disphosphates and diarsenates exhibit high ionic conductivity (cT,~,~lop3to 10-1 Scm-') and good cation exchange properties especially with Ag+ ions. At temperatures varying between -20 "C and 240 "C (depending on the compound) they undergo a reversible phase transition a f-* p which is associated with a loss of long range ordering of the Na ions and an increase in conductivity.The crystal structures suggest a two-dimensional conduction pathway and this has been confirmed by conductivity measurements on single crystals. Balsys and Davis have determined the structure of the new layered alkali transition metal oxide Li,~,,Na,,,,CoO,~, by powder neutron diffra~ti0n.l~~ The structure consists of alternating Li and Na layers interleaved between octahedral COO sheets with Li in an octahedral environment and Na in a trigonal prismatic environment 0. Mentre F. Abraham B. Deffontaines and P. Vast Solid Stute lonics 1994 72 293.'" B. Wang M. Greenblatt and J. Yan Solid Stute lonics 1994 69 85. 153 Y. Michiue and M. Watanabe Solid Stute lonics 1994 70171 186. C. Masquelier F. d'Yvoire E. Bretey P. Berthet and C. Peytour-Chansac SolidState lonics 1994,67,183. R. J. Balsys and R. L. Davis Solid State Ionics 1994 69 69. 494 P. R. Slater (between the COO layers). The structural data suggests that there is a tunnel for Na ion migration through this material but not for Li and preliminary conductivity measurements suggest some ionic conductivity in this material although the relative amount of ionic to electronic conductivity is unknown. The structural features suggest that this phase may be a candidate for use as a battery cathode material like LiCoO and NaCoO,.H Ion Conductors.-Perovskite-type phases are still attracting interest as a result of + their good H+ conductivity. Thangadurai et al. have investigated the layered perovskite phases of the Ruddlesden-Popper type H,Ln,Ti,O, (Ln = La Nd Sm and Gd) and observed moderate conductivity (-lo-' Scm-' at 673 K) in a hydrogen atmosphere which is likely to be protonic in nature.'56 The conductivity is attributed to the anion deficient layered perovskite Ln,Ti,O,Vac formed in situ by dehydration which interacts with water vapour in a hydrogen atmosphere in a manner analogues to Y doped BaCeO, and SrCeO,. The phases HLa,Ti,NbOlo and HCa,Nb,O,, possessing a slightly different layered perovskite structure exhibit higher conductivity to lop3Scm-' at 673 K) under the same conditions.The Ca-containing phase shows the highest conductivity suggesting that the acidity of the protons plays an important role in determining the H conduction. + Good proton conduction in H20 atmospheres have been demonstrated in two different non-stoichiometric mixed perovskites Sr,(Sc +xNbl -x)O,- (x= 0.05 and 0.1) and Ba,(Ca,~,,Nb,,,2)0,-,.'57 Conductivity has been studied in the range 3W550K where the proton conductivity is frozen in and was found to be higher than Yb doped SrCeO for the former and Nd doped BaCeO for the latter which exhibited the highest conductivity. An advantage of the present systems over rare earth doped SrCeO and BaCeO in that they do not show electronic conduction after treatment in highly reducing atmospheres although there is evidence for a small degree of hole conduction after treatment in pure 0,.One of the problems associated with the use of polymer electrolytes in cells such as the direct methanol-air fuel cell is the need for a polymer which retains high ionic conductivity above the boiling point of water so as to combine the advantages of solid polymer electrolytes with the enhanced catalytic activity above 100"C. Another advantage of the higher temperature is that it should also help to depress the poisoning effects associated with strongly adsorbed intermediates and/or impurities in the fuel (e.g. CO). To achieve such a high temperature stable polymer Savinelli et al. have equilibrated standard perfluorosulfonic acid polymer electrolytes such as NafionTM with a high boiling point Brernsted base phosphoric acid.' 58 The Nafion/H,PO electrolyte showed reasonably high conductivity (>0.05 Scm-I) at elevated tempera- tures.Zima et al. have prepared the intercalation compound LixVOP0,.2H,0 (x= 0.4-1.0) by redox intercalation of VOP0,.2H20 with LiI in a~et0ne.l'~ The conductivity of the parent phase was relatively high (-4 x Scm-' at ambient temperature) and was attributed to proton conduction since the conductivity of ls6 V. Thangadurai A. K. Shukla and J. Gopalakrishnan Solid State lonics 1994 73 9. 15' K.C. Liang Y. Du and A. S. Nowick Solid State lonics 1994,69 117. 15' R. Savinelli E. Yeager D. Tryk U. Landau J. Wainwright D. Weng K. Lux M. Litt and C. Rogers J. Electrochem. Soc.1994 141 L46. V. Zima L. Benes R. Siskova P. Fatena and J. Votinsky Solid State lonics 1994 67,277. Conducting Solids Covering Ionic and Electronic Conductors 495 dehydrogenated VOPO was several orders of magnitude lower. The conductivity was reduced with increasing Li content which is associated with the blocking of the conduction pathways by Lif-V4+ pairs. A crystal structure determination of the hexagonal high temperature phase Cs,H,(Se0,),.H20 has been performed by Merinov et al.'" The phase exhibits a transition from orthorhombic to hexagonal symmetry at -345 K with a correspond- ing increase in conductivity which is due to the disordering of the hydrogen bond network. Other Cation Conductors.-Hong et al. have observed a modified Ca F-Al,O structure in polycrystalline Ca FlP-type Al,O electrolytes.' The non-stoichiomet- ric formula of this modified P" phase is (Mg2xAl '4-,,0,,)(Ca,0). The structure consists of alternating blocks of All 0, (four layer-oxygen spinel blocks) and AI,,02 (six layer-oxygen spinel blocks). The phase contains higher Ca levels than for the ordinary F phase (x = 0.99 compared to 0.953) and the Ca2 ions have a better + conducting environment. Thus the modified CaP"-Al,O has a high conductivity o(ionic) = 5 x lo- Scm-' at 897 K. Problems are encountered in the preparation of Cuf ion conducting glasses due to the tendency for Cu'to spontaneously disproportionate to Cuo and Cu2+ during melting in the process of glass preparation. Machida et al. have prevented this by increasing the acidity of the melt by employing the CUT-Cu,WO,-CuPO glass system to stabilize CU+.',~ ESCA spectra have indicated the presence of only Cu' and the glasses showed ionic conductivity in the range lop2 to 10-4Scm-1 at room temperature.02-Ion Conductors.-The search is continuing for solid oxide fuel cells (SOFCs) which operate at lower temperatures (below 1273K) to avoid the problems associated with fuel cell operation at high temperatures such as electrode sintering and mechanical stress which arise from different thermal expansions of the constituents. One problem with using a lower temperature is that the rate of chemical reaction at the electrodes decreases resulting in large electrode overpotentials which are the main cause of the voltage drops in the cell at lower temperatures.Ishihara et al. have examined the cathodic overpotentials of the systems Lno~,Sro~,MnO (Ln = La Pr Nd Sm Gd Yb and Y) in the relatively low temperature (-900-1200K) region.163 Normally cathodes with Ln = La are used in SOFCs but cathodes with Ln = Pr showed better characteristics maintaining low overpotential values despite the low temperature operation and exhibiting a thermal expansion coefficient closer in value to yttria-stabilized zirconia (YSZ).The same power density was obtained in a SOFC with a Pro~,Sro,,Mn03 cathode at 973K as was achieved with a Lao~,Sro~,MnO cathode at 1073 K. Therefore Pro~,Sro~,MnO appears to be a promising cathode for low temperature operation of SOFCs. Another problem associated with low tempera- ture SOFCs operation is the poorer conductivity of the electrolyte at the lower temperatures.Tshii and Tajima have demonstrated good performance at lower operating temperatures (1073-1 173 K) in a solid oxide fuel cell using cubic stabilized 160 B.V. Merinov A. I. Baranov L.A. Shuvalov J. Schneider and H. Schulz Solid State lonics,1994,69,153. 161 Y.R. Hong B.B. Tang X.F. Wu and L.S. Li Solid State lonics 1994 70/71 121. 162 N. Machida Y. Matsuda T. Shigematsu N. Nakanishi and T. Minami Solid State lonics 1994,73,63. T. Ishihara T. Kudo H. Matsuda and Y. Takita J. Am. Ceram. Soc. 1994 77 1682. 496 P. R. Slater zirconia in the Zr0,-Sc,O,-Al,O (0.89-0.10-0.01) system as an electr~lyte.'~~ The power density at 1153 K (1.O W/cm2) was approximately comparable to a fuel cell with YSZ.Fagg et al. have investigated the reduced magnesium titanates Mg -,,Til -,,04 (0 < y < 0.5) as a possible high temperature anode for fuel cell and electrochemical reactor applications and as an alternative to Ni/ZrO cermets which experience problems due to Ni sintering and thermal mismatch with the YSZ electr01yte.l~~ The reduced magnesium titanate spinels exhibited similar thermal expansion characteristi- cs to YSZ with the best match for higher Ti oxidation states (3.75-3.95+). They showed good stability in reducing atmospheres and no reaction with YSZ at 1000"C. At higher temperatures some reaction was found but the product was found to be electrically conductive indicating that problems at the electrode/electrolyte interface would not be encountered.However the conductivities at fuel cell operating temperatures were slightly lower than targeted values ( > 1 Scm-'at 1000"C compared to a targeted value of lOScm-' for fuel cell operation). In addition to use as cathode materials perovskite materials have continued to attract significant interest as electrolyte materials for SOFCs. The oxide ion conductivity of the perovskite NdAlO doped with various cations has been examined by Ishihara et uZ.'~~The partial substitution of Ca for Nd has been shown to increase the conductivity with a maximum value for Nd,.,Ca,. A10 which represents the maximum solubility limit. Substituting Ga for A1 also raised the conductivity with a maximum value of -4 x lop2Scm-' at 1223 K (slightly higher than Ca stabilized ZrO but lower than YSZ) for Nd,.,Ca,,,Al,,,Ga,.,O, which may be a result of the enlarged lattice.The same authors have also found improved conductivity for LaGaO doped by Sr (for La) and Mg (for Ga).'67 The oxide ion conductivity of La,.,Sr,.,Ga,.,Mg,.,O (-0.2 Scm-at 1223 K) was higher than that of Sc-doped ZrO but slightly lower than that of 25% Y,O,-doped Bi203. In addition p-type semiconductivity in high 0 partial pressures was found to be suppressed for both systems. Aurivillius phases (Bi202)(Am- 1) have attracted significant interest due 1Bm03m+ to the observation of high oxide ion conductivity in phases of this type in particular in metal doped Bi,VO,, (BIMEVOX).Joubert et al. have investigated the new BIMEVOX series Bi,V -xMxOl (M = Sb Nb) which involves the partial substitu- and flt)y were ,!3t)ation of isovalent Nb or Sb for V. Structural phase transitions found to occur as a function ofcomposition.'68 The highest conductivity (lop2Scm-') at low temperature (590 K) was observed for y-Bi,Vl,7Sb,,301 The performance of this BiSbVOX was similar and even slightly better than those reported for some other BIMEVOX phases when ME = Cu or Ti. The crystal structure of the low temperature (a)form of Bi,V,O, has also been studied by the same group and shown to be monoclinic and not orthorhombic as previously ~1aimed.I~~ The (V03,5Vac,.5)2 -layers are broken into rows made up of tetrahedra and oxygen deficient octahedra.Sharma et al. have investigated anion-deficient Aurivillius phases of the general 16' T. Ishii and Y. Tajima J. Electrochem. Soc. 1994 141 3450. *6s D. P. Fagg S. M. Fray and J.T.S. Irvine Solid State lonics 1994 72 235. 166 T. Ishihara H. Matsuda and Y. Takita 1.Electrochem. Soc. 1994 141 3444. lh7 T. Ishihara H. Matsuda and Y. Takita J. Am. Chem. Soc. 1994 116 3801. Ih8 0.Joubert A. Jouanneaux M. Ganne R. N. Vannier and G. Mairesse Solid State lonics 1994,73 309. 169 0.Joubert A. Jouanneaux and M. Ganne Muter. Res. Bull. 1994 29 175. Conducting Solids Covering Ionic and Electronic Conductors 497 formula Bi,W -xCux06 2x possessing orthorhombic or tetragonal Bi,WO,-like ~ structure^.'^^ The tetragonal phase is stabilized for 0.7 Ix I0.8 and exhibits good oxide ion conduction (an abrupt increase about one order of magnitude in conductivity occurs in moving across the orthorhombic to tetragonal transformation) in the temperature range 50&900 K (67003 -1 x 10-Scm-'for x = 0.7 higher than that of Cu/Ti substituted Bi,VO,,,).A new oxygen deficient Aurivillius phase (Bi,O,)(NaNb,O,,,) exhibiting oxide ion conductivity has been reported by Pham et al.' ' A reversible phase transition occurs at 860"C probably due to an ordering of oxygen vacancies in the low temperature form resulting in an increased conductivity in the high temperature form (611733 = lo- Scm-'). The conductivity of this two-layer Aurivillius phase is nearly 1.5 orders of magnitude lower than the 1 layer system Bi,VO,.,. The corresponding phase (Bi,O,)(CaNb,O,) with no oxygen vacancies has as expected a lower ionic conductivity.Similar order-disorder transitions (at 775-800 "C) have been observed in the related oxygen-deficient Aurivillius phases (Bi,O,)(Sr,Nb,MO,~,) (M = Ga Al) which consist of intergrowths of the Aurivillius phase (Bi,O,)(SrNb,O,) and brownmillerite-like SrMO,. layers (to introduce oxygen vacancies).' 72 The phases show quite good oxide ion conductivity 01173K -3.1 x lo- Scm-' for M = Ga and 2.3 x 10-2Scm-1 for M = Al. The same group have also synthesized other similar compounds (Bi,0,)(BaBi,Ti3M0 2,5) consisting of intergrowths between the Aur- ivillius phase Bi,Ti,O, and the brownmillerite-like BaMO,. (M = Sc In Ga) layers with similar oxide ion conductivities (6'173K -4.9 x lop2 Scm-' for M = In).'73 All three materials show oxygen vacancy order-disorder transitions.For M = Sc there is an observed hysteresis for this phase transition due presumably to a slow relaxation process. The phase Bi,BaO,. has been examined by powder neutron diffra~ti0n.l~~ Although the cationic positions and large anisotropic thermal parameters of the oxygen atoms resemble the anti a-AgI structure the anionic positions actually correspond to those observed in the perovskite structure. Therefore contrary to observations for the related phase Bio,79Cdo~2101,39 this phase cannot be considered as an anti a-AgI structure. It can be better described as the coexistence of the two configurations of the perovskite structure inside the crystals.High ionic conductivity ~~ CJ -~ ~ Scm-I Ea = 0.90eV was observed which was attributed to the oxygen vacancies present in the structure. F-Ion Conductors.-Ito et al. have examined the crystal structure of the tetragonal form of the high fluoride ion conductor PbSnF determined by single crystal XRD.' 75 An ordered arrangement of Pb and Sn was seen with disordering of some of the fluoride ions which accounts for the high ionic conductivity in PbSnF,. The same group has reported preliminary single crystal structural studies for the F ion conductor ~-Pbo,9Ko~,Fl~,.'76 The conductivity of this phase is lo3 times higher than P-PbF, V. Sharma A. K. Shukla and J. Gopalakrishnan J. Muter. Chem. 1994 4 703. A.-Q. Pham M. Puri J. F. DiCarlo and A.J. Jacobson Solid State lonics 1994 72 309. 17' K. R. Kendall J. K. Thomas and H.-C. zur Loye Solid State lonics 1994 70/71 221. 173 J. K. Thomas K. R. Kendall and H.-C. zur Loye Solid State lonics 1994 70/71 225. 174 C. Michel D. Pelloquin M. Hervieu B. Raveau F. Abbattista and M. Vallino J. Solid State Chem. 1994 109 122. 175 Y. Ito T. Mukoyama H. Funatomi S. Yoshikado and T. Tanaka Solid State lonics 1994 67 301. 176 Y. Ito T. Mukoyama F. Kanamaru and S. Yoshikado Solid State lonics 1994 73 283. 498 P. R. Slater due to the presence of vacancies in the tetrahedral fluorine sites. There is structural evidence that indicates that the anharmonic vibration of the fluoride ion does not play a significant role in connection to the ionic conductivity but rather the high ionic conductivity may be ascribed to normal vacancies with easy migration of fluoride ions between tetrahedra via the vacancies.

ISSN:0260-1818    

DOI:10.1039/IC9949100467

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

26 Radiochemistry By DAVID S. URCH Chemistry Department Queen Mary and Westfield College University of London Mile End Road London El 4NS UK 1 Introduction This section of Annual Reports will consider recent progress in various aspects of radiochemistry but excluding the chemistry of the heavy radioactive elements and radiation chemistry. A few new books covering various aspects of the field have been published ‘Principles of Radiochemistry’,’ ‘Radiochemistry and Nuclear Methods of Analysis’,2 the third edition of Keller’s ‘Fundamentals of Radio~hemistry’~ and ‘Handbook of Hot Atom Chemistry’.& The launch of the latter was marked by an international seminar the proceedings of which were also published.4b An interesting review of eighty years of nuclear chemistry research in Hungary appeared re~ently.~ The various sections of this review will consider methods whereby specific isotopes may be made and/or purified the chemical effects of nuclear reactions the preparation of labelled compounds the effect of radiochemistry on the environment and finally a miscellaneous section.2 Isotope Production Many of the isotopes used in nuclear medicine are the daughters of long-lived isotopes. For convenience these isotopes are incorporated into some type of column from which the daughter can be eluted as and when required. A comprehensive and critical review of such ‘isotope generators’ has recently been published.6 Light Elements.-There is increasing interest’ in the production of 18F by the neutron irradiation of oxygen-containing lithium compounds [6Li(n,or)3H followed by ‘Principles of Radiochemistry’ ed.D. D. Sood N. Ramamoorthy and A. V. R. Reddy Indian Association of Nuclear Chemists and Allied Scientists Bombay India 1993. ‘Radiochemistry and Nuclear Methods of Analysis’ ed. W. D. Ehmann and D. E. Vance John Wiley and Sons New York USA 1993. C. Keller ‘Grundlagen der Radiochemie’ 3rd Ed Sauerlander Frankfurt-am-Rhine Germany 1993. (a) ‘Handbook of Hot Atom Chemistry’ ed. J. P. Adloff P. P. Gaspar M. Imamura A. G. Maddock T. Matsuura H. Sano and K. Yoshihara Kodansha Tokyo Japan and VCH Weinheim Germany 1992; (b) ‘Proceedings of the international seminar on the chemistry of high energy atoms’ ed. T. Matsuura Inst. Atomic Energy Rikkyo Univ. Yokosuka Kanagawa Japan 1993.I. Feher and I. Kiss Magyar Kemiai Folyoirac 1994 100 135. F. F. Knapp and S. Mirzadeh Eur. J. Nuciear Med. 1994 20 1151. ’ (a)J. Jimenez-Becerril D. Estevez and S. Bulbulian J. Radioanal. Nuclear Chem. 1994 187 419; (b) H. Kvaternik ‘Reactor-produced (“F) fluoride in the synthesis of (‘*F)labelled compounds’ Thesis Tech. Univ. of Vienna Vienna Austria 1991. 499 500 David S. Urch 160(3H,n)' 'F]. Tritium can be recovered' from irradiated lithium carbonate by distillation. The more usual route to "F is by ["O(p,n)'*F] using "0 enriched water but deleterious effects due to traces of metal ions have been reported' and improved results have been found' O using solid '0-enriched carbon dioxide. When water with only a low enrichment of "0 is irradiated with protons not only is "F produced but also 13N from the [160(p,a)'3NJ reaction.A careful choice of conditions" enables both labelled ["FI-fluoride and ["N]-nitrate(rr~,v) anions to be prepared simultaneously. 13N can also be made by the proton irradiation of carbon [12C(p,y)13N],12 if ethan01'~ is used as the target material ['3N]-ammonia results. The short-lived 16N can be made14 by the irradiation of water by fast neutrons [160(n,p)16N]. The positron emitter 38Kcan be made" in a low energy cyclotron by the proton irradiation of argon [38Ar(p,n)38K] whereas 63Ni requires the prolonged neutron irradiation of a 62Ni enriched target16 at high flux. Other transition metal isotopes 64Cu and 67Cu can be prepared17 from zinc targets.Zinc can also be used for the production of 67Ga when 68Zn is irradiated" with protons (28 MeV). 72Asand 73Se are both positron emitters and roles for both have been proposed in nuclear medicine. The former can be obtained from the decay of 72Se using an automated generator" and the latter is produced when copper arsenide2' is bombarded with protons. The low mass isotopes of bromine (75,2176,22and 7723)are also positron emitters with uses in nuclear medicine and can be made from arsenic by alpha particle irradiation. A new method for controlling the preparation of the radiopharmaceutical diagnostic agent * '"Kr has been described.24 82Kr is initially proton irradiated [82Kr(p,2n)' 'Rb]; the rubidium is then adsorbed on a cation exchange resin where it decays (T~,~ 4.6hr) to ""Kr.A procedure for the preparation of 82Sr from rubidium has been described25 but a mixture of 82Sr and 85Sr,26a together with isotopes of niobium,26b zirconium ("Zr) H. F. Rea F.A. Palma and F. M. de Ramirez J. Radioanal. Nuclear Chem. 1993 173 249. D. J. Schlyer M. L. Firouzbakht and A. P. Wolf Appl. Radiat. Isotopes 1993 44 1459. la M.L. Firouzbakht D. J. Schlyer S.J. Gatley and A. P. Wolf Appl. Radiat. Isotopes 1993 44,1081. R.A. Ferrieri D. J. Schlyer C. Shea and A. P. Wolf J. Labelled Compd. Radiopharm. 1993 32 118. V. I. Tchuev E. P. Derevyanko I.V. Ekaeva,V. G. Isotov,T. A. Katunina M. N. Klebanov,L. S.Larionov and N. S. Marchenkov ibid. 1993 32 470. l3 R.A. Ferrieri K. MacDonald D. J. Schlyer and A.P. Wolf ibid. 1993 32 461. l4 T. Akimoto T. Hirata and M. Narita in 'Radiation detectors and their uses' ed. M. Miyajima S. Sasaki Y. Yoshimura T. Iguchi and M. Nakazawa Nat. Lab. for High Energy Physics Tsukuba Japan 1993 p. 215. l5 S. M. Qaim G. Stoecklin F. Tarkanyi and Z. Kovacs J. Labelled Compd. Radiopharm. 1993 32,478. I' D. F. Williams G. D. O'Kelley and J. B. Knauer Radiochim. Acta 1994 64 49. S. Mirzadeh D.E. Rice and F. F. Knapp Jr. J. Labelled Compd. Radiopharm. 1993 32 474. l8 T. E. Boothe E. Tavano J. Munoz S. T. Carroll and P. M. Smith in 'New Trends in Radiopharmaceutical Synthesis Quality Assurance and Regulatory Control' ed. A. M. Emran Plenum Press New York NY USA. 1991 p. 169. D. R. Phillips V. T. Hamilton D. A. Nix W. A. Taylor D.J. Jamriska R. C. Staroski and R. A. Lopez Ref. 18 p. 173. 'O D. de F. Santos and R. Weinreich J. Labelled Compd. Radiopharm. 1993 32 464. C1. Brihaye M. Guillaume J.C. Depresseux D. Comar and J. Trumper ibid. 1993 32 445. 22 J. Mertens A. Hermanne D. Terriere and F. Lambert ibid. 1993 32 477. 23 F. Lambert and G. Siegers Appl. Radiat. Isotopes' 1994 45 11. 24 S. L. Regdos A. C. Mignerey N. R. Simpson and H. R. Adams Ref. 18 p. 451. 25 V. V. Golik,G. A. Kavkhuta L. F. Rozdyalovskaya L. A. Klokotskaya B. G. Luchkin and S. E. Chigrinov Vesti Acad. Navuk BSSR Sery. Fizika-Tekh. 1993 2 118. 26 (a)R. C. Heaton D. J. Jamriska Sr. and W. A. Taylor 'Process for strontium-82 separation' US Patent Doc. 5 167,938/A 1992; (b)D. R. Phillips D. J. Jamriska Sr. and V.T. Hamilton 'Recovery of niobium from irradiated targets' US Patent Doc. 5 296 203/A (1994); (c) R. C. Heaton D. J. Jamriska Sr. and W. A. Taylor 'Process for separation of zirconium-88 rubidium-83 and yttrium-88' US Patent Doc. 5,330 731/A 1994. Rad iochemistry 50 1 rubidium (83Rb) and yttrium (88Y)26c results from the proton irradiation of molybdenum. Other yttrium isotopes can be made27 using a 90Sr generator ("Y) or can be isolated28 from irradiated uranium (91Y). 95Zr is also found in neutron irradiated uranium. It decays to 95Nb and methodsz9 for the isolation and purification of this niobium isotope (chromatography ion exchange) have been described. Technetium.-Techniques for the preparation3' of 94mT~ (a short-lived positron emitting isotope) and its purification3' have been reported.Other light isotopes of technetium (95T~ can be made3' by gamma irradiation (50MeV) of 99Tc. and 96T~) Very much more effort has been directed towards the production of 99mTc and therefore towards ways in which 99Mo can be made. A popular source is spent fuel from nuclear reactors which contains 99Mo as a fission product. The problem is to extract pure 99Mo uncontaminated with any isotope of any other element.33 The use of low-enriched uranium (as the ~ilicide)~~ apparently facilitates the subsequent extrac- tion of 99Mo. New methods have been reported for the removal of non-fissioned uranium35 and for the separation of 99Mo from 132Te (another fission product).36 Another route to 99Mo is by the neutron irradiation of molybdenum but this has the disadvantage that only a small amount of 99Mo is produced.To some extent this problem may be overcome37 by concentrating the pertechnate solutions that can be eluted from columns made from neutron irradiated MOO,. Column design has also exercised people's minds of late the particular concern being to prevent the elution of molybdenum with the technetium. Chemical inc~rporation~~ of 99Mo into the gel of the column as molybd~phosphate~~ have both been suggested. or m~lybdocerate~' The preparation of the long-lived isotope 99Tc from neutron irradiated molybdenum trioxide has been de~cribed.~~ Finally another way in which 99Mo may be made42 is by the gamma (25 MeV) irridation of "'Mo ["'M~(y,n)~~Mo],but purification from niobium [100Mo(y,p)99Nb] is necessary.Heavy Elements.-'06Ru can be extracted from uranium fission products29b using ion exchange columns based on ammonium phosphomolybdate and stannic antimonate. A new method for the separation of "In from alpha bombardment of silver targets has " (a)B. T. Hsieh G. Ting H.T. Hsieh and L. H. Shen Appl. Radiat. Isotopes 1993,44,1473;(6)A. Dash and P. K. Bhattacharyya ibid. 1994 45 415. '' G. B. Maslova V. M. Gelis V. V. Milyutin and N. I. Polyakova Radiokhimiya 1992 34 78-82. 29 (a)N. R. Das K. Singh and S. Lahiri 'Nuclear and Radiochemistry Symposium' ed. V. Venugopal B. S. Tomar and D.D. Sood Dept. of Atomic Energy Bombay India 1992 p. 444; (6) A. Dash K.R. Balasubramanian and T. S. Murthy Ind.J. Techn. 1993 31 593. 30 R. J. Nickles B. T. Christian A. D. Nunn and C. K. Stone J. Labelled Compd. Radiopharm. 1993,32,447. 31 F. Roesch A. F. Novgorodov and S. M. Qaim Rudiochim. Acta 1994 64 113. 32 T. Sekine K. Yoshihara J. Safar L. Lakosi and A. Veres J. Radioanal. Nuclear Chem. 1994 186 165. 33 (a)S. A. Ali and H. J. Ache in 'Proc. Tnt. Meeting on Reduced Enrichment for Research and Test Reactors'. Argonne Nat. Lab. Ill. USA 1993,417;(b)S. L. Marshall L. Redey D. R. Vissers G. F. Vandegrift and J. E. Matos ibid. 443. 34 J. D. Kwok G. F. Vandegrift and J. E. Matos ibid. 434. 35 A. S. Rodriguez A. L. Ch. Acosta B. E. M. Lopez and L. A. Fucugauchi J. Radioanal. Nuclear Chem. 1994 178 417. 3h S.A. C. Mestnik and C.P.G. da Silva ibid. 1993 172 87.37 S. Seifert G. Wagner and A. Eckardt Appl. Radiat. Isotopes 1994 45 577. 3R S. P. Iyer D.V. S. Narasimhan L.N. Singh and R.R. Patel Ref. 29(a) p. 325. 39 M.T. El-Kolaly J. Rudioanal. Nuclear Chem. 1993 170 293. 40 M.A. El Absy A.I. Audah and I. M. El Naggar ibid. 1993 173 185. 41 W. Sun T. Wu J. Bao and M. Li Nuclear Power Engineering 1992 13 83. 42 M.G. Davydov and S.A. Mareskin Radiochemistry (New York) 1994 35 569 (Russian original Rudiokhimiya 1993 35(5) 91). 502 David S. Urch been reported43 whilst the heavier isotope '14Tn results44 from the neutron irradi- ation of 'I3In. 1231(positron emitter) is particularly useful in nuclear medicine and improvements in techniques for its production continue to be reported.45 An improved method for the purification of 137Cshas also been ann~unced.~~ 134La has potential as a radiopharmaceutical isotope and can now be easily obtained47 from a 34Ce gener- ator.Similarly 17'Lu arises from the decay of '72Hf. This isotope48 is made by the alpha irradiation of ytterbium [Yb(a,xn)' 72Hfl. The short-lived isotope of tantalum 178Ta has proved useful for cardiac imaging and a generator49 for its production (decay of 178W -z1,2 21.7d) has been described. The heavier isotope of tungsten Ig8W can be useds0 as the mother isotope in a new generator for '"Re. Methods for the production and purification of 1940s,parent isotope in the 1940s/'941r generator have been de~cribed.~' 191Pt can be made by the proton irradiation of natural irid- ium52 and a new heavy isotope of platinum 202Pt has been reported.53 When plati- num is irradiated with neutrons '99Au results,54 an isotope which can be used diagnos- ti~ally~~ in nuclear medicine.201T1 has similar applications and can be made by the proton irradiation of mercury thallium,56 or lead-204.s7 Whilst "Po arises naturally as part of the uranium decay chain it is more convenient to make it artifi~ially,~~ by the neutron irradiation of 'O'Bi. This isotope can also be used for the preparation of 211At [209Bi(a,2n)21 Lighter isotopes of astatine (208 209 and 210) are formed6' if 209Bi is bombarded with helium-3 nuclei. A method has been described for the prepara- tion for the first time,61 of pure 223Fr (decay of 227A~). Experimental details have been described for the purification of 223Ufrom thorium62 and of neptunium63 and plutonium64 from neutron-irradiated targets of 43 2.Mazgaj A. Kolaczkowski J. Mikulski A. F. Novgorodov and A. Zielinski Report 1505/c Inst. Nuclear Physics Cracow Poland 1990. 44 H. Tang J. Ding and Q. Lin J. Nuclear Radiochem. 1993 15 144. 45 (a)M. L. Firouzbakht D. J. Schlyer and A. P. Wolf,J.Labelled Compd. Radiopharm. 1993,32,243;(b)N. 1. Venikov V. I. Novikov and A. A. Sebiakin ibid. 1993 32 222; (c)N. V. Kurenkov A. B. Malinin A. A. Sebyakin and N.I. Venikov ibid. 1993 32 233. 46 V.N. Reddy G. S. Murthy and A. Dash Ref. 29(a) p. 412. 47 J. Zweit J. W. Babich and R.J. Ott J. Labelled Compd. Radiopharm. 1993 32 480. 48 S.K. Das and A. G. C. Nair Ref. 29(a) p. 436. 49 W. W.Layne and J.L. Lacy Ref. 18 p. 213. 50 G.A. Brodskaya and O.U. Gapurova Radiochemistry (New York) 1994 35 325 (Russian original Radiokhimiya 1993 35(3) 92). S. Mirzadeh D. E. Rice A. P. Callahan and F. F. Knapp Jr. J. Labelled Compd. Radiopharm. 1993,32 471. 52 A. M. B. Bittencourt Filha M. A. V. Bastos and J. A. Medeiros Ciencia e Cultura. Suplemento 1993,45500. 53 D. Yin Y. Li W. Huang and S. Shi Nuclear Techn. 1993 16 521. M. Akhtar A. Mushtaq H. M.A. Karim and M.A. Khan Radiochim. Acta 1994 64 137. 55 M. Bonardi F. Groppi G. Sanvito and M. Gallorini J. Labelled Compd. Radiopharm. 1993 32 483. 56 L. Fernandes S.T. 1. Yanagawa J. Mengatti C. Nakanishi and M. E. D. Acar Report 390 Inst. de Pesquisas Energeticas e Nucleares Slo Paulo Brazil 1993. 57 V.A. Ageev A. A. Klyuchnikov A. A. Odintsov A. D. Sazhenyuk V. N. Bukanov E.G. Vasil'eva and N. A. Shovkum Radiochemistry (New York) 1992 34 250 (Russian original Radiokhimiya 34(2) 122). 58 M.T. Azure and R. W. Howell Appl. Radiat. Isotopes 1994 45 637. 59 Z. Mazgaj and J. Mikulski Report 1610/c Inst. Nuclear Physics Cracow Poland 1992. 6o F. Szelecsenyi Z. Szuecs 0.Solin J. Bergman and S.-J. Heselius J. Labelled Cornpd. Radiopharrn. 1993 32 443. 61 Z. Szeglowski 0.Constantinescu M. Hussonnois A. Abdul-Hadi and G. J. Ardisson Radiochim. Acta 1994 64 57. 62 (a)M. Venkatesan S.V. Mohan T. N. Ravi R. Srinivasan V. R. Raman and G.R. Balasubramanian Ref. 29(a),p. 270; (b)C. I. Pius M. M. Charyulu A. V. Kadam and C. K. Sivaramarkrishnan Ref. 29(a),p. 117. 63 L.F.Bellido V.J. Robinson and H.E. Sims J. Radioanal. Nuclear Chem. 1993 172 107. 64 P. K. Mohapatra V. K. Manchanda and A. Ramaswami Ref. 29(a) p. 228. Rad iochemistry 503 uranium. The use of a crown ether in the organic layer enabled 235U to be preferentially extracted6' from aqueous solutions of uranyl chloride. Californium isotopes (245 and 246) are reported66 to be formed when 238U is bombarded with 12C ions. 3 Chemical Effects of Nuclear Transformations Solid State.-Much effort has been expended over many decades to determine the fate and chemistry of recoil atoms in crystal lattices. Usually the results of (n,y) reactions have been investigated by dissolving the crystals and determining the chemical nature of the labelled products.A further refinement has been to subject the crystal to a period of heating before dissolution-annealing. In some cases it was reported that yields would oscillate as the annealing proceeded but recent has failed to confirm this behaviour. It is remarkable that despite the number of compounds that have been irradiated there has been a sparsity of systematic programmes of study to elucidate fundamental reaction mechanisms in a logical way. A notable exception is that of Mueller,68 whose detailed studies of recoil processes in mixed crystals of complex octahedral halide anions continues (e.y. K2ReBr6-K2SnC16).69 Similarly the reactions of recoil ruthenium and recoil technetium in the same initial complex (ruthenocene7' or tris-bipyridineruthenium(I1) chloride7') can be compared by varying the irradiation (neutron for recoil Ru or gamma for recoil Tc) enabling specific mechanisms to be proposed.In a rather more conventional way work continues to ascertain the factors that control the fate of recoil bromine (as 80Br 80mBr and 82Br)72 in various bromates Sr,74 Sm and Y75) and iodine (1281)in iodates.76 Liquid State.-The charged-plate technique whereby recoil reactions take place in the presence of an electric field continues to help to determine the role of charged species in 'hot atom' chemistry. Recent studies of recoil bromine7 and iodine78 with aromatic substrates have shown that reactions of positive ions usually predominate. Miscellaneous.-The stereochemistry of a hot atom reaction in which the recoil species replaces another atom in a molecule has long fascinated chemists.Rack and his group continue79 to investigate the factors which can determine whether recoil chlorine (38Cl) will replace chlorine or fluorine with inversion or retention of configuration. Steric hindrance and atomic size have been shown to be important. Hot atom chemistry has a way of cropping up in odd places such as the chemical fate of plutonium in the 65 Y. Han W. Luo and S. Gao Chin. J. Nuclear Sci. Engineering 1993 13 58. 66 A. Ramaswami G. K. Gubbi J. N. Mathur R. J. Singh and M. S. Murali Ref. 29(a) p. 84. 67 H. Mueller J. Radioanal. Nuclear Chem. 1993 172 249. H. Mueller ihid. 1994 181 211. (cf. Ref. 4(b)). " H. Mueller Rudiochim. Acta 1993 62 189. 'O H. Matsue T. Sekine and K.Yoshihara ihid. 1993 63 179. 71 H. Shoji Y. Watanabe and N. Ikeda ibid. 1993 63 183. 72 R.S. Lokhande and V.G. Dedgaonkar J. Ind. Chem. SOC. 1992,69 122. 73 K. K. Sahu and D. Bhatta Radiochim. Acta 1994 64 67. 74 R.S. Lokhande Ref. 29(a) p. 108. 75 V.G. Dedgaonkar R.G. Apte and D.A. Bhagwat Ref. 29(a) p. 110. 76 R. Khare and S. P. Mishra Ref. 29(a) p. 86. 77 (a)S. P. Mishra and M. R. Zaman Ref. 29(a),p. 106; (b)S. P. Mishra and M. R. Zaman Ref. 29(a) p. 113. 78 S.P. Mishra N. P. Singh and M. R. Zaman lnd. J. Chem. Sect. A. 1994 33 170. 79 R. J. Meyer F. Roman R. B. Sharma R. A. Ferrieri and E. P. Rack Rudiochim. Acta 1993 62 181. 504 David S. Urch environment8’ and the reactions of 244Pu with interstellar diamond crystals” (if plutonium had been held in such crystals it would be possible to explain xenon isotope ratios).It is also of importance when the chemistry of the very heaviest elements is studied since the initial chemical reactions of the atoms of such elements are necessarily ‘hot’.82 4 Labelled Compounds New methods for the production of labelled compounds and the introduction of new isotopes for use in nuclear medicine continues to be a growth area.83 Greatest interest is centred on rapid methods for the incorporation of short lived positron emitting isotopes for imaging. Automation of such procedures is also receiving increasing attention. Another area of growth (and rightly so) is that of quality control,84 the testing of radiopharmaceutical products for radiochemical and medical purity.Tritium 3H.-Apart from conventional organic procedures in which a tritium labelled reagent is used tritium can be introduced into an organic compound in two main ways either by exchange or by addition to an unsaturated site. The exchange reaction can be initiated either by the use of tritiated water or tritium gas but in either case catalysts are often used and polymer supported catalysts have been shown to be especially Rhodium trichloride catalyst directs86 the exchange reaction to aromatic ortho-positions and to activated (6 +) hydrogen sites. Noble metal catalysts (often palladium based) have been used to in the preparation of tritium labelled heterocyclic bases (adenisine and thymidine derivatives). Directing the label to a specific site can most easily be achieved by the replacement of a labile group such as a halogen.However even in this reaction use is often made of palladium catalysts as in the preparation of labelled benzylic acid” or pyrethr~id~~ derivatives 19-C3H] cholesterol,90 cyfluthrin,” care~edilol,~~ and complex antipsychotic agents (CP-88059),93enzyme inhibitor^,^^ and retinoic acid receptors.95 80 1.0. Essien J. Radioanal. Nuclear Chem. 1994 178 165. 81 P. K. Kuroda Rudiochim. Acta 1993 62 27. 82 (a) D.C. Hoffman ihid. 1993 61 123; (h) M.K. Gober ‘Development and application of HPLC separations to study heavy ion reactions and chemical properties of the element 105’,Thesis Mainz Univ. Germany 1993. 83 M. J. Welch Abstract CHED22 207 meeting Amer.Chem. Soc. (San Diego) 1994. 84 P. Schmidt F.T. Lee and R. Lambrecht in ‘Proc. 1st Australian-Asian conference on radiation science and nuclear medicine’ Lucas Heights N.S.W. Australia 1993 p. 8. Australian Institute of Nuclear Science and Engineering. 85 J.R. Brewer J.R. Jones K. W.M. Lawrie D. Saunders and A. Simmonds ‘Tritiation of organic compounds by polymer-supported acid catalysts’ J. Labelled Compd. Radiopharm. 1994 34 391. 86 K. Oohashi and T. Seki J. Radiounul. Nuclear Chem. 1994 187 303. 87 (a)G. V. Sidorov and N. F. Myasoedov Biaorgunicheskaya Khimiya 1993,19 1220; (h)G. V. Sidorov and N. F. Myasoedov ibid. 1993 19 1215; (c) G. V. Sidorov and N. F. Myasoedov J. Labelled Compd. Radiopharm. 1994 34 353; (d) G. V. Sidorov and N. F. Myasoedov ibid.1994 34 339. 88 V. P. Shevchenko 1. Yu Nagaev and N. F. Myasoedov ‘Preparation of 3H-labeled benzilic acid derivatives’ Rudiochemistry 1994 35 574 (Russian original Radiokhimiya 1993 35(5) 97). nq B. Lath L. J. Greenfield and J. E. Casida J. Labelled Compd. Rudiopharm. 1993 33 613. 90 (a)V. P. Shevchenko I. Yu Nagaev A. V. Potapova and N. F. Myasoedov Rudiochemistry 1993,3518; (Russian original Radiokhimiya 1993 35 106). 91 U. Pleiss J. Roemer and R. Thomas J. Labelled Compd. Radiopharm. 1993 33 949. 92 S. G. Senderoff A. J. Villani S. W. Landvatter K. T. Games and J. R. Heys ihid. 1993 33 1091. 93 H. R. Howard K. D. Shenk T. A. Smolarek M. H. Marx J.H. Windels and R. W. Roth ihid. 1994 34 117. 94 A.Y.K. Chung J. W. Ryan W.E. Groves F.A.Valido and P. Berryer ibid. 1993 33 483. 95 M.I. Dawson P.D. Hobbs S. W. Rhee H. Morimoto and P.G. Williams ibid. 1993 33 633. Radiochemistry 505 Metallation can also be used to indicate the site for tritium exchange as in the replacement of potassium96 in the preparation of C3H]ibogaine. Another way of ensuring that the tritium label is in the desired location is to allow tritium gas to add to a double bond. The mechanism and kinetics of this reaction have been studied97 and the method used9' to prepare [17,18-3H]prostoglandin Ei. Palladium on charcoal catalyst was used in the preparation of labelled 4-amino-3- phenylbutanoic acid99 whilst the use of tris(triphenylphosphine)rhodium(I)chloride facilitated the partial reduction of a triple bond leading to the formation of labelled (E)-and (2)-4-aminobut-2-enoic acids.' O0 Catalytic hydrogenation has also been used to label biocompatible polymers,' O1 from acetylenic starting materials and in the preparation of C3H]proadifen from an allylic intermediate.' O2 A new and convenient method for the preparation of tritium from the reaction of sodium [3H]borohydride with cobalt(I1) chloride has been described.'03 As this reaction can be carried out on a small-scale in the laboratory it provides a very useful alternative source of tritium gas.Carbon (l 'C).-[' 'CIMethyl iodide remains one of the most versatile and useful reagents for the incorporation of carbon-1 1 into organic molecules. Recent examples include the preparation of ''C-labelled dopamine D-1 receptor ligands,' O4 epineph-rine,' O5 dapoxetine hydrochloride,'06 N-[11C-methyl]chlorophentermine,'07" meth-arn~hetarnine,"~~ prenorphine derivatives"' and 6-[11C]-D-glucose.1 O9 A significant increase in the radiochemical yield of [''C-methyl] anisole was recorded' lo when the reaction (methyl iodide plus phenol) was carried out in liquid ammonia near the critical point.Whilst ["Clcarbon dioxide can be used directly in many preparations (e.g. 1-[' 'C]polyhomoallylic fatty acids)"' it is also a source112 for labelled hydrogen cyanide and cyanogen bromide. The former can be used to make l-["C]-96 H.H. Seltzrnan D.F. Odear C. P. Laudernan F. I. Carroll and C. D. Wyrick ibid. 1994 34 367. 97 V.P. Shevchencko I. Yu Nagaev and N.F. Myasoedov Radiochemistry (New York) 1994 35 476 (Russian original Radiokhimiya 1993 35(4) 126).98 V. P. Shevchencko I. Yu Nagaev and N. F. Myasoedov Radiochemistry (New York) 1992 34 138 (Russian original Radiokhimiya 1992 34(1) 172). 99 R.K. Duke R.D. Allan C.A. Drew G.A.R. Johnston and K.N. Mewett J. Labelled Compd. Radiopharm. 1993 33 767. lo" R. K. Duke R.D. Allan C.A. Drew G.A. R. Johnston M. A. Long and C. Than ibid. 1993,33 527. J. C. Russell P. W. Stratford J. R. Jones and T.A. Vick ibid. 1993 33 957. T. Werner L. Gawell and S. B. Ross ibid. 1993 33 627. S. Malik M. Kenny G. Doss and J. Varghese ihid. 1994 34 471. lo4 (a) C. Halldin L. Farde P. Karlsson C.-G. Swahn H. Hall G. Sedvall C. Foged K. Hansen and F. Groenvald Nuclear Med. Biol. 1993,20,945;(b)R.F. Dannals J. Labelled Compd. Radiopharm. 1994,34 431. P. K. Chakraborty D. L. Gildersleeve D. M. Jewett S. A. Toorongian M. R. Kilbourn M. Schwaiger and D. M. Wieland Nuclear Med. Biol. 1993 20 939. lo6 E. Livni W. Satterlee and R. L. Robey ibid. 1994 21 669. lo' (a)H. Kizuka and D. R. Elrnaleh Nuclear Med. Biol. 1993,20,239; (h)M. Mizugaki T. Hishinuma and H. Nakarnura ibid. 1993 20 487. Io8 S. K. Luthra F. Brady D. R.Turton D. J. Brown K. Dowsett S. L. Waters and A.K. P. Jones Appl. Radiat. Isotopes 1994 45 857. Io9 (a)J. R. Grierson J. E. Biskupiak J. M. Link and K. A. Krohn Appl. Radiat. Isotopes 1993,44,1449;(b) J.R. Grierson J.E. Biskupiak J.M. Link J.H. Courter and K.A. Krohn J. Labelled Compd. Radiopharm. 1993 32 537. G. Jacobson K. E.Markides and B. Laangstroem Acta Chem. Scund. 1994 48 428. M.A. Channing and N. Sirnpson J. Labelled Compd. Radiopharm. 1993 33 541. 112 G. Westerberg and B. Laangstroern Acta Chem. Scand. 1993 41 974. 506 David S. Urch glucosamine,' l3 ['lC]oxalic acid' l4 (itself a useful intermediate) and [''Clbenzamide derivatives.' ' Labelled cyanogen bromide proved useful in the preparation1l6 of ["Clalbumin and ["Cltransferin. A new method for making [''Clphosgene has been described;'17 this compound can then be used"' in the preparation of labelled 2-thymine. ["Clnitromethane has been used to make a series of labelled amines,"' including [l-"Cldopamine. Nitrogen (13N).-Despite its short half-life there is still interest in the preparation of compounds labelled with nitrogen-13.The starting compound is usually [13N] ammonia for which improved production parameters have recently been reported.' 2o Methods for the incorporation of 13N into aminesI2' and polypeptides122 have been described. Oxygen ("O).-The shorter half-life of this isotope has greatly restricted its application as a label for radiopharmaceuticals. Even so the preparation of oxygen-15 labelled carbon monoxide carbon dioxide,' 23 and butan01'~~ have been reported. Fluorine ("F).-For the most part the labelling of a wide range of organic compounds for use in nuclear medicine procedures is accomplished by now standard methods. These can be exemplified by the techniques used to introduce '*F into dopamine derivatives. This can be achieved by nucleophilic substitution using labelled potassium fluoride and kryptofix 222 (dopamine D2);'25 by the location of the fluorine label at a specific site using regioselective demetallation (either tin 6[' 'Flfluor~dopamine~~~ or mercury 3-O-methyl-6[ ''F]flu~rodopa~~~); or by straightforward nucleophilic sub- stitution of a nitro group 6[18F]fluorodopamine.'28 The yield of labelled product in such a nucleophilic displacement reaction correlate^'^^ quite well with the 13C NMR chemical shift.Rapid and/or improved methods have been reported for the preparation of intermediates such as 4[' 'Flbromo-or i~do-benzene,'~~ cyclopropyl-4-[' 'F] fluorophenyl ket~ne,'~' ["F]fluoroacetone,' 32 4-['8F]fluorobenzylbromide,'33 and 113 J.-0. Thorell and E.S.Stone J. Labelled Compd. Radiopharm. 1993,32 586. l4 J.-0. Thorell S. Stone-Elander N. Elander ibid. 1993 33 995. Y. Anderson M. Bergstroem and B. Laangstroem Appl. Radiat. Isotopes 1994 45 707. G. Westerberg and B. Laangstroem ibid. 1994 45 773. 11' F.R. Dobbs M. Franceschini and T. J. Tewson J. Labelled Compd. Radiopharm. 1993 32 191. C. J. Steel G.D. Brown and K. Dowsett ibid. 1993 32 178. K.-0. Schoeps C. Halldin C.-G. Swahn P. Karlsson H. Hall L. Farde and K. Naagren Nuclear Med. Bio. 1993 20 669. M. S. Berridge and B. J. Landmeier Appl. Radiat. Isotopes 1993 44 1433. G.W. Kabalka M.M. Goodman J.F. Green R. Marks and D. Longford J. Labelled Compd. Radiopharm. 1993 32 165. P. Landais P. Waltz K. Rose R. E. Offord H. Tochon-Danguy P. Goethals and K.Strijckmans ibid. 1993 32 171. 123 R. Iwata and T. Ido ibid. 1993,32 454. lZ4 S. M. Moerlein G. G. Gaehle K. R. Lechner R. K. Bera and M. J. Welch ibid. 1993 32 162. F. Takao S. Sasaki M. Maeda T. Fukumura T. Tahara K. Masuda and Y. Ichiya ibid 1993,33 1108. 126 M. Namavari N. Satyamurthy and J. R. Barrio Abstract MED151 Ref. 83. 12' T. Chaly D. Bandyopadhyay R. Matacchien A. Belakhieff V. Dhawan S. Takikawa D. Margouleff and D. Eidelberg Appl. Radiat. Isotopes 1994 45 25. D. Yushin J. S. Fowler and A. P. Wolf J. Labelled Compd. Radiopharm. 1993 33 645. R. Rengan P. K. Chakraborty and M. R. Kilbourn ibid. 1993 33 563. R. Gail and H. H. Coenen Appl. Radiat. Isotopes 1994 45 105. W. R. Banks R. D. Borchert and H. Dahren ibid. 1994 45 75. 13' (a)L.Zheng and M. S. Berridge J.Labelled Compd. Radiopharm. 1993,32,296;(b)B. M. Kinsey and T. J. Tewson ibid. 1993 32 300. 133 (a)A. Majafi A. Peterson and C. A. Irvine Nuclear Med. Biol. 1993,20,401; (b)A. Najafi A. Peterson M. Buchsbaum S. O'Dell and F. Weihmuller ibid. 1993 20 549 Radiochemistry 507 ['8F]fluorocarboxylic acids' 34 which can be used in the production of complex radiopharmaceuticals. A new method has been described'35 for making ["F] fluoromethane which avoids the use of volatile iodomethane. The demetallation step is effected by the use of microwave radiation. Indeed microwaves have proved very popular of late in fluorine labelling procedures as in the preparation of ["F] fluoroderivatives of aporphine tetrali~~,'~~ morphine,'37 and 2[' 8F]fluorodeoxy-glucose.'38 Elements of Modest Mass.-Methods have been described for the preparation of 32P labelled phosphocholines' 39 and a range of 35Slabelled insecticide^'^^ (e.g.fenthion).Both 45Ti and 47Sc'4' have nuclear properties that make them attractive as chemotherapeutic agents and starting materials for future syntheses have been made at least for titanium,'42 e.g. labelled titatnium tetrachloride and butotitane. Anti- bodies,'43 and a-fet~protein'~~ have been labelled with 64Cuand 65Zn respectively. In these cases it would seem to be a matter of hope and faith that the 'labelled' protein is not altered by the labelling process. Rather more clearly defined is the situation in gallium (67Ga) labelled p~lyaminothiols'~~ where the gallium is nested within a polydentate ligand.An extension of this idea has been used in the synthesis'46 of 67Ga-defroxamine-dioxin. The incorporation of 77Br into p-bromospiroperidol has been re~0rted.l~~ 90Y is a pure /?-emitter and can be used both diagnostically and therapeutically. Methods for the 'direct' labelling of monoclonal antibodies with this isotope' 48,149 and also the development of polydentate ligands which can encapsulate 90Y and then be linked to such antibodies"* have been reported. Technetium (99"'Tc).-Technetium is probably the most popular isotope for radiopharmaceutical use at the present time. This popularity is partially due to the ease with which technetium can be incorporated into a very wide range of compounds by standard chemical methods.Recent progress was covered by a conference 'Topical Symposium on the Behaviour and Utilization of Technetium'.' 51 For the most part technetium is generated by the decay of 99Moin the form of the pertechnate(vI1) anion. This is then reduced (stannous chloride is widely used) and the lower valency 134 (a) S. Guhike H.H. Coenen and G. Stoecklin J. Labelled Compd. Radiopharm. 1993 32 108; (b) S. Guhike H. H. Coenen and G. Stoecklin Appl. Radiat. Isotopes 1994 45 715. 135 W.R. Banks M. R. Satter and H. Dahren ibid 1994 45 69. 136 S. Zijlstra T. J. de Groot L. P. Kok G. M. Visser and W. Vaalburg J. Org. Chem. 1993 58 1643. 13' S. Zijlstra T.J. de Groot G. M. Visser and W. Vaalburg J. Labelled Compd. Radiopharm. 1993,32,267. 13' R.Chirakal L. Girard G. Fimau and E. S. Garnett ibid. 1993 32 123. 139 H. P. Deigner and B. Fymys ibid. 1994 34 185. 14' M. Dias and R. Mornet ibid. 1994 34 73. 14' L. F. Mausner K.L. Kolsky R.C. Mease M. Chinol G. E. Meinken R. F. Straub S.C. Srivastava L. Pietrelli and Z. Steplewski ibid. 1993 32 388. 142 F. Oberdorfer B.K. Keppler Y. Zhou F. Helus and W. Maier-Borst ibid. 1993 32 441. 143 C. J. Anderson S. W. Schwarz P. A. Rocque M. J. Welch J. M. Connett L. W. Guo G. W. Philpott K. R. Zinn and C. F. Meares ibid. 1993 32 368. 144 I. L. Preiss Abstract NUCL22 Ref. 83 p. 1035. 14' C.S. John G. Minear R.K. Keast S. Kinuya and C.H. Paik Nuclear Med. Biol. 1993 20 217. Y. Fujibayashi Y. Takemura H. Taniuchi J. Konishi and A. Yokoyama J. Labelled Compd.Radiopharm. 1993 32 420. 14' Y. Huang and Y. Li Nuclear Techn. 1994,17 233. 14* J. Zhang Q. Lin X. Jin and J. Tian Chin. J. Nuclear Med. 1993 13 173. 149 2.Yang X. Jin H. Yu S. Bai S. Jiang Z. Mong L. Yang X. Wei and A. Tian J. Isotopes 1992,5 72. (a)J. K. Moran M. Li and C. F. Meares Abstract NUCL87 Ref. 83 p. 1051;(b)Y. Li C. Guang C. Ma and L. Jing J. Isotopes 1994 7 21. 51 Conference Report 'Topical Symposium on the behaviour and utilisation of technetium' Sendai Japan 1993 Radiochimica Acta 1993 63. 508 David S. Urch techentium incorporated into many complexes. Sulfur is adept at forming strong bonds to technetium and many new complexes with Tc-S bonds have been reported e.g. thioether~"~ and ~ysteine.''~ A range of mercapto-mono -di and -tri glycine complexes of pentavalent technetium has also been ~repared.'~~-l These com- 56 pounds can be used as renal imaging agents.Related complexes have also been prepared in which the techentium was complexed by nitrogen as well as sulfur'57 (using ligands such as N,N'-bis(mercaptoacetamido)ethylenediamine). The combination of sulfur and nitrogen has also been used'58 to prepare complexes of (TcO;) with 1,6-di(2-thienyl)-2,5-diazahexane, and similar ligands complexes which can be used as myocardium radiotracers. Radiopharmaceutical uses have also been found for TcV complexes of 2,3 dimercaptosuccinic acid.' 59 Further complexes of TcV have been prepared with fi-diketonate groups,16o amino acids,161 or ethylene diamine deriva- tives162 and in which the technetium is also triply bound to nitrogen.'63 Other ligands that have been used to prepare technetium radiopharmaceuticals have included hydroxamide,' 64 phosphine derivatives' 65 and phosphorus hydrazide.'66 When attempts are made to label various monoclonal antibodie~'~~ the bonding to the technetium is usually assumed to go via sulfur and nitrogen sites,168 although whether labelling always proceeds without perturbing the biological activity has been questioned. 169 Iodine (1231,1251,and 13'I).-The simplest method for labelling with radioactive iodine is by halogen exchange as in the preparation of 5[1231]iodonicotinamide'70 from the H.J. Pietzsch S. Seifert R. Syhre and H. Spies 'Ann. Report 92' ed. B. Johannsen Institute of Bioinorganic and Radiopharmaceutical Chemistry Research Centre Rossendorf Dresden Germany 1993 p.82. lS3 S. Mukherjee C. Sengupta J. Chatterjee P. Dobe and S. Banerjee Nuclear Med. Biol. 1993 20 413. 154 B. Johannsen B. Noll P. Leibnitz G. Reck S. Noll and H. Spies Radiochim. Acta 1993 63 133. 155 (a)J. Koemyei J. Toerkoe and J. Volford J.Radioanal. Nuclear Chem. 1994,186,189; (6)J. Koemyei J. Toerkoe J. Volford and F. Sztaricskai Magyar Kemiai Folyoirat 1994 100 189. G. Bormans B. Cleynhens P. Adriaens A. Verbruggen and M. de Roo J.Labelled Compd. Radiopharm.. 1993,33 1065. 15' S. Luo Z. Liu C. Zhang P. Zhao and Y. Fu J. Isotopes 1993 6 7. lSRN.C. Goomer P. V. Kulkarni A. Constantinescu P. Antich R. W. Parkey and J. R. Corbett Nuclear Med. Biol. 1994 21 657.IS9 (a)L. Lindemann C.Schuettler C. Neumann R. Michael S. Seifert and B. Johannsen Ref. 152 p. 41; (6) B. Noll H. J. Pietzsch H. Spies L. Dinkelborg B. Johannsen and W. Semmler Ref. 152 p. 100; (c) T. Hirano K. Tomiyoshi Y. Zhang T. Ishida T. Inoue and K. Endo Eur. J. Nuclear Med. 1994,21 82. 160 (a)A. Mutalib T. Sekine T. Omori and K. Yoshihara Ref. 151 p. 117; (6) A. Mutalib T. Sekine T. Omori and K. Yoshihara Ref. 151 p. 123; (c) A. Mutalib T. Sekine T. Omori and K. Yoshihara J. Radioanal. Nuclear Chem. 1994 178 311. A. Marchi R. Rossi L. Marvelli and V. Bertolasi Inorg. Chem. 1993 32 4673. T. Takayama T. Sekine and K. Yoshihara J. Radioanal. Nuclear Chem. 1993 176 325. V. Comazzi E. Bellande R. Pasqualini L. Ucelli A. Duatti and A. Marchi J.Labelled Compd. Radiopharm. 1993 32 10. 164 M. Nakayama H. Saigo and A. Koda Appl. Radiat. Isotopes 1994 45 735. ''' E. Deutsch Ref. 151 p. 195. 166 W.A. Volkert P.R. Singh K. K. Katti A. R. Ketring and K. V. Katti J. Labelled Compd. Radiopharm. 1993 32 15. 167 (a)T. Qu Y. Wu X. Wang Y. Liu Y. Ye and C. Wu Ref. 151 p. 209; (b)S.C. Archimandritis E. Belkas A. D. Varvarigou K. Cotsyfakis J. Malamitsi C. Proukakis G. Sivolapenko J.Zorzos and D. V. Skarlos. J. Labelled Compd. Radiopharm. 1994 34 323; (c) S. W. Schwarz C. J. Anderson P. A. Rocque M. J. Welch J. M. Connett G.W. Philpott and W. G. Li Nuclear Med. Biol. 1994,21,619; (d)G. L. Griffiths A. L. Jones H. J. Hansen and D. M. Goldenberg ibid. 1994 21 649. 16' M. Nakayama T. Terahara and R. Ikeda Appl.Radiat. Isotopes 1994 45 41. 169 E. John S. Wilder and M. L. Thakur Nuclear Med. Commun. 1994 15 24. 170 K. A. Bergstroem J. T. Kuikka H. Mussalo E. Laensimies S. Loetjoenen P. Penttilae and J. Hiltunen J. Labelled Compd. Radiopharm. 1993 33 593. Radiochemistry 509 corresponding bromo-compound. When this procedure was used to make o-[' 311] iodohippuric acid,I7' m-[' 'I]iodobenzylguanidine,' 72 and [1251]iodomazindol' 73 copper(1) was used as a catalyst in the presence of suitable reducing agents. Other procedures require the presence of an oxidizing agent such as 'iodo-gen' chloramine-T hydrogen peroxide or peracetic acid. In the case of recent reports for the preparation of 2['231]iodomelatonin'74 and [1251 311]iodotyrosine derivative^'^^ the relative merits of different oxidants have been evaluated.When chloramine-T is used labelled iodate ions can be formed.'76 This problem is presumably avoided when nitric acid is used as in the recently reported'77 preparation of 5-iodo-2'-deoxyuridine. The radio-iodine label can be directed to a specific site in a molecule by arranging for it to displace an organotin group (usually tributylstannyl) e.g. labelled iodo-caramiphen,' 78 aziridinyl 4-iodotamo~ifen'~~ and monoclonal antibodies' 8o via N-sucinimidyl4-methyl-3-(tri-n-butylstannyl) benzoate. This reaction is performed in the presence of an oxidizing agent chloramine-T for 1231and '251 iodouracils18' and ( -)-5-iodobenzovesamicol,' 82 iodo-gen for ['23T]iomazenil,183 peracetic acid for ['23]iododopamines'84 and hydrogen peroxide for 17a-[(E)-2-[ '251]iodoethenyl] androsta-4-6-dien- 17B-ol-3-one.' 85 This type of reaction has also been used to make labelled 2-iodo-4-(3-trifluoromethyl-3H-diazirin-3-yl)benyzlesters' 86 compounds which on photolysis generate carbenes.These carbenes insert into C-H bonds (in phospholipids for example) and bring the radioiodine with them. Rare Earth Elements.-Complexes of substituted nitrogen crown ethers with 153Gd,187153Sm and 166Ho'88 have been prepared and evaluated for their radiopharmaceutical potential. Rhenium (Ig6Re and lS8Re).-Since rhenium is very similar to technetium in its chemistry many of the techniques being used to produce rhenium-containing radiopharmaceuticals are the same as those used for technetium.Thus disulfide bridges in proteins and antibodies can be reduced to thi01s'~~ which can then bond to rhenium. Radioactive rhenium is most easily made as the per-rhenate anion and this is reduced with reagents such as stannous ~hloride"~ (see above for Tc). Lower valency ''I M. T. Al-Kolaly S. El-Bayoumy M. Raieh and A. El-Mothy J. Radioanal. Nuclear Chem. 1993,174,3. '12 J. Zhu W. Yao and J. Ma Nuclear Techn. 1993 16 695. E. Galinier J. E. Ombetta Y. Frangin J. C. Besnard D. D. Guilloteau and J. Mertens J. Labelled Compd. Radiopharm. 1994 34 487. D. du T. Rossouw and J.H. Langenhoven Appl. Radiat. Isotopes 1994 45 902. "'S. Li Y. Liu X. Lin S. Deng M. Li T. Zhu and G. Zhong Nuclear Techn. 1993 16 669. M. Szabo and G. Toth J.Radioanal. Nuclear Chem. 1993 176 169. "' M. A. Trivedi J. Labelled Compd. Radiopharm. 1993 33 607. '" D. W. McPherson F.F. Knapp Jr. and R. L. Hudkins ibid. 1994 34 239. 179 R. McCague and G. A. Potter 1994 ibid. 1994 34 291. P. K. Garg S. Garg and M. R. Zalutsky Nuclear Med. Bio. 1993 20 379. la' H. Dougan B. A. Rennie D. M. Lyster and S. L. Sacks Appl. Radiat. Isotopes 1994 45 795. ln2 M. E. Van Dort Y.-W. Jung D. L. Gildersleeve C. A. Hagen D. E. Kuhl and D. M. Wieland. Nuclear Med. Biol. 1993 20 929. Y. Zea-Ponce R. M. Baldwin S. S. Zoghbi and R. B. Innis Appl. Radiat. Isotopes 1994 45 63. H. Xiaoshu B. R. de Costa L. Kansam and D. Weinberger J. Labelled Compd. Rudiopharm. 1993 33 493. P. J. Diaz Cruz H. E. Smith B. J. Danzo J. A. Clanton and N.S. Mason ihid. 1993 33 853. 186 T. Weber Thesis Eidgenoessische Technische Hochschule Zurich Switzerland. 1994. IR7 K. Kumar K. Sukumaran C. A. Chang M. F. Tweedle and W.C. Eckelman J. Labelled Compd. Radiopharm. 1993 33 473. K. McMillan and T. Masterson Abstract TECH9 Ref. 83 p. 420. M.A. Majali Ref. 29(a) p. 298. "') M. A. Majali J. Radioanal. Nuclear Chem. 1993 170 471. 510 David S. Urch rhenium as oxorhenium(v) can form a series of complexes with thio1s''l and thio-acids.' 92 Heavy Elements.-An improved method for the preparation of trans-diamminedi-chloro[' 95"Pt]platinum(~~) A rather different type of 'labelling' has been rep~rted."~ has been described'94 for the incorporation of 212Pb into tobacco smoke aerosols. This should enable smoke clearance from the lungs to be monitored and human volunteers are being called for.Astatine ['"At] despite its short half-life can be used to label monoclonal antib~dies'~~,'~~ and can be directed to a specific site by replacement of an organotin group (see iodine above) N-succinimidyl-p[21 'At] astatobenzoate. 197 Automation in Labelling.-The short half-lives of the isotopes used in positron emission tomography for nuclear medicine have lead to a rapid growth in automated procedures' 98 for the incorporation of these isotopes into suitable compounds. A wide range of such techniques for the preparation and purification of labelled compounds is given in 'New trends in radiopharmaceutical synthesis quality assurance and regulatory control'.' '' More specific details for particular processes have been described for the use of ["C]methyl iodide in methylation2" and in the preparation of [I 'C]diprenorphine.'08~201Other 'robotic syntheses' have been used to prepare 6-[ '8F]fl~orodopa202 and 2-deoxy-2[18F]fluoro-~-glucose.203 Quality Control.-Whilst it is one thing to make (or have robots make) labelled compounds it is quite another to ensure that they are chemically pure radiochemi- cally pure and if for use as radiopharmaceuticals are free of traces of toxic impurities.Furthermore it is important to be able to establish the radiochemical integrity of a labelled compound after it has been stored for some time (the critical period could be minutes or months depending on the isotope). These topics are dealt with in some detail in reference 199 whilst specific aspects of quality control of radiopharmaceuticals in Japan204 and Germany205 have been discussed recently.A detailed study of auto-decomposition in [35S]-labelled amino acids has shown206 that 19' H. Spies T. Fietz and H. J. Pietzsch Ref. 152 p. 94. 192 H. Spies T. Fietz H. J. Pietzsch and D. Scheller Ref. 152 p. 103. 193 K. Kawai H. Maki Y. Nakano M. Akaboshi and W. Ehrlich Annual Reports Research Reactor Institute Kyoto University Japan 1992 25 78. 194 J. C. Strong D. A. Knight and A. Black Journal of Aerosol Science 1994 25 199. 19' D. S. Wilbur R. L. Vessella J. E. Stray D. K. Goffe K. A. Blouke and R. W. Atcher Nuclear Med. Bid.. 1993 20 917. 19' J. Jin S. Zhang M. Zhou and N.Liu J. Isotopes 1992 5 65. 19' R.H. Larsen S. P. Hassijell P. Hoff J. Alstad E. Olsen I.B. Vergote L.N. De Vos K. Nustad and J. Bjoergum J. Labelled Compd. Radiopharm. 1993 33 977. 19' G. Appleqvist C. Bohm H. Eriksson and S. Stone-Elander ibid. 1993 32 184. 199 'New trends in radiopharmaceutical synthesis quality assurance and regulatory control' ed. A. M. Emran. Plenum Press New York NY. USA 1991. 2oo R. Iwata C. Pascali M. Yuasa K. Yanai T. Takahashi and T. Ido J.Labelled Compd. Radiopharm. 1993. 32 148. S.K. Luthra S. Osman D.R. Turton V. Vaja K. Dowsett and F. Brady ibid. 1993 32 518. 202 G. Reddy M. Haeberle H.-F. Beer and A. Schubiger ibid. 1993 32 248. '03 (a)S. Dietrich-Wolber H. Knigge W. J. Obers F. Oberdorfer and W. Maier-Borst ibid. 1993,32 144; (b) M.Yu Kiselev D. V. Solov'ev and M. V. Korsakov Radiochemistry (New York) 1992,34,256 (Russian original Radiokhimiya 1992 34(2) 129). 204 'The 14th quality control survey for radioisotope in vitro tests in Japan 1992' Radioisotopes (Tokyo) 1993 42 1. 205 C. Decristoforo F. Chen and G. Riccabona Nukleamedizin 1993 32 144. 206 T. Kato K. Saito and N. Kurihara Appl. Radiat. Isotopes 1994 45 693. Radiochemistry 511 the pattern of labelled products formed is more closely mimicked by electron bombardment than by y-irradiation. Labelled iodine compounds are particularly sensitive to self-induced decomposition usually leading to free radioactive iodide anion as the main impurity (e.g. m-[l3']-iodobenzylg~anidine~~~). Other aspects of quality control concentrate mainly on the detection of trace impurities of other isotopes as in the case of 67Ga (65Zn and 68Ga)208 or 201T1 (200T1 202T1 and 203Hg),209or of chemical contaminants such as tin (Sn" or SnIV) in technetium preparations.21O 5 Environment The environmental aspects of the use of radiochemicals in power generation,21' in hospitals and in research are the subject of ever increasing attention (and about time too!).It is of course not all man made. Radon has been with us for some time so that an up-to-date bibliography212 will be quite useful. Technetium on the other hand has as you might say been resurrected recently and all aspects of its use and environmental impact have been reviewed.213 The greatest concern is however associated with the nuclear industry and its waste products.The European Community has undertaken large-scale research projects on specific aspects of the problem such as the ways in which radio-colloids would be carried by gr~undwater~'~ and the complexes that the various actinide ions might form with 'humic acid'.215 Specific aspects of the latter problem have also been reported for curium americium,2 l6 and neptunium2 ' as well as for actinide ions in general.218 The ways in which radioactive isotopes (usually fission products) might interact with different soil types and minerals219 has been the subject of many investigations. How for example might "Sr l'omAg,or 134Cs be incorporated220 into plants grown in the Mediterranean region in sandy-loam soils? Similarly the sorption of radioiodine by clays 'rich-soil' and alumina,221 the adsorption of radium by a range of minerals,222 the adsorption of lead and bismuth '07 (a) A.R. Wafelman J.H. Baijnen C.A. Hoefnagel and R.A. A. Maes ibid. 1994 45 183; (b) A. R. Wafelman R. Suchi C. A. Heofnagel and J. H. Beijnen Eur. J. Nuclear Med. 1993 20 614. P. Szentgyoergyi F. Rakias and E. Bodor Itd. Izotoptechnika Diagnosztika 1992 35 103. 209 L. Fernandes and C. P.G. da Silva J. Radioanal. Nuclear Chem. 1993,172 313. 'lo M. A.T. M. de Almeida and C. P. G. da Silva ibid. 1993 176 225. 'I1 Z. Yoshida and S. Kihara Denki Kagaku Oyobi Kogyo Butsuri Kagaku 1994 62 8. 212 E. Bujdoso J. Radioanal. Nuclear Chem. 1993 171 501. '13 K.H. Lieser Radiochim. Acta 1993 63 5.214 J. I. Kim B. Delakowitz P. Zeh,T. Probst X. Lin U. Ehrlicher,C. Schauer M. Ivanovich G. Longworth S. E. Hasler M. Gardiner P. Fritz D. Klotz D. Lazik M. Wolf S. Geyer J. L. Alexander D. Read and J. B. Thomas 'Colloid migration in groundwaters Geochemical interactions of radionuclides with natural colloids' Progress Reports Comm. Europ. Comm. Bruxelles Belgium and Tech. Univ. Muenchen Garching Germany 1993-94. J.I. Kim G. Buckau R. Klenze D. S. Rhee H. Wimmer P. Decambox P. Mauchien C. Moulin V. Moulin J. Tits C. Marquardt J. Riegel P. Sattelberger G. Herrmann N. Trautmann A. Diercks J. Vancluysen A. Maes G. Bidoglio and L. Righetto 'Effect of humic substances on the migration of radionuclides Complexation of actinides with humic substances' Progress Reports Comm.Europ. Comm. Bruxelles Belgium and Tech. Univ. Muenchen Garching Germany 1992 and 1993. 'I6 J.I. Kim D. S. Rhee H. Wimmer G. Buckau and R. Klenze Rudiochim. Acta 1993 62 35. '17 S.K. Jha and I.S. Bhat Ref. 29(a) p. 446. 218 E. Tipping Radiochim. Acta 1993 62 141. 219 S. Ahmed A. Mannan F. Naheed M. Daud and I.H. Qureshi in 'Modern Trends in Contemporary Chemistry' ed. H. Javed H. Pervez and R. Qadeer Pakistan Atomic Energy Commission Islamabad Pakistan 1993 89. 220 M. Vidal and G. Rauret J. Radioanal. Nuclear Chem. 1994 181 85. 221 S. Assemi and H.N. Erten ibid. 1994 178 193. 222 R. S. Wang F. Liu H. Cheng P. Nar A.S.Y. Chau X. M. Chen and Q.Y. Wu ibid. 1993 171 347. 512 David S. Urch isotopes223 and uranyl cations224 by montmorillonite and of 6oCo and 134Cs by shales,225 have all been investigated recently.The council of perfection would of course be that radioactive isotopes fission or actinide did not enter the environment at all and so another important line of research is to investigate the ways in which such isotopes can be taken from solution at source. Many impurities can be removed by crown ethers (alkali and alkaline earth ions,226 stronti~m~~~-~~’ ,and also lanthanides and actinides229) or by triphenylphosphine oxide.230 Other techniques have concentrated on the use of heterogeneous adsorption by alumina,231 by iron hydroxide (uranium,232 60C0233) or by manganese diox- ide(133Ba and 210Pb).234 Silica gel coated with ‘Versatic-10’ is reported235 to extract Uvl quantitatively from solution.51Cr and 125Sb can be removed from the liquid wastes from a pressurized water reactor by membranes impregnated with titania and zirconium phosphate.236 The use of polyamine ion exchange resins has been advocated237for the chelation of specific isotopes e.y. IB5W,99M0 and 125Sb7 by suitable modification conditions for the preferential extraction of individual elements. Some radioactive impurities are gaseous and in the case of tritium special alloys have been developed238 to adsorb it. Rather more of a problem is when tritium becomes adsorbed not as part of some recovery-purification programme but on building materials239 such as concrete. The final environmental problem (in many senses of the word) is the ‘disposal’ i.e. containment of long-lived nuclear waste.Glass is widely favoured as a possible encapsulant but for how long240 and what of changes in local pH?241 Groundwater circulating near such glasses (at 9OOC) might well become contaminated with radio-c~lloids~~~ and if the solutions are rich in salt further complications can 223 H.J. Ulrich and C. Degueldre Radiochim. Acta 1993 62 81. 224 R. A. Matzner J. M. Berg C. J. Chisholm-Brause and D. E. Morris Abstract ENVR229 Ref. 83 p. 586. 225 H.A. Einaggar M.K. Shehata M.F. Abdelsabour and M.R. Ezzeldin in ‘Proc. 5th Conference on Nuclear Sciences and Applications’ The Egyptian Society of Nuclear Sciences and Applications Cairo Egypt 1992 2 999. 226 V.V. Yakshin and O.M. Vilkova Radiochemistry (New York) 1993 35 58 (Russian original Radiokhimiya 1993 35(1) 80).227 F.A. Shehata S. H. Khalifa and H. F. Aly Ref. 225 3 389. 228 L. He X. Wong D. Yang R. Jiao and C. Song Report 00744 China Nuclear Information Centre Beijing China 1993. 229 R. Shu H. Zhao J. Hu and H. Huang Atomic Energy Sci. Techn. 1993 27 242. 230 Y. Zhu J. Tsinghua University. Sci. Techn. 1992 32 1. 231 G. Bernhard J. Radioanal. Nuclear Chem. 1994 177 321. 232 Y. Ye G. Marx and Ch. Keiling J. Nuclear Radiochem. 1993 15 134. 233 M.M. Bhutani K. Ramesh and S. Agarwal Ref. 29(a) p. 305. 234 D. Tait G. Haase and A. Wiechen J. Radioanal. Nuclear Chem. 1994 186. 235 U.S. Ray and K. Mitra Ref. 29(a) p. 294. 236 E.W. Hooper and P. Kavanagh Proc. Int. Conference. ‘Water Chemistry of Nuclear Reactors’ British Nuclear Energy Society London UK 1992 p.228. 237 S. C. Gupta B.B. Tak N. K. Mathur and C.K. Narang J. Radioanal. Nuclear Chem. 1993 170 3. ”’ M. Kitamura and S. Yamashita Japan Patent 5-341096/A. 1993. 239 (a)R. S. Dickson and J. M. Miller Report G91114 Canadian Fusion Fuels Technology Project Atomic Energy of Canada Ltd. Chalk River Ont. Canada 1991; (b)J. M. Miller J. A. Senohrabek and P. A. Allsop Report (39198 Canadian Fusion Fuels Technology Project Atomic Energy of Canada Ltd. Chalk River Ont. Canada 1992. 24” W. L. Ebert J. K. Bates C. R. Bradley E. C. Buck N. L. Dietz and N. R. Brown ‘Ceramic Transactions Environmental and Waste Management Issues in the Ceramic Industry’ ed. G. B. Mellinger American Ceramic Society 1994 39 333. 241 D. Oksoy L.D. Pye D. F. Bickford and W.G. Ramsey ibid. p. 365. 242 X. Feng E.C. Buck C. Mertz J. K. Bates J. C. Cunnane and D. Chaiko Report CP-78677 Argonne National Lab. Illinois USA 1993. Radiochemistry arise243 (for uranium244 and plutonium245). 6 Miscellaneous Standards.-The development of standard uranium samples for use with the isotope dilution method has been reported246 as well as the preparation of 45Ca for liquid scintillation counting. Tritium.-The thermodynamic properties of ditritium i.e. pressure-volume relation- ships as a function of temperature have been as have the diffusion coefficients for 3H.’H (and 2H2 and 1H2)249 in various zeolites. It has been found250 that the UV-induced oxidation of gaseous ditritium is enhanced by the presence of carbon tetrachloride.Some new patents have indicated how tritium may be incorporated into aerogels2’ ’ and into solid radioluminescent light so~rces.~ 52 Various.-‘Technegas’ has been shown2 53 to contain fullerene (C,,) type molecules harbouring a 99mTc atom within the cage. Thin films of ’7C0 and 59C0 can be laid on stainless steel foils electrochemically. The technique of thermochromatog- raphy when applied to volatile hexafluororacetylacetonates allows25’ an efficient separation of the elements present in ‘natural’ uranium. Dating.-The problems associated with the dating of aquifiers by 14C2’6 or for older structures by 36Cl or 4He (from uranium decay) have been critically examined257 and an improved method for the dating ofgypsum and anhydrite has been reported.258 The role played by technetium in natural nuclear reactors such as that at Okl~,~’~ and in estimating the age of the solar system has been described.260 243 Yu.M.Rogozin E.A. Smirnova V.G. Savonenkov A.S. Krivokhatskii V.A. Avdeev and E.Yu. Sagaidachenko Radiochemistry (New York) 1993 35 124 (Russian original Radiokhimiya 1993 35(1) 166). 244 P. M. Heppner Report BMFT 02U5998 Freie Univ. Berlin Germany 1992. 24s I. Pashalidis and J. I. Kim Report BMFT 02U5958 Technische Univ. Miinchen Garching Germany 1992. 246 (a) M. V. Ryzhinskij M. Yu. Vitinskij and A. V. Lovtsyus Radiokhimiya 1993 35(5) 104; (b)M. Yu. Vitinskij M. V. Ryzhinskij A. V. Lovtsyus and L. F. Solntseva ibid. 1993 35 112. 247 L. Rodriguez Barquero J.M.Los Arcos Merino and A. Malonda Grau Report 719 Centro de lnvestigaciones Energeticas Medioambientales y Tecnologicas Madrid Spain 1994. 248 E. R. Grilly J. Res. National Institute Standards Techn. 1993 98 679. 249 A. S. Polevoi Radiochemistry (New York) 1994 35(5) 609 (Russian original Radiokhimiya 1994 35(5) 138). 250 K. Hasegawa H. Fusumae S. Miyahara and M. Shinohara Toyama Daigaku Suiso Doitai Kino Kenkyu Senta Kenkyu Hokoku 1993 12 85. 251 G. A. Jensen D. A. Nelson and P. M. Molton US. Patent 5,100968/A Patent and Trademark Office Washington USA 1992. 252 C. S. Ashley C. J. Brinker S. Reed and R. J. Walko US. Patent 5,240,647/A Patent and Trademark Office Washington USA 1993. 2s3 D. W. J. Mackey W. M. Burch I. G Dance K. J. Fisher and G.D. Willett Nuclear Med. Commun. 1994 15(6) 430. 254 R. Gonzalez-Rimirez H. Jimenez-Dominiquez E. Ordonez-Regil A. Cabral-Prieto and S. Bulbulian J. Radioanal. Nuclear Chem. 1993 174 291. 255 E. V. Fedoseev S. S. Travnikov P. A. Korovaikov A. V. Davydov and B. F. Myasoedov Radiokhirniya 1993 35(5) 57. 2s6 P.K. Bishop P.C. Smalley D. Emery and J.A.D. Dickson J. Hydrology 1994 154 301. 257 E. Mazor ibid. 1994 154 409. 258 J. A. Fitzpatrick and J. L. Bischoff Radiochim. Acta 1994 64 75. 259 H. Hidaka K. Shinotsuka and P. Holliger ibid. 1993 63 19. P. K. Kuroda ibid. 1993 63 9.

ISSN:0260-1818    

DOI:10.1039/IC9949100499

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

27 Inorganic Mechanisms By N. WINTERTON lCl Chemicals & Polymers Ltd Runcorn Technical Centre The Heath Runcorn Cheshire WA7 4QD UK 1 Introduction The unravelling of the factors controlling the mechanisms of inorganic and or- ganometallic redox and substitution reactions in solution is important environment- ally biologically and industrially as well as intrinsically. The relevant literature for 1994 subject to the exclusions noted in the 1993 Report is organized as before except that organometallic redox reactions are now discussed in Section 4. Meagher and Rorabacher have developed a mathematical treatment for data from stopped flow spectrophotometry which may permit' the determination of second order rate constants as large as lo8M-'s-'. Alibrandi has described variable concentra- tion and non-isothermal3 methods for the acquisition of kinetic data.Kinetic equations for isotopic exchange allowing for the operation of an isotope effect have been rep~rted.~ 2 Redox Reactions Texts have appeared by Lappin' on mechanistic inorganic redox chemistry and by Scott6 on chaos waves and oscillations in chemical kinetics. Oxidation reactions of Mn(m) complexes7 and redox chemistry of Cr(1v)' have been surveyed. Long-range Electron Transfer.-The variations in rates of electron transfer with n in + [(bipy),Ru"'(CH,),Ru"(decbipy),] ,' C{Tr(CO)(P-Pz*)L),I [L = {PPh, OC6H4(CH2),py+)] (exponential dependence," except for n = l) and [Ru"(bipy) { 4-Me-bipy-4'-(CH2),(4,4'-bipy-4'-Me)l4 + (exponential dependence' N.E. Meagher and D. B. Rorabacher J. Phys. Chem. 1994 98 12 590. G. Alibrandi J. Chem. SOC. Chem. Commun. 1994 2109. G. Alibrandi Inorg. Chim. Acta 1994 221 31. S.R. Logan and G.P. Shannon React. Kinet. Catal. Lett. 1994 53 123. A.G. Lappin 'Redox Mechanisms in Inorganic Chemistry' Ellis Horwood New York 1994. S. K. Scott 'Oscillations Waves and Chaos in Chemical Kinetics' Oxford University Press Oxford 1994. ' S. Gangopadhyay M. Ali and P. Banerjee Coord. Chem. Rev. 1994 135/136 399. ' E.S. Gould Coord. Chem. Rev. 1994 135/136 651. K. Nozaki and T. Ohno Coord. Chem. Rev. 1994 132 215. lo R.S. Farid I.-J. Chang J.R. Winkler and H.B. Gray J. Phys. Chem. 1994 98 5176. E. H. Yonemoto G. B. Saupe R. H. Schmehl,S. M. Hubig R. L. Riley B.L. Iverson and T. E. Mallouk J. Am. Chem. SOC. 1994 116,4786. 515 516 N. Winterton for n = 1-5; similar for n = 5,7,8) are consistent with through-bond electron transfer for short chains and through-solvent pathways for longer chains. The effect of encapsulation by P-cyclodextrin was also studied.' Electron transfer between ferricytochrome c and a Mn(i1bporphyrin complex (tethered to a series of amphiphilic Zn porphyrins) embedded within a phospholipid bilayer is independent l2 of tether length suggesting that the tether is not the main electron-transfer pathway. A medium-mediated process is preferred. Competition between through-a-bond/through-space and through-a-bondlthrough-n-bond electron transfer between a donor-acceptor pair separated by a permethylated oligosilane has been explored.The effect of the structure and conformation of the peptide spacer in [(bipy),LRu" (spacer)R~"~L'(NH~),]~ + suggests14 that the shortest through-space distance is not always the most important determinant of the rate of electron transfer. A 1000-fold difference is seen" in the rate of intramolecular electron transfer between the haem Fe(i1) of cytochrome c and trans-[Ru"'(NH,),(isn)] incorporated at His-33 and [Fe"'(CN),] incorporated at Met-65. The donor-acceptor distance and other relevant factors are similar also suggesting' 'that the through-space distance between donor and acceptor is not the dominant factor even when reorganization energy and driving force factors are taken into account.Rate constants for intramolecular Fe(II) to RU(III) electron transfer in His-56- His-5 1- and His-42[Ru(NH3),]-modified cytochrome b suggestl6 that for the His-42 derivative a direct through-bond pathway dominates ivhereas for His-56 and His-5 1 modifications through-space pathways are important. The effects of [NaCl] and binding to cytochrome c on the rates of intramolecular electron transfer in a cytochrome b variant modified at Cys-65 with three different Ru(II kpolypyridine complexes have been associated' with solvent reorganization. Preliminary reports have appeared on intramolecular electron transfer between Fe(II) and RU(III)complex centres at Lys-86 and Lys-87 of cytochrome c18 and between Fe"=O and RU(II)bound to His-48 of horse heart myoglobin." Volume profile analysis reported for the first time for reversible intermolecular electron transfer,20'21 involving [RU(NH~),(~S~)]~+'~ and + or [C~(terpy)~]~+'~+ Fe(IrI/II) horse-heart cytochrome c suggests in both cases that the transition state lies equidistant between the reactant and product states on a volume basis.pH effects on the rate constants for the oxidation of the blue copper(1) protein pseudoazurin from Achromabacter cyclolastes by [Co(dipic),] -and [Co(phen),13+ point to active site protonation.22 The electron self-exchange rate constant for pseudoazurin has been l2 J.T. Groves G. D. Fate and J. Lahiri J. Am. Chem. Soc. 1994 116 5477. l3 F. C. De Schryver D. Declercq S. Depaemelaere E. Hermans A. Onkelinx J. W. Verhoeven and J.Gelan J. Photochem. Photobiol. A Chem. 1994 82 171. l4 S.S. Isied I. Moreira M. Y. Ogawa A. Vassilian B. Arbo and J. Sun J. Photochem. Photobiol. A Chem.. 1994 82 203. I. Moreira J. Sun M. 0.-K. Cho J. F. Wishart and S. S. Isied J. Am. Chem. Soc. 1994 116 8396. l6 E. Lloyd K. Chapman S.K. Chapman Z.-S.Jia M.-C. Lim N. P. Tomkinson G. .A. Salmon and A. G. Sykes J. Chem. Soc. Dalton Trans. 1994 675. J. R. Scott M. McLean S.G. Sligar B. Durham and F. Millett J. Am. Chem. Soc. 1994 116 7356. '*D. H. Heacock IT M. R. Harris B. Durham and F. Millett Inorg. Chim. Actu 1994 226 129. l9 C. Fenwick S. Marmor K. Govindaraju A. M. English J. F. Wishart and J. Sun J. Am. Chem. SOC. 1994 116 3169. *" B. Bansch M. Meier P. Martinez R. van Eldik C. Su J. Sun S.S. Isied and J.F. Wishart Inorg. Chem. 1994 33 4144. M. Meier and R. van Eldik Inorg. Chim. Acta 1994 225 95. 22 C. Dennison T. Kohzuma W. McFarlane S. Suzuki and A.G. Sykes Inorg. Chem. 1994 33 3299. Inorganic Mechanisms 517 measured by NMR methods.23 While the kinetics of [Co(terpy),12 + reduction of the oxidized form of the blue copper protein amicyanin from Thiobacillus versutus are uncomplicated oxidation of the reduced form by [Fe(CN),I3- or [Co(phen),13+ suggest24 that protonation/deprotonation and rate-controlling intramolecular isomerization occur. Competitive inhibition by redox-inactive [Cr(CN),13 -of the oxidation of the Fe"Fe"' purple acid phosphatase2 by [Fe(CN)J3 -(which displays saturation kinetics) is consistent with the importance in governing reactivity of a positively charged centre on the protein surface.A direct NMR method has been used to measure intermolecular electron transfer rates between haems in haemoglobin26 and to estimate self-exchange rates in the a-and fi-chains. Photoinduced electron transfer between magnesium or zinc myoglobin and cationic and anionic quenchers is controlled by conformational changes in the myoglobin.27 Protein-protein orienta-tion effects in electron transfer have also been studied.28 The effect of conformation on protein-mediated electron transfer has been studied the ore tic all^.^^ Artificial intelli- gence approaches are used to find the key residues involved in protein electron tran~fer.~' Bond3' has proposed that both chemical and electrochemical approaches could be employed in the study of redox reactions of simple metalloproteins.Other relevant studies are noted. 32-37 Intramolecular and Intervalence Electron Transfer.-[(H3N),Ru'"(0-l-oxo-13-dithiacyclooctane-S)Ru"(NH,),IS + isomerizes to [(H,N),Ru"(S-l-oxo-1 ,5-dithiacyc- lo~ctane-S)Ru"'(NH~)~]~ + by an intramolecular electron-transfer process.38 The rate constant for electron transfer within the triiron cluster of [Fe?'Fe"(O)(O 2CBu'),(py- d5)3] has been estimated39 from the temperature dependence of its IR spectrum. Intramolecular electron exchange between Ru" and Ru" in a mixed-valence complex formulated as [C~RU"(~~-C,H~CH,C,H~-~~)RU~~IC~] + is believed to be associated with migration of I.40 Time-resolved vibrational spectroscopy used to study 23 C.Dennison T. Kohzuma W. McFarlane S. Suzuki and A. G. Sykes J. Chem. Soc. Dalton Trans. 1994 437. 24 P. Kyritsis C. Dennison A. P. Kalverda G. W. Canters and A. G. Sykes J. Chem. Soc. Dalton Trans. 1994 3017. 25 M.A. S. Aquino and A. G. Sykes J. Chem. Soc. Dalton Trans. 1994 683. 26 C. Brunel A. Bondon and G. Simonneaux J. Am. Chem. Soc. 1994 116 11 827. " K. Tsukahara Y. Nishikawa C. Kimura N. Sawai and T. Sakurai Bull. Chem. Soc. Jpn. 1994,67,2093. 28 J. Cheng J. S. Zhou and N. M. Kostic Znorg. Chem. 1994,33 1600. 29 S.S. Skourtis J. J. Regan and J.N. Onuchic J. Phys. Chem. 1994 98 3379. 3" P. Siddarth J. Photochem. Photobiol. A Chem. 1994 82 117. " A.M. Bond lnorg. Chim. Acta 1994 226 293. 32 J. Jortner and M.Bixon J. Photochem. Photobiol. A Chem. 1994 82 5. 33 E. Guerrybutty E. Haselbach and P. Suppan Chimia 1994,48 391. 34 M.D. Todd A. Nitzan M.A. Ratner and J.T. Hupp J. Photochem. Photobiol. A Chem. 1994,82 87. 35 C. Gomez-Moreno M. Medina J. K. Hurley M. A. Cusanovich J. L. Markley H. Cheng B. Xia Y. K. Chae and G. Tollin Biochem. Soc. Trans. 1994 22 796 (Chem.Abstr. 1994 121 174619r). 36 H. E. M. Christensen 1. Coutinho L. S. Conrad J. M. Hammerstad-Pedersen G. Iversen M. H. Jensen J. J. Karlsson J. Ulstrup and A. V. Xavier J. Photochem. Photobiol. A Chem. 1994 82 103. 37 J.R. Reimers and N.S. Hush J. Photochem. Photobiol. A Chem. 1994 82 31. 38 M. Sano and H. Taube lnorg. Chem. 1994,33 705. 3y R. Wu S. K. Arap Koske R. P. White C. E. Anson U. A. Jayasooriya and R.D. Cannon J. Chem. Soc. Chem. Commun. 1994 1657. 4o M. Watanabe I. Motoyama and H. Sano lnorg. Chim. Acta 1994 225 103. 518 N. Winterton intermediatesinphotochemicallyinducedelectron has shown that the rate of electron transfer for the neutral pair [COC~~]/[CO(CO)~] formed from the corresponding ion-pair was greater41 for the first vibrationally excited state of the v(C0) for [Co(CO),] than for the vibrational ground state. The decrease in intramolecular electron-transfer rate in [(edta)Ru"LCo"'(NH,),] + with increasing Ru-Co separation is ascribed48 to solvent reorganization energy changes. S~lvent,~'-~~ pre~sure,~' temperat~re,,~ and other44,59-70 effects in inter- valence electron and energy transfer in homo,44*49,54,56,62,63 hetero,51,52,55,57,60,64,67,7 1,72 and trimetalli~~~,~~,~~?~~ complexes have been de- scribed.Back electron transfer in the photogenerated Ru"'LCO" complexes (L = 1,2-bis(2,2'-bipyridyl-4-yl)ethane)is non-adiabati~,~ pointing to no special role for the linker in contrast to L = CN- for which stronger electronic coupling between the metal centres is seen. Encapsulation by a series of dibenzocrown ethers affects + intervalence absorption of [{ Ru(NH,),} *pz] . Outer-sphere intervalence transfer75 in the ion-pair [Cr(NH3)6]3f/[Fe(CN)6]4-has been with the 41 K. G. Spears X. Wen and S. M. Arrivo J. Phys. Chem. 1994 98 9693. " J. R. Schoonover P. Chen W. D. Bates R. B. Dyer and T. J. Meyer Inorg. Chem. 1994 33 793. " C. Turro S.H. Bossmann G.E. Leroi J. K. Barton and N. J. Turro Inorg. Chem. 1994 33 1344. '' L.O. Spreer A. Li D.B. MacQueen C.B. Allan J.W. Otvos M. Calvin R.B. Frankel and G.C. Papaefthymiou Inorg. Chem. 1994,33 1753. '' \f. W. George J. J. Turner and J. R. Westwell J. Chem. Soc. Dalton Trans. 1994 2217. N. E. Katz S. L. Mecklenburg D. K. Graff P. Chen and T.J. Meyer J. Phys. Chem. 1994 98 8959 A-S. L. Mecklenburg D. G. McCafferty J. R. Schoonover,B. M. Peek B. W. Erickson and T. J. Meyer Inorg. Chem.. 1994 33 2974. " L.A. Andrade de Oliveira L. Della Ciana and A. Haim Inorg. Chim. Acta 1994 225 129. R. L. Blackbourn Y. Dong L.A. Lyon and J.T. Hupp Inorg. Chem. 1994 33 4446. ' ' D. V. Matyushov and R. Schmid J. Phys. Chem. 1994,98 5152. ' M.Furue K. Maruyama Y. Kanematsu T.Kushida and M. Kamachi Coord. Chem. Rev. 1994,132,201. '' W.M. Laidlaw and R.G. Denning Polyhedron 1994 13 1875. 53 Y. Wu C. Cohran and A. B. Bocarsly Inorg. Chim. Acta 1994 226 251. 54 K. W. Lau A. M.-H. Hu M. H.-J. Yen E. Y. Fung S. Grzybicki R. Matamoros and J. C. Curtis Inorg. Chim. Acta 1994 226 137. 55 W. M. Laidlaw and R.G. Denning J. Chem. SOC. Dalton Trans. 1994 1987. 56 M. L. Naklicki and R. J. Crutchley Inorg. Chim. Acta 1994 225 123. " D. Chatterjee H.C. Bajaj and A. Das Inorg. Chim. Acta 1994 224 189. 58 N.A. Lewis R. R. McNeer and D.V. Taveras Inorg. Chim. Acta 1994 225 89. 59 H. Kunkely V. Pawlowski and A. Vogler Inorg. Chim. Acta 1994 225 327. 6o G. Tsaur M.-C. Wu and A. Yeh J. Chin. Chem. SOC. (Taipei) 1994 41 431 (Chem. Abstr. 1994 121 244 12%).61 V. W.-W. Yam W.-K. Lee P.K.-Y. Yeung and D. Phillips J. Phys. Chem. 1994 98 7545. 62 A.-C. Ribou J.-P. Launay K. Takahashi T. Nihira S. Tarutani and C. W. Spangler Inorg. Chem. 1994 33 1325. '' C. A. Bignozzi R. Argazzi C. Chiorboli F. Scandola R. B. Dyer J. R. Schoonover and T. J. Meyer Inorg. Chem. 1994 33 1652. 64 Y. Wang and K.S. Schanze Inorg. Chem. 1994,33 1354. h5 L.A. Lucia and K. S. Schanze Inorg. Chim. Acta 1994 225 41. 66 R. Lin and T.F. Guarr Inorg. Chim. Acta 1994 226 79. 67 W. M. Laidlaw and R. G. Denning Polyhedron 1994 13 2337. 68 M.A. Watzky X. Song and J. F. Endicott Inorg. Chim. Acta 1994 226 109. 69 K. Kalyanasundaram and Md. K. Nazeeruddin Inorg. Chim. Acta 1994 226 213. 70 P. Forlano L.M. Baraldo J.A. Olabe and C.O.Della Vedova Inorg. Chim. Acta 1994 223 37. 71 F. Scandola,R.Argazzi C. A. Bignozzi and M. T. Indelli J. Photochem. Photobiol. A Chem.,1994,82,191. 72 M.T. Indelli C. A. Bignozzi A. Harriman J. R.Schoonover and F. Scandola,J. Am. Chem. SOC. 1994,116 3768. 73 J. F. Endicott X. Song M.A. Watzky and T. Buranda J. Photochem. Photobiol. A Chem. 1994,82,181. 74 J.T. Hupp and Y. Dong Inorg. Chem. 1994 33,4421. 75 R. Billing and D. E. Khoshtariya Inorg. Chem. 1994 33 4038. 76 G Stochel Polyhedron 1994 13 155. Inorganic Mechanisms 519 analogous inner-sphere system [(NH,),Cr"'(p-NC)Fe"(CN),] -. Ion-pairing effects on intramolecular electron transfer have been modelled.77 Selective excitation of the zinc-porphyrin subunit in a Zn"Ru"(terpy),Au"'-bisporphyrin complex leads to electron transfer to the Ru(terpy) spacer and then to the distant AU(III)centre.Related processes in covalently bound Zn"(porphyrinM(terpy) [M = Ru(II) R~(III] ,79 a Zn"(Ph,phen)Au"' (bisporphyrin),*' and a Zn"(porphyrin)-crown ether-Eu3 + complex" have been reported. Other studies of energy tran~fer~',~~ and excited state q~enching~,-~~ are also noted. Outer-sphere Electron Transfer and Self-exchange Reactions.-A V* for the reduction of [Fe(H20)J3 by [C0([9]aneS,),]~ agrees with a value computed from a + + volume cross relation A Vf = '/,(A Vf + A Vf,+ A v(i) + C) where A Vtl and A Vf are the volumes of activation for the self-exchange reactions for the couples [Fe(H2o),l2 +I3 + and [C0([9]aneS,),]~+/~+.Agreement is less satisfactory when the + reductant is [Co(sep)12 . Outer-sphere electron-transfer rate constants for the + reactions of [Co"'{ (X)N4S,sar)13 (X = H NH, Cl) with [CO"{(M~)(NH,)N,S~~H)]~ + or [Co"{(Cl,)N,~ar)]~+ have been measured.89 Kin- etics ofthe oxidation of related CO(III) cage compounds by positronium have also been described." Self-exchange rates for [Co{ (NH,)N,S,S~~H}]~+/~+ [CO{(H)N,S,S~~}]~+~~+ span five orders of and [CO{(M~)(NH,)N,S~~H}]~+~~+ magnitude.89 The self-exchange rate constant for [Co{(NMe),sar}] +I4+, for + [Co{fac-Me,-D,,-tricosaneN,)] +I2 and for [Ni(macrobi~ycle)X]~+'(~-(X = H,O n = 3; X = C1- n = 2) have also been The self-exchange rate constants for the couple [Cu"/'L] (L = syn- or anti-[14]aneS4-l ,8-diol) have been estimated directly from NMR spectroscopic line br~adening.~~ Studies of the oxidation of Cu'/L reveal the onset of 'gated' behaviour controlled by ligand conformation.A dual pathway is proposed94 in which the electron-transfer and conformational change occur sequentially via either the ground state or a metastable conformational form of the complex in either the CU(I) or CU(II) oxidation state. A 77 P. Piotrowiak Inorg. Chim. Acta 1994 225 269. 78 A. Harriman F. Odobel and J.-P. Sauvage J. Am. Chem. Soc. 1994 116 5481. 79 J.-P. Collin A. Harriman V. Heitz F. Odobel and J.-P. Sauvage J. Am. Chem. Soc. 1994 116 5679. 80 A. Harriman V. Heitz J.-C. Chambron and J.-P. Sauvage Coord. Chem. Rev 1994 132 229. 81 V. Krishnan E.E. Batova and V. Ya. Shafirovich J. Photochem. Photohiol. A Chem. 1994 84 233. 82 K.A. Opperman S.L. Mecklenburg and T. J. Meyer Inorg. Chem. 1994 33 5295. 83 H. Sun and M.Z. Hoffman J. Phys. Chem. 1994,98 11 719. 84 D. Tran C.K. Ryu and P. C. Ford Inorg. Chem. 1994 33 5957. us K. Tsukahara S. Asami M. Okada and T. Sakurai Bull. Chem. SOC.Jpn. 1994 67 421. 86 K. Tsukahara M. Okada S. Asami Y. Nishikawa N. Sawai and T. Sakurai Coord. Chem. Rev. 1994,132 223. R7 Z. Murtaza D. K. Graff A. P. Zipp L. A. Worl W. E. Jones Jr. W. D. Bates and T. J. Meyer J. Phys. Chem. 1994 98 10504. 88 M. R. Grace H. Takagi and T. W. Swaddle Inorg. Chem. 1994 33 1915. 89 T. M. Donlevy L. R. Gahan and T. W. Hambley Inorg. Chem. 1994 33 2668. 90 A.L.Fantola Lazzarini E. Lazzarini and M. Mariani J. Chem. SOC.,Faraday Trans. 1994 90,423. 91 P.V. Bernhardt A. M.T. Bygott R. J. Geue A. J. Hendry B. R. Korybut-Daszkiewicz P. A. Lay J. R. Pladziewicz A M. Sargeson and A. C. Willis Inorg. Chem. 1994 33 4553. 92 R. J. Geue A. Hohn S. F. Ralph A. M. Sargeson and A. C. Willis J. Chem. Soc. Chem. Commun. 1994 1513. 93 A. McAuley D. G.Fortier D. H. Macartney T. W. Whitcornbe and C. Xu J. Chem. Soc. Dalton Trans. 1994 207 1. 94 N.E. Meagher K.L. Juntunen M.J. Heeg C.A. Salhi B.C. Dunn L.A. Ochrymowycz and D.B. Rorabacher Inorg. Chem. 1994 33 670. 520 N. Winterton 106-fold difference between the self-exchange rate constant via these two pathways for the complex of the anti-form of the ligand was estimated.Self-exchange processe~~~,~~ and other outer-sphere electron transfer^'^.^^ have been treated theoretically. Reductions of [Mo~S,(H,O),,]~+ to the isostructural [Mo,S,(H,O),,]~+ by + Ti(rir) Cr(II) Eu(II) V(II),[Ru(NH,),]' +,and [C~(sep)]~ occur98 by outer-sphere processes. A self-exchange rate constant of 103.8* M -s-' for the couple [Mo,S~(H,O),,]~+/4+ was calculated. Sykes and coworkers reportg9-"' rate constants for the outer-sphere oxidation of the [(Mo~COS~(H,O),},]~' with [Co(dipic),] -. Reaction with [Fe(H,0)J3 proceeds uia parallel outer-sphere and + inner-sphere pathways. The effect of R on the outer-sphere redox reactions between [CO(NH,R),(H,O)]~+ (R = H Me Et) and [Fe(CN),],- (rate constants increase and ion-pair formation constants decrease with increasing size of R",) are primarily associated with solvation changes during electron transfer.Both outer-sphere of [MnO,] -by [Co"Wl,0,0]6- and the ~xidation"~ red~ction"~ of [M(CN),I4- (M = Mo W) by [Co"'Wl,0,0]5- are catalysed by alkali metals in the order K+ > Na' > Li'. Oxidation of [M(CN),I4- (x = 8 M = Mo W; x = 6 M = Fe) by Mn(m)-cydta c~mplexes''~ is outer-sphere. The kinetics of the Os(vm)-mediated oxidation of Cr(m) by [Fe(CN),I3- and of AS(III) and Sb(Ir1) by Ce(1v) and Mn(iIr) have been rep~rted.'~~.''~ T wo studies have appeared on the reduction of [Ag"'(H2ebbg)l3+ ; one108 reports a predominance of outer-sphere reaction for metalkcomplex reductants whereas the other,' O9 involving both inorganic and organic reductants proposes both inner- and outer-sphere processes.A self-exchange rate of 105.8*0.8 M-'s-l was estimated for the [Ag(H,ebbg)]3+/2+ ~ouple.''~ Outer-sphere electron transfer from [Co(edta)12 -to A-[Co(phen),13' leads' to a 20% enantiomeric excess (e.e.) of A-[Co(edta)] -,a chiral discrimination associated with hydrogen-bonding interactions evident from structural studies.' ' This homochiral (AA) preference is in contrast to the heterochiral (AA)preference observed with [M(phen),I3+ (M = Fe 0s). Reduction by [Ru(en),],+ involves AA preference (with only 2% e.e.).'" Oxidation of [C~(phen)~]~+ by A-[Co(gly)(ox),12- leads to 37% e.e. of A-[C~(phen)~]~+.' l2 Heterochiral stereoselectivity is also seen113 for 95 S. J. Formosinho and L.G.Arnaut J. Photochem. Photobiol. A Chem. 1994 82 11. 96 S.J. Formosinho and L.G. Arnaut THEOCHEM 1994 116 105 (Chem. Abstr. 1994 121 214072r). 97 T. Kakitani Inorg. Chim. Acta 1994 225 185. 98 M.C. Ghosh and E. S. Gould Inorg. Chim. Acta 1994 225 297. 99 P. W. Dimmock D. M. Saysell and A.G. Sykes Inorg. Chim. Acta 1994 225 157. loo M. Nasreldin C.A. Routledge and A.G. Sykes J. Chem. Soc. Dalton Trans. 1994 2809. M. Nasreldin Y.-J. Li F. E. Mabbs and A.G. Sykes Inorg. Chem, 1994 33 4283. lo' M. Martinez M.-A. Pitarque and R. van Eldik J. Chem. Soc. Dalton Trans. 1994 3159. G. A. Ayoko and J. Arabel Transition Met Chem. 1994 19 212. 104 M. Das-Sharma M. Ali S.Gangopadhyay S.K. Saha and P. Banerjee Indian J. Chem. Sect. A 1994,33 243 (Chem. Abstr.1994 120 201 607y). lo5 A. Dutta M. Ali S. Gangopadhyay and P. Banerjee Proc. Indian Acad. Sci. Chem. Sci. 1994,106,881 (Chem. Abstr. 121 287 353t). S. C. Hiremath S.A. Chimatadar and J. R. Raju Transition Met. Chem. 1994 19 636. lo' S.R. Kampli and S.T. Nandibewoor Proc. Indian Acad. Sci. Chem. Sci. 1994 106 837 (Chem. Abstr. 1994 121 287 352s). lox S.P.Ghosh M.C. Ghosh and E.S. Gould Inorg. Chim. Acta. 1994 225 83. lo9 R. Banerjee Proc. Indiun Acad. Sci. Chem. Sci. 1994 106 655 (Chem. Abstr. 1994 121 264794~). 'lo R. M. L. Warren L. ohrstrom G. J. Opiteck M. Shang and A.G. Lappin Inorg. Chim. Acta 1994,225 75. R. M.L. Warren K. J. Haller A. Tatehata and A. G. Lappin Znorg. Chem. 1994 33 227. ''' R. M. L. Warren A. Tatehata and A.G. Lappin J. Chem.SOC.,Dalton Trans. 1994 1655. 'I3 K. Bernauer E. Fuchs and D. Hugi-Cleary Inorg. Chim. Acta 1994 218 73. Inorganic Mechanisms 521 + outer-sphere electron transfer between optically active [Co"'L(H,O)] (L = promp MeO-promp) and optically active [Fe"(S,S)-L'] (L' = promp MeO-promp alamp). Cu" superoxide dismutase and A-and A-[Fe(pdta)12 -also react stereoselectively.' l4 Inner-sphere Electron and Atom Transfer.-Oxidation of [W,CUS,(H,O),,]~ to + [W3S,(H20)J4+ + Cu2+ by [Fe(H20),(OH)]2f is to be an inner- sphere process whereas [Fe(H,0),I3 reacts by an outer-sphere process as does + [Co(dipic),] -. [CO"'(NH,),(NHC(O)~~~~H}]~+ reacts with [Ti(aq)13+ (and [V(aq)12+) to form a binuclear complex (I) followed by electron transfer. This proceeds' ' via an outer-sphere process involving Ti(OH) + and an inner-sphere process involving the conjugate base of (I).[Cr(aq)I2+ reacts by an inner-sphere process only.' l6 In the substitution processes giving binuclear CN-bridged species from [M(NH3)5(H,0)]3+ (M = Ru 0s) and [M'(CN),]"- (M' = Fe Co n = 3; M' = Fe Ru n = 4) Taube and coworkers ascribe1I7 the anomalous rate for the reaction involving M = Os M' = Fe n = 3 to a one-electron oxidation of OS(III) by Fe(1Ir) coupled with the substitution. Related studies involving [Os(q2-H,)(H,0)(en),12+ and [Fe(CN),I4- have been described.' '* Steric effects associated with N-alkylation dominate' l9 the rates of oxidation of [Pt(diam)(diam')l2 by + [IrC1J2-in the presence of C1-. The oxidation of [Cr111(H,tou)(H20)]+ by [TO,] -[2Cr(111)+ ~~(vIx) = 2Cr(") + 3I(v)] involves [TO,] -coordination to Cr(xx1).l2' Reduction of [Cu"'{TeO,(OH),} ,] -by alkaline nitrite proceeds via initial complex formation between the reactants.I2' tran~-[Ru~'O,L(terpy)]~+ (L = MeCN H20) is reduced by PPh to RU(II) in successive kinetically distinguishable two-electron oxygen atom-transfer processes' 22 followed by solvolysis giving [Ru(NCMe),(terpy)12 + With dppe the first step RU(VI) to Ru(Iv) is first order in each reagent giving trans-[RU'~O(NCM~){OP(P~)~CH~CH~PP~~}(~~~~~)]~+, with a subsequent slower isomerization oxygen atom transfer.[MoV'CIO,Tp] transfers 0to PPh in dmf to give [MorVCIOL(dmf)] which itself reacts with [Fe"'Cl(ttp)] in a process thought 123 to involve chlorine atom transfer.Oxygen atom transfer between HOOSO and [MnCl(tmp)] [MnCl(tdcpp)] and [MnCl(obtmp)] takes place only in the presence of species capable of acting as axial ligand~.'~~ With excess [V0(aq)l2+ [V(O2)(H00)(aq)I2+ yields' 2s a series of vanadate oligomers by oxygen transfer and subsequent dioxygen release with [V(02)( 'O)(aq)I2+ as an intermediate. In the + reduction of trans-[RuO,{ [14]ane(NMe),}12 by iodide (giving trans-[RuO(H,O){ [14]ane(NMe),}12 + + 13) reaction via oxygen atom transfer [ORuV1OI2++ I-= [ORU'~OT]++ [H,O]+ = [ORU'"(H,O)]~' + HOI is pre- ferred to an outer-sphere mechanism.'26 Iodide oxidation by H,02 in the presence of J. R. Pladziewicz S.O.Gullerud and M.A. Accola Inorg. Chim. Acta 1994 225 151. '15 R. J.Balahura and M.D. Johnson Inorg. Chim. Acta 1994 225 245. C.S. Alexander and R. J. Balahura Inorg. Chem. 1994 33 1399. V.G. Poulopoulou Z.-W. Li and H. Taube Inorg. Chim. Acta 1994 225 173. l'' Z.-W. Li A. Yeh and H. Taube Inorg. Chem. 1994 33 2874. ''' A. Peloso and G. Trovo Gazz. Chim. Ital. 1994 124 109. 120 A. A. Abdel-Khalek S.M. Sayyah and F. F. Abdel-Hameed Transition Met. Chem. 1994 19 108. 12' K. K. S. Gupta and A. Sanyal Transition Met. Chem. 1994 19 329. 12' A. Dovletoglou and T.J. Meyer J. Am. Chem. Soc. 1994 116 215. lZ3 M.J. LaBarre A. Pacheco and J.H. Enemark Inorg. Chim. Acta 1994 226 259. 124 T.-J. Won B. M. Sudam and R. C. Thompson Inorg. Chem. 1994 33 3804. lZ5 H. N. Ravishankar M.K. Chaudhuri and T. Ramasarma Inorg. Chem. 1994 33 3788.126 T.-C. Lau K. W. C. Lau and K. Lau J. Chem. Soc. Dalton Trans. 1994 3091. 522 N. Winterton boric acid has also been studied.'27 Related sulfur-transfer processes involving [MoCl,(PMe,),] and SPMe,; oxygen transfers between [MoOCl,(PMe,),] and [WCl,(PMe,),] [MoV'O(O,)(dipic)] and [MoV'O(O,)(nta)] -with dmso and + [Co(en),(SCH,CH,NH,)]' chlorine-atom transfer comproportionations [WOCl,(PMe,),] + [WCl,(PMe,),] = [WOCl,(PMe,),] + [WC14(PMe,),];'29 oxygen-transfer catalysis by [MO~'O,(NCS),]~ -and [MoX,O,(dmso),] (X = F C1 Br);'30,'31 and the mechanisms of other o~ygen-'~~-'~~ and sulfur '36-transfer reactions have been described. + Miscellaneous Redox Processes.-[Ni(tacn),] reacts with SCN -either to form Ni(II) and SCN with separation of the products as the rate-determining step or Ni(I1) and [(SCN),]- * with electron transfer concerted with S-S bond f0rmati0n.I~~ Four parallel outer-sphere pathways have been re~olved'~' for the oxidation of N(m) (as HNO or NO,) to N(v) by [Ag1''(H,ebbg)13+ and its deprotonated forms.Oxidation of NO by AU(III)([AuC14]- [AuCl,(H,O)] and [AuCl,(OH)]-) first order in [NO,] and [Au(III)] is believed' 39 to involve two-electron processes giving Au(I) and NO:. The catalytic reduction to ammonia of hydrazine in [Ru"'(N,H,)(edta)] and redox reactions involving substituted hydroxylamines and Npv' or PuIV have been st~died.'~'-'~~ A t wo-electron process yielding azene as an intermediate is pro- posed'48 for the reaction of [FeO4I2- with NH,NH in aqueous solution with first order kinetic dependence on [FeOi-1 [NH,NH,] and [H'].The first-order decay of [FeV0J3- has been studied.'49 The oxidation of HS- by [NaP,W,00,,o]14- is first order in [HS-] and second order in the heteropolyanion with a complex pH dependence.' Additional studies have been undertaken on the reaction of chromate 121 C. Karunakaran and M. Padmanabhan Oxid. Commun. 1993,16,346 (Chem. Abstr. 1994,120,228 403r). 128 S. Campestrini F. Di Furia G. Labat and F. Novello J. Chem. SOC., Perkin Trans. 2 1994 2175. 129 K.A. Hall and J.M. Mayer Inorg. Chem. 1994 33 3289. H. Arzoumanian R. Lopez and G. Agrifoglio Inorg. Chem. 1994 33 3177. 130 131 F. J. Arnaiz R. Aguado and J. M. Martinez de Ilarduya Polyhedron 1994 13 3257.132 B. L. May H. Yee and D.G. Lee Can. J. Chem. 1994 72 2249. 133 1. Kawafune and G. Matsubayashi Bull. Chem. Soc. Jpn. 1994 67 694. 134 B.-H. Kim and W.-S. Jung J. Korean Chem. Soc. 1994,38 526 (Chem. Abstr. 1994 121 142671k). 135 J. Wang Y. Gao Y. Wang and Q. Shi Wuji Huaxue Xuebao 1994 10 35 (Chem. Abstr. 1994 120 332251a). 136 V. P. Fedin G. J. Lamprecht and A.G. Sykes J. Chem. Soc. Chem. Commun. 1994 2685. 137 M.-L. Hung and D. M. Stanbury Inorg. Chem. 1994,33 4062. 138 S. Mukhopadhyay and R. Banerjee J. Chem. SOC.,Dalton Trans. 1994 1349. 139 K. K. Sen Gupta A. Sanyal and P. K. Sen Transition Met. Chem. 1994 19 534. 140 G. Ramachandraiah J. Am. Chem. SOC. 1994 116,6733. 141 V. S. Koltunov S. M. Baranov and T. P. Zharova Radiokhimiya 1993,35,42 (Chem.Abstr. 1994,120 281 449m). 142 V. S. Koltunov S. M. Baranov T. P. Zharova and E. V. Abramina Radiokhimiya 1993,35,49 (Chem. Abstr. 1994 120 281 450e). 143 V. S. Koltunov and S. M. Baranov Radiokhimiya 1993 35 54 (Chem. Abstr. 1994 120 281 4510. 144 V. S. Koltunov S. M. Baranov T. P. Zharova and M. P. Shapovalov Radiokhimiya 1993,3571 (Chem. Abstr. 1994 120,281 453h). 145 V. S. Koltunov S. M. Baranov T. P. Zharova and E. V. Abramina Radiokhimiya 1993 35 79 (Chem. Abstr. 1994 120 281 454J). 146 V. S.Koltunov S.M. Baranov and M. P. Shapovalov,Radiokhirniya 1993,3585 (Chem. Abstr. 1994,120 28 1 455k). 147 V. S. Koltunov G.I. Zhuravleva and M. P. Shapovalov Radiokhimiya 1993,35,43 (Chem. Abstr. 1994 121 188 357r).148 M. D. Johnson and B. J. Hornstein Inorg. Chim. Acta 1994 225 145. 149 J.D. Rush and B.H. J. Bielski Inory. Chem. 1994 33 5499. 150 M. K. Harrup and C. L. Hill Inory. Chem. 1994 33 5448. Inorganic Mechanisms 523 with glutathione (GSH) particularly the f~rther'~'-'~~ kinetic characterization of the thioester [GSCrO,]- whose formation and dissociation is found to be catalysed by Zn2 .Its decomposition is complex and involves Cr" supported by the detection' 52 of + [Cr111(H,0)5(00)]2+ when studied in the presence of 0,. Related kinetic studies on the oxidation of glutathione by [Mn(~ydta)]-,'~~ [Fe(CN)6]3-,155 [C~(taab),]","~ and Te(1v) and Se(1v) compounds,' 57 as well as of DL-penicillamine by CT(VI),'~~ and have been reported.The kinetics of Br- oxidation by MO(VI~ W(v1tdiperoxo complexes 159,160 have been reported. The catalysis of the reaction of H,O and Br- or organic sulfides by [ReMeO,] involves peroxo intermediates.'6','62 The kinetics of the reduction of Mn(m-porphyrin complexes by [Co(sep)12+ are consistent with reaction at the periphery of the porphyrin ring.'63 The role of Ni,164 CU,'~~ Pd,166 and other meta1'67-'70 catalysts in the reduction of CO has been investigated. Reactions of Oxygen-containing Oxidants and Reductants.-From studies of the oxygen isotope composition of H,O and 0 produced from e- and y-irradiation of solutions of N,O and BrO in H,I80-enriched water it has been estimated'71 that for the reaction 0-+ H20 = OH-+ OH 1&100 reversible proton transfers take place for each hydrogen atom transfer.The rate constant of the exchange 180H + H,O = H,'*0 + OH is 57 & 6s-' at 30°C. Studies have been reported of the dismutation of 0; catalysed by Fe(IIttpcn c~mplexes,'~~ by CU(II) Mn(Ir) and Fe(m) complexes of the binucleating ligand egtb,' 73 by Mn(I1) complexes of [15]aneN (displaying activity at physiological PH),'~~ and by Mn(tpp).' 75 The saturation at high [A-] of the acceleration by added ions of the oxidation of [Cr(aq)I2' by H,O to give [CrX(OH)(H,O),]"+ (X = H,O n = 3; X = A n = 2) is 151 J. F. Perez-Benito D. Lamrhari and C. Arias J. Phys. Chem. 1994 98 12621. 15' J. F. Perez-Benito C. Arias and D. Lamrhari New J. Chem. 1994 18 663. 153 J. F. Perez-Benito C. Arias D. Lamrhari and A.Anhari Int. J. Chem. Kinet. 1994 26 587 S. Gangopadhyay M. Ali A. Dutta and P. Banerjee J. Chem. Soc. Dalton Trans. 1994 841. 155 G. Stochel P. Martinez and R. van Eldik J. Inorg. Biochem. 1994 54 131. 15' J. Labuda M. Vanickova V.V. Pavlishchuk and A.G. Kolchinskii Chem. Pap. 1994 48 78 (Chem. Abstr. 1994 121 264 771p). M. R. Detty A.E. Friedman and A. R. Oseroff J. Org. Chem. 1994 59 8245. 15' J.F. Perez-Benito D. Lamrhari and C. Arias Can. J. Chem. 1994 72 1637. 159 M. S. Reynolds S. J. Morandi J. W. Raebiger S.P. Melican and S. P. E. Smith Inorg. Chem. 1994,33 4977. '" G. E. Meister and A. Butler Inorg. Chem. 1994 33 3269. 16' J.H. Espenson 0.Pestovsky P. Huston and S. Staudt J. Am. Chem. Soc. 1994 116 2869. 16' K. A. Vassell and J.H.Espenson Inorg. Chem. 1994 33 5491. 163 R. J. Balahura and R.A. Kirby Inorg. Chem. 1994 33 1021. E. Fujita J. Haff R. Sanzenbacher and H. Elias Inorg. Chem. 1994 33 4627. 165 R. J. Haines R.E. Wittrig and C.P. Kubiak Inorg. Chem. 1994 33 4723. P. R. Bernatis A. Miedaner R. C. Haltiwanger and D. L. DuBois Organometallics 1994 13 4835. 0. Ishitani M. W. George T. Ibusuki F. P.A. Johnson K. Koike K. Nozaki C. Pac J. J. Turner and J. R. Westwell Inorg. Chem. 1994 33 4712. "'S. Chardon-Noblat M.-N. Collomb-Dunand-Sauthier A. Deronzier R. Ziessel and D. Zsoldos Inorg. Chem. 1994,33 4410. M.-N. Collomb-Dunand-Sauthier A. Deronzier and R. Ziessel J. Chem. Soc. Chem. Commun. 1994,189. "O W. Leitner Angew. Chem. Int. Ed. Engl. 1994 33 173. 171 U.K. Klaning E. Larsen and K. Sehested J. Phys. Chem. 1994 98 8946. M. Nakagawa K. Hanaoka A. Terasaki Y. Mori H. Hokazono M. Sato and T. Iida Chem. Lett 1994 1721. Z. R. Liao W. Q. Liu J. P. Liu Y. Q. Jiang J. Shi and C. L. Liu J. Inorg. Biochem. 1994 55 165. D. P. Riley and R.H. Weiss J. Am. Chem. Soc. 1994 116 387. K. Lang J. Vondrak and D. M. Wagnerova Collect. Czech. Chem. Commun. 1994 59 1059. 524 N. Winterton ascribed'76 to the involvement of [Cr"(H,O),A] in inner-sphere electron-transfer + processes. [Cr(00)(H20)J2+ (11)reacts'77 with [Ru(bipy)J3 + to give [Cr(H,0),I3+ and O, after rate-determining formation of [Cr(00)(H20),l3 + (111). The rate of homolysis of Cr-(00) in (111) is estimated to be > 10" greater than that for (11).Electroreduction of (111) proceed^'^',' 79 via [Cr(H,0),(OOH)]2 +. The superoxo complex [(H,0)4(OH)Rh111(p-0,)Rh"'(OH)(H,0)4]3 + forms the corresponding p-0;-complex on outer-sphere'80 one-electron reduction by I-and [IrC1,I3 -. While conditions were employed in which the effect of [Fe(CN),(H20)I3- was minimized attempts to measure the rate of the uncatalysed oxidation of [Fe(CN),I4- by H,O were though the upper limit established was more consistent with an outer-sphere process. The effects on H,O decomposition have been described of dimeric Mn(II)-gluconate complexes,' the axial coordination of nitrogen bases to cofacial Mn(rrr)-porphyrin complexes,183 the binuclear Mn(rrr)-Mn(rv) complex [Mn,(p-O),(dpa),] ,lS4 Fe(I1)-bis(salicy1aldimine) Schiff-base complexes,' 85 his-+ tidine-containing oligopeptidylcopper(rr) complexes,' ' Co(rr) complexes of phopdH,' 87 [(Fe(H,0)(bipy)2}2(p-O)],''8 and other metal complexes.189-'93 Inhibi- tion ofthe rate by added acetate that the dismutation of H,O catalysed by the complexes [(tmpdp)Mn"Mn"(p-OA~)]~ in the presence of water proceeds by + dissociation of p-OAc; the rate determining step' 94 is either inner-sphere two-electron intramolecular oxidation of [(tmpdp)Mn"Mn11(H,02)]3 to [(tmpdp)Mn"'Mn"'- + (0H),l3 or proton dissociation coupled to this oxidation.H,O disproportionation + by a series of spacer-linked Mn(rrr)-porphyrin dimers is controlled by the optimum Mn-Mn separation for cooperative intera~tion'~~ of the two Mn ions with H,O,. Products from the oxidation of [(~is-Ru"'(H,O)(bipy)~}~(p-O)]~+, a '[3,3]' com-plex in the notation employed to avoid any implications concerning charge localiz- ation with Ce(1v) include RuORu-[3,4] and -[4,5] species.At higher acidities a [5,5] species believed'96 to contain a coordinated bipy radical cation is detected. The role of these reactions in water oxidation has been in~estigated'~~ as has the electrochemi- cal oxidation of [Mn40,(OBz)7(dbm)2]- in the presence of dbm- which leads to the W. Gaede and R. van Eldik Inorg. Chem. 1994 33 2204. 17' A. Bakac J.H. Espenson and J.A. Janni J. Chem. Soc. Chem. Commun. 1994 315. 17' C. Kang and F.C. Anson Inorg. Chem. 1994 33 2624. J.H. Espenson A. Bakac and J. Janni J. Am. Chem. SOC.,1994 116 3436. S.P. Ghosh M.C. Ghosh and E.S. Gould Int. J. Chem. Kinet. 1994 26 665. l8I D. G. Bray and R. C. Thompson Inorg. Chem. 1994 33 905. C. Rocha and A.M. da Costa Ferreira Int. J. Chem. Kinet. 1994 26 1121. 183 Y. Naruta and M. Sasayama Chem. Lett. 1994 2411. Y. Nishida T. Akamatsu K. Tsuchiya and M. Sakamoto Polyhedron 1994 13 2251. I. A. Salem M. Y. El-Sheikh A. B. Zaki and U. Nickel Int. J. Chem. Kinet. 1994 26 955. J. Ueda T. Ozawa M. Miyazaki and Y. Fujiwara J. lnorg. Biochem. 1994 55 123. R.V. Prasad and N.V. Thakkar J. Mol. Catal. 1994 92 9. S. Menage J. M. Vincent C. Lambeaux and M. Fontecave J. Chem. Soc. Dalton Trans. 1994 2081. '" I.A. Salem J. Mol. Catal. 1994 87 25. 19* I.A. Salem Polyhedron 1994 13 1547. Iy1 0.Costisor S.Policec and M. Mracec Chem. Bull. Tech. Univ. Zimisoara 1992 37 31 (Chem. Abstr. 1994 121 118 669v). W. Zhu and W. He Huadong Yejin Xueyuan Xuehao 1994 11 75 (Chem. Abstr. 1994 121 264767s). 193 W. Zhu and W. He Huadong Yejin Xueyuan Xuebao 1994,11 107 (Chem. Abstr. 1994,121,264768t). 194 P.J. Pessiki and G.C. Dismukes J. Am. Chem. SOC. 1994 116 898. 195 Y. Naruta and M. Sasayama J. Chem. SOC. Chem. Commun. 1994 2667. Y. Lei and J.K. Hurst Znorg. Chem. 1994 33 4460. lY7 Y. Lei and J.K. Hurst Znorg. Chim. Acta 1994 226 179. Inorganic Mechanisms 525 Mn,O partial cubane complex [Mn,O (OBz),(dbm),] Sawyer and coworkers have studied'99 the kinetics of the formation of H,O and [Fe"'(dipic)(dipicH)] from [Fe"(dipicH),] and 0 in py/HOAc solution and the reaction of H,O with excess complex to give a Fenton reagent.Meyerstein and coworkers in a review,200 distinguish between Fenton and 'Fenton-like' reagents on the basis of the nature of the electron-transfer process and the likelihood of forming free OH '. The nature of the radical species involved in the decomposition of the peroxo complex [VO(O,)(H,O),(pic)] has been investigated.,'' Oxygen acts as an inhibitor of the chain decomposition of [Ti(0,)(ox),l2 -initiated by Ti(m) Cr(n) or V(II).~'~ The chemistry of Fe(I1) and CO(II) dioxygen carriers,,03 the addition of 0 to Ni(r1)-thiolato complexes,2o4 and copper-dioxygen complexes205 have been reviewed. + [Cu,(NCEt),DI2 [D = 1,2-bis(5-pyridyl-2-(N,N-bis(2-pyridyl)methyl}amino-methyl)ethane a dinucleating ligand analogous to the mononucleating L = tris((2-pyridy1)methyl)aminel reacts206 with 0 at low temperatures to give complexes in which one Cu and then two Cu have bound but non-bridging 0 ligands; the rate of formation of the mono-adduct is similar to that of the formation of the analogous monodioxygen complex of the mononucleating ligand from [Cu'(NCEt)L] .Forma-+ tion of a p-(peroxo)dicopper(II) complex [CU,(~-O,)D]~+ is much more rapid than the equivalent reaction for the mono-nucleating ligand associated entirely with differences in the entropies of activation. From kinetic studies on a related complex,2o7 rate-determining dioxygen-adduct formation is preferred from a number of mechanis- tic possibilities. [{ CuBr(Et,en)},O,] formed from the CU(I) dimeric species [(C~Br(Et,en)},],~~~ decomposes to [(Cu"Br(Et,en)}O] with tt of 3.2 & 0.1h at 25°C.The process differs from that of analogous Et,en complexes in which intramolecular Cu(1tperoxide electron transfer is preferred. Kinetic data are re- ported209 for 0 addition reactions of Co(~k3,2,3-tet and -3,3,3-tet complexes the subsequent isomerization of monobridged p-peroxo monohydroxo complexes to the dibridged olate form the conversion of the latter into the monobridged dicobalt p-peroxo-dihydroxo complex and the irreversible reaction of the C0(11)-0 adducts to CO(III) complexes. 0 activation by trans-[FeCI,(cyclam)] +,,lo by dinuclear CU(I) complexes of xylylene ligands with two bis[2-(2-pyridyl)ethyl]amine moieties at- tached, '' the reversible formation of p-peroxodiferric complexes from 19' S.Wang H.-L.Tsai K. S. Hagen D. N. Hendrickson and G. Christou J. Am. Chem. Soc. 1994,116,8376. 199 C. Kang A. Sobkowiak and D.T. Sawyer Inorg. Chem. 1994 33 79. 2oo S. Goldstein D. Meyerstein and G.Czapski Free Radical Bid. Med. 1993,15,435 (Chem. Abstr. 1994 120 191 752a). M. Bonchio V Conte F. Di Furia G. Modena S. Moro and J. 0.Edwards Inorg. Chem. 1994,33,1631. 'O' N. Shinohara M. Iwasawa and T. Akiyama Bull. Chem. SOC. Jpn. 1994 67 1033. '03 P. R. Warburton and D. H. Busch in 'Perspectives on Bioinorganic Chemistry' ed. R. W. Hay J. R. Dilworth and K. B. Nolan JAI Press Greenwich CT 1993 Vol. 2. 204 M. Y. Darensbourg P. J. Farmer T. Soma D. H. Russell T. Solouki and J. H. Reibenspies 'Act.Dioxygen Homogeneous Catal. Oxid. [Proc. Int. Symp.]' ed. D. H. R. Barton A. E. Martell and D.T. Sawyer Plenum New York N.Y. 1993 209 (Chem. Abstr. 1994 121 164754s). '05 N. Kitajima and Y. Moro-oka Chem. Rev. 1994 94 737. '06 N. Wei D.-H. Lee N.N. Murthy Z. Tyeklar K. D. Karlin S. Kaderli B. Jung and A. D. Zuberbiihler Inorg. Chem. 1994,33 4625. 207 M. Becker S. Schindler and R. van Eldik Inorg. Chem. 1994 33 5370. '08 M.A. El-Sayed K.Z. Ismail T.A. El-Zayat and G. Davies Inorg. Chim. Acta 1994 217 109. '09 S. Cabani N. Ceccanti R. Pardini and M. R. Tine Gazz. Chim. Ital. 1994 124 327. 'lo Y. Nishida and N. Tanaka J. Chem. SOC.,Dalton Trans. 1994 2805. '11 K. D. Karlin M. S. Nasir B. I. Cohen R. W. Cruse S. Kaderli and A. D. Zuberbuhler J.Am. Chem. SOC. 1994 116 1324. 526 N. Winterton [Fe(OBz)(Tp”)],” and the formation from [Co”(H,0)(papd)12 + and 0 of the corresponding superoxo and p-peroxo complexes” have been reported. Rate- determining C-H bond cleavage is proposed with hydrogen tunnelling from the kinetics of decomposition of [(Co”L),(p-O,)] (IV) (L = Tp”) formed214 from 0 and Co” complexes of Tp”. Tunnelling is not evident for analogous reactions involving (IV) [L = [9]ane(NPri),]. ‘80-labelling studies have established that reaction of 0’ with [Fe!(bf)(Me,hdp)]+ (in which the two iron centres are bridged by the carboxylato group of bf and two phenolate groups) in air216 occurs 103-104fold faster than analogues not having the phenolate residues. Related studies have been described by Feig and Lippard2I7 on carboxylate alkoxo bridged complexes of Fe(r1).The effect on oxygen affinity of the basket size in Fe and Co complexes of the so-called ‘picnic basket’ porphyrins has been studied.,’’ Steric effects on the rates of 0 (and CO) dissociation in [FeL(Me,im)(por)] associated with the two methylene chains of varying lengths linking a durene moiety to the porphyrin in por (a durene-capped porphyrin) are less than expected.219 Mn(I1)-induced decomposition of [HOOSO,] -in HX follows22o the rate law -d[HOOSO;]/dt = k[HOOS0;][Mn2+]3’2/[Hf] ’/’ with k sensitive to both the nature and concentration of X-. A free-radical chain mechanism with bimolecular initiation is proposed with the amount of [SzOs]2- arising from chain termination being a measure of chain length (ca.15-20). Parallel reactions involving [Mn(aq)12+. [Mn(HSO,)] +,and [Mn(SO,)Mn]’+ are proposed221 for reaction between Mn(I1) and the peroxomonosulfate radical SO -[a key process for Mn(rI1) regeneration in the Mn(IIr/II)-catalysed autoxidation of S(rv) in aqueous acid]. The Ag+-catalysed oxidations by [S,OS]’- of [Co(en),(glygly)]’+ and [CO”W,,O~,]~- and the oxidation of bis(macrocycle)dinickel(iI) complexes by [s208]’-have been catalyticeffects ofFe2+ Fe3+ Mn2+,or Cu” were~een,,~ st~died.~’~-’’~No for the reaction of ozone with an excess of S(IV) present as SO;H,O HSO, and SO:- though the reaction is accelerated by 0 and by increased pH. Catalytic effects associated with addition of Fe(I1) and Fe(II1) were observed226 in related studies of the reaction of S(rv) with H,O,.Further mechanistic studies of the iron-catalysed autoxidation of bisulfite in aqueous sol~tion,~’~~~~’ of the oxidation of 0x0-S(rv) ’I’ N. Kitajima N. Tamura H. Amagai H. Fukui Y. Moro-oka Y. Mizutani T. Kitagawa R. Mathur K. Heerwegh C. A. Reed C. R. Randall L. Que Jr. and K. Tatsumi J. Am. Chem. Soc. 1994 116 9071 ’13 M. Maeder and H.R. Macke Inorg. Chem. 1994,33 3135. ’I4 0.M. Reinaud and K.H. Theopold J. Am. Chem. Soc. 1994,116 6979. ’I5 S. Mahapatra J. A. Halfen E. C. Wilkinson L. Que Jr. and W. B. Tolman J. Am. Chem. Soc. 1994,116 9785. ’I6 Y.-M. Chiou and L. Que Jr. Angew. Chem. Int. Ed. Engl. 1994 33 1886. ’” A. L. Feig and S. J. Lippard J. Am. Chem. Soc. 1994 116 8410.’I8 J.P. Collrnan X. Zhang K. Wong and J.L. Braurnan J. Am. Chem. Soc. 1994 116 6245. ’19 S. David B.R. James D. Dolphin T.G. Traylor and M.A. Lopez J. Am. Chern. Soc. 1994 116 6. 220 Z. Zhang J.O. Edwards and P.H. Rieger Inorg. Chim. Acta 1994 221 25. ”’ J. Berglund L. I. Elding G. V. Buxton S. McGowan and G. A. Salmon J. Chem. Soc. Faraduy Trans. 1994 90,3309. 222 P. Mohanty N. Das and J. K. Dei J. Indian Chem. Soc. 1994,71,143(Chem. Abstr. 1994,121,287 336q). 223 S. Dholiya A. Prakash and R.N. Mehrotra Indian J. Chem. Sect. A 1994,33,219 (Chem. Abstr. 1994 120 201 605w). 224 S.V. Rosokha and Y. D. Lampeka J. Coord. Chem. 1994 31 39. lZ5 C.F. Botha J. Hahn and J. J. Pienaar Atmos. Environ. 1994 28 3207. 226 L. Breytenbach W. van Pareen J.J. Pienaar and R.van Eldik Atmos. Environ. 1994 28 2451. 227 J. Ziajka F. Beer and P. Warneck Atmos. Environ. 1994 28 2549. 228 C. Brandt I. Fabian and R. van Eldik Inorg. Chem. 1994 33 687. Inorganic Mechanisms 527 species by [Tl(H2O)J3+ [Pt(CN),C1J2 - and Ni(rv) c~mplexes,~~~-~~~ and of the oxidation of SO;-by Cr(vr) have also been described.,, Non-metal Redox Reactions.-The rate constants and activation parameters for the forward (general-base assisted) and reverse (general-acid assisted) reaction CI + H,O = HOCl + Cl-+ H+ have been reevaluated using stopped-flow spec- Rate troph~tometry.~~~ constants have been obtained for the reactions Cl,(aq) + Br-= BrCl (by the pulsed-accelerated flow method),, and 235 NH,C1 + Br = NHBrCl + Br-+ H+; NH,C1 + Br = NHBrCl + 2Br-+ H+; NH,Cl + HOBr = NHBrCl + H,O; NH,C1 + OBr-= NHBrCl + OH- with nuc- leophilic attack of the lone pair on N bringing about Br+ transfer from its carrier.In excess Br,,NBr,Cl is formed and decays with a t+ of cu. 5 min at pH 6.2. The rate of bromous acid disproportionation 2HBr0 = HOBr + BrO + H+ is first order in uH+ second order in [Br(rrr)] and independent of [Br-].236 The kinetics of disproportionation of HOI (giving I-and 10 ) have also been Scavenging of hydrogen atoms by [TO,] -and [TO,] -in aqueous solution is believed to proceed by hydrogen-atom transfer giving HO and a reduced iodine species.,,* The kinetics of the reaction Me,NBH + 2HN0 + [H,O]+ = Me,NH+ + B(OH) + N,O + H + H,O have been reported.239 At low pH where protonation to give [NH,OH] suppresses reaction with Br, NH,OH reacts slowly with Br with + 1 :2 stoichiometry to give nitrous acid.,,' A subsequent slower reaction of [NH,OH] + with HONO gives N,O.The reaction is believed to involve a Br+ transfer to give NHBrOH which reacts rapidly with more Br giving NBr,OH. This loses Br- to give BrNO and then HONO. At pH 5-6 the reaction is much faster with the intermediate NHBrOH disproportionating to NH,OH and NBr,OH which hydrolyses to NO; and Br- . An eight-reaction scheme has been to describe the reactions of HO,SC(NH)NH and BrO; which has the stoichiometry 2Br0; + 3H0,S C(NH)NH + 3H,O = 3SO;-+ 3CO(NH,) + 2Br-+ 6H+ in excess sulfinic acid and 4Br0 + 5H02SC(NH)NH + 3H,O = 5SO:-+ 5CO(NH,) + 2Br2 + 6H+ in excess bromate with the oxidizing species being HOBr and Br, and the reaction BrO + Br-+ 2H' = HBrO + HOBr being rate determining.The self-exchange rate for the couple NH20H+/NH20H was estimated to be 5 10-*3~-1~-from a study of the oxidation of excess NH,OH by [IrC1,I2- (catalysis by Cu2+ and Fe2+ suppressed by oxalate),, having the rate law -d[IrCl;-]/dt = k,K,[jIrCl; p][NH,OH]/([H+] + Ka) where k is associated with 229 J. Berglund P. Werndrup and L. I. Elding J. Chem. Soc. Dalton Trans. 1994 1435. 230 J. Berglund R. Voigt S. Fronaeus and L.I. Elding Inorg. Chem. 1994 33 3346. 231 S. Bhattacharya M. Ali S. Gangopadhyay and P. Banerjee J. Chem. Soc. Dalton Trans. 1994 3733. 232 M. Wawrzenczyk and M. Cyfert Pol. J. Chem. 1994 68 1615 (Chem. Abstr.1994 121 239265~). 233 T.X. Wang and D. W. Margerum Inory. Chem. 1994,33 1050. 234 T.X. Wang M.D. Kelley J.N. Cooper R.C. Beckwith and D. W. Margerum Inorg. Chem. 1994 33 5872. 235 M. Gazda and D. W. Margerum Inorg. Chem. 1994 33 118. 23h R. de Barros Faria I. R. Epstein and K. Kustin J. Phys. Chem. 1994 98 1363. 237 V. W. Truesdale C. Canosa-Mas and G. W. Luther 111 J. Chem. SOC. Faraday Trans. 1994 90,3639. 238 S. P. Mezyk R. MacFarlane and D. M. Bartels J. Phys. Chem. 1994 98 12 594. 239 K.E. Bell and H.C. Kelly Spec. Puhl. n R. Soc. Chem. 1994 143 (Current Topics in the Chemistry of Boron) 94 (Chem. Abstr. 1994 121 188417k). 240 R. C. Beckwith J.N. Cooper and D. W. Margerum Inorg. Chem. 1994 33 5144. 241 C. R. Chinake R. H. Simoyi and S.B. Jonnalagadda J.Phys. Chem. 1994 98 545. 242 M.-L. Hung M.L. McKee and D. M. Stanbury Inorg. Chem. 1994 33 5108. 528 N. Winterton the transfer of an electron from NH,OH to Ir(Iv). Diazene an intermediate in the acid-assisted hydrolysis of azodiformate [O,CN=NCO,] -,undergoes dismutation 2N,H = N + NZH4 with second order kinetics243 and a deuterium kinetic isotope effect pointing to concerted transfer of both H atoms from a cis-N,H to trans-N,H after a trans-cis isomerization. A further has confirmed that the rate law for the oxidation of NO by 0 in aqueous solution takes the form -d[NO]/dt = k[N0I2 [O,]. Azide-trapping experiments support N,O as a reactive intermediate. The empirical rate law obtained in studies of the reaction of S(IV) and N(III) oxoacids suggestz4’ that HONO and HSO are the most important reacting species with HON(S0,); -the only identifiable S-N-oxoanion product.Mixed sulfur-nitrogen oxides such as ON(SO,)i- HON(SO,)z- and HONH(S0,)- to be involved in redox reactions of Mn(I1) and Mn(III) in aqueous solution may be responsible for the inhibition of metal-catalysed autoxidation of sulfur(1v) oxides in flue-gas desulfurization. The kinetics of the reaction of NO with [SCN] ,Br, CO have been in~estigated.’~’ The anaerobic decomposition of dithionite involves three distinct pathways:248 two are dominant at high [SO:-] one involving heterolytic cleavage of S,Oz- the other a homolytic cleavage with trithionate a key species; the third is dominant at lower [SO:-]. The reduction of polythionates by dithionite has also been Oscillating Reactions and Chemical Chaos.-A book on the dynamics of these phenomena has appeared.6 Mn(I1)-catalysed Belousov-Zhabotinsky reactions have been studied in aqueous2’’ and mixed aqueous organic sol~tion.~~~~~~~ The reaction intermediates in the oscillating reactions based on the permanganate/oxalic acid/sulfuric acid system have been shown from studies of the auxiliary reactions Mn(IrI)/oxalic acid/H,SO and Mn(Iv)/oxalic acid/H,SO, to be [Mn”(ox),] -and a soluble Mn(1v) complex.253 Various aspects of the Belousov-Zhabotinsky (B-Z) reaction have been st~died:,’~-*~~ acid intermediacy of 1,1,2,2-ethanetetracarboxylic 243 H.R.Tang and D.M. Stanbury Inorg. Chem. 1994 33 1388. 244 M. Pires M. J.Rossi and D. S. Ross Int. J. Chem. Kinet. 1994 26 1207. 245 M. GeiBler and R. van Eldik Polyhedron 1994 13 2983. 24h F. F. Prinsloo J. J. Pienaar R. van Eldik and H. Gutberlet J. Chem. Soc. Dalton Trans. 1994 2373. 247 G. Czapski J. Holcman and B. H. J. Bielski J. Am. Chem. Soc. 1994 116 11 465. 24H D.A. Holman and D. W. Bennett J. Phys. Chem. 1994 98 13 300. 249 V. Muenchow and R. Steudel Z. Anorg. Allg. Chem. 1994 620 121. 250 S. S. Sun H.-P. Lin Y.-F. Chen and J.-J. Jwo J. Chin. Chem. Soc. 1994,41,651 (Chem. Ahstr. 1995,122 55 474a). 2s1 P. V. Lalitha R. Ramaswamy G. Ramakrishnan and P. S.Rao Spectrochim. Acta Part A 1994,50,2345. 252 G. Maya P.V. Lalitha and R. Ramaswamy Can. J. Chem. 1994 72 1537. 253 V. Pimienta D. Lavabre G. Levy and J. C. Micheau J.Phys. Chem. 1994 98 13 294. 254 J. Wang P.G. Srarensen and F. Hynne J. Phys. Chem. 1994 98 2098. 25s J. Kosek P.G. Ssrensen M. Marek and F. Hynne J. Phys. Chem. 1994 98 6128. 256 P. E. Strizhak T. S.Ivashchenko and A. L. Kawczynski Pol. J.Chem. 1994,68,2047(Chem. Ahstr. 1995 122,65458h). 257 M. Dolnik J. Kosek V. Votrubova and M. Marek J. Phys. Chem. 1994 98 3707. 258 K. Rhathena and A.N. Ojha J. Ind. Chem. Soc. 1994 70 715 (Chem. Abstr. 1994 121 255 1932). 25y Z. Huang and K. Zhou Wuli Huaxue Xuehao 1994 10 449 (Chem. Ahstr. 1994 121 19 252x). 260 C. An X. Fang Y. Liu Z. Lin and R. Cai Wuhan Duxue Xuebao Ziran Kexueban 1993,56 (Chem. Ahstr. 1994 121 25765h). 261 X. Fang C. An Y. Liu Z. Lin and R. Cai Wuhan Daxue Xuebao Zirun Kexuehan 1994 100 (Chem.Abstr. 1994 121 188 423j). 2h2 D. Zhang L. Gyorgyi and W. R. Peltier Chaos 1993 3 723 (Chem. Ahstr. 1994 121 213979e). 263 G. Markham and K. Bar-Eli J. Phys. Chem. 1994 98 12248. 264 K. Kurincsorgei I. Szalai I. Molnarperl and E. Koros React. Kinet. Catal. Lett. 1994 53 115. Inorganic Mechanisms 529 rather than tartronic acid in the Ce(Iv)/malonic acid system;265 saturation of the reactive layer in a B-Z reaction-diffusion system by oxygen increasing the region in parameter space that supports propagation of solitary waves;266 observation of both inhibiting and activating reaction-diffusion waves in a shallow liquid layer in the absence of oxygen;267 classification of chemical waves based on an analysis of the shape of the dispersion ~~rve;~~~,~~~ photolumines~ence~~~ and other photochemi- ca1271 effects; stirring effects in bimolecular reactions and their relation to the B-Z reaction in a closed batch reactor;272 magnetic resonance imaging of the dynamics of kinematic waves arising from frequency gradients in an anisotropically cooling oscillating B-Z reaction;273 B-Z reaction in reversed micelles of AOT in octane;274 transitions between two steady states in the bistability region induced by the application of an electric current;275 and spiral break-up induced by an electric current.276 Oscillating reactions catalysed by a Ni"'(tim) complex in a bro-mate-pyruvic acid-sulfuric acid system have been described.277 Bistability has been studied in the nitric acid-hydroxylamine CSTR The unbuffered reaction between BrO and NH,OH is found to be strongly autocatalysed by H+.Bistability is exhibited in a flow reactor. Oscillations occur when the system is perturbed with an inflow of The oxidation of NH20H by BrO undertaken in the presence of ally1 alcohol displays clock-type kinetics and if gaseous products are removed aperiodic oscillations.2 82 Irregular oscillations are observed in a BrO,/SCN- batch system purged with nitrogen.283 Studies of the effect of transition metals on the oscillating reactions of thiourea and a variety of oxidants allow some discrepancies from earlier reports to be understood.284 A 14-step mechanism has been proposed285 to simulate the observed kinetics of the reaction between thiourea (used without purification) and bromate in acid.The dynamics of the chemical waves produced in the CI0,/thiourea286 and in the iodide/nitric systems are much affected by the exothermicity of the reaction. Studies of the chlorine 265 Y. Gao H.-D. Forsterling Z. Noszticzius and B. Meyer J. Phys. Chem. 1994 98 8377. 266 M. D. Eager M. Santos M. Dolnik A. M. Zhabotinsky K. Kustin,and I. R. Epstein J.Phys. Chem. 1994 98 10750. 267 M. Marek P. Kaitanek and S.C. Miiller J. Phys. Chem. 1994 98 7452. 268 R. R. Aliev and V. N. Biktashev J. Phys. Chem. 1994 98 9676. 269 R.R. Aliev J. Phys. Chem. 1994 98 3999. 'lo P. Ruoff Chem. Phys. Lett. 1994 226 295. 271 M.K. Ram Reddy Zs. Nagy-Ungvarai and S.C. Miiller J. Phys. Chem. 1994 98 12255. '"J. HlavaEova and P. SevEik J. Phys. Chem. 1994 98 6304.'13 S. Su M. Menzinger R. L. Armstrong A. Cross and C. Lemaire J. Phys. Chem. 1994 98 2494. '14 V.K. Vanag and D.V. Boulanov J. Phys. Chem. 1994,98 1449. '15 G. Dechert and F.W. Schneider J. Phys. Chem. 1994 98 3927. 276 J. J. Taboada A. P. Munuzuri V. Perez-Munuzuri M. Gomez-Gesteira and V. Perez-Villar Chaos 1994 4 519 (Chem. Abstr. 1994 121 309 275y). 277 Y. J. Zhang Z.Q. Xu L. Zhao N. L. Hu F.X. Xie and S. S. Ni Chin. Chem. Lett. 1994,5,295 (Chem. Abstr. 1994 121 66652n). 278 A. Horvath G. Pota and G. Stedman Int. J. Chem. Kinet. 1994 26 991. '19 E. Jones G. Pota and G. Stedman Catal. Lett. 1994 24 211 (Chem. Ahstr. 1994 120 254621e). 280 G. Pota and G. Stedman ACH Models Chem. 1994 131 229. M. Orban and I. R. Epstein J. Phys. Chem. 1994 98 2930."' L. AdamEikova T. Vranova and I. Valent Int. J. Chem. Kinet. 1994 26 347. 283 I. Valent and L. AdamEikova J. Phys. Chem. 1994 98 4304. 284 C. J. Doona and D. M. Stanbury J. Phys. Chem. 1994 98 12630. 285 R. H. Simoyi I. R. Epstein and K. Kustin J. Phys. Chem. 1994 98 551. 2R6 C. R. Chinake and R. H. Simoyi J. Phys. Chem. 1994 98 4012. 2R7 I. P. Nagy A. Keresztessy J. A. Pojman G. Bazsa and Z. Noszticzius J. Phys. Chem. 1994 98 6030. 530 N. Winterton dioxide-iodide the critical effect of IC1 or I as an intermediate in the ClO,/I-/malonic acid system,290 complex behaviour in the ClOi/SCN- and ClO,/SCN-~scillators,~~'~~~~ and the UV light ' sensitivity of the oscillatory ClO;/Cl-/iodomalonic acid system in a semi-batch have been described.Dioxygen is confirmed as a critical species in the iodate-catalysed decomposition of H,O (Bray reaction). Pressure effects on the oscillatory behaviour of the system have been described. 94 The Briggs-Rauscher system iodate/H ,0,/M~(II), the 9 iodate-arsenous acid297 system (including consideration of convective effects298) the H,0,/SO~-/[Fe(CN)6]4-~y~tern,~~~~~'~ and photoinduced effects in the H,0,/[Fe(CN)6]4-system3'' have been studied. Other investigations have been reported on propagation of chemical waves through capillary tubes3' and in thin gel layers.303 3 Substitution Six Coordination.-House has proposed304 that the rank order of AS* for thermal or Hg2 +-assisted aquation of a series of chloro-amine and chloro-ammine complexes reveals the effect of spectator ligands on the degree of interchange occurring as reaction proceeds.Two st~dies~'~~~'~ have reexamined the ring-opening processes in the hydrolysis of [CoL,(CO,)]"+ to ~is-[CoL,(H,0),]("~~)+. Both studies propose a pre-equilibrium protonation of CO; -followed by rate-determining ring opening and unimolecular cleavage of cis-[Co(H,0)(C03H)L41'"f I)+. Ring opening is much more sensitive than subsequent decarbo~ylation~~~ to the nature of L,. Aquation of a new trans-diastereoisomer of [CoC12(Me,cyclam)] occurs3o7 with retention of configur- + ation via a dissociative process involving a distorted square-pyramidal activated complex. Binuclear oxalato-bridged Cr(II)-Cr(III) intermediates are prop~sed~'~-~'' for the fast Cr(I1)-catalysed aquations of cis-[Cr(H,O),(bipy)(ox)] (to + [Cr(H,O),(ox)] +) [Cr(bipy),(ox)] +,and [Cr(NCS)4(ox)]3-.The aquation kinetics of [CoX(amine)(en),12 + (X = C1 Br) [Cr(Hpa)(ox),12 -,and of em-trans(py)-mer-288 M. Dolnik L. F. Abbott and I.R. Epstein J. Phys. Chem. 1994,98 10 124. 289 A. Hjelmfelt and J. Ross J. Phys. Chem. 1994 98 1176. 290 G. Rabai J. Phys. Chem. 1994 98 5920. 291 C.J. Doona and S.I. Doumbouya J. Phys. Chem. 1994,98 513. 292 C.R. Chinake E. Mambo and R.H. Simoyi J. Phys. Chem. 1994 98 2908. 293 G. Rabai and I. Hanazaki J. Phys. Chem. 1994 98 10550. 294 G. Laurenczy and M.T. Beck J. Phys. Chem. 1994 98 5188. 295 P.V. Lalitha N. Balasubramanian and R. Ramaswamy Collect. Czech. Chem. Cornmun. 1994,59 1596. 296 I.Love Int. J. Chem. Kinet. 1994 26 1143. 297 R.S. Li J. Chem. Phys. 1994 101 3840. 298 J. Masere D. A. Vasquez B. F. Edwards J. W. Wilder and K. Showalter J. Phys. Chem. 1994,98,6505. 299 V.K. Vanag Y. Mori and I. Hanazaki J. Phys. Chem. 1994 98 8392. 300 G. Rabai and I. Hanazaki J. Phys. Chem. 1994 98 2592. 301 Y. Mori G. Rabai and I. Hanazaki J. Phys. Chem. 1994,98 12968. 302 A. Toth V. Gaspar and K. Showalter J. Phys. Chern. 1994,98 522. '03 A.M. Zhabotinsky L. Gyorgyi M. Dolnik and I. R. Epstein J. Phys. Chem. 1994 98 7981. 304 D.A. House Comments Inorg. Chem. 1994 16 229. 305 S. S. Massoud and R. B. Jordan Inorg. Chim. Acta 1994 221 9. 306 D. A. Buckingham and C. R. Clark Inorg. Chem. 1994 33 6171 307 B.-H. Chen C.-Y. Lai Y. Yuan and C.4. Chung J.Chem. Soc. Dalton Trans. 1994 2959. 308 A. Katafias and P. Kita Pol. J. Chem. 1994 68 1889 (Chern. Abstr. 1994 121 239263s). 309 K. Mesbah and P. Kita Pol. J. Chem. 1993 67 2047 (Chem. Abstr. 1994 121 66724n). 310 A. Katafias and P. Kita Pol. J. Chem. 1992 66 1707 (Chem. Abstr. 1994 121 118634e). Inorganic Mechanisms 531 [CrCl(ampy)(triamine)12+have been described.31 lP3l3 Zinato314 has reviewed the chemistry of chromium(uI)-cyano-amineand -ammine complexes including mechan- istic aspects. Saturation kinetics for sulfur-donor ligand exchange in [Fe(CN),LI3 -(L = 1,4-thioxane 1,4-dithiane) is ascribed315 to the operation of a dissociative (D) mechanism. Rates ofaquation of these3' andrelated3I6 complexes [M(CN),(dtdp)] -(M = Fe Ru) and [Ru(NH3),(dtdp)12+ have also been reported.+ + [Cr(big),(pyridine 2-aldoximato)I2 forms317 from ~is-[Cr(big),(H,O),]~ by associative interchange. [M(H,0),(acpt)12+ (M = Fe(m) Cr(m) forms from [M(H,0)6]3f in aqueous acid by318 reaction of the enol tautomer of acptH with M3+ and [M(0H)l2'. I and Idprocesses have been proposed for reactions of respectively Fe3+ and [Fe(OH)I2 + with ald~xime-~l~ ligands. Forma- and hydro~amic~~'-type tion of [Rh(H,0),(~al)]~+ from [Rh(H20)6]3+ and salH is associative321 whereas displacement of H,O in [Ru(H2O),(tap),l2 by pyridine-2-aldoxime (LH) giving + [Ru(tap),L]+ is3, dissociative. An I process is preferred323 for the anation of [Ru(H,O)(Hedtra)] to [RuI(Hedtra)] -. Anation of [Cr(H,O),(nta)] by NCS- has been described.324 The anomalies associated with rates of substitution of H,O in [M(NH3)5(H20)]3+ (M = Ru 0s) by [M'(CN),]"- (M' = Fe(m) CO(III) n = 3; M' = Fe(Ir) Ru(II) n = 4) have already been discussed.117 Rapid displacement of H,O in [WO(CN),(H,0)I2- by pic- is followed by a ca.103-fold slower ring closure325 to give [WO(CN),(y2-pic)l2 -. The nitrido ligand in [OsN(CN),(H,O)] -labili~es~,~ trans-H,O towards substitution by N; . Dissociative substitution is proposed327 for the replacement of H,O in [ReN(CN),(H,0)I2- by CN-. Activation volume and related suggest that [Co(H,O),(Me,[ 141 aneN,)I2+ reacts with O, to give [CO(OO)(H,O)L]~+ via an interchange process with insignificant electron-transfer in the transition state. The large positive A V* for dissociation of 0 from [CO"'(OO)(H,O)L]~+ is consistent with electron-transfer preceding partial 0 release.A linear relationship329 between the activation par- ameters for the substitution in toluene of L in [CrCl(py-X)(tpp)] by 1-methylimidazole and the basicity of py-X is consistent with a limiting dissociative mechanism D.An Id mechanism for the substitution of H,O in aquocobalamin has been confirmed in two 311 J. Zsako and C. Varhelyi Magy. Kem. Foly. 1994 100 257 (Chem. Abstr. 1994 121 118 541x). '12 E. Kita Pol. J. Chem. 1993 67 645 (Chem. Abstr. 1994 121 244056s). 313 D. A. House S. Schaffner R. van Eldik A. McCauley and M. Zhender Inorg. Chim. Acta 1994,227 11. 314 E. Zinato Coord. Chem. Rev. 1994 129 195. 31s S. da S. S. Borges A. L. Coelho I.S. Moreira and M.A. B. de Araujo Polyhedron 1994 13 1015. 316 I. de Sousa Moreira and D. W. Franco Inorg. Chem. 1994 33 1607. 317 C. C. Mukhopadhyay and G. S. De Transition Met. Chem. 1994 19 49. 318 C.A. Blanco and J. Sumillera New J. Chem. 1994 18 223. 319 R.K. Mohanty A.K. Das and M. Das Ind. J. Chem. Sect. A 1994 33,932 (Chern. Abstr. 1994 121 214 146t). 320 S. Bandyopadhyay and D. Banerjea J.Ind. Chem. SOC. 1994,71,483 (Chem. Abstr. 1995,122,116 118m). 321 A.K. Ghosh and G. S. De Ind. J. Chem. Sect. A 1994 33 929 (Chem. Abstr. 1994 121 264746j). 322 B. Mahanti and G. S. De Transition Met. Chem. 1994 19 201. 323 A. Das H. C. Bajaj and D. Chatterjee Transition Met. Chem. 1994 19 111. 324 H. G. Visser J. G. Leipoldt W. Purcell and D. Mostert Polyhedron 1994 13 1051.32s A. Roodt S. S. Basson and J.G. Leipoldt Polyhedron 1994 13 599. 326 H. J. van der Westhuizen S. S. Basson J. G. Leipoldt and W. Purcell Polyhedron 1994 13 717. 327 *L.J. Damoense W. Purcell and J.G. Leipoldt Transition Met. Chem. 1994 19 619. 32n M. Zhang R. van Eldik J.H. Espenson and A. Bakac Inorg. Chem. 1994 33 130. 329 M. Inamo S. Sugiura H. Fukuyama and S. Funahashi Bull. Chem. SOC.Jpn. 1994 67 1848. 532 N. Winterton st~dies,~~',~~' Studies involving a with significant precursor-complex f~rrnation.~~' series of inorganic anions suggest that electronic effects are more important than steric effects.331 Principal component analysis has been applied to five experimental quantities (including logk for the displacement of py) for a series of 23 alkyl- cobaloximes [C~R(py)(dmg)~].~~~ Rates of axial substitution of L in [Co"'L(s- + bqdi),] (L = SbPh, AsPh,) support an associative interchange process.333 [(H,0)4Fe(p-OH),Fe(H20)4]4t reacts rapidly with 1,2-dihydroxy-3,5-benzenesul-fonate to give a dimeric complex more slowly dissociates to a monomeric complex and [Fe(H20)6]3t.The rate law for the hydrolysis of trans-[(NH3)3(H,0)Co(p-OH)Co(NH3)3(H20)]4+ aqueous HCI (giving in [CoCl,(NH,),(H,O)] and [CO(NH,),(H,O),]~+) contains acid-dependent and + -independent terms.335 Single bridge cleavage of [Co(ta~n)(p-OH),Co(tacn)]~ -+ occurs more rapidly336 than a similar cleavage in [(tacn)Co(p-OH),(p-+ + CH3C(0)NH)Co(tacn)13 . [(tmpa)Cr(p-O)(p-RC02)Cr(tmpa)]3aquation in-volve~~~~ rate-limiting carboxylate-bridge fission to give the short-lived [(RCO,)(tmpa)Cr(p-O)Cr(H,O)(tmpa)] before condensing intramolecularly to [(tmpa)Cr(p-OH),Cr(tmpa)] +.Replacement of terminal ligands in a p-oxo-p-carboxylato diiron complex of Fe(1Ir) with bipy occurs at each iron successively with rates (statistically corrected) which are Kinetic evidence has been reported339 for the formation of a 1 1 complex between [Mo,O,(H,O),]~+ and [vo(H20)512+. In aqueous solutions of f~c-RS-all-trans-[Co"'L,1~-[LH = N-(phos-phonomethyl)glycine] all eight possible geometric isomers interconvert rapidly by both twist and I mechanism^.^^' The isomerization of the chiral complexes [Co(edma),] + [Co(ida)(edma)] ,and [Co(mida)(edma)] ,341 the kinetics of ternary-complex formation of Co(r1) with nsa or pada and nta N,N'-edda N,N-edda dien or trien,342,343 of Ni(I1) with 2-aminomethylbenzimidazole and ~alicylaldehyde,~~~ and of Mn(rr)(M = Co Ni) with nta and SCN -,phen or bipy have been reported.345 The kinetics of complexation of [Cu(ida)] and [Cu(mida)] with NH or NH,Me via dissociative interchange with rate-determining axial coordination of the entering ligand;346*347 and the Cu(r~)-p- diketone complexation kinetics348 have also been described.330 F. F. Prinsloo M. Meier and R. van Eldik Inorg. Chem. 1994 33 900. 33' H. M. Marques 0.Q. Munro B. M. Cumming and C de Nysschen J. Chem. Soc. Dalton Trans. 1994 297. 332 L. Randaccio S. Geremia E. Zangrando and C. Ebert Inorg. Chem. 1994 33 4641. 333 S.Nemeth and L.I. Simandi Inorg. Chem. 1994 33 5964. 334 J. Chatlas and R. B. Jordan Inorg. Chem. 1994,33 3817. 335 K. Abdur-Rashid T. P. Dasgupta and J. Burgess J. Chem. Soc. Dalton Trans. 1994 2321. 336 P. Andersen H. Matsui K. M. Nielsen and A. S. Nygaard Acta Chem. Scand. 1994 48 542. 337 T. F. Tekut and R. A. Holwerda Inory. Chem. 1994,33 5254. 338 S.P. Watton A. Masschelein J. Rebek Jr. and S. J. Lippard J. Am. Chem. SOC. 1994 116 5196. 339 D. 0.Martire M. R. Feliz and A. Capparelli Transition Met. Chem. 1994 19 154. 340 D. Heineke S. J. Franklin and K. N. Raymond Inorg. Chem. 1994 33 2413. 341 T. Yasui T. Ama and H. Kawaguchi Polyhedron 1994 13 1963. 342 D.N. Hague and A.R. White J. Chem. SOC. Dalton Trans. 1994 3645. 343 M. A. Cobb D.N. Hague and A.R. White J. Chem. Soc. Dalton Trans. 1994 51. 344 A. C. Dash A.N. Acharya and R.K. Sahoo J. Chem. Soc. Dalton Trans. 1994 3727. 345 Sm. P. Chattopadhyay and D. Banerjea Polyhedron 1994 13 1981. 346 I. Fabian J. Chem. Soc. Dalton Trans. 1994 1355. 347 I. Fabian Con$ Coord. Chem. 1993 14th (Contributions to Developments of Coordination Chemistry) 349 (Chem. Abstr. 1994 120 228 398t). 348 J. Verdu and C. A. Blanco Int. J. Chem. Kinet. 1994 26 743. Inorganic Mechanisms 533 Base Hydrolysis.-Kinetics of the base hydrolysis of em-trans(py)-mer-[CrCl(ampy)(dpt)]'+ and exo-ci~(py)-mer-[CrCl(ampy)(2,3-tri)]~ +,suggest3I3 that pyridine coordinated cis to the leaving group does not accelerate the process compared with that in the analogous exo-mer-[CrC1(en)(2,3-tri)l2.Stereoretentive OH- + catalysed substitution of C1- in cis-[CrCl(OH)(bipy),] and base hydrolysis of + [Co(tacn)(daes)13' leading to [Co(OH),(tacn)] and then to [Co(ta~n)(OH),Co(tacn)]~have been st~died.,~~,~~' + Stereoselective isomerization by base of chiral complexes [Co(edma),] ,[Co(ida)(edma)] and [Co(mida)(edma)] + is thought to proceed uia five-coordinate intermediates formed by Co-0 rupture in the corresponding conjugate base.341 Base hydrolysis of [(tmpa)Cr(p-O)(p-RC0,)Cr(tmpa)l3+ (R # H) is to involve pre-equilibrium displacement of a pyridyl arm of tmpa by OH-followed by rate-determining opening of the RC0,-bridge with [(tmpa)Cr(p-OH),Cr(tmpa)] formed from either solvent or + coordinated OH -. Four Coordination.-Rate and equilibrium constants and activation parameters including a full volume profile have been reported3 51 for the aquation/anation reactions of [PtCI,(R-en)] and [PtCl(H,O)(R-en)]+ where R is a range of bicyclo- a1kyl groups.[Pt C1 ,(1R,2S,4S)-endo-2-aminomethyl)-2-amino-7-oxa bicycle[2.2.11 heptane}] is hydrolysed by a mechanism involving a five-coordinate intermediate rather than by a dissociative process with nucleophilic assistance of the 2-substituted norbornyl group. The rate of hydrolysis of [PtCI,{ 1,2-bis(n-XC,H4)-en)] (V) (n = 4 X = OMe CN F)is only weakly dependent on X and is also independent of [H'] in the range pH 2.2-7.2.352The slower hydrolysis of rneso-(V) (n = 2 X = OH) compared with the d-and !-isomers is ascribed353 to the presence of an extra Pt-0 contact in the meso-diastereoisomer hindering the approach of an incoming H,O.Both forward and reverse reactions [PtClL]' + am = [Pt(am)LI2++ C1-(L = 2,6-bis (met h ylsulfan ylmeth yl )p yridine 1,2- bis (p henylsulfany1)ethane) follow a two- term rate 1a~.~~~,~~~ For the forward reaction the second order rate constant is little affected by the basicity of am with steric effects being more important. Amine loss is very sensitive to the nature of am with an contribution to the Pt-N(sp3) bonding being proposed. Steric effects are also believed to be responsible for the 10 range in second-order rate constants for the displacement of either L = 5-aminoquinoline or diethyl sulfide from cis-[PtPh,(CO)L] by a series of aliphatic amines of similar basicity but of widely differing steric requirement^.^ 56 For the most sterically hindered amines reaction proceeds solely by a pathway independent of nucleophile probably involving initial dissociation of L.Halide displacement from [PtXYL] [L = 1,2-bis(phenylsul-fany1)ethane; XY = CI, Br, BrI ClT] with the nucleophiles C1- Br- and I-have been reported.357 The displacement of dmso in cis-[PtR,(dmso),] by bromazepam or 349 K. Mesbah and P. Kita Pol. J. Chem. 1993 67 2241 (Chem. Abstr. 1994 121 92888~). 350 E. Larsen S. Larsen G.B. Paulsen J. Springborg and D.-N. Wang Acta Chem. Scand. 1994,48 107. 351 J.-L. Jestin J.-C. Chottard U. Frey G. Laurenczy and A. E. Merbach Inorg. Chem. 1994 33,4277. 352 P.J. Bednarski and B. Triimbach Transition Met.Chem. 1994 19,513. 353 G.St. Nikolov N. Trendafilova H. Schonenberger R. Gust J. Kritzenberger and H. Yersin Inorg. Chim. Acta 1994 217 159. 354 B. Pitteri G. Marangoni and L. Cattalini J. Chem. Soc. Dalton Trans. 1994 3539. 355 M. Bellicini L. Cattalini G. Marangoni and B. Pitteri J. Chem. Soc. Dalton Trans. 1994 1805. 356 R.Romeo G.Arena L. M. Scolaro M. R. Plutino G. Bruno and F. Nicolo Inorg. Chem. 1994,33,4029. 357 B. Pitteri G.Marangoni L. Cattalini and L. Canovese J. Chem. Soc. Dalton Trans. 1994 169. 534 N. Winterton bipy via an associative mechanism for R = C1 and a (very much slower) dissociative process for R = Me. Rates of exchange of N-donor site for a series of monodentate Me,phen complexes cis-and trans-[PtX,(y1-Me,phen)(PPh3)] (X = C1 Br 1) and trans-[PtX(q1-Me,phen)(PPh3),]+are highly dependent on the trans ligand.359 The ca.104-fold larger rate constants for the substitution of the aqua ligand trans to the Pt-C bond in [Pt(H,0){C,H3X(CH2NMe2)}(NC5H4S03-3)] compared with [Pt(H,O)(dien)]’+ are not associated with any mechanistic change the processes in both cases being associative.360 The second order rate constants for the complexation of trans-[PtCl,(NH,),] trans-[PtCl(NH,),(H,O)]+ and trans-[Pt(NH3)2(H,0)2]2+ with the nucleoside inosine are in the ratios 1:200 10. Competition studies involving C1- and inosine allowed rate constants for the anation of the mono- and di(aqua) complexes to be estimated.361 Substitution reactions in cis-[Pt(NH,),(l-MeU),] cis-[PtCl(NH,),(l-MeU)] and cis-[Pt(NH,),(l-MeU)(H,O)] -are all to be associative processes.Sadler and coworkers have that 5’-GMP selectively displaces S-bound Met in [Pt(dien) {MeSCH,CH,CH(CO,)(NH:)}] in the presence of the other bases 5’-AMP + 5’-TMP and 5‘-CMP an observation which suggests a novel process for DNA platination. The order of reactivity364 for 5’-GMP with [PtCl(am),(MeIm-N3)] + is (am) = en > cis-(NH,) > tvuns-(NH,),. 5’-Nucleotides were found to be more reactive than 3’-nucleotides. The second generation anticancer drug carboplatin [Pt(NH,),(cbdca-O,O’)] gives a very stable ring-opened complex [Pt(NH,),(met- S)(cbda-0)] on reaction with L-methionine a complex detected as a metabolite.365 Other work related to the mode of action of antitumour platinum compounds366 includes studies of the reactions between cis-[Pt(NH,),(ntmp)] and [Pt(R,S-dach)(ntmp)] with oligonucleotide^,^^^ the reaction of oligonucleotides with di- + platinum complexes,368 the reactivity369 of [Pt(diamine)(soa)] and [Pt(dia-+ mine)(sob)] with 5’-GMP and the reaction3” of cis-[PtC1,(NH3),] with metal- lothienin.Related studies have been undertaken on Pd(I1) complexes.371 Reaction of [PdCl,(Me,en)] with Nu (Nu = inosine or 5’-INP) follows a two-step process uia the reactive species [PdCl(H,O)(Me,en)]+ and [Pd(Nu)(H,O)(Me,en)]’ +,with the steric effects of the amine ligand bringing about a change in reaction mechanism. The formation of [Pd(NH,),(cbdca-O,O’)] from [Pd(NH,),]’+ and cbdcaH involves372 358 M. Cusumano A.Giannetto and D. Minniti Inorg. Chim. Acta 1994 215 41. 359 F. P. Fanizzi M. Lanfranchi G. Natile and A. Tiripicchio Inorg. Chem. t994 33 3331. 360 M. Schmiilling A. D. Ryabov and R. van Eldik J. Chem. Soc. Dalton Trans. 1994 1257. 361 M. Mikola and J. Arpalahti Inorg. Chem. 1994 33 4439. 362 M Schmiilling B. Lippert and R. van Eldik Inorg. Chem. 1994,33 3276 363 K. J. Barnham M. I. Djuran P. del Socorro Murdoch and P. J. Sadler J. Chem. SOC. Chem. Commun. 1994 721. 364 D. Gibson G. M. Arvanitis and H. M. Berman Inorg. Chim. Acta 1994 218 11. 365 K. J. Barnham U. Frey P. del Socorro Murdoch J. D. Ranford P. J. Sadler and D. R. Newell J. Am. Chem. Soc. 1994 116 11175. 366 ‘Metal Complexes in Cancer Chemotherapy’ ed. B. K. Keppler VCH Weinhem 1993. 367 M.J. Bloemink J. P. Dorenbos R. J. Heetebrij,B. K. Keppler J. Reedijk and H. Zahn Inorg. Chem. 1994 33 1127. 368 P. K. Wu Y. Qu B. Van Houten and N. Farrell J. Inorg. Biochern. 1994 54 207. 369 A. Pasini G. D’Alfonso C. Manzotti M. Moret S. Spinelli and M. Valsecchi Inorg. Chem. 1994 33 4140. 370 B. L. Zhang and W.X. Tang J. Inorg. Biochem. 1994 56 143. 371 S. Suvachittanont and R. van Eldik Inorg. Chem. 1994 33 895. 372 K. J. Barnham M. I. Djuran U. Frey M. A. Mazid and P. J. Sadler J. Chem. SOC. Chem. Commun. 1994 65. Inorganic Mechanisms 535 rate-determining loss of NH,. [Pd(H,O)(bet-O)(en)]'+ and [Pd(en)(bet-0),I2+ formed from [Pd(H,0),(en)12+ rapidly exchange373 bet ligands at 353 K. Substitu-tion of tht in t~UnS-[Pd(C6F5)2(tht)2] by 2-methylpyridine associatively whereas the equilibrium of cis-and trans-[Pd(C,F,),(tht),] involves isomerization via [Pd(c,F,),(tht)].Equilibrium interconversion of cis- and trans-[(Rh(p-Cl)(CO) (PPh,)},] is also to proceed via a three-coordinate intermediate [RhCl(CO)(PPh,)]. Halide-bridge cleavage by substituted pyridines in square planar Pd and Pt complexes has been Replacement of acetate by trifluoroacetate in the ortho-metallated Rh(n) complex [Rh2(0,CMe),((C,H,)PPh2)] has also been studied kinetically.377 Phosphine exchange between trans-[IrCl(CO)(PPh,),] and trans-[PtHCl(PPh,),] proceeds diss~ciatively.~~~ The activation parameters for the breaking of the P-Ag bond in [(q6-p-cymene)Ru(p-pz),Ag(PPh3)] have been re- ported.379 Kinetics of replacement of Hbig in [Cu(Hbig),12+ by glycine or a-alanine (LH) to give the intermediate [Cu(Hbig)L+ and then [CuL,] have a ligand-dependent term (associative process) and a ligand-independent term (solvent-assisted dissocia- ti~n).,~' A re-e~amination~~l of the hydrolysis of [Cr,0,12- in the presence of the weakly nucleophilic base tris reveals evidence of two processes ascribed to the formation and decay of [CrO,(tris)].Similar studies in phosphate buffer point to3' the reversible formation of [HOP(0)20Cr207]4- which loses [Cr0,12- in a rate-determining process to give [(HO),POCr0,12- which reacts further both spontaneously as well as by specific H +,OH -,and general-base catalysis. Chromatoperiodate intermediates have also been postulated383 from studies of the periodate-catalysed oxygen exchange between [Cr0,12- and water.Despite the requirement that the conversion of the incompletely cuboidal [Fe,S,] + active site of aconitase (in its inactive form) into the [Fe(p-S),Fe(p-S),Fe] form + requires cleavage of one Fe-S(cys) and two Fe-S bonds and the formation of one Fe-S and two Fe-S(cys) bonds the reaction displays384 simple kinetics with a [H']- dependence. [Fe,S,]' the reduced form of the active site reacts385 with Fe(II) Mn(n) and CO(II) to give [Fe,MS,I2+ with values of the formation-rate-constants being >lo5 smaller than the rate constants for water-exchange in [M(H,0),]2+. The slowing of the reaction of L = RS- Br- with [Fe,S,Cl,(NCMe)] -as [L] is increased is the of a shift in mechanism with the lability of MeCN reduced by 373 T.G.Appleton A. J. Bailey D. R. Bedgood Jr. and J. R. Hall Inorg. Chem. 1994 33 217. 374 D. Minniti Inorg. Chem. 1994 33 2631. 375 G. Giordano and E. Rotondo Polyhedron 1994 13 2507. 376 D.St.C. Black G.B. Deacon and G. L. Edwards Aust. J. Chem. 1994 47 217. 377 S. Garcia-Granda P. Lahuerta J. Latorre M. Martinez E. Peris M. Sanau and M. A. Ubeda J. Chem. SOC.,Dalton Trans. 1994 539. 378 R. L. Rominger J. M. McFarland J. R. Jeitler J.S. Thompson and J.D. Atwood J. Coord. Chem. 1994 31 7. 379 D. Carmona J. Ferrer M. P. Lamata L. A. Oro,H.-H. Limbach G. Scherer J. Elguero and M. L. Jimeno J. Organomet. Chem. 1994 470 271. A.K. Das Transition Met. Chern. 1994 19 395. 381 N. E. Brasch D.A. Buckingham and C.R. Clark Inorg. Chem. 1994,33 2683 382 N. E. Brasch D.A. Buckingham and C. R. Clark Aust. J. Chem. 1994 47 2283. 3n3 A. Okumura M. Kitani and M. Murata Bull. Chem. SOC. Jpn. 1994 67 1522. 3n4 H.-Y. Zhuang and A.G. Sykes J. Chem. SOC.,Dalton Trans. 1994 1025. 385 K.Y. Faridoon H.-Y. Zhuang and A.G. Sykes Inorg. Chem. 1994 33 2209. 386 R. A. Henderson and K. E. Oglieve J. Chem. Soc. Chem. Commun. 1994 1961. 536 N. Winterton ~ complexation of L. The reaction [Fe4S4X412 (X =C1 Br) +RS-=[Fe4S4X,(SR)I2-+ X-is ~atalysed,~~ by protons though the site of protonation is not known. Five Seven and Higher Coordination Number.-A negative AP expected for an I process is seen388 for water exchange and complex formation for [Cu(H,O)(tren)I2 +. Both homometallic and heterometallic exchange of halide in the five-coordinate complexes [RuHX(CO)(PR,),] [IrH,X(PR,),] and [RuX(PR,)Cp*] (X = C1 Br) is rapid compared with similar exchanges involving X = H OSiPh, and C,Ph and involves389 the intermediacy of halide- or hydride-bridged dimers.An associative mechanism is proposed390 for the substitution of iodide in the trigonal bipyramidal [PdI(pp,)]+ by P(OMe),. Reaction of [RuHCl(PPh,),] with a series of alkenes proceeds by parallel associative and dissociative with the latter predominating. Rate-determining phosphine dissociation competes with a unimolecu- lar process392 in the cis-trans equilibration of the triply metal-metal bonded [{ WCI,(NHBu')(PR,)},] (R = Me, Me,Ph). Structural correlation analysis used for the determination of reaction pathways in five-coordinate metal complexes has been reviewed.393 The isomerization of trigonal bipyramidal isomers of the oxacalix[3]arene complex [TiIV(acac)L] (L = t-butyloxacalix[3]arene) has been studied.394 Substitution of OH- in seven-coordinate [Re111(OH)(terpy)2]2+ by SCN- involves39s a rapid pre-equilibrium protonation followed by rate-determining replace- ment of H,O possibly via a six-coordinate intermediate.Ligand Exchange.-Funahashi Swaddle and coworkers have reported the need to correct for the effect of paramagnetic relaxation on apparent AV* values for exchange reactions in solution measured by NMR.396 Three distinct pathways have been for the "0 exchange between labelled [(H,0)4Cr(y-OH),Cr(H20)4]4+ and bulk water two corresponding to exchange of water cis (slow) and trans (fast) to the bridging OH with the third arising from the release of label from Cr(p-OH),Cr via fission and reformation of the bridge.Water exchange in [Cu(H,0)(tren)12+ is >lo3 times slower than for [CU(H,O),]~+ and is believed388 to involve associative interchange I,. Greater steric interactions in [M(NH,Me),(H20)l3+ (M = Cr Co Rh) compared with [M(NH3)s(H,0)]3+ cause the mechanism of water exchange to become more dissociatively activated.398 For the pentaamine complexes water exchange is I for M = Cr I for M = Co and borderline for M = Rh. Studies on the MRI contrast agents have been extended399 to include complexes of the amido ligand dtpa-bmaH,. Water exchange in 3R7 R.A. Henderson and K. E. Oglieve J. Chem. Soc. Chem. Commun. 1994 377. 38R D. H. Powell A. E. Merhach I. Fabian S. Schindler and R. van Eldik Inorg. Chem. 1994 33 4468. 389 J.T. Poulton B. E. Hauger R. L. Kuhlman and K.G. Caulton Inorg. Chem. 1994 33 3325. 390 S. I. Aizawa and S. Funahashi Chem. Lett. 1994 2023. '')' G. Alibrandi and B. E. Mann J. Chem. Soc. Dalton Trans. 1994 951. 392 H. Chen F.A. Cotton and Z. Yao Inorg. Chem. 1994 33 4255. 3')3 T. Auf der Heyde Angew. Chem. Int. Ed. Engl. 1994 33 823. 3y4 P. D. Hampton C. E. Daitch T. M. Alam Z. Bencze and M. Rosay Inorg. Chem. 1994 33 4750. 395 J. Rall F. Weingart D. M. Ho M. J. Heeg F. Tisato and E. Deutsch Inorg. Chem. 1994 33 3442. 396 H. D. Takagi K. Matsuda S. Aizawa S. Funahashi S.D. Kinrade and T.W. Swaddle Can. J. Chem. 1994 72 2188. 3L)' S.J. Crimp L. Spiccia H.R. Krouse and T. W. Swaddle Inorg. Chem. 1994 33 465. 39H G. Gonzilez B. Moullet M. Martinez and A.E. Merhach Inorg. Chem. 1994 33 2330. 399 G. Gonzilez D. H. Powell V. Tissieres and A. E. Merbach J. Phys. Chem. 1994 98 53. Inorganic Mechanisms 537 [Gd"'(H,O)(dtpa-bma)] is found to be limiting-dissociative (D).3999400 Exchange between free and coordinated water in [La"'(NO,),(H,O)] in MeCN has also been Water-exchange kinetics are included in a review4' of the chemistry of aqua-organotransition metal ions. The rate law for exchange of I8O between [Cr0,12-and solvent H,O catalysed by periodate is interpreted383 in terms of a reversible condensation between chromate and periodate.to form [0,Cr01(0),(OH),] -. Studies of the equilibrium between planar [Ni(cr)12 + and the six-coordinate solvate [Ni(MeOH),(cr)I2 preclude a two-step mechanism with a five-coordinate intermedi- + ate for the solvent exchange process.403 Exchange of oxygen-bound dmso is slower404 + in [Co(dmso),{tmpyp(4)}] than in [CoCl(dm~o){tmpyp(4)}]~+. Exchange of D-cysteine in the ternary complex [Cu"(X-cys)(L-gly)] (X = L D) was found to be ca. 1.7 times faster than the L diastereois~mer.~~~ Ligand-exchange kinetics in [RhX(PPh,),] and in [RhHClX(PPh,),] (X = C1- ONO, NH,) have been studied by magnetization-transfer methods.406 Exchange of free acacH with [Ce(acac),] (and the effect of added dmso) are exp1ained4O7 in terms of parallel reactions both via a nine-coordinate intermediate [Ce(acacH)(acac),] one involving proton transfer from acacH to a departing acac- the other involving opening of an Ce-acac chelate ring.Reactions of Coordinated Ligands and Linkage Isomerism.-Proton-transfer kinetics involving [M0,(CN),]'" ,)-(M = Mo(Iv) W(IV); n = 2 Tc(v) Re(v); n = l), + exemplified by the reaction [MoO(CN),(0H)l3-+ OH-= [MoO,(CN),] 4-+ H,O have been studied by Merbach and coworkers.408 The role of ligand protonation in the hydrolysis of carbonato-Co(II1) complexes has already been described. 5,3 Aquation of [Os(NH,),(q ,q -CH,=CHCO ,H),] + to [Os(NH,),(H,0)(q2-CH2=CHC02H)]2+, accelerated by HX (X = PF,) proceeds by dissociation of the q2-link and protonation at the d electrons of the metal followed by substituti~n.~~~~~~~ With X = Cl or CF,SO, X adds to the fi-carbon after the q2-link opens followed by protonation to give OS(IV)-H complexes without loss of the q1 ligand.In base H-D exchange on the SCH,H groups of [Co(tacn)(daes)13+ is several orders of magnitude faster than for other CH groups in the complex with Ha being 10times faster than H,; the differences are associated4' ' with differences in p,-d interactions in the relevant carbanions and intramolecular hydrogen-bond formation. Similar activation has been noted for [Co(tame)(aeaps)13 +,which is in equilibrium with a Co-carbon-bonded form.41 C-H-bond activation associated with metal 400 S. Aime M. Botta M. Fasano S. Paoletti P. L. Anelli F. Uggeri and M. Virtuani Inorg.Chem. 1994,33 4707. 401 Z.G. Chen and C. Detellier Can. J. Chem. 1994 72 1797. 402 U. Koelle Coord. Chem. Rev. 1994 135 623. 403 J.K. Beattie and W. E. Moody J. Coord. Chem. 1994 32 155. 404 M. Lin and L.G. Marzilli Inorg. Chem. 1994 33 5309. 405 A. Hanaki Chem. Lett. 1994 1263. 406 L.A. Bengtsson B.T. Heaton J.A. Iggo C. Jacob G. L. Monks J. Ratnam and A.K. Smith J. Chem. SOC. Dalton Trans. 1994 1857; Corrigendum J. Chem. Soc. Dalton Trans. 1994 3335. 407 T. Mihara H. Tomiyasu and W.-S. Jung Polyhedron 1994 13 1747. 408 A. Roodt J.G. Leipoldt L. Helm and A. E. Merbach Inorg. Chem. 1994 33 140. 409 F. S. Nunes and H. Taube Inorg. Chem. 1994 33 311 1. 410 F.S. Nunes and H. Taube Inorg. Chem. 1994 33 3116. 411 P. Kofod E. Larsen and J. Springborg Acta Chem.Scand. 1994 48 611. 412 P. Kofod E. Larsen J. Springborg S. Larsen T. A. Larsen R. J. Geue and G.H. Searle Aust. J. Chem. 1994 47 11 1. 538 N. Winterton complexation has been investigated for 1 -methylimidazole4' coordinated to Cr(m) acetonitrile4I4 bonded to CO(I) and Cp in [l.l]metall~cenophanes.~~~ Swaddle Sargeson and coworkers from studies of cage complexes of Rh(111),~~' propose mechanisms of formation of the contracted N@) and CU(II),~~ cavity cage complex [Co(Me,0H-absar)13 from the nitro-capped [Co(Me,NO,- + sar)] ;of related reactions of the N,S,-cage complex [Co(NO2-capten)l3 +;and for + the formation of trans-(O,O)-[C~(H,O)(dhnc)]~ + .In the formation of lactic acid from methylglyoxal by cycb-Cr(m) complexes bidentate coordination of methylglyoxal is followed by protonation dehydration carbocation formation intramolecular 1,2- hydride shift and depr~tonation.~~~ Metal-ion catalytic effects have been described for carboxylate-ester hydroly- sis,423-426on nitrile427-430 and amide and for phosphate-ester transe~terification~~~.~~~ and hydrolysis,438446 including nucleosides and nucleo- tide~,4~~-~" with particular interest in the role of rare earth metals.432,437,439 449 4487 413 E.Buncel 0.Clement and I. Onyido J. Am. Chem. SOC. 1994 116 2679. 414 E. Fujita and C. Creutz inorg. Chem. 1994 33 1729. 415 U. T. Mueller-Westerhoff T. J. Haas G. F. Swiegers and T. K. Leipert J. Organomet. Chem. 1994,472 229. 416 R. J. Geue P. Osvath A.M. Sargeson K.R. Acharya S. B. Noor T. N. Guru Row and K. Venkatesan Aust. J. Chem. 1994 47 51 1. 417 I. I. Creaser T. Komorita A.M. Sargeson A.C. Willis and K. Yamanari Aust. J. Chem. 1994,47,529. 418 P. Osvath and A.M. Sargeson Aust. J. Chem. 1994,47 807. 419 P. M. Angus B.T. Golding S. S. Jurisson A. M. Sargeson and A. C. Willis Aust. J. Chem. 1994,47,501. 420 R. J. Geue M.B. McDonnell A. W.H. Mau A.M. Sargeson and A. C. Willis J. Chem. SOC.,Chem. Commun. 1994,667. 421 P. V. Bernhardt J. M. Harrowfield D. C. R. Hockless and A.M. Sargeson Inorg. Chem. 1994,33,5659. 422 E. Bang J. Eriksen L. M~rnsted and 0.Mernsted Acta Chem. Scand. 1994 48 12. 423 M. H. Jeong J.G. Noh T. W. Kim C. S. Kim and S.Y. Hong Bull. Korean Chem. SOC.,1994 15 263 (Chem. Abstr. 1994 121 56 773p).424 E. Kimura I. Nakamura T. Koike M. Shionoya Y. Kodama T. Ikeda and M. Shiro J. Am. Chem. SOC. 1994 116,4764. 425 H. Chakraborty N. Paul and M. L. Rahman Transition Met. Chem. 1994 19 524. 426 H. Chakraborty and M. L. Rahman Transition Met. Chem. 1994 19 481. 42' A. Erxleben I. Mutikainen and B. Lippert J. Chem. SOC.,Dalton Trans. 1994 3667. 428 T. Yamaguchi H. Adachi T. Ito and Y. Sasaki Bull. Chem. SOC. Jpn. 1994 67 3116. 429 E.C. Wilkinson Y. Dong and L. Que Jr. J. Am. Chem. Soc. 1994 116 8394. 430 Z.N. da Rocha G. Chiericato Jr. and E. Tfouni Inorg. Chem. 1994 33 4619. 431 M. H. Chou D. J. Szalda C. Creutz and N. Sutin Inorg. Chem. 1994 33 1674. 432 M. Yashiro T. Takarada S. Miyama and M. Komiyama J. Chem. SOC. Chem. Commun. 1994 1757.433 L. Zhu and N.M. KostiC Inorg. Chim. Acta 1994 217 21. 434 L. Zhu L. Qin T.N. Parac and N. M. KostiC J. Am. Chem. SOC. 1994 116 5218. 435 K. B. Nolan L. P. Ryan and E. B. Gonzalez Inorg. Chim. Acta 1994 215 55. 436 D. Wahnon R.C. Hynes and J. Chin J. Chem. Soc. Chem. Commun. 1994 1441. 437 K.O. A. Chin and J.R. Morrow inorg. Chem. 1994 33 5036. 438 A. Tsubouchi and T.C. Bruice J. Am. Chem. SOC. 1994 116 11 614. 439 N. Takeda M. Irisawa and M. Komiyama J. Chem. Soc. Chem. Commun. 1994 2773. 440 C. 0.Rodriguez de Barbarin N. A. Bailey D. E. Fenton and Q. He Inorg. Chim. Acta 1994,219 205. 441 J.A. Connolly M. Banaszczyk R.C. Hynes and J. Chin Inorg. Chem. 1994 33 665. 442 J. K. Yang S.I. Chang S.G. Ryu and Y. S. Yang Bull. Korean Chem. Soc. 1994,15,261 (Chem.Abstr. 1994 121 108984e). 443 A. J. Burn S. K. Dewan I. Gosney K. G. McKendrick C. P. Warrens J. P. Wastle and C. W. Watson J. Chem. SOC. Perkin Trans. 2 1994 373. 444 J. Suh,N. Kim and H. S. Cho Bioorg. Med. Chem. Lett. 1994,4,1889(Chem. Abstr. 1994,121,230869m). 445 R. Breslow and B. Zhang J. Am. Chem. Soc. 1994 116 7893. 446 C.0.Rodriguez de Barbarin N. A. Bailey D. E. Fenton and Q. He Inorg. Chim. Acta 1994 219 205. 447 S.S. Massoud J. Inorg. Biochem. 1994 55 183. 448 J. Sumaoka S. Miyama and M. Komiyama J. Chem. SOC. Chem. Commun. 1994 1755. 449 J.R. Morrow and V. M. Shelton New J. Chem. 1994 18 371. 450 R. 0. Dempcy and T.C. Bruice J. Am. Chem. Soc. 1994 116 4511. Inorganic Mechanisms 539 The role of binuclear metal complexes has also been reviewed.45 ' Hydroxyethylphos-phate forms a monodentate complex with [Co(H,O),(tren)I3 + (and is thereby rapidly hydrolysed) whereas a bidentate complex resistant to hydrolysis is formed441 with [Co(H2O),(trpn)l3+ .Ce(1v) effects a 10' ,-fold acceleration under physiological conditions for the hydrolysis of 3',5'-cyclic monophosphates of adenosine and guanosine in aqueous media made homogeneous by the addition of y-cy~lodextrin.~~~ Cu(1)-catalysed decarboxylation of malonic the intermediacy of metal formyls in amine-catalysed reactions of [trans,trans-W(CO),(NO)(NH=NH)(PPh3),] + ,453 the enhanced reactivity of N' and N7 towards alkylation associated454 with coordination of cyclen in fac-[M(CO),L] (L = cyclen M = Cr Mo) and the oxidation of thioether mustards by t-butyl hydroperoxide catalyzed by hetero- have all been studied.Nitroarene~~,~ polyoxometalate~~~~ react with [Ru(CO),fdppe)] uia a rate-determining electron transfer. [ArNO,] -and + [Ru(CO),(dppe)] react further to give CO and [Ru(CO),(q'-ONAr)(dppe)]. The kinetics of the reaction of [WCl(CO),]- and OMe- have been as part of an investigation of the synthesis of formaldehyde [W(OMe)(CO),] -= [WH(CO),] -+ H,CO. Carboxylate-carbonyl exchange in [Fe(' 3C0,SnMe3)(CO),Cp*] to give [Fe(CO,SnMe,)(CO)(' 3CO)Cp*] with decarboxylation to give [Fe(SnMe,)(CO)(' 3CO)Cp*]. Methanolysis of [Co(COMe)(CO),] is reported459 to proceed via nucleophilic displacement of [Co(CO),] -at the acyl carbon. Addition of MeO-to [M(CO),{C(OMe)Ph}] (M = Cr W) believed to give [M(CO),{C(OMe),Ph)] - is slower than the corresponding reaction for MeOC(O)Ph associated with charge delocalization in the complex.460 Mechanistic aspects of other reactions of metal ~arbenes,~~ of a phosphinidene complex,464 and of complexed isocyanide aminocarbene and aminocarbyne have also been described.Catalysis of substitution reactions of trans-[W(NCMe),(PMe,Ph)(q2-C0Me)Cpl2 + and related complexes by tertiary phos- phine~~~* results from the reversible reaction of the phosphine at the carbonyl carbon of the acetyl group as in [W(NCMe),(PMe,Ph){q2-C0Me(PMe,Ph)}Cpl2+, in which the q2 ligand exerts a strong cis-labilizing effect. Pentavalent phosphorus intermediates have been proposed469 in the deamination of aminophosphites coor- dinated to [FeL,Cp] (L = CO PPh,) by reaction with OH-.Oxidation of phosphite 451 M. W. Gobel Angew. Chem. Int. Ed. Engl. 1994 33 1141. 452 D. J. Darensbourg M. W. Holtcamp B. Khandelwal and J. H. Reibenspies Inorg. Chem. 1994,33 531. 453 T.-Y. Cheng J.C. Peters and G. L. Hillhouse J. Am. Chem. SOC. 1994 116 204. 454 V. Patinec J. J. Yaouanc H.Handel J. C. Clement and H. des Abbayes Inorg. Chim. Acta 1994,220,347. 455 R.D. Gall M. Faraj and C.L. Hill Inorg. Chem. 1994,33 5015. 456 S. J. Skoog J. P. Campbell and W. L. Gladfelter Organometallics 1994 13 4137. 457 C. Ovalles C. Fernandez and D.J. Darensbourg J. Mol. Catal. 1994 93 125. 458 J.R. Pinkes and A. R. Cutler Znorg. Chem. 1994,33 759. 459 J. Sovago A. Sisak F. Ungvary and L.Marko Inorg. Chim. Acta 1994 221 297. 460 C. F. Bernasconi F. X. Flores J. R. Gandler and A. E. Leyes Organometallics 1994 13 2186. 461 M.F. Gross and M.G. Finn J. Am. Chem. SOC. 1994 116 10921. 462 D. F. Harvey E.M. Grenzer and P.K. Gantzel J. Am. Chem. SOC. 1994 116 6719. C. Bouancheau A. Parlier M. Rudler H. Rudler J. Vaissermann and J. C. Daran Organometallics 1994 13 4708. 464 J.-T. Hung,S.-W. Yang P. Chand,G. M. Gray and K. Lammertsma,J. Am. Chem. SOC. 1994,116,10966. 465 M. A. N. D. A. Lemos M. F. C. Guedes da Silva and A. J. L. Pombeiro Inorg. Chim. Acta 1994,226,9. 466 F.E. Hahn M. Tamm and T. Lugger Angew. Chem. Int. Ed. Engl. 1994 33 1356. 467 B. Crociani F. Di Bianca A. Fontana E. Forsellini and G. Bombieri J. Chem. SOC. Dalton Trans. 1994 407.468 V. Skagestad and M. Tilset Organometallics 1994 13 3134. 469 H. Nakazawa K. Kubo K. Tanisaki K. Kawamura and K. Miyoshi Inorg. Chim. Acta 1994,222 123. 540 N. Winterton to phosphate by dioxygen coordinated to dicobalt-obisdien complexes has been studied.470 [W(SPh),(CO)(phen)(q'-SO2)]reacts to give [W(SPh),O,(CO)(phen)] CO and elemental sulfur in a first-order process (rate unaffected by excess CO) ' to involve rate-determining S-0 bond cleavage. Buckingham in a review472 of linkage isomerism of thiocyanate complexed to CO(III) has proposed a new mechanistic classification for metal substitutions. Noteworthy are the mechanistic contributions of Jackson and coworkers in their of 0-and N-bound [C0(NH,),(2-pyridone)]~+,the use 474 of regiospecifi- cally 'N-labelled complexes to demonstrate intramolecular linkage isomerism via a proposed q2 n-bonded intermediate in [Co(NH,),(5-methyltetrazolato)]2 +,and 'to distinguish between neighbouring group participation and n-bonded inter- mediates in N-to-N ligand rearrangement in [Co(NH,),(succinic amide nitrile)] +.of Hg2+-induced aquation of [Cr(CN)(NH,)J2+ suggest that 1:1and 1:2 adducts are formed and that linkage isomerization of [Cr(CNHg)(NH3),l4+ to [Cr(NH,),(NCHg)l4+ occurs. Linkage isomerism is also seen in L-cysteinesulfinato- N,S complexes477 of Co"' glutamic acid complexes478 of Pt" sulfoxide com- plexes479*480 of Ru" and Ru"' alizarin complexes481 of Ru" in reactions482 associated with tautomeric forms of acetamide and 1,l-dimethylurea with Pt" in pyridazine and 4-methylpyridazine complexes483 of Pt" and Re' and in the slow intramolecular isomerizati~n~~~ of [Pt(CN)4C1(OS0,)]3 -to [Pt(CN),C1(S0,)I3 -.Activation par- ameter~~~~ for the process [Ru,C(CO),,(p-q2 :q2 :q2-C,H6)] +[Ru,C(CO),,(q6-C&,)] suggest that the isomerization is associative with p2-q3:q3-C,H6 or p2-q4:q2-C6H6 bonded species proposed as transition states or intermediates.Metal-ion Complexation with Macrocycles-Further studies have appeared on the effect of solvent on the alkali metal ion of complexation and decomplexation with 'bibracchial lariat' ethers [15]aneO,(NR) and [18]ane04(NR) with pendant arms R = CH,CH,OCH, CH,CH,0H.485,486 Decomplexation of the ligand C22C5 from [Li(C22CS)]+,a unimolecular process,487 is slower in acetonitrile than in methanol or dmf.In contrast [Li(C221)]+ exchanges Li+ by a bimolecular process involving a transition state in which C221 is bound to 2 Li'; the binding of the second lithium is 470 R. J. Motekaitlis and A. E. Martell Inorg. Chem. 1994 33 1032. 471 R. F. Lang T. D. Ju C. D. Hoff J. C. Bryan and G. J. Kubas J. Am. Chem. SOC. 1994 116 9747. 472 D.A. Buckingham Coord. Chem. Rev. 1994 1351136 587. 473 P. M. Angus and W.G. Jackson Inorg. Chem. 1994 33 411. 474 W.G. Jackson and S. Cortez Inorg. Chem. 1994 33 1921. 475 P. M. Angus and W.G. Jackson Inorg. Chem. 1994 33 1569. 476 M. Rievaj D. Bustin J. MocLk P. Riccieri and E. Zinato Inorg. Chim. Acta 1994 216 113. 477 F. M. D. Akhter M. Kojima M. Hirotsu S. Kashino and Y.Yoshikawa Chem. Lett. 1994 2393. 478 Y.-A. Lee J. Hong 0.-S. Jung and Y. S. Sohn Bull. Korean Chem. Soc. 1994,15,669(Chem. Abstr. 1994 121 244 203b). 479 D.O. Silva and H. E. Toma Can. J. Chem. 1994 72 1705. 480 A. Tomitaand M. Sano Inorg. Chem. 1994 33 5825. 4R1 A. DelMedico P. R. Auburn E.S. Dodsworth A. B. P. Lever and W. J. Pietro Inorg. Chem. 1994 33 1583. 482 D.P. Fairlie T.C. Woon W.A. Wickramasinghe and A.C. Willis Inorg. Chem. 1994 33 6425. 4x3 E. W. Abel E. S. Blackwall P.J. Heard K. G. Orrell V. Sik M. B. Hursthouse M. A. Mazid and K. M. A. Malik J. Chem. SOC. Dalton Trans. 1994 445. 484 P.J. Dyson B. F.G. Johnson and D. Braga Inorg. Chim. Acta 1994 222 299. 485 J.B. Lucas and S. F. Lincoln J. Chem. SOC. Dalton Trans. 1994 423. 486 J.B.Lucas and S. F. Lincoln Inorg. Chim. Acta 1994 219 217. 487 R. Dhillon and S.F. Lincoln Aust. J. Chem. 1994 47 123. Inorganic Mechanisms 541 ascribed to the presence of the extra ether oxygen in the macrocycle. A V* for the loss of L from [Na(C222)] + in ethylenediamine is large and positive consistent488 with a dissociative process. The effect of side-arm amide and ester groups in a series of aza-crown ethers on the mechanisms of sodium-ion exchange has also been re-For ligands containing a tertiary amide side-arm direct exchange of Na+ between two ligand molecules was observed.490 Anion effects are noted491 in Li' and Na' complexation by crown ethers and an acylic polyether in the low donor-number solvent nitromethane. Binding between Ca2 + and 4-(N-monoaza- 15- crown-5)-4'-phenylstilbene has been on the picosecond timescale.The half-lives for decomplexation of Na+ K' and Rb' complexes of a series of calixspherands in CDCl saturated with water have been estimated.493 Ag+ is shown494 to tunnel intramolecularly between two binding-sites in 1,3-alternate calixC4larenes in a process facilitated by metal-.n interactions. Rate laws for the acid dissociation of tetraazamacrocycles from [Cu"LI2 + in nitric acid have been reported49s for [12]aneN4 (/cobs = kl[Htl2 + k,[H+]) [13]aneN4 (kobs = k,[H+]) and [15]aneN4 and [16]aneN4 (kobs = k4[Ht]/(l + k,[H+]). The violet transient formed on basification of a solution of [Ni"'([ 14]aneN4)I3 'results from deprotonation of ligand N-H.496 Acid dissociation of the N,02 macrocycle [from 2,6-bis(2-aminophenoxymethyl)pyridineand glyoxal] from its CU(II) complex occurs in two stages the slower second stage following the rate law kobs= k + k [H '1 where k represents a small solvolytic contribution.Dissociation is to proceed via a diprotonated intermediate with the cleavage of the second Cu-N bond being rate determining. A similar mechanistic scheme is proposed498 for acid dissociation of 5,7-dioxo-[ 14]aneN4 from its complexes with CU(II) or Ni(II). Protonation of the amide oxygen precedes rate-determining M-N(amide) bond cleavage. Structural evidence from CU(II) complexes of 5-0x0-[ 14]aneN4499 is consistent with such a suggestion. Pb(I1) exchange between a series of N,O,- macrocycles has been studied by 207Pb NMR spectroscopy.500 Rates of formation of Ln(m) complexes (Ln = Ce Eu Yb) of dota suggestso1 that + initial rapid formation of diprontonated [Ln(H,dota)] occurs (in which only carboxylate oxygens are bound) followed by a slower OH -catalysed rearrangement to [Ln(dota)] -.Dissociation of [Ln(dota)] -(Ln = Gd Eu) is proton assisted.Similar processes have been proposedso2 for reactions involving Ln(m) (Ln = Y Gd Ga In) 488 S. Aizawa and S. Funahashi Bull. Chem. Soc. Jpn. 1994 67 1048. 4R9 Y. Li G. Gokel J. Hernandez and L. Echegoyen J. Am. Chem. Soc. 1994 116 3087. 490 Y. Li and L. Echegoyen J. Am. Chem. Soc. 1994 116 6832. 491 P. Firman E. M. Eyring and S. Petrucci J. Phys. Chem. 1994 98 147. 492 P. Dumon G. Jonusauskas F. Dupuy Ph. Pee C.Rulliere J.-F. Letard and R. Lapouyade J. Phys. Chem. 1994 98 10391. 4y3 W. I. Twema Bakker M. Haas C. Khoo-Beattie R. Ostaszewski S. M. Franken H. J. den Hertog Jr. W. Verboom D. de Zeeuw S. Harkema and D.N. Reinhoudt J. Am. Chem. Soc. 1994 116 123. 494 A. Ikeda and S. Shinkai J. Am. Chem. Soc. 1994 116 3102. 49s W.-J. Lan and C.-S.Chung J. Chem. SOC.,Dalton Trans. 1994 191. 496 G. De Santis L. Fabbrizzi A. Poggi and A. Taglietti Inory. Chem. 1994 33 134. 497 R. W. Hay M.M. Hassan D. E. Fenton and B.P. Murphy Transition Met. Chem. 1994 19 559. 49R R. W. Hay and M. M. Hassan Trunsition Met. Chem. 1994 19 129. 499 L. Siegfried M. Neuburger M. Zehnder and T.A. Kaden J. Chem. Soc. Chem. Commun. 1994 951. J. Kim C. J. Yoon H. J. Yoo G. Kim and S.J. Kim J. Korean Chem.Soc. 1994,38,41 (Chem. Abstr. 1994 120 254 554k). "' E. Toth E. Brucher 1. Lazar and I. Toth lnorg. Chem. 1994 33 4070. H. -Z. Cai and T.A. Kaden Helo. Chim. Acta 1994 77 383. 542 N. Winterton and do3a and those of H3he-do3a H3hp-do3a and H3hip-do3a with Ln(m) with the second order rate constant for the base catalysed reorganization dependent on nitrogen basicity.'03 Evidence was also presented that CGd(Hhip-do3a)l dissociates by both an acid-dependent and an acid-independent route. The two conformations adopted by the complex [Yb"'(dota)] -are involved in slow intra- and intermolecular exchange.504 The effect of chelate-ring size and substitution at carbon on the rates of dissociation of linearsos and cyclicso6 polyaminopolycarboxylates from their com- plexes with Ln(m) (Ln = Ce Eu Yb) have been described.Measurements of the rate of dissociation of dtpa-bis(amide) ligands from Ce(m) and Gd(II1) complexes suggest that increased ring size leads to lower rates associatedso7 with coordination of the amido oxygen. A rate constant for the acid-induced formation of [Cr"'(H,0),(y3-Hnta)] + from [Cr"'(H,O),(y"-nta)] is Kinetics of the formation and dissociation of yttrium and gadolinium complexes of a cyclic polyazaphosphinic of [Ce"'(heha)13-,509 the formation5" of [Cr(edta)] -from [Cr(H,O),(ox)] +,the formation511 of [Cr(dtpa)12- from [Cr(en),l3+ ands1 of [Tc"'(tu)(Hedta)] from + [Tc(tu),] and various related reactions5 3-s have been reported. [H2edta] -and [Hnta12- are reportedSl6 to be the most reactive species involved in the associative substitution reactions of [V"'(gly),] by edta and nta.Exchange of nta in lanthan- ide-nta complexes has been described.'I7 Replacement of L = arsenazo I11 in its complexes with Gd(1Ir) by edta and dtpa occurss18 by two processes one fast (associated with a 1 :1 L :Gd complex) and one slow (associated with a 2 1 complex). Reports have appeareds'9-s22 on the complexation of Fe(m) by a series of tetradentate ligands exemplified by H,slalh. Reaction may proceed either via [Fe(H,0),I3+ or [Fe(H,O),(OH)I2+ with the initial steps involving the coordina- tion of the carbonyl oxygen or the phenolato ~xygen."~ Related studies on the formation of Fe(m) complexes with malonodihydroxamic and succinohydroxamic K.Kumar T. Jin X. Wang J. F. Desreux and M. F. Tweedle Znorg. Chem. 1994 33 3823. V. Jacques and J. F. Desreux Inorg. Chem. 1994 33 4048. 505 K.-Y. Choi K. S. Kim and C. P. Hong Bull. Korean Chem. SOC. 1995,15,782 (Chem. Abstr. 1994,122 65 434b). 506 K.-Y. Choi K. S. Kim and J.C. Kim Bull. Chem. SOC. Jpn. 1994 67 267. K.-Y. Choi K. S. Kim and J.C. Kim Polyhedron 1994 13 567. 508 K. P. Pulukkody T. J. Norman D. Parker L. Royle and C.J. Broan J.Chem.SOC.,Perkin Trans. 2,1993. 605. '09 K.-Y. Choi and C. P. Hong Bull. Korean Chem. SOC. 1994 15 293 (Chem. Abstr. 1994 120 332280j). 'lo V.A. Raman Orient. J. Chem. 1993 9 102 (Chem. Ahstr. 1994 120 228426a). '11 V. Garg S. Kumar and P.S. Relan Orient. J. Chem. 1994 10 34 (Chem. Abstr. 1994 121 214 138s).512 M. Hashimoto H. Wada T. Omori and K. Yoshihara Radiochirn. Acta 1993,63,173(Chem. Abstr. 1994. 120 201 561d). 513 S.J. Franklin and K.N. Raymond Inory. Chem. 1994 33 5794. 514 L. Carlton R. D. Hancock H. Maumela and K. P. Wainwright;J. Chern. SOC. Chem. Commun. 1994. 1007. 515 M. G. Basallote R. Vilaplana and F. Gonzalez-Vilchez Polyhedron 1994 13 1853. 'I6 Y. Ikeda R.M. Hassan M. M. abd El-Fattah Y.Y. Park and H. Tomiyasu Collect. Czech. Chern. Commun. 1994 59 1077. 517 J. Ren F. Jing F. Pei W. Wang and J. Ni Wuli Huaxue Xuebao 1994,10,785 (Chem. Abstr. 1994,121 239281~). "* K. B. Reddy S. Cao E. C. Orr I. Fabian R. van Eldik and E. M. Eyring J. Chem. SOC. Dalton Trans. 1994 2497. 519 T. Ozawa K. Iwai K. Jitsukawa H. Masuda and H. Einaga Polyhedron 1994 13 1523.520 T. Ozawa K. Jitsukawa H. Masuda and H. Einaga Polyhedron 1994 13 2343. s21 T. Ozawa K. Jitsukawa H. Masuda and H. Einaga Ber. Bunsenges. Phys. Chem. 1994 98 66. 522 T. Ozawa K. Jitsukawa and H. Einaga Ber. Bunsenges. Phys. Chem. 1994 98 59. Inorganic Mechanisms 543 acids3,’ and the complexation of Ni(I1) and CO(II) with Hlhp~’,~ have also been reported. In the latter study evidence is presented to indicate that [Fe(H,0)J3+ reacts associatively and [Fe(H,O) (OH)] reacts dissociatively. Complexation in + aqueous acid between [Fe(H,0),l3 and hexadentate tripodal ligands (tren linked to + three 2,2’-dihydroxybiphenyl moieties) proceedss24 via [Fe(H20)5(OH)]2 or + [(H,O),Fe(OH) Fe (H O),] depending on the ligand.+ The second-order rate constants for the proton-assisted dissociation of N-methyl- acetohydroxamate from tris bis and mono complexes with Fe(m) are,s2s respectively 8.6 x lo3 1.02 x lo2 and 3.2 x M-ls-l with an acid-independent pathway also being seen for the mono complex. Dissociation of 1 :1 Fe(rr1) complexes of a series of methylene-chain-bridged dihydroxamic acids [HL = {CH ,N(OH)C(O)} ,(CH2) (n = 2,4,6,7,8)] involves526 a dimeric complex [Fe2L2I2’ for n I6 and a monomeric complex [FeL]’ for n 2 6. For II = 6 both mono-and dimeric complexes are important. Rates of removal of Fe(n1) from its complexes with citrate by desferrioxamine B and 3-hydroxy- 1,2-dimethyl-4-pyridone’ 27 and of the formation and dissociations2’ of the ferric complex of pyoverdin PaA a biological ligand with two hydroxamic and a dihydroxyquinoline coordination sites bound to a peptide chain are reported.EXAFS529-5 3 1 (including stopped-flow EXAFS530,’3 ’) has been used to character- ize some of the species involved in the reaction between a Hg(1r)-porphyrin complex and CU(II). H,tpps reacts in acetate buffer to give the homodinuclear complex [Hg2(tpps)(OAc),14- in which each Hg(I1) binds to pyrrole nitrogens above and below the plane of the ligand. CU(II)exchanges with one Hg(I1) bound to the porphyrin to give a heterodimetallic intermediate which collapses to give [Cu(tpps)I4-. Acid dissocia- tion of divalent metals (Zn Cd Pd) from [M(tpps)14- is inhibited by 18-crown-6 (18C6),’32 ascribed to the formation of a less-reactive intermediate [M(tpps)- (18C6)I4-.Removal of Bi(Ir1) from a bis{tetrakis(N-methy1-3-pyridyl)porphyrin} complex is ~atalysed’~~ by base as well as by acid and anions. Other studies of porphyrins have been rep~rted.’~~-’~~ Main Group Reactions.-A dinuclear transition state [(HO),B(p-OH)B(OH)3]- is proposed537 from the activation parameters for boron interchange between B(OH) 523 H. C. Malhotra and A. Kumar Proc. Indian Natl. Sci.Acad. Part A 1994,60,419(Chem. Abstr. 1994,121 264 77%). 524 G. Serratrice C. Mourral A. Zeghli C. G. Beguin P. Baret and J.-L. Pierre New J. Chem. 1994,18,749. 525 M.T. Caudle and A. L. Crumbliss Inorg. Chern. 1994 33 4077. s26 M.T. Caudle L. P. Cogswell 111 and A. L. Crumbliss Inorg. Chern. 1994 33 4759. 527 B.Faller and H. Nick J. Am. Chem. Soc. 1994 116 3860. 52R A.-M. Albrecht-Gary S. Blanc N. Rochel A.Z. Ocaktan and M.A. Abdallah lnorg. Chem. 1994 33 6391. 529 M. Tabata and K. Ozutsumi Bull. Chem. SOC.Jpn. 1994 67 1608. s30 H. Ohtaki Y. Inada S. Funahashi M. Tabata K. Ozutsumi and K. Nakajima J. Chem. Soc. Chem. Commun. 1994 1023. s31 Y. Inada S. Funahashi and H. Ohtaki Rev. Sci. Instrum. 1994 65 18. 532 M. Tabata K. Suenaga and J. Nishimoto Inorg. Chem. 1994 33 5503. 533 G.-P. Chacko and P. Hambright Inorg. Chem. 1994 33 5595. s34 R. Fujiyoshi T. Arai and M. Katayama J. Rndioanal. Nucl. Chem. 1994,185 133 (Chem. Abstr. 1995 122 65 474q). s3s Z.-Q. Pan J.-G.Ren and Z.-B. Qin Gaodeng Xuexiao Huaxue Xuebao 1994,15,565 (Chem. Abstr. 1994 121 164832r).536 Z. Pan P. Dong J. Ren and Z. Qin Wuhan Daxue Xuebao Ziran Kexueban 1993,90(Chem. Abstr. 1994 120 254 607e). 537 K. Ishihara A. Nagasawa K. Umemoto H. Ito and K. Saito lnorg. Chem. 1994 33 3811. 544 N. Winterton and [B(OH),] -. pH-jump measurements that equilibration between [A1(H,0)J3 and 3’,4’,7‘-trihydroxy-3-methoxyflavylium + cation a model for the natural pigment anthocyanin is controlled by complexation between A~(III) and the minor anionic quinonoidal form of the ligand. Dissociative exchange5 39 between free and Al(Iu)-bound ATP in a 1:2 complex via the intermediacy of a 1:1 complex is governed by A1-0 bond rupture. Solvent isotope effects and anion inhibition of enzyme-catalysed CO hydration have been reported.540 [(Me,Si),C {SiMe,OC(O)Me)(SiMe,X)] (VI) (X = C1) reacts with MeOH in MeOH/dioxan containing NEt to give (VI) (X = OMe) as the sole product whereas [(Me,Si),C(SiMe,OMe)(SiMe,Cl)] gave [(Me,Si),C(SiMe,OMe),] at a much slower rate ascribed to anchimeric assistance by the carbonyl oxygen of the acetoxy group in (VI).541 The reactivity of (VI) decreases along the series X = Cl % NCS N % F.The slower reaction with CF,CH,OH to give [(Me,Si),C (SiMe,OCH,CF,)(SiMe,OH)] rather than the expected (VI) (X = OCH,CF,) is associated with the suppression of anchimeric assistance by hydrogen-bonding between the more acidic OH and the acetoxy carbonyl oxygen. Reactions of [(Me,Si),C(SiMe,X)] (X = C1 Br I ONO,) with Y-= N; F- SCN- OCN- have also been studied. ’42 Structure-reactivity relationships in the solvolysis of SiMe,Ph(OPh) that the observed general-base catalysis results from base-assisted deprotonation of the incoming solvent nucleophile.Trifluoroethanol- ysis544of SiMe,Ph(OPh) solvolysis of methyl-substituted 1-phenylsilatrane in acetic a~id,’~’ ligand metathesis between SiMeC1 and cyclo-[(OSiMe,),] in the presence of trifluoromethanesulfonic alcoholysis of Bua(Pr’O) -,,SiSH (n = 0-3),547and medium effects on base-catalysed hydrolysis of SiHAr3’48,549 have also been studied. Labelling experiments dem~nstrate’’~ competitive terminal and internal Si-Ph bond cleavage in the reactions of [H(PhMeSi),H] with one or two moles of CF,SO,H. On reaction with a third mole of CF,SO,H rearrangement proceeds via + [HMe(CF,SO,)SiSiMeSiXMeH] (X = Ph CF,SO,).The low value of k,/k for direct N-to-N proton transfer between 5N-ammonium and ammonia in H,O-D,O points’” to a process that is nearly encounter controlled. Edwards and Plumb have reviewed the chemistry of per ox on it rite^.^^^ In studies relevant to atmospheric 53R 0.Dangles M. Elhabiri and R. Brouillard J. Chem. SOC., Perkin Trans. 2 1994 2587. 539 I. Dellavia J. Blixt C. Dupressoir and C. Detellier lnorg. Chem. 1994 33 2823. 540 I.-M. Johansson and C. Forsman Eur. J. Biochem. 1994 224,901 (Chem. Abstr. 1994 121 199339n). s41 C. Eaborn P. D. Lickiss and A.D. Taylor J. Chem. SOC.,Perkin Trans. 2 1994 1809. 542 Y.Y. El-Kaddar C. Eaborn and P.D. Lickiss J. Organomet. Chem. 1993 460 7. 543 P.E. Dietze and Y.Y. Xu J.Org. Chem. 1994 59 5010. s44 P. E. Dietze C. Foerster and Y. Xu J. Org. Chem. 1994 59 2523. 545 C. L. Frye and R. D. Streu Main Group Met. Chem. 1993 16 217 (Chem. Abstr. 1994 120 2986830. 546 J. Jiang M. A. Brook and J. M. Dickson Heteroat. Chem. 1994,5,275 (Chem. Abstr. 1994,121,255 8978). s47 J. Pikies and W. Wojnowski Phosphorus Sulfur Silicon Relat. Elem. 1993,78,133(Chem. Abstr. 1994,120 164 308d). 54R J. J. Tondeur A. Borghese and G.Vandendunghen Bull. SOC.Chim. Belg. 1993 102 165 (Chem. Abstr. 1994 120 191 780h). 549 J. J. Tondeur G.Vandendunghen and A. Borghese Bull. SOC.Chim. Belg. 1993,102,313 (Chem. Ahstr. 1994 120 217 798x). s50 J. Y. Corey D. M. Kraichely J. L. Huhmann and J. Braddock-Wilking Organometallics 1994,13,3408. 551 A. Bambauer B.Brantner M. Paige and T. Novakov Atmos. Environ. 1994 28 3225. s52 J.O. Edwards and R.C. Plumb Prog. lnorg. Chem. 1994,41 599. Inorganic Mechanisms 545 hemi is try,^^^-^^^ the kinetics of the reaction 2NO,(g) + H,0(1) = 2H' + NO + NO have been investigated in bulk water and in a laboratory cloud chamberss3 and shown to be first order in [NO,] for both regimes. A reinterpreta-tionSs6 of the mechanism of hydrolysis of [(NPCl,),NSOCl] favours a dominance of steric rather than electronic factors. HO and not perborate is the reacting species in the hydrolysis of triaryl phosphate in the presence of H,O, metaborate and boric The rates of acid and alkaline hydrolysis of monofluorophosphorous acid HFP(O)(OH) are ca. 100 times faster than similar reactions for F,P(O)OH or FP(0)(OH),.ss8 Both intramolecular and intermolecular alkoxy group exchange has been observed559 in Te(OR) (R = Et Pri).A.F. Janzen has reviewed the reaction mechanisms of inorganic fluoro compounds.560 The rate of reaction between Cl,(aq) and Br- to give [BrCl,] -,measured by the pulsed-accelerated-flow technique is close to diffusion controlled.234 [Br,]' -into Br' and Br- with a rate constant of 1.9 x 104s-1. Solvent and Other Medium Effects.-Solvent effects on electron transfer have been reviewed.s62 Inclusion of [Fe"(rpC,H,CH,NMe,)Cp] by P-cyclode~trin~~~ + reduces the rate of oxidation by [Co(dipic),] -ca. 50-fold. Inclusion564 of [py~(CH,),pyz]~ + (n = 8-12) in a-cyclodextrin decreases the rate constants for both the formation and dissociation of monomeric and dimeric complexes with [Fe(CN),(H,0)l3-.The kinetics of the assembly of the rotaxane [(NC)sFe{pyz(CH,),pyz.a-CD}Fe(CN)5]4-on mixing the complex dimer and a-cyclodextrin are consistent with rate-determining dissociation of a [Fe(CN)J3 -unit inclusion of a-CD and rapid recomplexation.s65 Crown ethers reduce but do not eliminate the alkali-metal catalysis of the demethylation of methyl phosphates by iodides66 (not seen when PhS- is the nucle~phile~~~). LiF is a weaker catalyst for the hydrolysis of aryl phosphates compared with other alkali metal fluorides.568 Decomposition of [co,(c0)8] and [Co,(CO) ,]in toluene containing dissolved polymer to modify solution viscosity slows with increasing [poly(styrene)] above the coil overlap concentration consistent with the view569 that decomposition is governed by diffusion.Viscosity effects of electron-transfer processes in ambient temperature 5s3 C.L. Perrin T. J. Dwyer and P. Baine J. Am. Chem. SOC. 1994 116 4044. 5s4 M. Hofmann and P. von R. Schleyer J. Am. Chem. SOC. 1994 116,4947. 5ss C. E. Kolb J. T. Jayne D.R. Worsnop M. J. Molina R. F. Meads and A. A. Viggiano J. Am. Chem. Soc. 1994 116 10314. 556 H. Winter A. Meetsma J. C. van de Grampel and A. L. Spek Heteroat. Chem. 1994,5,343 (Chem. Abstr. 1995 122 17841k). 557 J. Toullec B. Azize and M. Moukawim C. R. Acad. Sci. Ser 11:Mec. Phys. Chim. Sci. Terre Univers. 1993 317 1575 (Chem. Abstr. 1994 121 83498J). '" K. Dishman L. A. Karnell and J. W. Larson Int.J. Chem. Kinet. 1994 26 455. 559 H.E. Gottlieb S. Hoz I. Elyashiv and M. Albeck Inory. Chem. 1994 33 808. 560 A.F. Janzen Coord. Chem. Rev. 1994 130 355. s61 G. Merenyi and J. Lind J. Am Chem. SOC. 1994 116 7872. 562 F. Sanchez-Burgos M. L. Moya and M. Galan Proy. Reaction Kinet. 1994 19 1. 563 J. A. Imonigie and D.H. Macartney Inorg. Chim. Acta 1994 225 51. s64 D.H. Macartney and C.A. Waddling Inory. Chem. 1994 33 5912. s6s R. S. Wylie and D.H. Macartney Supramol. Chem. 1993 3 29 (Chem. Abstr. 1994 121 239 2250. M. Mentz A.M. Modro and T.A. Modro J. Chem. Res. 1994 46. 56' M. Mentz A.M. Modro and T.A. Modro Can. J. Chem. 1994 72 1933. 568 M. Mentz A.M. Modro and T.A. Modro J. Chem. SOC. Chem. Commun. 1994 1537. 569 R. Tannenbaum Inorg. Chim.Acta 1994 227 233. 546 N. Winterton chloroaluminate ionic liquids have also been in~estigated.'~' Both [Rh(CO)KrCp*] and [Rh(CO)(alkane)Cp*] are intermediates in the formation of [RhHR(CO)Cp*] in the photoinitiated reaction of [Rh(CO),Cp*] in liquid krypton.57 19572 Magnetic field effects have been investigated on chemical wavess7 produced in unstirred solutions of [Co"(pdta)12- and H,O, and on radical pr~cesses.'~~~'~' The formation of polymer-bound species' 76 on photolysis in supercritical CO of polyethylene impregnated with [Mn(CO),Cp] is suppressed by CO H, or N,. Photolytic formation of [Mn(CO),(N,)Cp*] from [Mn(CO),Cp*] and N proceeds as readily in supercritical CO as in supercritical Xe.577 Oxidations of CO and H have been studied in supercritical The rate constant for the chain dispropor- tionation of [(Fe(CO),Cp},] with dppe increases linearly with the concentration of [NBU,][PF,].'~' Kinetic salt effects on the oxidation of [Fe(CN),(bipy)]'- cis-+ [Fe(CN),(bipy),] and [Fe(bipy),12 by [s20B]2-are primarily associatedsB1 with interactions between the added electrolyte and the solvent.Solvent,'82 anion,583 and surfactantSB3 effects on the base hydrolysis of (a$-S)-[Co(o-methoxybenzoato)(tet-ren)] have been reported. Micellar effects on electron-transfer reactions between + [Co(terpy),12 and cationic and anionic CO(III) oxidants,584 on the redox behaviour + of [Fe,S,Cp,l2 +,58s and on Ni(I1) complexation by alkoxypicolinic acids and alkoxypyridine aldoximesSB6 have been described as have medium effects on the solvolysis'87 and base hydrolysis588 of [CoC1(NH,)J2+ of uncharged CO(III) complexes 89 of Fe"-Schi ff base complexes '90 on substitutions at CO"',~ '-'9s s.70 Z.J.Karpinski S. Song and R.A. Osteryoung Inorg. Chim. Acta 1994 225 9. '71 A.A. Bengali R. H. Schultz C. B. Moore and R.G. Bergman J. Am. Chem. SOC. 1994 116,9585. '72 R. H. Schultz A. A. Bengali M. J. Tauber B. H. Weiller E. P. Wasserman K. R. Kyle C. B. Moore and R.G. Bergman J. Am. Chem. Soc. 1994 116 7369. '73 X. He K. Kustin I. Nagypal and G. Peintler Inorg. Chem. 1994 33 2077. s74 M. Mukai H. Tanaka Y. Fujiwara and Y. Tanimoto Bull. Chem. Sac. Jpn. 1994 67 3112. "' D. Biirssner H.-J. Wolf€ and U.E. Steiner Angew. Chem. Int. Ed. En& 1994 33 1772. 576 M.J. Clarke S. M. Howdle M. Jobling and M. Poliakoff J. Am. Chem. SOC.,1994 116 8621. '" J. A. Banister M. W. George S. Grubert S. M. Howdle M. Jobling F. P.A. Johnson S. L. Morrison M. Poliakoff U. Schubert and J. R. Westwell J. Organomet. Chem. 1994 484 129. s78 H. R. Holgate and J. W. Tester J. Phys. Chem. 1994 98 800. '79 H. R. Holgate and J. W. Tester J. Phys. Chem. 1994 98 810. "O M. P. Castellani E. T. Hesse and D. R. Tyler Organometallics 1994 13 399. E. Mufioz M. del mar Graciani R. Jimenez A. Rodriguez M. L. Moya and F. Sanchez Int. J. Chem. Kinet. 1994 26 299. '" A.N. Acharya and A.C. Dash J. Chem. SOC.,Faraday Trans. 1994 90 3293. 583 A.N. Acharya and A.C. Dash Int. J. Chem. Kinet. 1994 26 681. 584 K.M. Davies A. Hussam B. R. Rector Jr. I. M.Owen and P. King Inorg. Chem. 1994 33 1741. 585 M. Lawson and J. Jordanov Inorg. Chim. Acta 1994,226 341. 586 M. Hebrant A. Bouraine C. Tondre A. Brembilla and P. Lochon Langmuir 1994 10 3994. 587 K. H. Halawani and C. F. Wells Transition Met. Chem. 1994 19 364. '" G. Calvaruso F. P. Cavasino C. Sbirziolo and M. L.T. Liveri J. Chem. SOC. Faraday Trans. 1994,90 2505. 589 E.-E.A. Abu-Gharib J. Chin. Chem. SOC. (Taipei) 1994 41 413 (Chem. Abstr. 1994 121 164825r). 590 E.-E.A. Abu-Gharib J. Ind. Chem. Soc. 1994 71 537 (Chem. Abstr. 1995 122 198118~). 591 A.A. Zaghloul S.A. El-Shazly M.T. Mohamed F. M. Abdel Halim and M. F. Arnira Phys. Chem. (Peshawar Pak.) 1992,11 89 (Chem. Abstr. 1994,120 254609g). 592 C.C. Mukhopadhyay and G.S. De Indian J. Chem. Sect A 1994 33 664 (Chem.Abstr. 1994 121 92 895p). 593 J. Shan and S. Shen Hebei Daxue Xuebao Ziran Kexueban 1994 14 41 (Chem. Abstr. 1994 121 66 730m). 594 0.GranEieova and M. LeioviE Transition Met. Chem. 1994 19 465. '9' L.G. Reiter T.V. Patskova R.R. Polyakov and 0.V. Repik Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 1994 37 47 (Chem. Abstr. 1995 122 65 423x). Inorganic Mechanisms 547 cr(111)5 94.5 96-5 98 and RU(II)~" centres and on P-0 us. S-0 cleavage in phenyl phosphatosulfate.600 4 Organometallics a-Bonded Organotransition Metal Compounds.-Van Eldik Cohen and Meyer- stein6' ' have concluded that ligand interchange is rate-determining in metalkarbon a-bond formation M" + R' = RM("+') involving formal oxidation of M. Rates of homolysis of [CrR(H,O)J2' (R = CH,C,H,Y-p) are independent6' of added 0, aqueous Fe(II1) or [COX(NH,),]~+ (X = Cl Br) though the additives and Y affect the nature of the organic products.From the dependence of the product distribution on [Fe"'] a rate constant for the oxidation of PhCH; by [Fe(H20)6]3+ was estimated. The volume of activation for the reaction [Cr(CH2CH,0H)(H,0)S]2+ = [Cr(H20)6]3+ + CH,=CH + OH- is negative (associated603 with an early transition-state with limited C-0 bond stretch) whereas for the analogous reaction of [Cr(CH,CH,NH,)(H,0)J3 +,A V* is positive (suggesting a transition-state in which more C-N bond stretching has occurred). Pressure effects on rates point to Cr-C heterolysis rather than P-elimination for the spontaneous and acid-catalysed decompo- sition of [Cr(CH,CH(OH),}(H,0)5]2+.Heterolysis of [CrR(H20)J2+ (R = CH,OH CMe,OH) (and related trans-[CrR(H,O)([ 15]aneN4)I2+ (VII)) is accelerated in the presence of [(HO),P(O)O] -. The kinetic parameters and lack of significant acceleration for cis-[CrR(H,O)(nta)] - suggest604 that labilization in- volves trans-coordination of phosphate. A dissociative mechanism is proposed. Excess (VII) (R = CHMe, CH,Ph) is oxidized by iodine (and [IrCl6l2-) in a chain process initiated by electron tran~fer.~"-~'~ With I,,I and tr~ns-[CrR(H,O)([15]aneN,)]~+ are formed with the latter then decomposing homolytically with rate constants ca. lo6 times greater than those for spontaneous homolysis. Two pathways were delineated608 for the thermolysis of [PdXEt(PMe,),] (X = OPh OAc SPh C1 Br) the predomi- nant one involving dissociation of X to give [PdEt(S)(PMe,),] +.The stereospecific P-hydride elimination from [CO(M~O,CCHDCHCO,M~)(CO)~] occurs6o9 by a pre-equilibrium CO dissocia- tion followed by fast intramolecular formation of [CoH(CO),(alkene)]. The retention of ligand stereochemistry following repeated exchange of trans-CHD=CHD(L) with 596 S.A. El-Shazly A. A. Zaghlol K.A. Odah S.M. Zourab and M. F. Amira Sci. Phys. Sci. 1993,5 185 (Chem. Abstr. 1994 121 19 197r). 597 J.-H. Shan and T.-Y. Liu Huaxue Xuebao 1994 52 1140 (Chem. Abstr. 1995 122 6548511). 598 J. Shan Q. Ling and A. Wang Wuli Huaxue Xuebao 1994,10,728 (Chem. Ahstr. 1994,121,188 428q). 599 B. Mahanti and G. S. De Transition Met.Chem. 1994 19 201. 6oo T. Eiki S. Negishi M. Izumi N. Ishida and H. Hada Bull. Chem. SOC. Jpn. 1993 66 2931. 601 R. van Eldik H. Cohen and D. Meyerstein Inorg. Chem. 1994 33 1566. 602 Z. Zhang and R.B. Jordan Inorg. Chem. 1994 33 680. 603 H. Cohen R. van Eldik W. Gaede A. Gerhard S. Goldstein G. Czapski and D. Meyerstein Inorg. Chim. Acta 1994 227 57. 604 W. Gaede and R. van Eldik Inorg. Chirn. Acta 1994 215 173. 605 S. Shi and H. C. Zeng J. Organomet. Chem. 1994 484 59. 606 S. Shi Transition Met. Chem. 1994 19 299. 607 S. Shi J. Organomet. Chem. 1994 468 139. 608 F. Kawataka Y. Kayaki I. Shimizu and A. Yamamoto Organometallics 1994 13 3517. 609 I. Kovacs F. Ungvary and L. Marko Organometallics 1994 13 1927. 548 N. Winterton [Os,(COj,L] with other evidence argues against6" the operation of a diradical mechanism.a-Bond metathesis involving catecholborane and [RuMe(PPh,)Cp] giving [RuH(PPh,)Cp] and MeBcat proceeds6' 'via a four-centre transition-state involving partial B-H cleavage during B-C formation. The rates of [Ru(SiR,)(PMe,),Cp] (R = HCI, Cl, MeHCl MeCl, Me,Cl) and [RuH,(PMe,),Cp]Cl formation from [RuH(PMe,),Cp] and ClSiR via a cationic silyl hydride intermediate cover six orders of magnitude,612 reflecting electronic rather than steric factors. The formation of cis-[Pt(CD,)(CH,Si(CD j2CH2Si(CD3),)(PPh3),] as the only product in the thermolysis of ~~s-[P~(CH,S~(CD,),),(PP~~)~], establishes613 that that rearrange- ment involves a Si-Me bond cleavage. Dissociation of PPh precedes fl-carbon migration from Si to Pt with CH,SiMe migrating regiospecifically to the Si of a proposed y2-silene-Pt intermediate.A novel Si-C cleavage is seen6 l4 in the equilib- rium between [RuZ(p-CH2)(SiMe,)(p-CI)Cp~] and [Ru,(p-CH,SiMe,)(p-C1 jCpz]. Isomerization of [W(SiMe,)(SiR,X)Cp,] to [W(SiMe,X)(SiR,MejCp,] highly de- pendent on the nature of R and X is thought615 to proceed via a tungsten-silylene cation following loss of X-. [Co"'Me(pc)] reacts in an S,2 process with PhS- to give PhSMe and [Co'(pc)]- though with complex kinetics that approach a constant rate at high [PhS-I attributable6I6 to the formation of inert [Co"'Me(pc)(SPh)] -. Activation parameters for the Co-C homolysis in [Co(CMe,CNj(tap)] were obtained by NMR line broadening.617 Brown and Evans6' * have produced a corrected set of activation parameters for the thermolysis of the Cox bond for base-on neopentylcobalamin in water.The same authors have also established6I9 that the thermolysis of epimers of neopentylcobalamin is a homolytic process in neutral aerobic aqueous solution with side-chain motions affecting entropies of activation. Studies 620 of the acid-catalysed heterolytic cleavage of Co-C in coenzyme B, and methyl(5'-deoxyribofuranosy1)cobalamin suggest that the reactions should be seen as an I nucleophilic substitution at CO(III) by water. CO(I)cobalamin is methylated by [NMe,Ph]+ in aqueous solution with a second order rate constant ca.lo4 smaller621 than that for the analogous reaction with MeI. Co-C bond formation and cleavage in B, derivatives has been reviewed by Pratt.622 Carbonyl Insertion Alkyl Migration and Related Reactions.-The maximum at n = 4 for the rate of thermal decarbonylation of [Mn(COR)(CO),] (R = n-C,H2,+1 n = 1-17) and the variation with n ofthe rate constants for carbonyl insertion reactions 610 R.T.Hembre D. L. Ramage C. P. Scott and J. R. Norton Organometallics 1994 13 2995. 611 J. F. Hartwig S. Bhandari and P.R. Rablen J. Am. Chem. Soc. 1994 116 1839. 612 F.R. Lemke J. Am. Chem. Soc. 1994 116 11 183. 613 B. C. Ankianiec V. Christou D.T. Hardy S. K. Thomson and G. B. Young J. Am. Chem. Soc. 1994,116 9963. 614 W. Lin S. R. Wilson and G. S. Girolami Organometallics 1994 13 2309. '15 D.C. Pestana T.S. Koloski and D.H. Berry Organometallics 1994 13 4173.616 W. Galezowski and E. S. Lewis J. Phys. Org. Chem. 1994 7 90. B. B. Wayland A. A. Gridnev S. D. Ittel and M. Fryd Inorg. Chem. 1994 33 3830. 'I8 K. L. Brown and D. R. Evans Inorg. Chem. 1994 33 6380. 619 K. L. Brown X. Zou and D.R. Evans Inorg. Chem. 1994 33 5713. 620 L.E.H. Gerards and S. Balt Rec. Trav. Chim. Pays-Bas 1994 113 137. 621 J.M. Pratt P. R. Norris M. S. A. Hamza and R. Bolton J. Chem. Soc. Chem. Commun. 1994 1333. 622 J. M. Pratt in 'Metal Sons in Biological Systems' ed. H. Sigel and A. Sigel Biological Properties of Metal Alkyl Derivatives Marcel Dekker Snc. New York 1993 Vol. 29. Inorganic Mechanisms 549 of the related compound [MnR(CO),] on reaction with PPh, are associated 623 with the relative contribution of electronic and steric effects.The solvent dependence and the dependence of the rate constants on R and R’ for the carbonylation of CUR’($- C,H,R),] to give the q2-COR’ complexes suggest6, that insertion of CO into U-C is not rate determining. The 108-fold range in rate constants for reaction of CO with a series of solvento complexes cis-[MnMe(CO),(S)] and other data indicate625 that CO dissociation from [Mn(COMe)(CO),] in weakly coordinating solvents leads to an q2-acyl complex rather than a solvento complex. The complexes [FeR(CO),($-ind)] (R = CHMe, Me) react626 with phosphines [P(C,H,X-p),] by rapid formation of a molecular complex (equilibrium constant increasing with increasing electron with- drawing power of X) followed by rate-determining alkyl migration to give [Fe(COR)(CO)L($-ind)] (independent of the nature of L).At low temperatures cis-[PtMeX((S,S)-bdpp]] (X = C1 SnCl, and CO) form627 cationic cis-[PtMe(CO)((S,S)-bdpp)]Xfaster for X = SnCl than for X = C1 and at higher temperatures CO insertion occurs giving [Pt(COMe)Cl( (S,S)-bdpp)] or [Pt(COMe)CO( (S,S)-bdpp)][SnCl,]. [PdR(S)L,] is much more reactive628 to- + wards CO insertion than [PdRXL,]. In the presence of CO cis-[Pt(COEt)(COMe)(PPh,),] equilibrates629 via intermolecular scrambling to cis-[Pt(COEt),(PPh,),] and cis-[Pt(COMe),(PPh,),]. Carbonylation of trans-[PtR’(COCOR)(PPh,),] to cis-[Pt(COR’)(COCOR)(PPh,),] (reactivity order R’ = Et $. Ph > Me) proceeds via an initial replacement of PPh by CO. Trans- [PtR(R’)(PPh,),].[R(R’) = Me(Et); Me(Ph); Et2] undergoes6,’ carbonylation to produce cis-[PtR(COR‘)(PPh,),]. Alkyl migration rather than CO insertion is the preferred mechanism for Pd(r1) and Pt(11) alkyls complexed with bidentate diphos- phines in which the two P atoms can be distinguished by NMR spectroscopy.631 Reactivity of CO insertion-deinsertion of [PtRL(pyca)] (R = Me Et; L = organophosphine pyridine) is markedly dependent6, on the donor capacity of L and the rigidity of the chelate. Dimethylacetylene dicarboxylate inserts6 into the Pt-Pt bond of the complex [Pt,I,(p-Ppy,),] in a concerted reaction via a four-centre transition-state. CO insertion into Pd-Me and Pt-Me bonds in heterobimetallic complexe~~~~,~~~ has also been studied. Ligand Displacement Reactions of Metal Carbonyl and Other Low Valent Com- pounds.-The trend to more positive values of AV* for the thermal ring-closure h23 J.-A.M.Andersen and J.R. Moss Organometallics 1994 13 5013. 624 C. Villiers and M. Ephritikhine J. Chem. Soc. Dalton Trans. 1994 3397. 625 W. T. Boese and P. C. Ford Organometallics 1994 13 3525. 626 M. Bassetti L. Mannina and D. Monti Organometullics 1994 13 3293. 627 I. Toth T. Kegl C. J. Elsevier and L. Kollar Inorg. Chem. 1994 33 5708. 628 Y. Kayaki F. Kawataka I. Shimizu and A. Yamamoto Chem. Lett. 1994 2171. 629 J.-T. Chen Y.-S. Yeh C.4. Yang F.-Y. Tsai G.-L. Huang B.-C. Shu,T.-M. Huang Y.-S. Chen G.-H. Lee M.-C. Cheng C.-C. Wang and Y. Wang Organometallics 1994 13 4804. 630 B.-C. Shu T.-M. Huang F.-Y. Tsai S.-L.Huang M.-C. Chen G.-H. Lee J.-T. Chen and Y. Wang J. Chin. Chem. SOC. (Taipei) 1994 41 763 (Chem. Ahstr. 1995 122 160 886J). 631 P. W. N. M. van Leeuwen C. F. Roobeek and H. van der Heijden J. Am. Chem. SOC. 1994,116,12 117. 632 H. Jin and K.J. Cavell J. Chem. SOC.,Dalton Trans. 1994 415. 633 L.Y. Xie and B.R. James Inorg. Chim. Acta 1994 217 209. 634 P. Braunstein M. Knorr and T. Stiihrfeldt J. Chem. Soc. Chem. Commun. 1994 1913. 635 A. Fukuoka T. Sadashima I. Endo N. Ohashi Y. Kambara T. Sugiura K. Miki N. Kasai and S. Komiya Oryanometallics 1994 13 4033. 550 N. Winterton reactions of [W(CO),(N-N)] (N-N = 4,4-R2bipy) on increasing the steric hindrance of N-N reveals636 a gradual shift to a mechanism with more dissociative character with greater W-CO bond weakening for the more sterically hindered N-N.The observations contrast with earlier studies on related Mo complexes. cis-[W(CO),{P(OMe),}(bipy)] is inert637 to ring closure up to 150 "C. The equilibrium between638 [W(CO),{PPh,CH,CH(PPh,),}] and [W(CO),{PPh,CH (PPh,)CH,PPh,}] and between639 bipy and py-pz bidentate coordination in fuc-[ReX(CO),(pzbipy)] (X = Cl Br I) have been studied. Basolo has reviewed6,' ring-slippage mechanisms of CO substitution reactions in n-bonded fused-ring complexed metal carbonyls. The unusually low value for AH* for the ring-slippage reaction of [Mn(CO),(q'-diphos)(y6-C13H9)], compared with values for monodentate P-donors is attributed6,' to the formation of an intermediate stabilized by chelate formation.Assuming that the transition state for the reaction of [Cr(CO),(q6-arene)] with phosphines in hydrocarbon solvents occurs on the way to an unobserved [Cr(CO),L(q4-arene)] intermediate a linear correlation642 exists between AH * and changes in resonance energy of the arene attributable to the localization of the n bonds in the proposed y4-intermediate. Other haptotropic rearrangements have been in~estigated.~~~-~~~ CO labilization in [W(CO),{ O,CCH,NR(R'))] -for R(R') = (H), H(Me) compared with R(R') = Me is to solvent-assisted deprotonation at N leading to a substitutionally labile amide intermediate. Alkene displacement from [M(C0),(q2-alkene)] by L = PPh or P(OEt) in alkanes (a dissociative process649 with changes in AH * revealing a pronounced triad effect) substitution of cod from [Mo(CO),(q4-cod)] by dppm (rate determining associative cleavage of one Mo-alkene bonds6,') reaction of RC-CH with a series of triruthenium carbonyl halide clusters (agostic interactions in the transition state and steric effects invoked6 'to account for the higher rates compared with RC-CR) have been reported.Electronic and steric effects on the substitution of CO by 21 P-donors in the reaction of [Ru,C(CO) ,]to give [Ru,C(CO),,L] show6,' that adduct formation followed by CO dissociation occurs for smaller nucleophiles (cone angle < 133") and a second-order process with no evidence for adduct formation occurs for larger nucleophiles (cone angle > 136"). Rates of CO loss in the adducts are reduced by 636 S.Cao K. B. Reddy E. M. Eyring and R. van Eldik Organometallics 1994 13 91. 63' C. Kayran S. ozkar and E. I. M. Sultan J. Chem. Soc. Dalton Trans. 1994 2239. 638 R. L. Keiter E. A. Keiter D. M. Olson J. R. Bush W. Y. Lin and J. W. Benson Organometallics,1994,13 3752. 'j9 A. Gelling K.G. Orrell A. G. Osborne and V. Sik J. Chem. Soc. Dalton Trans. 1994 3545. 640 F. Basolo New J. Chem. 1994 18 19. 641 R.N. Biagioni A. D. Luna and J. L. Murphy J. Organomet. Chem. 1994,476 183. 642 S. Zhang J. K. Shen F. Basolo T. D. Ju R. F. Lang G. Kiss and C. D. Hoff Organometallics 1994,13 3692. 643 H. Nagashima T. Fukahori M. Nobata A. Suzuki M. Nakazawa and K. Itoh Organometallics,1994,13 3427. 644 R. L. Beddoes J. R. Hinchcliffe A.-L. A. B. de Souza and M. W. Whiteley J.Chem. Soc. Dalton Trans. 1994 2303. 645 P. J. Dyson B. F.G. Johnson and D. Braga Inorg. Chim. Acta 1994 222 299. 646 R.S. Herrick R. R. Duff and A. B. Frederick J. Coord. Chem. 1994 32 103. 647 F. H. Forsterling and C. E. Barnes Organometallics 1994 13 3770. 648 D.J. Darensbourg E.V. Atnip K. K. Klausmeyer and J. H. Reibenspies Inorg. Chem. 1994 33 5230. 649 B. J. Huber and A. J. Poe Inorg. Chim. Acta 1994 221 215. 65" A. Tekkaya C. Kayran S. ozkar and C.G. Kreiter Inorg. Chem. 1994 33 2439. J.K. Shen and F. Basolo Gazz. Chim. Ital. 1994 124 439. 652 D. H. Farrar A.J. Poe and Y. Zheng J. Am. Chem. Soc. 1994 116 6252. Znorganic Mechanisms 551 increasing ligand size and electron donicity. For larger P donors significant reorganiz- ation in the transition state is facilitated by nucleophiles achieving a high degree of Ru-P bond formation.CO substitution in [Cp;Mo,Co,S,(CO),] and [Cp;Mo,Co,S,(CO),] by PPh is an associative process with a pre-equilibrium adduct formation followed by CO dissociation.653 Displacement of PPh,Me in trans-[Mo(N2)(PPh,Me),1 by tripodal ligands such as pp3 proceeds654 by initial phosphine dissociation. [Cp*M(p-S),IrCp*] (M = Rh Ir) formed6 by reversible loss of phosphine from [Cp*(Me,P)MS,IrCp*] dimerizes to form the cubane [(Cp*MS),(Cp*TrS),]. [Ir,Rh,(CO) 1(PPh3)] is a mixture of two isomers [PPh bound axially to either one basal Rh (kinetically preferred) or Ir (thermodynamically preferred)656] which isomerize intramolecularly with positive A V* supporting dissociative migration.Kinetic studies of the formation of [Ru6C(C0)16]2 -from [Ru6(C0)18]2- have been de~cribed.~” [RU~(CO)~ a CO-bridged intermediate formed by photodissociation of CO from [Ru,(CO),,] takes up CO to give [Ru(CO),] and [Ru,(CO),] via658[RU,(CO)~,(~-CO)]. A semi-bridged intermedi- ate [(CO),Re(p-CO)Mn(CO),(4,4’-Me2bipy)] is formed on the photodi~sociation~~~ of CO from [(C0),ReMn(CO),(4,4-Me2bipy)]. Further studies on photochemical CO loss from [{Fe(CO),Cp},] in matrices reveal evidence660 for the reversible formation of [(Fe(CO)Cp),] with an unsupported Fe-Fe bond from [Fe,(p- CO),CP,l~ Correlations with the stereoelectronic properties of entering nitrile ligands have been investigated661 in the kinetics for displacement of acetone from [Fe(COMe) (CO)(acetone)Cp]+.Solvent displacement of [R~(q‘-arene)(q‘-arene’)]~+ giving [Ru(S),l2+ (S = H,O EtOH MeCN and dmso) has been reported.662 CO substitution in the half-open chromocene carbonyls e.g. [Cr(CO)Cp*(q’-C,H,)] is found to be disso~iative.~~~,~~~ Solvent and catalytic effects on the reaction of [Cr(CO),] with toluene665 have been described. Processes on the picosecond timescale have been studied in the loss of CO on photoexcitation of [Cr(CO),] in cyclohexane;666 in related studies on [M(CO),(acac)] (M = Rh Ir)667 and [Fe(CO),] ;668 in the recombination of photodissociated CO from carb~nylmyoglobin,~~~ and in the geminate recombination efficiency of CO and 0 in complexes with a ‘picket fence’ 653 0.J. Curnow J. W.Kampf M. D. Curtis J.-K. Shen and F. Basolo J. Am. Chem. Soc. 1994 116,224. ‘j4 M. A. Mafie, M. J. Fernandez-Trujillo and M. G. Basallote J. Chem. SOC.,Dalton Trans. 1994 1717. 655 D.A. Dobbs and R.G. Bergrnan Inorg. Chem. 1994 33 5329. 656 G. Laurenczy G. Bondietti A. E. Merbach B. Moullet and R. Roulet Helv. Chim. Acta 1994 77 547. b5’ S. A. Roth and J. R. Shapley J. Coord. Chem. 1994 32 163. 6s8 F.-W. Grevels W.E. Klotzbiicher J. Schrickel and K. Schaffner J. Am. Chem. Soc. 1994 116 6229. 659 B. D. Rossenaar T. van der Graaf R. van Eldik C. H. Langford D.J. Stufkens and A. VlEek Jr. Inorg. Chem. 1994 33 2865. ‘‘O F.A. Kvietok and B.E. Bursten J. Am. Chem. Soc. 1994 116 9807. 661 A. L. Fernandez A. Prock and W. P. Giering Organometallics 1994 13 2767.662 T. Karlen A. Hauser and A. Ludi Inorg. Chem. 1994 33 2213. 663 J. J. Chung B.G. Roh and Y. C. Park Bull. Korean Chem. SOC.,1993,14 549 (Chem. Abstr. 1994,120 218029j). 664 J. J. Chung and B. G. Roh Bull. Korean Chem. Soc. 1993 14 669 (Chem. Abstr. 1994 120 24541 lj). 665 M. Prokesova I. Prokes M. Hudecek and S. Torna Monatsh. Chem. 1994 125 901. h66 S.-B. KO,S.-C. Yu and J. B. Hopkins Bull. Korean Chem. SOC. 1994 15 762 (Chem. Ahstr. 1995 122 92 600j). T. P. Dougherty W.T. Grubbs and E.J. Heilweil J. Phys. Chem. 1994 98 9396. S. K. Nayak G. J. Farrell and T. J. Burkey Inorg. Chem. 1994 33 2236. 669 S. Nakashirna and T. Kitagawa J. Am. Chem. SOC.,1994 116 10 318. 552 N. Winterton model haem.670 Kinetics of the binding of 0 and CO to a series of four-atom-linked capped Fe-porphyrin complexes671 have also been studied.Redox Reactions.-Rates of dimerization halogen-atom-transfer reactions with halometal complexes and redox reactions involving [Fe(CN),I3 -and tmpd have been reported672 for [W(CO),(q-C,H,CO,)] -in aquious solution. Tmpd catalyses the disproportionation of the 17-electron radical [Mo(CO),Cp] to give [Mo(CO),Cp] -and [Mo(CO),(NCMe)Cp] which are thermodynamically di~favoured~~~ + compared with the dimer [{ Mo(CO),Cp},]. Curvature in kinetic plots at long reaction times for the chain disproportionation reaction of [{ Fe(CO),Cp),] with dppe result5,' from a salt effect associated with the formation of ionic products [Fe(CO),Cp] -and [Fe(CO)(dppe)Cp] . The second-order rate constant for dimerization of the 17-+ electron radical species [Cr(CO),Cp] is much smaller (8.4 x lo5M-s-at 243 K I than for [Cr(CO),Cp*] (1.7 x lo7M-ls-' at 228 K).674Product studies and failure to trap radical intermediates point to675 heterolytic W-0s fission in [(Me,P)(OC),OsW(CO),].[Mn(CO),(NO)Cp'] + (and its indenyl analogue) reduced to a 19-electron radical in the presence of phosphorus donors suffers rapid electron- transfer-catalysed CO substitution,676 giving [Mn(CO)L(NO)Cp'] +.Similar studies on [Fe,N(CO) ,]-are reported.677 Electron-transfer reactions of metal carbonyl anions have been classified.678 [MoX,Cp*] (X = Cl Br) is reduced by [Mo,Y,CpT] (Y = Cl Br I) to [Mo,Y,Cpt][MoX,Cp*]. For Y = C1 Br further reaction to give [Mo,Y -nX,Cpz] and halide exchange between cation and anion are believed679 to proceed via a common associative intermediate.Nucleophilic attack by N; at carbonyl carbon in cis-[{Co"'(q -C H,PP h ),) Re (CO),] is 5400 times fas ter6 ** + than in C~S-[(CO"(~~-C~H~PP~~)~)R~(CO),]~. Oxidant-dependent pathways have been investigated6,1 in the reaction of [Mo,(p- C,Me,)Cp,] to give [Mo,(p-C,Me,CH,)Cp,] +. [CPh,] reacts by one-electron + oxidation followed by H ' abstraction [FeCp,] by a two-electron process followed + by H+ loss. Reduction682 of [Cr(CO),(q6-C ,HI')] to the corresponding 19-electron [Cr(C0)3(q6-C,3Hlo)] -is accompanied by loss of H' to give the 18-electron carbon-centred anion [Cr(CO),(q6-C ,H9)] -which isomerizes haptotropically to the metal-centred anion [Cr(CO),(q'-C ,H9)] -.A similar H loss on one-electron reduction of [ReO(ecd)] has also been described.683 On irradiation mer-670 T. G. Grogan N. Bag T.G. Traylor and D. Magde J. Phys. Chem. 1994 98 13 791. 671 N. Bag T. M. Grogan D. Magde C. Slebodnick M. R. Johnson and J.A. Ibers J. Am. Chem. SOC.,1994 116 11 833. 672 Z. Zhu and J. H. Espenson Organometallics 1994 13 1893. 673 J. Balla A. Bakac and J. H. Espenson Organometallics 1994 13 1073. 6'4 T. C. Richards W. E. Geiger and M. C. Baird Organometallics 1994 13 4494. 675 J. L. Male H. B. Davis R.K. Pomeroy and D.R. Tyler J. Am. Chem. SOC. 1994 116,9353. 676 Y. Huang C. C. Neto K. A. Pevear M. M. B. Holl D. A. Sweigart and Y. K. Chung Inorg. Chim. Acta 1994 226 53. 677 P. Zanello F.Laschi A. Cinquantini R. Della Pergola L. Garlaschelli M. Cucco F. Demartin and T. R. Spalding Znorg. Chim. Acta 1994 226 1. 678 J. D. Atwood M. S. Corrainepandolfino Y. Q. Zhen W. S. Striejewske and P. Ang J.Coord. Chem. 1994 32 65. 679 H.-B. Kraatz and R. Poli J. Organomet. Chem. 1994 475 167. I. M. LorkoviC M. S. Wrighton and W. M. Davis J. Am. Chem. SOC. 1994,116 6220. "' N.G. Connelly B. Metz and A. G. Orpen J. Chem. SOC.,Chem. Commun. 1994 2109. S. V. Kukharenko L. N. Novikova V. V. Strelets and N. A. Ustynyuk Russ. Chem. Bull. 1994 43 41. 683 J.E. Anderson C. M. Murphy S. M. Sawtelle and D. S. Edwards Inorg. Chim. Acta 1994 225 323. Inorganic Mechanisms 553 [MnX(CO),(bipy)]. (X = C1 Br I) yields684,685 the 16-electron radical [Mn+(CO),(bipy-)] which dimerizes to [{Mn(CO),(bipy)),] and reacts with phos- phines to give [Mn(CO),(PBu:)(bipy' -)I [Co"'R(py)(Hdmg),] (R = Me Bz) is rapidly reduced with e; to give a transient believed686 to be [Co"R(Hdmg),].This reacts with the parent compound to give dialkyl cobalt complexes in processes different from those obtained by chemical reduction. Electron-transfer between + [Co"'Me(py)(Hdmg),] and 2 [Ni'(tmc)] shows complex kinetics.687 [Co"Me(py)(Hdmg),] believed to be an intermediate hydrolyses to CH and [Co"(py)(Hdmg),]. The reaction688 of [Co'(tpp)] -(formed from [Co"'(tpp)] and + hydroquinone dianion) with alkyl halides to give [Co"'R(tpp)] and homolytic reactions of [Fe"'R(porphyrin)] have also been investigated.689 Oxidative Addition and Reductive Elimination.-Activation volumes A V* for the oxidative addition of Me1 to Pd(I1) in [PdMe,(bipy)] to give [PdMe,I(bipy)] support the proposed S,2 mechanism.690 Oxidative addition of RI (R = Me Et Pr") to [MI,(CO),] -(M = Rh giving [RhI,(CO)(COR)] -;M = Ir giving [IrI,R(CO),] -) is also thought69' to be S,2 with relative rates for the two nucleophiles k,,/k, being ca.150 R = Me; 220 R = Et; and 140 R = Pr". The rates of oxidative addition692 of RSSR with [W(CO),(NCEt)(phen)] to give [W(CO),(phen)(SR),] viaintermediates in which the disulfide is coordinated increase in the order R = Bu' 4Me < PhCH < Ph. In contrast [W(CO),(PPr:),] produces the 17-electron radical [W(SR)(CO),(PPr',),].693 Two groups have studied the thermal reactions of [RhHClPh(CO)(PMe,),] formed on irradiation of trans-[RhCl(CO)(PMe,),] and ben~ene.~~~.~~~ CPtMe,I(dppe)l undergoes competing ethane formation and a reversible e1iminatior-1~~~ of Me1 via a common cationic five-coordinate intermediate [PtMe,(dppe)] +-.The large positive A V* for the reductive elimination process [PdMe,I(bipy)] = [PdMeI(bipy)] + C2H6 points to a transition state with significant bond cleavage associated with the partial reduction of the Pd(1v) centre.690 Carbene intermediates have been pro- p~~ed~~~-~~~ from studies of the effect of C1-and SCN- on the rates of reductive 684 G. J. Stor S. L. Morrison D. J. Stufkens and A. Oskam Organometallics 1994 13 2641. 685 D. J. Stufkens J.W. M. van Outersterp A. Oskam B. D. Rossenaar and G.J. Stor Coord. Chem. Rev. 1994 132 147. 686 M. Kumar E. Natarajan and P. Neta J. Phys. Chem. 1994,98 8024. 687 S. Shi Transition Met. Chem. 1994 19 126. S. Fukuzumi and J. Maruta Inorg. Chim. Acta 1994 226 145. 689 B. Song and H. M. Goff Inorg. Chim. Acta 1994 226 231. 690 C. Ducker-Benfer R. van Eldik and A. J. Canty Organornetallics 1994 13 2412. 691 P. R. Ellis,J. M. Pearson A. Haynes H. Adams,N. A. Bailey and P. M. Maitlis Organornetallics 1994,13 3215. 692 R. F. Lang T. D. Ju G. Kiss C.D. Hoff,J.C. Bryan and G. J. Kubas Inorg. Chem. 1994 33 3899. 693 R. F. Lang T. D. Ju G. Kiss C. D. Hoff J. C. Bryan and G. J. Kubas J. Am. Chem. SOC. 1994,116,7917. 694 S.E. Boyd L.D. Field and M.G. Partridge J. Am. Chem. SOC. 1994 116 9492 69s G. P. Rosini W.T. Boese and A. S. Goldman J. Am. Chem. Soc. 1994 116 9498. 696 K.I. Goldberg J.-Y. Yan and E.L. Winter J. Am. Chem. SOC. 1994 116 1573. 697 V. V. Zamashchikov V.G. Popov and E. S. Rudakov Kinet. Katal. 1994,35,372 (Chem. Abstr. 1994 121 109 224u). 698 V. G. Popov and V. V. Zamashchikov Kinet. Katal. 1994,35,379 (Chem. Abstr. 1994 121 109 225v). 699 V. V. Zamashchikov V. G. Popov E. S. Rudakov and S. A. Mitchenko Russ. Chem. Bull. 1993,42,2055. 700 V.V. Zamashchikov and V.G. Popov Teor. Eksp. Khim. 1993 29 154 (Chem. Abstr. 1994 120 270 796w). 701 V. V. Zamashchikov V. G. Popov E. S. Rudakov and S.A. Mitchenko Dokl. Akad. Nauk. 1993,333,34 (Chem. Abstr. 1994 120 191 018r). 554 N. Winterton elimination of ethane from [PtMe2C1,l2-. Depending on pH [Pt(CH,CH,NH,f )Cl,] -undergoes reductive elimination7' via S,2 attack by C1- on the a-C of trans-[Pt(CH,CH,NH~)CI,(H,O)] to give ClCH,CH,NH and [PtCl,]'-or via intramolecular attack on N on the a-C to give aziridine and [PtC1,I2 -.From studies of the oxidation of [Pt"Cl,(q-C,H,)] -by isotopically enriched ['95PtC1,]2 -,Bercaw and coworkers prefer7' oxidation of the intermediate [Pt11Cl,(CH,CH,0H)]2-by electron transfer to one involving alkyl transfer. Brown and Guiry have shown that the rates of reductive elimination from complexes [PdMePh(P-P)] is facilitated by P-P with a large bite angle.704 Kurosawa and coworkers have reported705 that in the cis-reductive elimination reactions of [PdArL(q3-crotyl)] complexes the relative rates of isomerization and elimination are controlled by the electronic character of L.Reduction elimination reactions of [PdMeRR'X(N-N)],706 of SiMePh from ci~-[PtMe(SiPh,)(PMePh,),],~~~ of H from [TaH(EHPh)(OSiBu',),] (E = N P As),708 and of [Te(SiPh,),] from [Zr(TeSiPh,),(q 5-C 5H4B~t)2] 709 have all been studied. Hydrogen and Hydrido Comple~es.-[RhClH,(olefin)(PPh~)~],having cis phosphines and cis hydrides has been shown7" by parahydrogen-induced polarization to be an intermediate in the hydrogenation of olefins catalysed by [RhCl(PPh,),] . The concentration of the catalytically inactive binuclear complex [H,(PPh,),Rh(p- Cl),Rh(PPh,)(olefin)] also observed is suppressed by low concentrations of PPh,. Related studies of hydrogenations by [M(CO),(q4-nbd)] (M = Cr Mo) have been described."' [OsH(CO),L,] hydrogenates ethylene under mild conditions giving + cis,mer-[OsH(C2H4),L3]+ ,with intramolecular H migration to bring H and C2H4 into a cis stereochemical rearrangement being a key step established by isotopic- labelling [MoH(q3-C,H7)(dppe-rc2P)(dppe-k-P)] (VIII) (which equilibrates with [M~H,(q~-C,H,)(dppe-k-~P)(dppe-k-P)]) reacts with HC1 to give [MoH,Cl,(q3- C,H,)(dppe-~~P),] and Bu'CH,C(Me)=CH via rapid protonation of Mo in (VIII) followed by intramolecular hydrogen migration to form7' [MoH(q2-Me,C=CH,)(dppe-t~~P),]~.[ReH,(CO)(NO)L,] [L = PPr; P(OPr'),] shows rapid exchange between the Re-H sites believed to involve a dihydride-dihydrogen + exchange mechanism ; rner,trans-[ Re(?,-H2)(CO),(PR,),I does not equilibrate with the dihydride analogue undergoes facile exchange with D, and catalyses H,/D equilibrium with HD.7'5 Kinetic data for a similar equilibration involving mixed 702 V.V. Zamashchikov S. A. Mitchenko and S. M. Slinkin Russ. Chem. Bull.. 1994 43 478. '03 G.A. Luinstra L. Wang S.S. Stahl J.A. Labinger and J.E. Bercaw Organometallics 1994 13 755. 704 J. M. Brown and P. J. Guiry Inorg. Chim. Acta 1994 220 249. 705 H. Kurosawa K. Shiba K. Hirako K. Kakiuchi and I. Ikeda J. Chem. Soc. Chem. Commun. 1994,1099. '06 B. A. Markies A. J. Canty J. Boersma and G. van Koten Organometallics 1994 13 2053. 707 F. Ozawa T. Hikida and T. Hayashi J. Am. Chem. SOC. 1994 116 2844. 'OR J. B. Bonanno P.T. Wolczanski and E. B. Lobkovsky J. Am. Chem. SOC.1994 116 11 159. 709 D. E. Gindelberger and J. Arnold Organometallics 1994 13 4462. 710 S. B. Duckett C. L. Newell and R. Eisenberg J. Am. Chem. SOC. 1994 116 10 548. 'I1 A. Thomas M. Haake F.-W. Grevels and J. Bargon Angew. Chem. Int. Ed. Engl. 1994 33 755. 'I2 T. J. Johnson A. Albinati T. F. Koetzle J. Ricci 0.Eisenstein J.C. Huffman and K.G. Caulton Inorg. Chem. 1994 33 4966. 'I3 R.A. Henderson and K.E. Oglieve J. Chem. SOC.,Dalton Trans. 1994 767. 'I4 V. Bakhmutov T. Burgi P. Burger U. Ruppli and H. Berke Organometallics 1994 13 4203. 'Is D. M. Heinekey B. M. Schomber and C. E. Radzewich J. Am. Chem. SOC. 1994 116 4515 Inorganic Mechanisms M-Au clusters (M = Pt Pd) (e.g.[pt(A~pPh~),]~+) that H activation occurs at the M-Au bond. D2/H,0 exchange is also ~atalysed.~'~ The rate constants + for H atom exchange in trans-[MH(H,)L,] (M = Fe Ru 0s; L = (CH,P(C,H,-R-p),} 2) increase with increasing electron-releasing character of R associated with an increase in the ease of H-H homoly~is.~~~ Intermolecular and intramolecular H exchange are both observed719 in [RuH(q2-H,)(dmpe),].Li and propose that substitution of L in tran~-[Os"(q~-H,)L(en),]~ proceeds via dissocia-+ tion of L with the intermediate stabilized by rearrangement to [0~'~H,(en),]~ +. AH+ for hydride site-exchange in [IrH,X(PBu\Ph),] (X = C1 Br I) shows7, little variation with X. The kinetics of H dissociation from 18-electron [IrH,(H,)X(PBu\Ph),] were also studied. Isomeric dihydrogen complexes are believed723 to form from [IrBr,H(PPr\),] and H,.Replacement of L = Cp with L = Tp in [IrH,(PMe,)L]+ alters724 the ground state structure from a trihydride to a H,/H structure. NMR spectroscopic st~dies~,~,~,~ reveal a slight preference of D for the hydride site. [WH,Cl,L,] (L = PMe,Ph) exchanges with D by a process involving dissociation of L.726 [PtH(H2)L2]+ (L = PBu;) formed from [PtH,L,] and CF3S0,H [claimed727 as the first dihydrogen complex of P~(II)] shows no H/H scrambling on the NMR timescale at room temperature. 716 M.A. Aubart B.D. Chandler R.A.T. Gould D.A. Krogstad M.F.J. Schoondergang and L.H. Pignolet Inorg. Chem. 1994 33 3724. 717 M. A. Aubart J. F. Dor Koch and L. H. Pignolet Inorg. Chem. 1994 33 3852. 718 E. P. Cappellani S.D. Drouin G. Jia P. A. Maltby R.H. Morris and C. T.Schweitzer,J. Am. Chem. Soc. 1994 116 3375. 719 L. D. Field T.W. Hambley and B. C. K. Yau Inorg. Chem. 1994 33 2009. 720 Z.-W. Li and H. Taube J. Am. Chem. Soc. 1994 116 9506. 721 Z.-W. Li and H. Taube J. Am. Chem. Sac. 1994 116 11 584. 722 B. E. Hauger D. Gusev and K.G. Caulton J. Am. Chem. Soc. 1994 116 208 723 V. I. Bakhmutov A. B. Vymenits and V. V. Grushin Inorg. Chem. 1994 33 4413. 724 D.M. Heinekey and W.J. Oldham Jr. J. Am. Chem. Soc. 1994 116 3137. 725 M. Paneque M.L. Poveda and S. Taboada J. Am. Chem. SOC.,1994 116 4519. 726 H. Rothfuss J.C. Huffman and K.G. Caulton Inorg. Chem. 1994 33 2946. 727 D. G. Gusev J. U. Notheis J. R. Rambo B. E. Hauger 0.Eisenstein and K. G. Caulton J. Am. Chem. Soc. 1994 116 7409.

ISSN:0260-1818    

DOI:10.1039/IC9949100515

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Bioi norgan ic Chemistry By J. D. CRANE School of Chemistry University of Hull Kingston- upon- Hull North Humberside HU6 7RX UK 1 Introduction The rapid development of bioinorganic chemistry over recent years has prompted the publication of three new text books all intended as support texts for advanced up-to-date undergraduate courses. An increased number of specialist reviews covering recent research has also been published; the majority of these are referenced in the appropriate following sections but a few are of more general scope. A complete issue of Chemical Reviews was devoted to metal-dioxygen complexes with particular emphasis on metalloenzymes and their corresponding model systems.’ The scope of the chemical and electrochemical techniques available for the investigation of electron-transfer processes of metal lop rote in^^ and the nature of slow proton-transfer processes in metal lo enzyme^^ have both been reviewed.The uses of X-ray diffraction absorption and solution scattering techniques to obtain important structural information on metalloproteins have also been discu~sed.~ The extensive use of macrocyclic complexes as models for the transition metal sites of metalloenzymes has been reviewed,6 as has the design and synthesis of more complex systems intended to model the overall enzyme function rather than simply that of the metal centre of the active site in i~olation.~ Finally recent research developments relating to the status of A13+ as a neurotoxic ion have been discussed.* 2 Magnesium and Calcium The biological coordination chemistry of the Mg’ ion has been re~iewed.~ + Several enzymes containing magnesium sites essential for activity have been structurally (a)S.J. Lippard and J. M. Berg ‘Principles of Bioinorganic Chemistry’ University Science Books California 1994; (b) W. Kaim and B. Schwederski ‘Bioinorganic Chemistry’ Wiley Chichester 1994; (c) I. Bertini H. B. Gray S. J. Lippard and J. S. Valentine ‘Bioinorganic Chemistry’ University Science Books California 1994. Chem. Rev. 1994 94 p. 567. A.M. Bond Inorg. Chim. Acta 1994 226 293. K. W. Kramarz and J. R. Norton Prog. Inorg. Chem. 1994 42 1. S. S. Hasnain Pure Appl. Chem. 1994,66 51. V. McKee Adv. Inorg. Chem. 1994 40 323. A. M. Reichwein W. Verboom and D.N. Reinhoudt Red. Trav. Chim. Pays-Bas 1994 113 343. R.B. Martin Acc. Chem. Res. 1994 27 204. C.B. Black H.-W. Huang and J.A. Cowan Coord. Chem. Rev. 1994 135/136 165. 558 J. D. Crane GIu216 170 \ OH Figure 1 Structures of the magnesium sites of (a)catechol O-methyl transferase with bound inhibitor (3,5-dinitrocatechol) and (b) Dxylose isomerase with bound glucose (left Mg occupies site I) + characterized.lo-l3 The X-ray crystal structure of catechol O-methyl transferase at 2.0A resolution has shown that the Mg2+ ion is six-coordinate with the inhibitor (3,5-dinitrocatechol) occupying the proposed site of substrate binding (Figure la)." The coordination environment of the Mg2+ ion at the active site of P-galactosidase from Escherichia coli has also been described." The crystal structure of u-xylose isomerase from Streptornyces olivochrornogenes has been determined with bound substrates D-glucose (Figure lb) and 3-O-methyl-~-glucose as well as in the absence of substrate.The tightly bound Mg2+ ion in site-I was largely unaltered. However two alternative positions for the Mg2+ ion in site-I1 were identified.12 Replacement of Glu-180 with Lys generated a mutant which lacked the site-I Mg2 + ion and displayed a greatly reduced catalytic activity.' The structure and function of calcium binding proteins in the nucleus have been re~iewed,'~ and the important structural features which increase the affinity of cation binding sites for the Ca2+ ion have been discussed.15 The possible roles of Ca2+ and C1- ions in the chemistry of the oxygen-evolving complex of photosystem I1 have also been reviewed.3 Vanadium The reaction kinetics of the vanadium chloroperoxidase from Curvularia inaequalis have been shown to be similar to those of the vanadium bromoperoxidase from Ascophyllurn nodosum and in addition it was demonstrated that HOCl was formed as a reaction product.' A study of the competitive bromination of 2-methylindole and phenol red by the vanadium bromoperoxidase from A. nodosum has shown that the enzyme-catalysed formation of free HOBr does not explain the selective bromination of 2-methylindole. l8 However the evidence is consisent with the preferential binding of 10 J. Vidgren L. A. Svensson and A. Liljas Nature(London) 1994 368,354.11 R. H. Jacobson X.-J. Zhang R. F. DuBose and B. W. Matthews Nature(London) 1994 369 761. 12 A. Lavie K.N. Allen G.A. Petsko and D. Ringe Biochemistry 1994 33 5469. 13 K. N. Allen A. Lavie A. Glasfeld T.N. Tanada D. P. Gerrity S.C. Carlson G. K. Farber G. A. Petsko and D. Ringe Biochemistry 1994 33 1488. 14 J. S. C. Gilchrist M. P. Czubryt and G. N. Pierce Mol. Cell. Biochem 1994 135 79. 15 M. Nayal and E. Di Cera Proc. Natl. Acad. Sci. USA. 1994 91 817. 16 A. Boussac and A. W. Rutherford Biochem. SOC. Trans. 1994 22 352. 17 J. W. P. M. Schijndel P. Barnett J. Roelse E. G. M. Vollenbroek and R. Wever Eur. J. Biochem. 1994 225 151. 18 R. A. Tschirret-Guth and A. Butler J. Am. Chem. SOC. 1994 116 411. Bioinorganic Chemistry 559 2-methylindole to the enzyme followed by its bromination by an enzyme-generated + 'Br ' species.Functional and structural models for the vanadium haloperoxidases have also been reported." In addition the solution chemistry of V3+ [VO]" and [SO,]' -ions in blood cells from the tunicate Ascidia ceratodes has been investigated with sulfur K-edge X-ray absorption spectroscopy and EPR spectroscopy.20 4 Manganese The X-ray crystal structure of the manganese peroxidase from Phanerochaete chrysosporium at 2-06A resolution has been reported. The essential Mn2+ ion is coordinated by two water molecules and four carboxylate ligands including one propionate from the proximal dioxygen binding haem group (Figure 2)." The electronic absorption and MCD spectra for superoxidized manganese catalase from Lactobacillus plantarum and a range of di-p-oxo [Mn"'MnlV] model complexes have been reported and compared indicating that the superoxidized enzyme is likely to contain a bent di-p-oxo [Mnll'Mn'V] core probably with an additional third bridging group." The EPR signals of the [MnlllMn'V] states of the manganese catalases from L.plantarum and Thermus thermophilus have been studied at a selection of microwave frequencies and have been interpreted through detailed simulation^.^ The study of several manganese catalases and relevant functional model complexes has indicated that the generation of mixed-valence [Mn"Mn"'] or [MnlllMnlV] states is detrimental to the activity of the catalyst; the presence of a bridging carboxylate group may suppress the formation of these states.' The catalase activity of one dimanganese model complex has been studied in detail and shown to occur in two sequential two-electron steps { [Mn"Mn"] + [Mn"'Mn"'] + [Mn"Mn"]} and furthermore no spectroscopic evidence for any mixed-valence intermediates was found.' Recent developments concerning the currently accepted model (Figure 3) for the tetraman- ganese site of the oxygen-evolving complex of photosystem I1 have been discussed.26 An EXAFS study of this biosite consistent with this proposed model has also been reported.5 Iron Non-haem Biosites The X-ray analysis of crystals of apo-ferritin from Escherichia coli before and after soaking in a solution of Fe2+ ions has revealed the presence of three iron-binding sites l9 (a)G.J.Colpas B. J. Hamstra J. W. Kampf,and V. L. Pecoraro J. Am. Chem. Soc. 1994,116,3627; (b)C.J. Carrano M. Mohan S. M. Holmes R. de la Rosa A. Butler J. M. Charnock and C. D. Garner Inorg. Chem. 1994 33 646. 2o P. Frank B. Hedman R. M. K. Carlson and K.O. Hodgson Inorg. Chem. 1994 33 3794. 21 M. Sundaramoorthy K. Kishi M.H. Gold and T.L. Poulos J. Bid. Chern. 1994 269 32 759. 22 D. R. Gamelin M. L. Kirk T. L. Stemmler S. Pal W. H. Armstrong J. E. Penner-Hahn and E. I. Solomon J. Am. Chem. Soc. 1994 116 2392. 23 @)A. Haddy G. S. Waldo R. H. Sands and J. E. Penner-Hahn Inorg. Chem. 1994,33,2677;(h) M. Zheng S.V. Khangulov G.C. Dismukes and V. V. Barynin Inorg. Chem. 1994 33 382. 24 M. Shank V. Barynin and G.C.Dismukes Biochemistry 1994 33 15433. 2s (a)P. J. Pessiki S.V. Khangulov D. M. Ho and G. C. Dismukes J. Am. Chern. Soc. 1994,116,891; (b) P.J. Pessiki and G.C. Dismukes J. Am. Chem. Soc. 1994 116 898. 26 K. Wieghardt Angew. Chem. Int. Ed. Engl. 1994 33 725. 27 V. J. DeRose 1. Mukerji M. J. Latimer V. K. Yachandra K. Sauer and M. P. Klein J. Am. Chem. SOC. 1994. 116 5239. 560 J. D. Crane Figure 2 Structure of the active site of manganese peroxidase O-Mn-0 I /\ I Figure 3 Proposed structure of the tetramanganese site of the oxygen-evolving complex of photosystem II per subunit.28 Two of these sites constitute an iron(Ir1) dimer which resembles haemerythrin and other pox0 diiron biosites and are proposed to be similar in structure to the ferroxidase centres of human ferritin.The third is a mononuclear site on the inner surface of the protein shell and is postulated to act as the nucleation centre for the unusual iron(II1) core cluster observed for this ferritin. In addition 57Fe Mossbauer studies of two ferritins have shown that the iron(m) dimers at the ferroxidase centres are transferred into the ferritin core (or indeed to another ferritin molecule) as mononuclear species.29 EXAFS studies of iron(II1) phosvitin from chicken egg have shown the presence at low iron loading of octahedral iron(m) ions with six O-donor ligands (mostly phosphorylated serine residues) at an average distance of 1.94A.30At a higher iron loading level (50 irons per protein) however the average iron environment switches to between four- and five-coordinate.Four amonabactin siderophores from the Gram-negative bacterium Aerornonas hydrophila have been isolated and characterized. 31 The coordination of pyoverdin PaA a siderophore from Pseudomonas aeruginosa with Fe3 ions has been inves- + 28 P. D. Hempstead A. J. Hudson P. J. Artymiuk S.C. Andrews M. J. Banfield J. R. Guest and P. M. Harrison FEBS Lett. 1994 350 258. 29 E. R. Bauminger A. Treffry A. J. Hudson D. Hechel N. W. Hodson S.C. Andrews S. Levi I. Nowik P. Arosio J. R. Guest and P. M. Harrison Biochem. J. 1994 302 813. 30 S. Mangani P. L. Orioli A. Scozzafava L. Messori and P. Carloni BioMetals 1994 7 104. 31 J. R. Telford J. A. Leary L. M. G. Tunstad B. R. Byers and K.N. Raymond J. Am. Chem.Soc.1994,116 4499. Bioinorgunic Chemistry 561 tigated.32 The binding of Sc3+ and In3+ ions to transferrin has been studied by 45Sc and I3C NMR and electronic absorption spectro~copy.~~ The observed binding constant for In3+/transferrin was found to be loi8 substantially lower than previously reported values. 'H NMR studies of the iron@) form of the superoxide dismutase from Escherichia coli have shown that the structure of the active site is similar to that of the structurally characterized iron(m) form; the mononuclear iron centre remains coordinated to three histidine residues and one aspartate. 34 X-ray absorption spectroscopic studies of the iron@) form of native soybean lipoxygenase- 1 have shown that the metal centre is five-coordinate but that it increases to six-coordinate in the presence of methanol.In addition EXAFS studies of the iron(II1) form have indicated the presence of a hydroxide ligand with a short Fe-OH distance of 1.8881.35The presence of both five- and six-coordinate forms for iron@) soybean lipoxygenase-1 has also been established by near-IR CD/MCD studies.36 The recent X-ray crystal structure determination of the hydroxylase component of methane monooxygenase and its consequences for understanding the biological conversion of methane into methanol have been reviewed.37 The reaction of the reduced [Fe"Fe"] form of methane monooxygenase from Methylococcus capsulatus (Bath) with dioxygen has been investigated with low temperature optical and 57Fe Mossbauer spectro~copy.~~ The enzyme sample was freeze-quenched between 0.15 and 3s after the addition of dioxygen and the known spectra for the [Fe"Fe"] and [Fe"'Fe"'] forms were subtracted from the 57Fe Mossbauer spectra recorded.The analysis of the resulting spectra revealed the formation of a relatively long-lived intermediate (Q) which was also observed by stopped flow spectrophotometry ;the combined evidence was consistent with its assignment as a [Fe'VFe'V] state with non-equivalent iron sites. Furthermore a precursor to Q was identified in the 57Fe Mossbauer spectra. This precursor was diamagnetic with equivalent iron centres and was proposed to be the initially formed [Fe"'{p-O~-}Fe"'] state of the enzyme. The redox potentials of the diiron site in the similar methane monooxygenase from Methylosinus trichosporium OB3b have been determined and the formation of the [Fe"Fe"] [Fe"Fe"'] and [Fe"'Fe"'] states monitored by EPR and 57Fe Mossbauer spectros~opy.~~ ESEEM and ENDOR spectroscopic studies of the diiron(I1) forms of methane monooxygenase and azidohaemerythrin have also been rep~rted.~' The assembly of the diiron(m)/tyrosyl radical site of ribonucleotide reductase from Escherichia coli has been investigated in some detail with the combination of stopped flow spectrophotometry EPR and 57Fe Mossabauer spectroscopy enabling the 32 A.-M.Albrecht-Gary S. Blanc N. Rochel A. Z. Ocaktan and M. A. Abdallah Inorg. Chem. 1994,33,6391. 33 (a)J. M. Aramini and H. J. Vogel J. Am. Chem. SOC. 1994,116 1988; (b)W.R. Harris Y.Chen and K. Wein Inorg. Chem. 1994 33 4991. 34 L.-J. Ming J. B. Lynch R.C. Holz and L. Que Jr. Inorg. Chem. 1994 33 83. 35 R. C. Scarrow M. G. Trimitsis C. P. Buck G. N. Grove R. A. Cowling and M. J. Nelson Biochemistry 1994 33 15023. 36 M.A. Pavlosky and E.I. Solomon 1.Am. Chem. SOC. 1994,116 11 610. 37 (a)A. C. Rosenzweig and S. J. Lippard Acc. Chem. Res. 1994,27,229; (b)B. Krebs and N. Strater,Angew. Chem. Int. Ed. Engl. 1994 33 841. 38 K. E. Liu D. Wang B. H. Huynh D. E. Edmondson A. Salifoglou and S. J. Lippard J. Am. Chem. SOC. 1994 116 7465. 39 K. E. Paulsen Y. Liu B. G.Fox J. D. Lipscomb E. Miinck and M.T. Stankovich Biochemistry 1994,33 713. 40 B. M. Hoffman B. E. Sturgeon P. E. Doan V. J. DeRose K. E. Liu and S. J. Lippard J. Am. Chem.SOC. 1994,116 6023. 562 J. D. Crane identification of some key intermediate states.41 The spectroscopic evidence was inconsistent with the previously proposed formation of iron(Iv) or p-peroxodiiron(II1) species. However it confirmed the presence of a diiron(rII)/radical species as the precursor to the p-0x0 diiron (III) site and also indicated that a tryptophan radical cation (A,, = 560nm) is the species directly responsible for the generation of the tyrosyl radical. Interestingly it has been reported that for mouse ribonucleotide reductase the tyrosyl radical is not essential for enzyme activity.42 The formation of the p-0x0 diiron(Ir1) site of ribonucleotide reductase by reaction of the [Fe"Fe"] form with "0 has been investigated by resonance Raman spectroscopy; the dioxygen molecule is the source of the pox0 bridge.43 Repetition of this reaction for the mutant Phe-208 -+Tyr resulted in the hydroxylation of the Tyr-208 residue to DOPA (dihydroxyphenylalanine) which subsequently coordinated to one of the iron centres as a catecholate ligand.However in this case it was shown that the introduced second oxygen atom of the DOPA-208 residue originated from a water molecule rather than from dioxygen. The mixed valence [Fe"Fe"'] form of ribonucleotide reductase has also been investigated by EPR spectro~copy.~~ The reconstituted [Co"Co"] form of ribonucleotide reductase from E. coli has been investigated by visible absorption EPR and 'H NMR spectroscopy. Unlike the extremely air sensitive [Fe"Fe"] form of this protein this system displayed no reactivity towards di~xygen.~~ Resonance Raman studies of the diiron site of stearoyl-ACP A9 desaturase have shown that structurally it belongs to the same class of iron proteins as methane monooxygenase and ribonucleotide reductase and a structure for the site has been proposed (Figure 4).46However the reaction of the [Fe"Fe"] form with "0 does not result in the incorporation of an l800x0 bridge in contrast to the reported properties of ribonucleotide reductase.The mechanism of reaction of the mixed-valence [Fe"Fe"'] form of the purple acid phosphatase uteroferrin with a range of phosphates and the redox reactivity of this metalloprotein have also been in~estigated.~~ A series of potential functional model complexes for diiron biosites has been described.The reaction of [Fe,(H,0),(p-O)(tmpa)2]4+ with Bu'OOH/O in the presence of alkane substrates has been reported as a functional model for methane monooxygenase (R,CH -+ R,COH; R,CH -+ R,C=O) and the use of radical clock substrates has confirmed that for this complex the alkane functionalization proceeds by a free-radical process.48 Examples of diiron(I1) model complexes that bind dioxygen to form reactive p-peroxo diiron(ri1) complexes have been in~estigated.~~ The ability of a p-0x0 diiron(m) model complex to promote the hydrolysis of acetonitrile to yield a 'l (a)N. Ravi J. M. Bollinger Jr. B. H. Huynh D. E. Edmondson and J. Stubbe J. Am. Chem. Soc. 1994,116 8007; (b)J. M. Bollinger Jr. W.H.Tong N. Ravi B. H. Huynh D. E. Edmondson and J. Stubbe J. Am. Chem. SOC. 1994 116 8015 8024. 42 M.A. Henriksen B. S. Cooperman J. S. Salem L.-S. Li and H. Rubin J. Am. Chem. SOC.,1994,116,9773. 43 J. Ling M. Sahlin B.-M. Sjoberg T. M. Loehr and J. Sanders-Loehr J. Biol. Chem. 1994 269 5595. 44 (a)M. Atta K. K. Anderson R. Ingemarson L. Thelander and A. Graslund J. Am. Chem. SOC.,1994,116 6429; (b)R. Davydov S. Kuprin A. Graslund and A. Ehrenberg J. Am. Chem. SOC.,1994 116 11 120. 45 T.E. Elgren L.-J. Ming and L. Que Jr. Inorg. Chem. 1994 33 891. 46 B. G. Fox J. Shanklin J. Ai T. M. Loehr and J. Sanders-Loehr Biochemistry 1994 33 12 776 '' (a)M. A. S. Aquino J.-S. Lim and A. G. Sykes J. Chem.SOC.,Dalton Trans. 1994,429; (b)M. A. S. Aquino and A.G. Sykes J.Chem. SOC.,Dalton Trans. 1994 683. 48 R. M. Buchanan S. Chen J. F. Richardson M. Bressan L. Forti A. Morvillo and R. H. Fish Inorg. Chem. 1994 33 3208. 49 (a)A. L. Feig and S. J. Lippard,J. Am. Chem. SOC.,1994,116,8410; (b)Y.-M. Chiou and L. Que Jr. Angew. Chem. lnt. Ed. Engl. 1994 33 1886. Bioinorganic Chemistry GIu~’~ I Figure 4 Proposed structure of the diiron site of stearoyl-ACP A’ desaturase coordinated amide ligand has also been reported.” In addition the synthesis reactivity and spectroscopic properties of a range of structural models for the diiron sites of purple acid phosphatases,” and general models for [Fe2(p-O)(p-02CR),12 + and [Fe2(p-O)(p-0H)l3 cores in metalloproteinss2 have been described. + The X-ray crystal structure of the [2Fe-2S] ferredoxin I from Equiseturn aruense at 1.88 resolution has been reported.53 Individual site-directed mutagenesis of each of the four cysteine ligands to a serine residue in the [2Fe-2S] ferredoxin from Anabaena 7120 has been described.54 The effect of these four mutations on the stability and properties of the iron cluster was investigated by EPR and ‘H NMR spectroscopy.Although the stability of the cluster was found to be reduced these studies demonstrated that serine can act as a substitute for a cysteine ligand in some cases. The X-ray crystal structures of the oxidized form of the high potential [4Fe4S] iron-sulfur protein isolated from Ectothiovhydospira vacuolata at 1.8 A resolution and the 2C4Fe-4S-J ferredoxin from Clostridium acidurici at 1.84A resolution have been reported.” The oxidized forms of this latter ferredoxin and a similar protein from C.pasteurianum have been investigated by ‘H NMR spectroscopy and the signals for the protons of the coordinated cysteine residues identified and assigned.s6 It has also been reported that under reducing conditions all eight Fe ions of the ferredoxin from C. pasteurianum could be reversibly replaced with Cd2+ ions without denaturing the protein. In contrast only a small degree of incorporation was found for Zn2+ and Co2+ and there was no evidences7 for any incorporation of Ni2+ Cu2 +,or Mn2+.The electronic structures of both the reduced [4Fe4S] + form and the oxidized [3Fe4S] + 50 E. C. Wilkinson Y. Dong and L. Que Jr. J. Am.Chem. Soc. 1994 116 8394. 51 (a) E. Bernard W. Moneta J. Laugier S. Chardon-Noblat A. Deronzier J.-P. Tuchagues and J.-M. Latour Angew. Chem. Int. Ed. Engl. 1994 33 887; (b) P. N. Turowski W.H. Armstrong S. Liu S.N. Brown and S.J. Lippard Inorg. Chem. 1994,33,636; (c)B. Krebs K. Schepers B. Bremer G. Henkel E. Althaus W. Miiller-Warmuth K. Griesar and W. Haase Inorg. Chem. 1994 33 1907. 52 (a)S. P. Watton A. Masschelein J. Rebek Jr. and S. J. Lippard J. Am. Chern. Soc. 1994,116,5196;(h) Y. Zang G. Pan L. Que Jr. B.G. Fox and E. Munck J. Am. Chem. SOC. 1994 116 3653. 53 S. Ikemizu M. Bando T. Sato Y. Morimoto T. Tsukihara and K. Fukuyama Acta Crystallogr. Sect. D 1994 50 167. 54 H. Cheng B. Xia G.H. Reed and J. L. Markley Biochemistry 1994 33 3155. 55 (a) M.M. Benning T.E. Meyer I. Rayment and H. M. Holden Biochemistry 1994 33 2476; (b) E. D. Duee E. Fanchon J. Vicat L.C. Sieker J. Meyer and J.-M. Moulis J. Mol. Biol. 1994 243 663. 56 I. Bertini F. Capozzi C. Luchinat M. Piccioli and A.J. Vila J. Am. Chem. Soc. 1994 116 651. 57 F. Bonomi M.L. Ganadu G. Lubinu and S. Pagani Eur. J. Biochem. 1994 222 639. 564 J. D.Crane form of the ferredoxin from Thermococcus litoralis have been investigated by 'H NMR spectro~copy.~~ The Tyr-19 residue proximal to the [4Fe4S] cluster in the high potential iron-sulfur protein from Chromatiurn vinosurn has been replaced with the structurally similar 3-fluorotyrosine residue and 19FNMR spectroscopy used to probe the environment of this For the reduced cluster the observation of two I9F signals in a 2 :1 ratio indicated that the hindered rotation of the aromatic ring was possibly accompanied by a favourable interaction between the C-F bond and the [4Fe4S] cluster.In contrast only a single downfield peak was observed for the oxidized form of the protein. The nature of three strong NH --S hydrogen bonds to the [Fe,S,(S-Cys),] -cluster of the hydrogenase from Desulfovibrio gigas has been investigated by pulsed ENDOR and TRIPLE resonance experiments.60 The structures of the native [4Fe4S] form of aconitase with and without bound substrate and the inactive [3Fe4S] form which lacks the labile non-cysteine coordinated iron atom have been investigated by resonance Raman spectroscopy.61 The binding of metal ions to the C3Fe-4S-J clusters of aconitase and the ferredoxin from Pyrococcusfuriosus to generate [MFe,S,] cubes (M = TI+ Mn2+ Fe2+ Co2+)has been reported.62 The kinetics of the conversion of the incomplete cuboidal [3Fe-4S] cluster of inactive aconitase into a linear cluster at high pH have been investigated (Figure 5).63 The properties of iron-sulfur clusters have also been investigated through the detailed spectroscopic study and theoretical modelling of relevant model systems.64 Figure 5 Schematic representation of the conversion of the incomplete cuboidal form of the [3Fe-4S] cIuster of aconitase to the linear form at high pH 6 Iron Haem Biosites The general nature of the interaction between NO and iron haem proteins has been re~iewed.~' The binding of NO to both the Fe2+ and Fe3+ forms of the haem of NO 58 A.Donaire C. M. Gorst Z. H. Zhou M. W. W. Adams and G. N. La Mar J. Am. Chem. SOC.,1994,116 6841. 59 S. M. Lui and J. A. Cowan J. Am. Chem. SOC. 1994 116 4483. 6o P.E. Doan C. Fan and B. M. Hoffman J. Am. Chem. SOC.,1994 116 1033. " L. K. Kilpatrick M.C. Kennedy H. Beinert R. S. Czernuszewicz D. Qiu and T.G. Spiro J. Am. Chem. SOC.,1994 116 4053. 62 (a)W. Fu J. Telser B. M. Hoffman E.T. Smith M. W. W. Adams M. G. Finnegan R. C. Conover and M.K. Johnson J. Am. Chem. SOC. 1994,116,5722; (b)K. Y. Faridoon H.-Y. Zhuang and A.G. Sykes Inorg. Chem. 1994 33 2209. 63 H.-Y. Zhuang and A.G. Sykes J. Chem. SOC. Dalton Trans. 1994 1025. 64 (a)R. S. Czernuszewicz L. K. Kilpatrick S. A. Koch,and T. G. Spiro J.Am. Chem. SOC.,1994,116,7134; (b) J. Gloux P. Gloux B. Lamotte J.-M. Mouesca and G. Rius J. Am. Chem. SOC.,1994,116,1953; (c)E. L. Bominaar S.A. Borshch and J.-J. Girerd J. Am. Chem. SOC. 1994 116 5362. 65 A. Tsai FEBS Lett. 1994,341 141. Bioinorganic Chemistry synthase has been investigated by resonance Raman spectroscopy and the possible role of NO as an inhibitor for this enzyme has been discussed.66 A new resonance Raman band for oxyhaem (Fe-0,) proteins has been identified by isotopic substitu- For haemoglobin this band occurs at 425cm-1 (l60,), ti~n.~~ 405cm-1 ("O,) and 423 and 407 cm- ' (l60l8O)and has been assigned to the Fe-0-0 bending mode (hFeoo).The same approach has been used to identify the Fe-C-0 bending mode of CO adducts of haems for example hFeCO= 367 cm- ' for the 12C'60adduct of haemoglo- bin.68 This is significantly lower than the previously accepted value of ca.575 cm- ' for this mode and has been explained by tentatively assigning the higher frequency band to either a combination mode with a porphyrin vibration or a Fe-C deformation mode. In marked contradiction to these findings others have confirmed the assignment of the n U haem Figure 6 Hydrogen-bonding to the tightly bound dioxygen molecule of the haemoglobin from ascaris hFeCOfundamental to a band between 574 and 568 cm- for linear and slightly bent haem Fe-CO model complexes.69 The haemoglobin from the parasitic nematode ascaris is 100 times better at binding dioxygen than conventional haemoglobin; this high affinity has been explained by the identification of two hydrogen bonds (to proximal tyrosine and glutamate residues) to the bound dioxygen (Figure 6) rather than the usual one (to a histidine re~idue).~' The replacement of Val-68 of human myoglobin with Asp Asn and Glu residues results in the binding of a water molecule as the sixth ligand for the first two mutants whereas for the third mutant the Glu-68 residue itself coordinates the iron ~entre.~' The intramolecular reduction of the FeIV=O form of horse heart myoglobin by a pentaammineruthenium(11) complex bound to a surface histidine (His-48) has been in~estigated;'~ the Ru-haem distance is 12.7A and the rate of the intramolecular electron transfer was 0.19 & 0.02s-l.The 66 J.Wang D. L. Rousseau H. M. Abu-Soud and D.J. Stuehr Proc. Natl. Acad. Sci. USA. 1994,91,10 512. 67 S. Hirota T. Ogura E. H. Appelman K. Shinzawa-Itoh S. Yoshikawa and T. Kitagawa J. Am. Chem. Soc. 1994 116 10564. 68 S. Hirota T. Ogura K. Shinzawa-Itoh S. Yoshikawa M. Nagai and T. Kitagawa J. Phys. Chem. 1994,98 6652. 69 (a)S. Hu K. M. Vogel and T. G. Spiro J. Am. Chem. SOC.,1994,116 11 187; (b)G. B. Ray X.-Y. Li J. A. Ibers J.L. Sessler and T.G. Spiro J. Am. Chem. Soc. 1994 116 162. 70 I. De Baere M. F. Perutz L. Kiger M. C. Marden and C. Poyart Proc. Natl. Acad. Sci. USA. 1994,91 1594. 71 T. E. Zewert H. B. Gray and I. Bertini J. Am. Chem. Soc. 1994 116 1169. 72 C. Fenwick S. Marmor K. Govindaraju A. M. English J. F. Wishart and J. Sun J. Am. Chem.Soc.1994 116 3169. 566 J. D. Crane X-ray crystal structure of the cyanomet form of sulfmyoglobin C has also been reported.73 Current knowledge concerning the regio- and stereoselective chemistry of the cytochrome P-450 enzymes has been ~ummarized.~~ Recent developments in the modelling of the structure and reactivity of cytochrome P-450 have also been de~cribed.~' The X-ray crystal structure of cytochrome P-45OterP at 2.3 8 resolution is very similar in overall structure to that of cytochrome P-450cam.76 Molecular dynamics simulations of the dioxygen-bound iron(rr) form of cytochrome P-45OCa have supported the proposal that the proximal Thr-252 residue stabilises this complex through hydrogen-bonding to the bound dioxygen molecule.In addition these simulations were consistent with the Thr-252 residue being involved in the subsequent proton transfers which lead to the formation of the putative Fe"=O intermediate. The study of kinetic solvent isotope effects for the activation of dioxygen by cytochrome P-45OCam has also indicated that the residues Thr-252 and Asp-251 (and possibly one water molecule) are involved in the proton transfers to di~xygen.~' Several low-spin iron(II1) forms of camphor-free cytochrome P-45OCam with aromatic bases (pyridine imidazole etc.) coordinated to the iron centre have been investigated by 'H NMR spectroscopy; a partial assignment of the high-spin camphor-bound form was also reported.79 ENDOR studies of the chloroperoxidase from Caldariornycesfumago have shown that the haem iron coordination sphere is very similar to that of cytochrome P-45OCam, with axial cysteinyl/aqua coordination.'' The P-460 haem of hydroxylamine oxidoreductase from Nitrosomonas europaea has been proposed to form an unusual dihaem cluster with a c-type cytochrome; an EPR and 57Fe Mossbauer spectroscopic investigation of the coupling between these two haems indicated the possible presence of a bridging ligand." The X-ray crystal structure of the fungal peroxidase from Arthromyces ramosus at 1.9 8 resolution is very similar to that of lignin peroxidase from Phanerochaete chrysosp~riurn.~~ A resonance Raman study of cyanide binding to the haem of horseradish peroxidase has identified both linear and bent Fe-CN binding ge~metries.'~ In addition the replacement of Phe-41 of horseradish peroxidase with a Leu residue yields a mutant which catalyses the sulfoxidation of aryl alkyl sulfides with much higher enantioselectivity than the wild-type en~yrne.'~ The X-ray crystal structure of the electron-transfer complex formed from the three proteins amicyanin methylamine dehydrogenase and cytochrome cS5 from Pavacoc-cus denitrijicans at 2.4 A resolution has been reported." The structures of cytochromes c2 from P.denitrijicans and Rhodobacter sphaeroides and cytochrome c3 from 73 S.V. Evans B. P. Sishta A.G. Mauk and G. D. Brayer Proc. Natl. Acad. Sci. USA 1994,91 4723. 74 K. Oguri and H. Yamada Ann. Rev. Pharmacol. Toxicol.,1994 34 251, '' (a) M. Hirobi Pure Appl. Chem. 1994 66 729; (b) D.Mansuy Pure Appl. Chem. 1994,66 737. 76 C. A. Hasemann K. G. Ravichandran. J.A. Peterson and J. Deisenhofer J. Mol. Bid 1994 236 1169. 77 D.L. Harris and G.H. Loew J. Am. Chem. SOC.,1994 116 11671. 7' J. Aikens and S. G. Sligar J. Am. Chem. Soc. 1994 116 1143. 79 L. Banci I. Bertini S. Marconi R. Pierattelli and S.G. Sligar J. Am. Chem. SOC.,1994 116 4866. '"Y.-C. Fann N. C. Gerber P. A. Osmulski L. P. Hager S. G. Sligar and B. M. Hoffman J.Am. Chem. Soc. 1994 116 5989. " M.P. Hendrich M. Logan K. K. Anderson D. M. Arciero J. D. Lipscomb and A. B. Hooper J. Am. Chem. Soc. 1994 116 11961. " N. Kunishima K. Fukuyama H. Matsubara H. Hatanaka Y. Shibano,and T.Amachi J.Mol. Biol. 1994 235 331. '3 J. Al-Mustafa and J. R. Kincaid Biochemistry 1994 33 2191.84 S.-I. Ozaki and P. R. Ortiz de Montellano J. Am. Chem. Soc. 1994 116 4487. '5 L. Chen R. C. E. Durley F. S. Mathews and V. L. Davidson. Science 1994 264 86. Bioinorganic Chemistry 567 Desulfovibrio desulfuricans have also been determined.86 The importance of the peptide backbone for mediating electron-transfer processes in proteins has been investigated using modified cytochrome c (horse heart).87 It was found that intramolecular electron transfer from the haem was much faster to a metal centre bound to His-33 rather than to Met-65 even though these two surface residues are approximately the same distance from the haem (ca. 15.5A). The effect of site-directed mutagenesis on the axial ligation of cytochrome c has also been studied; the replacement of Phe-82 with His resulted in this residue displacing the Met-80 ligand and the replacement of Met-80 with Cys was shown to yield a cysteinyl ligated haem.88 In addition a model has been reported for calculating the effects of site mutations and complex formation on the reduction potentials of cytochrome c and cytochrome c ~xidase.~~ The X-ray structure of the Fe”-0 complex of a yeast cytochrome c oxidase mutant (Trp-191 -+ Phe) indicated that only the proximal His residue is available for hydrogen-bonding to the proposed transient Fe”’-OOH form of the wild-type enzyme.” X-ray studies of cytochrome aa3 from Bacillus subtilis have revealed a structure very similar to cytochrome c oxidase.However it lacks the Cu site.” The Cu,-Fe (haem a3)distance is reported to be 3.70 8 and the presence of a sulfur-bridging ligand was proposed.In addition a vibrational study of CO-bound cytochrome c oxidase and several mutants has been reported which supports the proposal that Cu and the two haems a and a3 adopt a mutually linear arrangement.92 Optical absorption flow-flash techniques have been used to investigate the early steps in the reaction of reduced cytochrome c oxidase with di~xygen.~~ An IR study of the photodynamics of CO bound cytochrome c oxidase has shown that upon photolysis the CO molecule is transferred from haem a3 to Cu extremely quickly (within 1 ps) from which it dissociates on the microsecond time~cale.~~ Several model complexes for the Cu,/haem u3site of cytochrome c oxidase have also been rep~rted.’~ Several iron(1rr) chlorin complexes have been studied as models for cytochromes d and d (Figure 7).96 The substrate binding (SO:- NO, NO NH,OH etc.) and 86 (a) M.M. Benning T.E. Meyer and H. M. Holden Arch. Biochem. Biophys. 1994 310 460; (b) H.L. Axelrod G. Feher J. P. Allen A. J. Chirino M. W. Day B. T. Hsu and D. C. Rees Acta Crystallogr. Sect. D 1994,50,596; (c)M. Czjzek F. Payan F.Guerlesquin M. Bruschi and R. Haser J.Mol. Biol. 1994,243 653. ’’ I. Moreira J. Sun M. 0.-K. Cho J.F. Wishart and S. S. Isied J. Am. Chem. Soc. 1994 116 8396. *’ (a)B.K. Hawkins S. Hilgen-Willis G. J. Pielak and J. H. Dawson J.Am. Chem. Soc. 1994,116,3111; (b) G. Smulevich M. J. Bjerrum H. B. Gray and T. G. Spiro Inorg. Chem. 1994 33 4629. *’ H.-X.Zhou J. Am. Chem. Soc. 1994,116 10362. M.A. Miller A. Shaw and J. Kraut Nut. Struct. Biol. 1994 1 524. ” L. Powers M. Lauraeus K. S. Reddy B. Chance and M. Wikstrom Biochim Biophys. Acta 1994,1183 504. ” J. P. Hosler Y. Kim J. Shapleigh R. Gennis J. Alben S. Ferguson-Miller and G. Babcock J. Am. Chem. Soc. 1994 116 5515. y3 M. I. Verkhovsky J. E. Morgan and M. Wikstrom Biochemistry 1994 33 3079. 94 R. B. Dyer K. A. Peterson P. 0.Stoutland and W. H. Woodruff Biochemistry 1994 33 500. y5 (a) J.P. Collman P.C. Herrmann B. Boitrel X. Zhang T.A. Eberspracher L. Fu J. Wang D.L. Rousseau and E. R. Williams J. Am. Chem. Soc. 1994 116,9783; (b) K. D. Karlin A. Nanthakumar S. Fox N.N. Murthy N. Ravi B. H. Huynh R. D. Orosz and E. P. Day J. Am. Chem. Soc. 1994,116,4753; (c) S.C. Lee M. J. Scott K. Kauffmann E. Miinck and R. H. Holm J. Am. Chem. Soc. 1994,116,401;(d) M. J. Scott and R. H. Holm J. Am. Chem. SOC. 1994 116 11 357. y6 (a)S. Ozawa Y. Watanabe S. Nakashima T. Kitagawa and I. Morishima J. Am. Chem. SOC. 1994 116 634;(b) S. Ozawa Y. Watanabe and I. Morishima,J.Am. Chem.SOC. 1994,116,5832; (c) A. M. Bracete S. Kadkhodayan M. Sono A.M. Huff C. Zhuang D.K. Cooper K. M. Smith C. K. Chang and J.H. Dawson Inorg. Chem. 1994,33,5042;(d)S. Ozawa Y. Watanabe and I. Morishima Inorg. Chem. 1994 33,306; (e) S. Ozawa E. Sakamoto Y. Watanabe and I. Morishima J.Chem. SOC.,Chem. Commun. 1994 935. 568 J. D. Crane Figure 7 Proposed structures for the chlorin cofactors of (a) cytochrome d and (b) cytochrome d reactivity of the coupled [4Fe4S]-sirohaem centre of dissimilatory sulfite reductase from Desulfouibrio uulgaris have been in~estigated.~~ Two structural and spectroscopic model complexes for this biosite have also been described.98 7 Cobalt The biosynthesis of vitamin B12 and the nature of vitamin B12 binding sites in enzymes have been re~iewed.~' A high resolution (0.9A) neutron study of the solvent structure of crystalline vitamin B, at 15K has been reported."' A kinetic study of ligand substitution reactions for aquacobalamin (vitamin B 2a) has demonstrated that substituted pyridines deviate from the usual dissociative interchange mechanism.' '' For these ligands the evidence indicated the formation of a strong precursor complex ascribed to favourable corrin/pyridine interactions.The X-ray crystal structure of cobalt p-cyanoimidazolylcobamide has been determined." The axial imidazole ligand induces relatively little upward folding of the corrin ring an observation consistent with the proposal that the steric bulk of the coordinated nucleotide base in vitamin B, is responsible for the substantial deformation of the corrin ring. 8 Nickel The structure and chemistry of nickel biosites has been revie~ed,''~ as has the study of model systems for these metalloenzymes. lo4An X-ray absorption spectroscopic study of the dinickel sites in the ureases from jack bean and Klebsiella aerogenes has been reported.' O5 The evidence indicated the presence of five-coordinate nickel@) centres 97 (a)S.M. Lui W. Liang A. Soriano and J. A. Cowan J. Am. Chem. SOC.,1994,116,4531; (b)W. Liang and J.A. Cowan Inorg. Chem. 1994 33 4604. 98 (a)L. Cai and R. H. Holm J. Am. Chem. SOC.,1994,116,7177; (b)S. M. Luiand J. A. Cowan J. Am. Chem. SOC. 1994 116 11 538. 99 (a) L. Milgrom Chem. Br. 1994 30,923; (b)J. Stubbe Science 1994 266 1663. loo J. P. Bouquiere J. L. Finney and H. F.J. Savage Acta Crystallogr. Sect. B 1994 50 566. lol F. F. Prinsloo M. Meier and R. van Eldik Znorg. Chem. 1994 33 900. B. Krautler R. Konrat E. Stupperich G. Farber K. Gruber and C. Kratky Inorg. Chem. 1994,33,4128. lo3 A. F. Kolodziej Prog. Inorg. Chem. 1994,41,493. lo4 M.A. Halcrow and G. Christou Chem. Rev. 1994,94 2421. lo5 S. Wang M. H. Lee R. P. Hausinger P. A. Clark D.E. Wilcox and R.A. Scott Znorg. Chem. 1994,33 1589. Bioinorganic Chemistry HO Figure 8 Proposed structure for the dinickel site of urease with bound inhibitor (2-mercaptoethanol) with N,O-donor ligands of which two or three are histidine residues. Addition of the inhibitor 2-mercaptoethanol resulted in the replacement of one non-histidine residue from each metal centre with an S-donor ligand (presumably the inhibitor) and the appearance of a new feature which was proposed to correspond to a Ni-Ni distance of 3.26 8 indicating that the thiolate inhibitor is probably bridging the two metal centres and demonstrating the proximity of the two nickel centres in the native enzyme (Figure 8). A resonance Raman study of carbon monoxide dehydrogenase from Clostridiurn thermoaceticurn has demonstrated that the CO molecule binds to iron and not to nickel at the mixed-metal centre.lo6 Based on this observation a mechanism for the function of this biosite was proposed in which a methyl group is transferred from the nickel centre to the iron-bound CO molecule and the resulting acetyl group is subsequently transferred to coenzyme A. EPR and 57Fe Mossbauer spectroscopic studies of the hydrogenase from Chromatiurn vinosurn have indicated that in addition to a nickel centre one [3Fe-4S] cluster and two [4Fe4S] clusters there may also be a mononuclear low-spin iron(Ir/rrI) centre that mediates the interaction between the nickel centre and the [3Fe-4S] luster.''^ The redox centres of the hydrogenase from Desulfovibrio gigas have been investigated by oxidative titrations.'" The Nix state of the enzyme was found to be stable in the strict absence of dihydrogen and dioxygen and the assignment of this state as a nickel hydride was discussed in relation to the possible formulations of the other known states.Nickel L-edge X-ray absorption spectroscopy has been used to investigate the electronic structure of nickel-recon- stituted rubredoxin from Pyrococcus furiosus and the data interpreted through comparison with a range of relevant model complexes.'09 A few new model complexes for the nickel site in hydrogenase have also been reported."'-' Reaction of (1) with dioxygen yields the sulfenate derivative (2) which could then be easily electrochemically reduced back to (1) in the presence of an oxygen-atom acceptor (PPh,).' ''Based on these observations it was proposed that this system may represent a model for the reductive reactivation of 0,-deactivated 106 D.Qiu M. Kumar S. W. Ragsdale and T.G. Spiro Science 1994 264,817. 107 K. K. Surerus,M. Chen J. W. van der Zwaan F. M. Rusnak M. Kolk E. C. Duin S. P.J. Albracht and E. Munck Biochemistry 1994 33 4980. 108 D. P. Barondeau L. M. Roberts and P.A. Lindahl J. Am. Chem. Soc. 1994 116 3442. 109 J. van Elp G. Peng B.G. Searle S. Mitra-Kirtley Y.-H. Huang M. K. Johnson Z. H. Zhou M. W. W. Adams M. J. Maroney and S. P. Cramer J. Am. Chem. SOC. 1994 116 1918. 110 P.J. Farmer,J.-N.Verpeaux C. Amatore M. Y. Darensbourg and G. Musie J. Am. Chem. SOC. 1994,116 9355. 111 S.B. Choudhury M. A. Pressler S. A. Mirza R. 0.Day and M. J. Maroney Znorg. Chem. 1994,33,4831. 112 S. C. Shoner M. M. Olmstead and J.A. Kovacs Inorg. Chem. 1994 33 7. 570 J. D. Crane hydrogenase enzymes. The chemical reasons for the presence of a nickel selenocysteinyl ligand in the hydrogenase from Desulfovibrio baculatus instead of the more commonly found cysteinyl ligand has been discussed with reference to a series of thiolate and selenolate model complexes.' '' 5 Copper The structure of blue copper proteins and the effects of the inflexible protein-imposed metal coordination geometry on the spectroscopic properties of these systems have been reviewed. '' The X-ray crystal structures of the type-I copper proteins pseudoazurin (Methylobacterium extorquens) plastocyanin (poplar) and amicyanin (Thiobacillus versutus) have been reported.' l4 Crystals of cadmium(r1)-reconstituted azurin have been prepared by diffusing Cd2 -t ions into previously prepared crystals of the apo-protein; subsequent solution of the structure at 1.8A resolution indicated that the cadmium site was only slightly different from the corresponding copper(I1) form of the protein.' The nature of the Cu-S(Cys) bond in type-I and type-I1 copper proteins has been investigated by resonance Raman spectroscopy."6 A range of new copper sites was prepared by site-directed mutagenesis of azurin and Cu,Zn superoxide dismutase; the position of the vcus band (420-3 10cm-') can be correlated to changes in the metal coordination geometry.A partial 'H NMR spectroscopic assignment of pseudoazurin from Achrornobacter cycloclastes has been used to determine" an electron self-exchange rate constant of about 2.8 x lo3M-' s-'. This low value was consistent with the proposal that the surface residue His-81 mediates electron transfer and that the surrounding residues impede the approach of two protein molecules in an appropriate orientation. The pH dependence of the electron transfer reactions of this protein and amicyanin from Thiobacillus versutus with redox-active transition metal complexes has also been reported.Il8 The roles of the two copper centres of nitrite 113 B. G. Malmstrom Eur. J. Biochem. 1994 223,711. 114 (a) T. Inoue Y. Kai S. Harada N. Kasai Y. Ohshiro S. Suzuki T. Kohzuma and J.Tobari Acta Crystallogr. Sect. D 1994,50 317; (b)B. A. Fields H. H. Bartsch H. D. Bartunik F. Cordes J. M. Guss and H.C. Freeman Acta Crystallogr. Sect. D 1994 50 709; (c) A. Romero H. Nar R. Huber A. Messerschmidt A. P. Kalverda G. W. Canters R. Durley and F. S. Mathews J. Mol. Biol. 1994 236 1196. 115 K. A. Blackwell B. F. Anderson and E.N. Baker Acta Crystallogr. Sect. D 1994 50 263. 116 C. R. Andrew H. Yeom J. S. Valentine B. G. Karlsson N. Bonander G. van Fouderoyan G. W. Canters T. M. Loehr and J. Sanders-Loehr J. Am. Chem. Soc. 1994 116 11 489. 117 C. Dennison T. Kohzuma W. McFarlane S. Suzuki and A. G. Sykes J. Chem. Soc. Dalton Trans. 1994 437. 118 (a)C. Dennison T. Kohzuma W. McFarlane S. Suzuki and A. G. Sykes J. Chem. Soc. Chem. Commun.1994,581; (b)C. Dennison T. Kohzuma W. McFarlane S. Suzuki and A. G. Sykes Inory. Chem. 1994 33 3299; (c) P. Kyritsis C. Dennison A. P. Kalverda G. W. Canters and A.G. Sykes J. Chem. Soc. Dalton Trans. 1994 3017. Bioinorganic Chemistry Figure 9 Structure of the dicopper site of nitrite reductase reductase from Alcaligenes faecalis S-6 have been investigated by a combination of site-directed mutagenesis and X-ray crystallographic studies (Figure 9)."' The type-I copper site (Cu,) was found to be essential for electron transfer to the adjacent type-I1 copper active site (Cu,). The binding of nitrite to the type-I1 copper site has also been demonstrated by an EPR and ENDOR spectroscopic study of a similar protein.'20 The redox properties of both copper centres have been reported and pulse radiolysis studies have been used to investigate the intramolecular electron transfer from the type-I copper site to the type-I1 copper site.'21 The structure and reactivity of the tricopper biosites of the blue copper oxidases (ascorbate oxidase laccase etc.) have been reviewed.' 22 The mononuclear copper site of galactose oxidase from Dactylium dendroides has been investigated by X-ray absorption spectroscopy; the copper site has four N,O-donor ligands in its oxidized copper@) forms but appears to be three-coordinate in the reduced copper(1) form.123 The measurement of the 2H/180kinetic isotope effects for the reactivity of the copper protein dopamine-p-monooxygenase has shown that the 0-0 bond of bound dioxygen is cleaved prior to substrate activation and a new mechanism has been proposed which incorporates this finding.124 The coordination environments of the two copper centres of this protein have also been investigated by EXAFS and IR spectro~copy.~~ The dioxygen-binding copper site is coordinated by two histidine residues one S-donor ligand and one unidentified weakly bound ligand which was easily displaced by CO;an electron-transfer role was proposed for the second copper site.Recent developments in the study of the dicopper CU site of cytochrome c oxidase have been reviewed.126 EPR spectroscopic studies have indicated a mixed valence copper (I/II) formulation and resonance Raman spectroscopy has demonstrated the presence of type-I copper cysteinyl c~ordination.'~~ An EXAFS study of the CU site 119 M.Kukimoto M. Nishiyama M. E. P. Murphy S. Turley E.T. Adman S. Horinouchi and T. Beppu Biochemistry 1994 33 5246. 120 B. D. Howes Z. H. L. Abraham,D. J. Lowe,T. Bruser R. R. Eady and B. E. Smith Biochemistry 1994,33 3171. 121 (a)T. Kohzuma S. Shidara and S. Suzuki Bull. Chem.SOC.Jpn. 1994,67,138; (b)S. Suzuki T. Kohzuma Deligeer K. Yamaguchi N. Nakamura S. Shidara K. Kobayashi and S. Tagawa J. Am. Chem. Soc. 1994,116 11 145. 122 A. Messerschmidt Adv. Inorg. Chem. 1994 40,121. 123 K. Clark J. E. Penner-Hahn M. Whittaker and J. W. Whittaker Biochemistry 1994,33 12 553. 124 G. Tian J. A. Berry and J. P. Klinman Biochemistry 1994 33 226. 125 B. J. Reedy and N. J. Blackburn J. Am. Chem.Soc. 1994 116 1924. 126 P. Lappalainen and M. Saraste Biochim. Biophys. Acta 1994 1187 222. 127 (a)C. von Wachenfeldt S. de Vries and J. van der Oost FEBS Lett. 1994,340 109; (b)C. R. Andrew J. Han S. de Vries J. van der Oost B. A. Averill T. M. Loehr and J. Sanders-Loehr,J. Am. Chem.SOC.,1994 116 10805. 572 J. D. Crane has shown that a short Cu-Cu distance of 2.58 may be present and the possible presence of a delocalized Cu(lS)Cu(1.5) mixed valence state with a Cu-Cu bond has been postulated by comparison with a recently reported model complex.'28 The X-ray crystal structures of azide-inhibited bovine Cu,Zn superoxide dismutase and the corresponding cyanide-inhibited enzyme from Xenopus laeuis have been reported.' 29 The self-deactivation of Cu,Zn superoxide dismutase by its reaction product hydrogen peroxide is associated with the selective formation of a 2-0x0-histidine group at His-1 18.l3' The spectroscopic effects of replacing the bridging imidazolate ligand (His) of this biosite with a non-coordinating Ala residue have also been investigated.' 31 A resonance Raman spectroscopic study of several oxy- haemocyanins has demonstrated that they all contain a p-q2 :q2-peroxide moiety,' 32 with the 0-0stretching mode occurring at ca.745cm-' and the asymmetric Cu-peroxide stretch at ca. 542cm-I. The nature of the peroxide to Cu2+ charge- transfer bands of oxyhaemocyanin has also been Aspects of the structure and reactivity of copper biosites have also been investigated through the study of relevant model complexes a spectroscopic model for the copper(r1)-thiolate coordination of type I copper sites has been investigated;' 34 the structure and reactivity of a proposed functional model for nitrite reductase has been reported;' two stable mononuclear copper(I1)-superoxide complexes have been prepared as models for the binding of dioxygen at a copper centre;'36 and the reactivity of several dinuclear copper complexes towards the binding and activation of dioxygen has been studied.'37 10 Zinc The general structures of zinc metalloproteases and zinc fingers have been reviewed.13* The X-ray crystal structure of the alkaline phosphatase from Escherichia coEi at 2.0 8 resolution has been determined (Figure 10a).Although His-372 is not directly coordinated to the zinc centre the replacement of this residue with Ala yielded a mutant with substantially altered catalytic a~tivity.'~' The structures of a zinc amidase (Figure lob) and the phosphate-bound form of bovine carboxypeptidase A have also 12' N.J. Blackburn M. E. Barr W. H. Woodruff J. van der Oost and S. de Vries Biochemistry 1994,33 10 401. 129 (a)K. Djinovic-Carugo F. Polticelli A. Desideri G. Rotillo K. S. Wilson and M. Bolognesi,J. Mol. Biol. 1994,240,179;(b)K. Djinovic-Carugo A. Battistoni M. T. Carri F. Polticelli A. Desideri G. Rotilio A. Coda and M. Bolognesi FEBS Lett. 1994,349,93. K.Uchida and S. Kawakishi J. Biol. Chem. 1994 269 2405. 131 J.A. Graden L.M. Ellerby J.A. Roe and J.S. Valentine J. Am. Chem. SOC. 1994 116 9743. 132 J.Ling L. P. Nestor R. S. Czernuszewicz T.G. Spiro R. Fraczkiewicz K. D. Sharma T. M. Loehr and J. Sanders-Loehr J. Am. Chem. SOC. 1994 116 7682. 133 F. Tuczek and E.I. Solomon 1.Am. Chem. SOC. 1994 116 6916. 134 D.Qiu L. KiIpatrick N. Kitajima and T.G. Spiro J. Am. Chem. SOC. 1994 116 2585. 135 (a)J.A. Halfen S.Mahapatra M. M. Olmstead and W. B. Tolman,J. Am. Chem. SOC. 1994,116,2173;(b) J. A. Halfen and W. B. Tolman J. Am. Chem. SOC. 1994 116 5475. 136 (a) M.Harata K. Jitsukawa H. Masuda and H. Einaga J. Am. Chem. SOC. 1994 116 10817; (b) K. Fujisawa M. Tanaka Y. Moro-oka and N. Kitajima J. Am. Chem. SOC. 1994 116 12079. 13' (a) K. D. Karlin M. S. Nasir B. I. Cohen R.W. Cruse S. Kaderli and A.D. Zuberbiihler J. Am. Chem. SOC.,1994 116 1324; (b) S.Mahapatra J.A.Halfen E. C. Wilkinson L. Que Jr. and W. B. Tolman J. Am. Chem. SOC. 1994,116,9785;(c)W. E.Lynch D. M. Kurtz Jr. S. Wang and R. A. Scott J.Am. Chem. SOC. 1994 116 11 030. 13' (a) N. M. Hooper FEBS Lett. 1994,354,l;(b)M. Schmiedeskamp and R. E. Klevit Curr. Opin. Struct. Biol. 1994 4 28. 139 X. Xu X.-Q. Qin and E. R. Kantrowitz Biochemistry 1994,33 2279. 573 Bioinorganic Chemistry Asp327 '.\I Zn-His33' His'70 "hjs412 C Figure 10 Structures of the zinc sites oJ (a) alkaline phosphatase and (b) a zinc amidase His57 Hism Figure 11 Proposed structure of the dizinc site of phosphotriesterase been rep~rted.'~' A range of metal-substituted derivatives (Co' +,Ni2+,Cu2+,Zn2+ Hg' +)of the zinc endopeptidase astacin has been prepared and the metal coordination environments investigated spectroscopically and crystallographically.14'The nature of the dizinc site of phosphotriesterase has been studied by individual site-directed mutagenesis of each of the seven histidine residues (His -+ Asn) of the protein.A site structure has been proposed (Figure 11) based on the chemical activity of these rnutants.l4' The structures of zinc metallothionein and its cadmium and mercury reconstituted forms have been studied by XAFS.'43 An analysis of the coordinated cysteine 3J113cd,1H NMR coupling constants for cadmium-substituted metallothionein and other cysteine rich proteins has revealed a Karplus-type dependence on the torsional angle about the CdS-CH bond.'44 The binding of Cu+ and [Tc0l3 ions to Zn-metallothionein and + the resulting displacement of Zn2 + ions have also been in~estigated.'~~ The relevance of macrocyclic polyamine zinc complexes as functional models for zinc biosites has been re~iewed.'~~ A mononuclear functional model for zinc esterase 140 (a)X.Cheng X.Zhang J. W. Pflugrath and F. W. Studier Proc. Natl. Acad. Sci. USA 1994,91,4034;(b) S. Mangani M. Ferraroni and P. Orioli Inorg. Chem. 1994 33 3421. 141 F. X.Gomez-Ruth F. Grams 1. Yiallouros H. Nar U. Kiisthardt R. Zwilling W. Bode and W. Stocker J. Bid. Chem. 1994 269 17 111. 14' J. M. Kuo and F. M. Raushel Biochemistry 1994 33 4265. 143 D.T. Jiang S. M. Heald T. K. Sham and M. J. Stillman J. Am. Chem. SOC. 1994 116 11 004. 144 0.Zerbe D.L. Pountney W. von Philipsborn and M.VaSak J. Am. Chem. SOC. 1994 116 377. 145 (a)A. R. Green A. Presta Z. Gasyna and M. J. Stillman Inorg. Chem. 1994,33,4159;(b) W. B. Jones T.E. Elgren M.M. Morelock R.C. Elder and D.E. Wilcox Inorg. Chem. 1994 33 5571. 14' E. Kimura Prog. Inorg. Chem. 1994 41 443. 574 J. D. Crane Figure 12 Model complex for the molybdenumlhaem site of sulfite reductase amidase and phosphatase activity,'47 and a possible structural model for dizinc biosites have also been re~0rted.l~~ 11 Molybdenum and Tungsten Biosites and the Nitrogenases The bioinorganic chemistry of molybdenum and tungsten pterin-containing enzymes has been reviewed.14' An EPR spectroscopic study of formate dehydrogenase H from Escherichia coli has revealed the coordination of a selenocysteine residue to the molybdenum centre.15' The presence of a selenium ligand at the molybdenum centre of the nicotinic acid hydroxylase from Clostridiurn barkeri has also been demonstrated by EPR spectroscopy.However in this case selenocysteine ligation was ruled out as the selenium-containing species could be removed from the protein upon denaturation."' In addition the essential role of the selenium in this enzyme was demonstrated by the isolation of its sulfur analogue from cells cultured in a selenium-deficient medium; the selenium form of the enzyme was found to be over 300 times more active. A few relevant model complexes (Figure 12) for molybdenum and tungsten biosites have also been reported.' 52 The recent advances in determining the structure of the MoFe protein of nitrogenase and the resulting insights into the structure and function of the nitrogenases in general have been amply reviewed.' In addition the thermodynamics of nitrogenase activity have been discussed.' 54 Two EXAFS studies of the FeMo cofactor have shown' 55 that 14' M. Ruf K. Weiss and H. Vahrenkamp J. Chem. Soc. Chem. Commun. 1994 135. X.-M. Chen Y.-X. Tong and T.C. W. Mak Inorg. Chem. 1994,33,4586. 149 J. H. Enemark and C.G. Young Adv. Inorg. Chem. 1994 40 2. ''O V. N. Gladyshev S.V. Khangulov M. J. Axley and T. C. Stadtman Proc. Natl. Acad. Sci. USA 1994,91 7708. 15' V. N. Gladyshev S. V. Khangulov and T. C. Stadtman Proc. Natl. Acad. Sci USA 1994 91 232. (a)P. Basu A.M. Raitsimring M. J. LaBarre I. K.Dhawan J. L. Weibrecht and J. H. Enemark J. Am. Chem. Soc. 1994,116,7166; (b) I.K. Dhawan A. Pacheco and J. H. Enemark J. Am. Chem. Soc. 1994 116,7911; (c) A. A. Eagle S. M. Harben E. R. T. Tiekink and C. G. Young 1.Am. Chem. Soc. 1994,116 9749. (a) D.C. Rees M. K. Chan and J. Kim Adv. Inorg. Chem. 1994 40 89; (b) J. Kim and D. C. Rees Biochemistry 1994,33,389; (c) R. R. Eady and G. J. Leigh J. Chem. Soc. Dalton Trans. 1994,2739;(d) G.J. Leigh New J. Chem. 1994 18 157; (e) J.B. Howard Ann. Rev. Biochem. 1994 63 235. lS4 R. A. Alberty J. Biol. Chem. 1994 269 7099. lS5 (a)S.D. Conradson B. K. Burgess W. E. Newton A. Di Cicco A. Filipponi Z. Y. Wu C. R. Natoli B. Hedman and K. 0.Hodgson Proc. Natl. Acad. Sci. USA 1994,91 1290; (b) H. I. Liu A. Filipponi N. Gavini B.K. Burgess B. Hedman A. Di Cicco C. R. Natoli and K. 0.Hodgson J. Am. Chem.Soc. 1994 116 2418. Bioinorganic Chemistry selenophenol binds at an iron centre rather than to molybdenum but that cyanide appears to bind at the molybdenum centre. ENDOR spectroscopic studies of the dithionite-reduced state of the MoFe protein of the nitrogenase from Klebsiella pneumoniae have shown that a variety of substrates and inhibitors do not bind at or near to the FeMo cofactor indicating that a more reduced state is required for substrate binding.'56 In addition no evidence was found to indicate the presence of protons at the unusual trigonal iron centres of the FeMo cofactor. A theoretical model for the binding of dinitrogen to an Fe face of the FeMo cofactor has also been reported.' 57 A new analysis of the EPR and 57Fe Mossbauer spectroscopic data for the Pox redox state of the P-clusters of nitrogenase has been described.15* A 57Fe Mossbauer characterization of the iron clusters in the VFe nitrogenase from Azotohacter vinelandii has also been reported.'59 Finally the FeV cofactor has been removed from VFe nitrogenase and successfully replaced with a FeMo cofactor.' 6o Interestingly although this hybrid displays the same reactivity towards dinitrogen as expected for MoFe nitrogenase its reduction of acetylene (to a mixture of both ethene and ethane) and inhibition by carbon monoxide are characteristic of VFe nitrogenase. 156 B.D. Howes K. Fisher and D.J. Lowe Biochem. J. 1994 297 261. Is' I.G. Dance Aust. J. Chem. 1994 47 979. 15' J.-M. Mouesca L. Noodleman and D.A. Case Inorg. Chem. 1994 33 4819. lSy N. Ravi V. Moore S.G. Lloyd B. J. Hales and B. H. Huynh J. Bid. Chem. 1994 269 20920. V.G. Moore R.C. Tittsworth and B.J. Hales J. Am. Chem. Soc. 1994 116 12 101.

ISSN:0260-1818    

DOI:10.1039/IC9949100557

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

29 Fullerene Chemistry By M.J. ROSSEINSKY Inorganic Chemistry Laboratory University of Oxford South Parks Road Oxford OX1 3QR UK 1 Introduction As in the years following the bulk synthesis of c60 in October 1990 1994 has seen a large amount of activity in fullerene chemistry and physics. This Report is a necessarily selectike account of the 1994 literature with the focus on fullerene-like carbons and their inorganic chemistry with a less thorough coverage of the rapidly developing field of organic derivitization of c60 and its homologues. The proceedings of a NATO AS1 and a book on molecular fullerene chemistry have 2 C, and the Higher Fullerenes Synthesis Separation and Physical Properties LDTOFMS has shown that 0.1ppm of C, is present in the Allende mete~rite.~ Although indications of an hcp as well as the fcc polymorph of C, have been known for some time 1994 saw the first preparation and crystallographic analysis of an hcp single crystal of C,,.4 A dynamic light scattering study showed that the hydrodynamic radius of C6 is 6.4 & 0.1 8 in ben~ene.~ 30-40 nm particles of C6 have been shown to be formed by vapour condensation in a flow system.‘ The effect of temperature and pressure have been the subject of considerable interest a molecular dynamics study indicates that c60 melts at above 4000 K.7 Synchrotron powder X-ray diffraction revealed that the threshold pressure for the onset of orientational ordering in space group Pa3 at room temperature is less than 0.5GPa.8 Application of more than 10GPa causes the lines to broaden and 23 GPa produces an amorphous ‘collapsed fullerite’ phase.’ Heating C, to higher temperature under 5 GPa pressure followed by quenching allowed isolation of metastable fcc (T = 3400 “C a = 13.6A) and rhombohedra1 phases (T= 5-800 “C,a = 9.22 A c = 24.6 A).In the toluene-insoluble ’ ‘Physics and Chemistry of the Fullerenes’ NATO AS1 Series C Vol. 443 ed. K. Prassides 1994. ‘The Chemistry of the Fullerenes’ A. Hirsch Thieme Verlag 1994. L. Becker J. L. Bada R. E. Winans and T.E. Bunch Nature 1994 372 507. J. L. de Boers S. van Smaalen V. Petricek M. Dusek M. A. Verheijen and G. Meijer Chem. Phys. Lett. 1994 219 469. * Q. Ying J. Marecek and B. Chu J. Chem. Phys. 1994 101 2665. A. S. Gurav T.T. Kodas L.-M.Wang E.I. Kauppinen and J. Joutsensaari Chem. Phys. Lett. 1994,218 304. ’ S. G. Kim and D. Tomanek Phys. Rev. Lett. 1994 72 2418. ’A. P. Jephcoat J.A. Hriljac L. W. Finger and D. E. Cox Europhys. Lett. 1994 25 429. J. Haines and J. M. Leger Solid State Comrnun. 1993 90 361. 577 578 M. J. Rosseinsky rhombohedra1 phase the close c6O-c60 centre to centre separation is accompanied by IR Raman and NMR signatures of the formation of c6o-c,o bonds." These phases revert to fcc c60 after heating to 300°C. The physical properties of c60 continue to attract attention. The orientational ordering transition at 260K is accompanied by a 1% reduction in the diamagnetic susceptibility showing a novel effect of a cooperative phase transition on a molecular property detailed ab initio calculations show that the diamagnetic susceptibility of C, is very sensitive to the molecular structure with a 0.07% change in C-C bond lengths producing a 1.2% change in the susceptibility.' Measurement of the picosecond absorption spectrum of a photoexcited c60 film revealed an optical absorption assigned to free (tl12< 15ps) and self-trapped (tlIz-250 ns)excitons.12 Exposure of a C, thin film to oxygen reduces the photoconductivity by several orders of magnitude as traps are created which reduce the carrier lifetime.' Photodiodes have been made from MEH-PPV sensitized with C,,.14 An A1/C6,/Au sandwich device has potential for application in the area of fast non-linear optoelectronic detectors.' Photo- and electro-luminescent emission from c60 have been studied.16 The 1.2K phosphores-cence of c60 has been assigned to both triplet state and shallow trap or exciton emission.Significant advances in the synthesis and purification of C6 and the higher fullerenes have been made. c60can be formed from the natural source camphor.' An improved chromatographic separation using a Norit-Elorit stationary phase and toluene followed by 1,2 dichlorobenzene eluants allows isolation of c60 and 98% pure C70 in one pass." Two different calixarenes can be used to isolate c60 by fractional precipitation.20 I3C CPMAS NMR has been used to study the fullerene-calixarene interaction in these complexes.2' A flash chromatography method for the isolation of gram quantities of C7 has been reported,22 while the differential solubilities of C6 and C70 in CS or o-xylene produces a simple method for the isolation of >99.5% pure c60 or >99% pure C7,.23 At 970 K vacuum effusion on a baffled distillation column with a linear temperature gradient has been shown to allow synthesis of 99.97% pure C60.24 lo Y.Iwasa T. Arima R. M. Fleming T. Siegrist 0.Zhou R. C. Haddon L. J. Rothberg K. B. Lyons H. L. Carter Jr. A. F. Hebard R. Tycko G. Dabbagh J. J. Krajewski G. A. Thomas and T. Yagi Science 1994 264 1570. I' (u) A. P. Ramirez R.C. Haddon 0.Zhou R. M. Fleming J. Zhang S. M. McClure and R. E. Smalley Science 1994,265.84;(b)W. Luo H. Wang R. S. Ruoff J. Cioslowski and S. Phelps,Phys. Rev. Lett. 1994 73 186. T. W. Ebbesen Y. Mochizuki K.Tanigaki and G. Hirua Europhys. Lett. 1994 25 503. l3 C.H. Lee G. Yu B. Kraabel D. Moses and V.I. Srdanov Phys. Rev. B 1994 49 10572. l4 G. Yu K. Pakbaz and A. J. Heeger Appl. Phys. Lett. 1995 64 3422. C.H. Lee G. Yu D. Moses and A.J. Heeger Appl. Phys. Lett. 1994,65 664. l6 H. J. Byrne A. T. Werner J. Anders W. K. Maser M. Kaiser L. Akselrod W. W. Ruhle A. Mittelbach and S. Roth J. Modern Optics 1994 41 1243. l7 D. J. Vandenheuvel 1. Y. Chan E. J. J. Groenen J Schmidt and G. Meijer Chem. Phys. Lett. 1994,231 111. K. Mukhopadhyay K. M. Krishna and M. Sharon Phys. Rev. Lett. 1994 72 3182. l9 R. Taylor G.J. Langley H. W. Kroto and D. R.M. Walton J. Chem. SOC. Chem. Commun. 1994 15. (a)J. L. Atwood G. A. Koutsantonis C. L. Raston Nuture 1994,368,229; (b)T.Suzuki K. Nakashima and S. Shinkai Chern. Lett. 1994 699. R. M. Williams J. M. Zwier J. W. Verhoeven G. H. Nachtegaal and A. P. M. Kentgens J. Am. Chem. SOC. 1994 116 6965. 22 W.A. Scrivens A.M. Cassell B. L. North and J. M. Toor J. Am. Chern. Soc. 1994 116 6939. 23 X. Zhou Z. Gu Y. Wu Y. Sun Z. Jin,Y. Xiong B. Sun,Y. Wu H. Fu,and J. Wang Curbon 1994,32,935. 24 R.D. Averitt J. M. Alford and N. J. Halas Appl. Phys. Lett. 1994 65 374. Fullerene Chemistry 579 Asymmetric osmylation allows resolution of c76 C,, and c84 c76 and C, are configurationally stable at the limit of their thermal stability.” The search for a rational synthesis of c60 continues and the preparation of C3oHl2 a hydrocarbon which constitutes half of c, and would dimerize to yield a ‘nonisolated pentagon’ D, C, isomer was achieved this year., The crystallography and polymorphism of C70 has been clarified a DSC study emphasized the importance of sample purity and indicates that both the majority equilibrium fcc and minority metastable hcp phases undergo two first order transitions associated with the successive freezing of rotation of the long molecular axis and spinning about that axis., Single crystal X-ray diffraction shows the C, molecules rotate freely in the hexagonal modification about the principal molecular axis (space group P6,/mm~).,~ Dilatometry showed three first order transitions in single crystals.29 Analysis of pulsed neutron diffraction measurements of the pair correlation function revealed C-C bond lengths of between 1.38 and 1.48A.30 Calorimetric determination of the heat of formation per C atom shows that C, (36.5 kJ mol-’) is more stable than c60 (38.8kJ mol-1).31 Helium pressure during fullerene synthesis strongly influences the fractions of the three known isolated pentagon isomers of C, which are formed with high pressure favouring the energetically most stable C, structure.32 Semi-empirical calculations on all 55 candidate isomers of c76 (those fitting the experimental 13C NMR) reveal the isolated pentagon D isomer as the most stable supporting the isolated pentagon rule.33 Both TEM and EELS studies show that C7 adopts an fcc structure.34 The electrochemistry of the D and D, isomers of c84 has been measured separately in pyridine each isomer displays five waves with the first three reversible in each cage.35 Laser ablation of C, films has provided evidence36 for two C , species a closed case fullerene (of D, or T symmetry) and a C, dimer whose structure is most probably the lowest energy dimer3 resulting from [2 + 21 cycloaddition of two 6 6 bonds.The area of gas-phase growth of fullerenes and metallocarbohedranes has been the subject of a recent review.3* 25 J.M. Hawkins M. Nambu and A. Meyer J. Am. Chem. SOC. 1994 116 7642. 26 P. W. Rabideau A. H. Abdourazak H. E. Folsom Z. Marcinow A. Sygula and R. Sygula J. Am. Chem. Soc. 1994 116 7891. ” A. R. McGhie J. E. Fischer P. A. Heiney P. W. Stephens R. L. Cappelletti D. A. Neumann W. H. Mueller H. Mohn and H. U. Meer Phys. Rev. B Condens. Matter 1994 49 12614.28 E. Blanc H.-B. Buergi R.Restori D. Schwarzenbach P. Stellberg and P. Venugopalan. Europhys. Lett. 1994 27 359. 29 C. Meingast F. Gugenberger G. Roth M. Haluska and H. Kuzmany 2.Phys. B Condens. Matter 1994 95 61. 30 A.V. Nikolaev T.J.S.Dennis K. Prassides and A.K. Soper Chem. Phys. Lett. 1994 223 143. 31 H. D. Beckhaus S. Verevkin C. Ruchardt F. Diederich C. Thilgen H. U. Termeer H. Mohn and W. Muller Angew. Chem. Int. Ed. Engl. 1994 33 99. ‘2 T. Wakabayashi K. Kikuchi S. Suzuki H. Shiromaru Y. Achiba J. Phys. Chem. 1994 98 3090. 33 S.J. Austin P. W. Fowler G. Orlandi D. E. Manolopoulos and F. Zerbetto Chem. Phys. Lett. 1994,226 219. 34 J.F. Armbruster H.A. Romberg P. Schweiss P. Adelmann M. Knupfer J. Fink R.H. Michel J. Rockenberger and F.Hennrich 2. Phys. B Condens. Matter 1994 95 469. 35 P. Boulas M. T. Jones K. M. Kadish R. S. Ruoff D. C. Lorents and D. S. Tse J. Am. Chem. Soc. 1994 116 20. 36 J. M. Hunter J. L. Fye N. M. Boivin and M.F. Jarrold J. Phys. Chem. 1994 98 7440. 37 N. Matsuzawa A. Masafumi D. A. Dixon and G. Fitzgerald J. Phys. Chem. 1994 98 2555. 38 M.T. Bowers ACC. Chem. Res. 1994 27 324. M. J. Rosseinsky 3 Fullerene Chemistry Molecular Chemistry.-A review of the structure and reactivity of c60 has been published.39 The solubilization of fullerenes in aqueous media continues to attract attention (see also under Organic chemistry). Both molecular and colloidal (10nm diameter) C6 are found in aqueous micellar solutions of the non-ionic surfactant Triton X-100.40 The reaction of C6 in CS with a saturated solution of y-cyclodextrin in ethanolic water has been shown to provide a mild route to the 1 :1 inclusion complex which is water soluble (0.33 mg mL- I) and displays two reversible one- electron reductions of the C6 molecule when dis~olved.~~ NMR and UV-visible studies of the 2 1 and 1 :1 adducts of y-cyclodextrin with c60 in water have been rep~rted.~' y-Cyclodextrin can also solubilize C, in water,43 and polyvinylpyrrolidine can be used to solubilize c60 and C, in water.44 The reactivity of fullerenes with hydrogenating agents shows the expected addition across the 6 6 double bonds.C60H2" and C7,H2" products are formed by diimide reduction.45 Zinc/acid reduction also results in C6& and C6,H4.46 C6& was shown to react with one equivalent of BH3-THF to give six C6oH4 isomers.47 Equilibrium studies and ab initio calculations on C70 show that 1,2 addition (using BH in THF) is favoured and the 1,9 isomer of C7oHz is more stable than the other experimentally observed 7,8 isomer (Figure l).48 Fluorine reacts with c60 to yield products with a variety of stoichiometries and isomers and this year has seen some clarification of the effect of reaction conditions on product formation.Sodium fluoride mediated fluorination at 250 "C yields 60% of a single structure of C6oF48 (the two enantiomers are shown in Figure 2).49 XPS studies of fluorinated C6oF solids indicate the formation of CF and CF groups at high fluorination levels (c6oFs3) due to breaking of some C-C bonds in the cage and the presence of oxygen as epoxide in the contaminant C6,F,0,.50 The compound C60F48 is 1.38 v easier to reduce than c60 and forms C6oF4g - reduction to C6oFi is followed by fluoride loss to give C60F47- which can then be reduced to C6OF;T .51 The reactivity of c60 with other strongly oxidizing species has also been studied extensively.Reaction with AsF in SO yields a non-conducting solid with a body-centred tetragonal str~cture.~ The reaction of MoF6 with c60 gives oxidized 39 H. W. Kroto R. Taylor and D. R. M. Walton Pure Appi. Chem. 1994 66 2091. 40 A. Beeby J. Eastoe and R.K. Heenan J. Chem. Soc. Chem. Commun. 1994 173. 41 P. Boulas W. Kutner M. T. Jones and K. M. Kadish J. Phys. Chem. 1994 98 1282.42 T. Anderson G.Westman 0.Wennerstroem and M. Sundahl J. Chem.Soc. Perkin Trans. 2 1994 1097. 43 T. Anderson M. Sundahl G. Westman and 0.Wennerstrom Tetrahedron Lett. 1994 35 7103. 44 Y.N. Yamakashi T. Yagami K. Fukuhara S. Sueyoshi and N. Miyata J. Chem. SOC.,Chem. Commun. 1994 517. 45 A. G.Avent A. D. Darwish D. Heimbach H. W. Kroto M. F. Merdine J. P. Parson C. Remars R. Roers 0.Ohashi R. Taylor and D.R.M. Walton J. Chem. Soc. Perkin Trans. 2 1994 15. 46 C. C. Henderson C. M. Rohlfing R. A. Assink and P. A. Cahill Angew. Chem. Int. Ed. Engi. 1994,33,786. 47 M.S. Meier P. S. Corbin V.K. Vance M. Clayton M. Mollman and M. Poplawska Tetrahedron Lett. 1994 35 5789. 48 C.C. Henderson C. M. Rohlfing K.T. Gillen and P. A. Cahill Science 1994 264 397. 49 A.A. Gakh,A. A. Tuiman J. L. Adcock R. A. Sachleben and R.N. Compton J. Am. Chem. Soc. 1994,116 819. D. M. Cox S.D. Cameron A. Tuinman A. Gakh J. L. Adock R. N. Compton E. W. Hagaman K. KniaL J. E. Fischer R. M. Strongin M. A. Cichy and A. B. Smith 1.Am. Chem. SOC. 1994 116 1115. 51 F. Zhou G.J. Van Berkel and B.T. Donovan J. Am. Chem. Soc. 1994 116 5485. 52 W.R. Datars T. R. Chien R. K. Nkum and P. K. Ummat Phys. Rev. €3 Condens. Matter 1994,50,4937. Fullerene Chemistry Figure 1 The structure of 7,8-C7,H (Reproduced by permission from Science 1994 264 397) ss RR Figure 2 The RR and SS enantiomers of C,,F,,. Fluorine atoms are omitted in the Schlegel diagrams-the lettering corresponds to distinct 9F NMR resonances of Juorine hound to the indicated carbons.(Reproduced by permission from J. Am. Chem. SOC. 1994 116 820) 582 M. J. Rosseinsky products containing MoF,.,~ c60 has been shown to react with SO, either neat or in fuming sulfuric acid to initially form radical cations which are intermediates in the formation of C6,(S03) (x z 3.5) sultones with C-S bonds.54 NO gas multiply nitrates c60 in toluene solution.55 Ozonolysis yields a mixture of oxidized products with ketone ester and epoxide functionalities.s6 Binary molecular solids in which there is no charge-transfer between c6 and the other molecule have produced some interesting chemical and structural features though the compounds are of course electrically insulating. (P4)2C60 is the first example of host-guest chemistry of the P molecule which occupies trigonal prismatic sites between close packed c60 layers stacked in a simple hexagonal manner.57 C60’4C6H6 has been shown by single crystal X-ray diffraction at 104K to have a honeycomb-like arrangement of c60 stacks with the channels containing ben- zene-the authors suggest the structure may be considered as a macroscopically ordered nanocomposite of fullerene and benzene domains.58 As would be predicted by consideration of the electrode potentials for the relevant redox couples TTF type donors seem insufficiently reducing to form charge-transfer salts with c60.The 1:1 complex BDMT-TTeF :c60is insulating and the structural data indicate that there is no charge-transfer to c60 from the organic donor.s9 Octamethylene-TTF can also be crystallized as a 1 1adduct with c60-again the crystal structure and high resistivity indicate the absence of charge-tran~fer.’~ A detailed electron diffraction study of iodine de-intercalation from (12)2C60 suggests the reaction proceeds by shearing along { 1010) type planes.60 A beautiful reaction is the intercalation of c60 into graphite by displacement of pre-intercalated aromatic hydrocarbons.61 Further investigations of proposed noble metal fullerene polymers have been made with the preparation of amorphous C6oPt species6 and a detailed electron diffraction study of the C6,Pd system this revealed small crystals of Pd for n = 1 and for 25% of the n = 3 sample 10% of the Pd3C6 sample contains a = 11.38 bcc crystallites for which a structural model based on 3 perpendicular sets of linear chains is proposed.63 Reaction of (Na(crown)+ ),C& with [PPNICl in acetonitrile afford (PPN+),CiO and the single crystal X-ray structure is interpreted in terms of a Jahn-Teller distortion of the C$ anion.64 Electrocrystallized Ph4PC6,.Ph,C1 adopts a supercell of the CsCl ‘3 A.Harnwi G. Dondainas and J. Dupuis Mol. Cryst. Liq. Cryst. Sect. A 1994 245 301. s4 G. P. Miller M. A. Buretea M. M. Bernado C. S. Hsu and H. L. Fang J. Chem. SOC. Chem. Commun. 1994 274. ’’ S. Roy and S. Sarkar J. Chem. Soc. Chem. Commun. 1994 275. 56 R. Malhotra S. Kumar and A. Satyarn J. Chem. Soc. Chem. Commun. 1994 1339. ” (a) R. E. Douthwaite M.L.H. Green S.J. Heyes M. J. Rosseinsky and J.F.C. Turner J. Chem.Soc. Chem. Commun. 1994 1367; (b)I. W. Locke A. D. Darwish H. W. Kroto K. Prassides R. Taylor and D. R. M. Walton Chem. Phys. Lett. 1994 225 186. 58 H. B. Buergi R. Restori P. Schwarzenbach A. L. Balch J. W. Lee B. C. Noll and M. M. Olrnstead Chem. Muter. 1994 6 1325. 59 (a)P. Wang W.-J. Lee I. Shcherbakova M. P. Cava and R. M. Metzger Synth. Met. 1994,64,319 (6)G. Saito T. Terarnoto A. Otsuka Y. Sugita T. Ban M. Kusunoki and K. Sakaguchi Synth. Met. 1994,64 359. 6o X. B. Zhang X. F. Zhang S. Amelinckx and H. Werner Appl. Phys. A 1994 58(2) 107. 61 B.A. Averill T. E. Sutto and J. M. Fabre Mol. Cryst. Liq. Cryst. Sect. A 1994 244 77. H. Nagashima Y. Kato H. Yarnaguchi E. Kimura T. Kawanishi M. Kato Y. Saito M. Haga and K. Ttoh Chem. Lett. 1994 1207.63 J. M. Cowley M.-Q. Liu B. L. Ramakrishna T. S. Peace A. K. Wertsching and M. R. Pena Carbon 1994 32 746. 64 P. Paul Z. Xie R. Bau P.D. W. Boyd and C. A. Reed J. Am. Chem. Soc. 1994 116 4145. Fullerene Chemistry Figure 3 The crystal structure of Ph,PC,,.Ph,PCI showing the pseudocubic sub-lattice of phosphorous atoms; for clarity the phenyl rings are omitted (Reproduced from J. Chem. SOC.,Chem. Commun. 1994,403) structure with c60 and C1-ordered in the anionic positions (Figure 3).65 EPR measurements have shown that Ph4PC,,.Ph,PI undergoes a dynamic Jahn-Teller distortion which becomes static below 140 K.66 Alkali Metal Ful1erides.-Several review articles have been published .6 There have been important developments in this area with a new superconductor with the highest T (40K)yet discovered for a molecular system and the structural characterization of a new family of polymers.Those who do not regard this field as chemistry should take note! The monotonic increase of T (superconducting transition temperature) with lattice parameter in the A3C6 family means that cS3c60 has long been sought. It was finally synthesized by Palstra et al. 68 by reduction of c60 with Cs metal dissolved in liquid h5 U. Bilow and M. Jansen J. Chem. Soc. Chem. Commun. 1994 403. 66 B. Gotschy M. Keil H. Klos and 1. Rystau Solid State Commun. 1994 92 935. 67 A. P.Ramirez,Superconductivity Rev. 1994,1,1(56);M. Gelfand Superconductivity Rev. 1994,1,103;M. L. Cohen Phil. Mag. B,1994,70 627. 6R T. T. M. Palstra 0.Zhou Y.Iwasa P. E. Sulewski R. M. Fleming B. R. Zegarski Solid State Commun. 1994 92 71. 584 M.J. Rosseinsky ammonia followed by deammoniation under vacuum at 150"C. However the crystal chemistry of this metastable system is complex with both body centred cubic (bcc) A15 and defect A,C, structures being formed. The value of T reaches a maximum of 40 K under 15 kbar of hydrostatic pressure. The increase of T under pressure is particularly important as it is counter to the conventional BCS theory and the observed pressure dependence of T in the lower transition temperature A,C,O systems. The very existence of monoanionic A,C, phases (A = K Rb Cs) has been controversial for some time. RblC, has the face-centred cubic (fcc) rock-salt- structure with the Rb' cation on the octahedral site of the fcc array at high temperature and recent work has revealed that this may be conserved by quenching to low temperat~re.,~ Slow cooling however leads to an orthorhombic compound in which one lattice parameter (9.31A) implies very short contacts between the C, molecules.Structure refinement7' shows the material contains one dimensional polymer chains in which the C, units are connected by 1.44 A inter molecular bonds between 6:6 bonds on adjacent molecules (Figure 4). The polymer is a one dimensional metal at high temperatures and undergoes a spin density wave transition at low temperature. Polymer formation occurs from the high temperature phase where the dynamically disordered anions can adopt relative orientations which allow the [2 + 21 cycloaddition reaction to occur.Similar polymerization is seen for CsIC6, and in rapidly cooled K,C,,. Single crystals of K'C, can be grown by a vapour phase route.71 Non-superconducting Li,CsC, has orientationally disordered C:; anions and a spherical harmonic orientation distribution function analysis indicates the observed scattering density is consistent with covalent Li *. * C bonding.72 The structural influence of sodium on the tetrahedral site in a cubic close packed C, array is to produce at room temperature the orientational order found in C, itself below 260 K-this was shown by powder neutron diffraction in N~,CSC,,;~~ the transition to a high temperature disordered phase occurs at 299K.74 Several studies on the physical properties of superconducting A3C, compounds have been reported.Preparation of 85Rb- and 87Rb- (isotopically pure) Rb3C, allowed the demonstration of a zero isotope effect once again ruling out alkali-metal C, optic modes from the pairing mechanism.75 13C NMR T,Tmeasurements (which allow an estimate of N(E,) in a Fermi liquid picture) confirm a previously proposed weak to medium coupling BCS electron-phonon coupling mechanism involving phonons with a frequency above 600 K and a Stoner parameter of 3 eV spin-' carbon-'.76 A debate in the literature concerning the true conduction electron spin hy 0.Chauvet G. Oszlany L. Forro P. W. Stephens M. Tegze G. Faigel and A. Janossy Phys. Rev. Lett. 1994 72 2721. 'O P. W. Stephens G.Bortel G. Faigel M. Tegze A. Janossy S. Pekker G. Oszlanyi and L. Forro Nuture 1994 370 636. S. Pekker A. Janossy L. Mihaly 0.Chauvet M. Carrad and L. Forro Science 1994 265 1077. 72 I. Hirosawa K. Prassides J. Mizuki K. Tanigaki M. Gevaert A. Lappas and J. K. Cockcroft Science 1994 264 1294. 73 K. Prassides C. Christides I. M. Thomas J. Mizuki K. Tanigaki I. Hirosawa and T. W. Ebbesen Science 1994,263 950. 74 K. Tanigaki I. Hirosawa T. Manako J.S. Tsai J. Mizuki and T. W. Ebbesen Phys. Rev. B Condens. Mutter 1994 49 12 307. l5 B. Burk V. H. Crespi A. Zettl and M. L. Cohen Phys. Rev. Lett. 1994 72 3706. 76 Y. Maniwa T. Saito A. Ohi K. Mizoguchi K. Kume K. Kikuchi I. Ikemoto S. Suzuki and Y. Achiba J. Phys. SOC.Jpn. 1994 63 11 39. Fullerene Chemistry r 1 ~=14.233 m -1.44kO.15 1.9W0.15 f-/=\ A >i( 3 1 2 Figure 4 Polymer chains in Rb,C, (Reproduced by permission from Nature 1994 370 636) resonance signal from Rb3C, has beg~n.~~'',~ An STM investigation of Rb3C, has revealed effective grain sizes of a few hundred nanometers which is important in " (a)M.Kosaka K. Tanigaki I. Hirosawa Phys. Rev. Lett. (Comment) 1994 72 3130; (h) A. Janossy 0. Chauvet S. Pekker J. R. Cooper L. Forro M. Tegze and G.Faigel Phys. Rev. Lett. (Reply) 1994,72(19) 3131. 586 M.J. Rosseinsky interpreting the small superconducting shielding fractions which are often observed.78 Studies of the environmental stability of the superconducting fullerides indicate that though very unstable to dry air oxygen and water,79 the application of Si and %/A1 protective layers to Rb,C, films can maintain superconducting properties in air for up to 8 hours.80 Direct information on phase equilibria in the Na-C, binary phase diagram has been provided by a high temperature solid state electrochemical study showing solid solution in NaXC6 for 2 < x < 3 and for 3.3 < x < 11." A lower temperature polymer electrolyte solid state electrochemical study indicates several line phases in this composition range.82 Lithium fullerides prepared by low temperature elec- trochemistry have been characterized by electron diffra~tion.~ The electronic properties of the fullerides have been the major points of interest thus far but the catalytic activity of the M6C60 phases (M = Cs K Na) to H,-D exchange and ethene hydrogenation which is comparable to that of the noble metals suggests this will be a profitable area for future PES studies indicate that none of the phases (prepared at high temperature in contrast to reference 68) are metallic at room temperature-slow caesium diffusion was also noted.8 Though fullerides with metal concentrations which require filling the t, band for Li and Na have been known for some time all the previous evidence indicated that no more than six potassium cations could be intercalated into c60.However photoemis- sion studies of c60 deposited on K multilayers indicates population of the t, band corresponding to 6 < x < 12.86 Alkaline earth metal fullerides with x > 3 also have the C, t, levels occupied in a naive ionic view of the bonding.However resonant PES shows that Ba6C60 has 25% Ba character at the Fermi energy with strong metalkarbon hybridization with both the t, and t, levels.87 The Sr-C, system has been identified as the only fulleride in which fcc and bcc phases coexist (x = 3 bcc A15 and fcc phases coexist). Sr,C, (bcc) has been shown to be superconducting at 4 K.** As separation techniques improve more studies of the intercalation chemistry of higher fullerenes can be expected. No new superconductors have emerged yet. Preliminary structural work on the K,C, phase diagram reveals a dependence on the starting polymorph (hcp or fcc) at low x with both C70 modifications yielding a potassium saturated fcc K9C70 phase89 and in contrast with the bcc 78 H.P. Lang V. Thommen-Geiser K. Lueders M. Kraus M. Baenitz and H.-J. Guentherodt Mol. Cryst. Liq. Cryst. Sect. A 1994 245 289. 79 D. R. Riley D. Jurbergs J. P. Zhou J. Zhao and J. T. McDevitt Solid State Commun. 1994 88 431. 80 N. Okuda H. Kugai T. Uemura K. Okura Y. Ueba and K. Tada Jpn. J.Appl. Phys. Part 1,1994,33(4A) 1851. 81 J. H. Kim A. Petric P.K. Ummat and W.R. Datars J. Phys. Condens. Mutter 1994 6 5387. 82 S. Lemont J. Ghanbaja and D. Billaud Muter. Res. Bull. 1994 29 465. 113 S. Lemont J. Ghanbaja and D. Billaud Mol. Cryst. Liq. Cryst. A 1994 244 203. 84 S. Serizawa I. Gabrielova T. Fujimoto T. Shido and M. Ichikawa J. Chem. SOC.,Chem. Commun. 1994 799. 85 J. M. Gildemeister and G.K.Wertheim Chem. Phys. Lett. 1994 220 181. 86 L.Q. Jiang and B.E. Koel Phys. Rev. Lett. 1994 72 140. (17 M. Knupfer F. Stepniak and J. H. Weaver Phys. Rev. B,1994 49 7620. 88 A. R. Kortan N. Kopylov E. Ozdas A. P. Ramirez R. M. Fleming and R. C. Haddon Chem. Phys. Lett. 1994 223 50 1. 89 M. Kobayashi Y. Akahama H. Kawamura H. Shimohara H. Sato and Y. Saito Phys. Rev. B,1993,48 16877. 90 M. Kobayashi Y. Akahama H. Kawamura H. Shimohara H. Sato and Y. Saito Fullerene Sci. Technol. 1993 1 449. Fullerene Chemistry structures of the metal-saturated A& phases formed by these metals. Alternative more rapid synthetic routes than the gas-phase metal vapour plus C, solid reactions have been sought. Solution routes still involved extended heating to desolvate the metal cations.The decamethylmanganocenide anion has allowed isolation of the solvated fulleride Na(THF),C,,,91 and has been used to prepare K3C,,.92 The compound Na,C,,(THF) (x r 0.4 y z 2.2) is a further solvated sodium fulleride which is metallic at room temperat~re.~~ K3C, can be prepared in under 60 seconds total reaction time using a microwave-induced argon plasma.94 TDAE C, and Magnetic Fullerene Compounds.-The salt TDAE C, (TDAE is tetrakisdimethylaminoethylene) continues to attract attention in view of the magnetic transition at 16 K. A dependence of T on preparation technique has been observed with a maximum T of 24 K in materials which appear from Raman spectroscopy to be non-stoichi~metric.~~ Microwave conductivity measurements show both the magni- tude S cm-') and temperature dependence of the conductivity are non-metallic ruling out explanations of the magnetic transition based on itinerant electron^.^ The methyl protons of the TDAE molecule show a strongly temperature dependent NMR chemical shift but the shift observed below T is much smaller than would arise from ferromagnetic ordering of all the C; EPR measurements also indicate a smaller than expected local field below Tc.98The EPR line is homogeneously broadened above 16 K and inhomogeneously broadened below the tran~ition.~~ The existence of a spontaneous magnetization below 15K has been revealed by ac susceptibility (the non-zero value of the imaginary part of the susceptibility indicates non-zero ordered moments) and precise dc measurements of hysteresis (a coercive field of 1.6 G is measured at 5 K).lo0 The search for other amines which might produce charge-transfer salts with similar properties continues.The tertiary amines 1,8- diazabicyclo (5.4.0)undec-7-ene (DBU) and 1,5-diazabicyclo (5.3.0) non-5-ene (DBN) afford moisture- and air-sensitive 2 1 salts when reacted with C, in toluene. The DBU salt exhibits a cusp in XTat 70K while the DBN salt has a Weiss constant of -4 K.'" Organic Chemistry.-The area of methanofullerene chemistry (addition of carbenes or their equivalents to c60)has been active and is the subject of a comprehensive review.' O2 The competition between the 'open' methanoannulene fulleroid formed by 5 :6 addition and the cyclopropane 6 :6 methanofullerene is illustrated by the addition of MeCO,C,H,CHN, which yields the 5,6 fulleroid initially this then thermally isomerizes to the more stable methanofullerene.Interestingly addition of a third 91 R.E. Douthwaite A. R. Brough and M. L.H. Green .I. Chem. SOC. Chem. Commun. 1994 267. 92 X. Liu W.C. Wan S. M. Owens and W. E. Broderick J. Am. Chem. Soc. 1994 116 5489. 93 H. Kobayashi H. Tomita H. Moriyama A. Kobayashi and T. Watanabe J. Am. Chem. SOC. 1994,116 3153. 94 R. E. Douthwaite M. L. H. Green and M. J. Rosseinsky J. Chem. SOC.,Chem. Commun. 1994 2027. 95 D. Mihailovic K. Lutar A. Hassanien P. Cevc and P. Venturini Solid Stute Commun. 1994,89 209. 96 A. Schilder H. Klos 1. Rystau w. Schuetz and B. Gotschy Phys. Rev. Lett.1994 73 1299. 97 R. Blinc J. Dolinsek D. Arcon D. Mihailovic and P. Venturini Solid State Commun. 1994 89 487. 98 P. Cevc R. Blinc V. Erzen D. Arcon B. Zalar D. Mihailovic and P. Venturini Solid Stute Commun. 1994 90,543. '' P. Cevc R. Blinc D. Arcon D. Mihailovic P. Venturini S. K. Hoffmann and W. Hilczer Europhys. Lett. 1994 26 707. loo S. Atsushi T. Suzuki R.J. Whitehead and Y. Maruyama Chem. Phys. Lett. 1994 223 517. H. Klos I. Rystau W. Schuetz B. Gotschy A. Skiebe and A. Hirsch Chem. Phys. Lett. 1994,224,333. F. Diederich L. Isaacs and D. Philp Chem. Sac. Rev. 1994 23 227. M.J. Rosseinsky electron to the fulleroid isomerizes it to the methan~fullerene.'~~ A combined experimental and PM3 computational study of the preference for the 6,6-closed methanofullerene and 5,6-open fulleroid over the 6,6-open and 5,6-closed isomers indicates that the preservation of [5] radialene type bonding found in C, is decisive in favouring the two observed isomers (see Figure 5(a) for depictions of these struc- tures).' O4 A single crystal X-ray diffraction study has confirmed the cyclopropane structure for 6,6-closed methano-bridged fullerenes [(3,4-dimethyoxyphenyl)-phenyl-methanolC, (Figure 5),with the bridgehead C(ltC(2) bond of 1.6114(7) 8 clearly indicating the bonding to be cyclopropane-like.' O5 Synchrotron powder X-ray diffraction shows that the 6,5 open annulene isomer of C6 ,H undergoes orientational ordering to Pa3 symmetry at 290K.'06 Successive carbene addition allows the isolation of regioisomers of bis and tris adducts of C, and di(ethoxycarbony1) rnethylene,lo7 which may be converted into water-soluble malonic acid derivatives by treatment with sodium hydride.'08 Diethynylmethanobuckminster fullerene en- visaged as a building block for joint cyclo[n]carbon-fullerene molecular carbon allotropes has been prepared.'" These species may be coupled using CuCl to produce dimeric methanofullerenes linked by butadiynyl groups.' lo Reaction of diazomethane with C70 in toluene produces a mixture of isomeric pyrazolines which are thermally convertable into annulenes (C70 has eight types of bond and four distinct 6:6 bonds).'' Aziridines are formed by nitrene addition across the 6:6 junction of C, (N-aminophthalimide + Pb(OAc) in chlorobenzene) to yield mono to tetra adducts in contrast to reactions with alkyl azido reagents which yield open azafulleroids.' l2 Reaction with the azide Me(OCH,CH,),N attaches a short hydrophilic chain to the hydrophobic c60molecule forming an open azaannulene structure by addition across a 6:5 junction the molecule is amphiphilic and forms monomolecular films on spreading toluene solutions at the air-water interface.' l3 The 6 :6 junction aziridine urethane C60NC0,CH,CH is prepared by addition of the azidoformic ester:' l4 the supermesityl group can also be attached as a 6,6 aziridine via the azidoformate.This can be thermally converted into the isomeric oxazole in which 0 and N bind vicinally to the carbons of the 6 :6 junction (Figure 6)." One-step cycloaddition of a dendritic azide (M 3429 amu) yields an open annulene monosubstituted C, azafulleroid (Figure 7) with a glass transition temperature of 325 K.' l6 Amino-acid and amido M.Eiermann F. Wudl M. Prato and M. Maggini J. Am. Chem. Sac. 1994 116 8364. F. Diederich L. Isaacs and D. Philp J. Chem. SOC.,Perkin Truns. 2 1994 391. J. Osterodt M. Nieger and F. Voegtle J. Chem. Soc. Chem. Commun. 1994 1607. lo6 A. N. Lommen P. A. Heiney G. B. M. Vaughan P. W. Stephens D. Liu D. Li A. L. Smith A. R. McGhie and R. M. Strongin Phys. Rev. B Condens. Mutter 1994 49(18) 12 572. I"' A. Hirsch 1. Lamparth and H. R. Karfunkel Angew. Chem. Int. Ed. Engl. 1994 33 437. lox I. Lamparth and A. Hirsch J. Chem. SOC. Chem. Commun. 1994 1727. Io9 Y. An Y. Rubin C. Schaller and S.W.McElvany J. Org. Chem. 1994 59 2927. 'lo H. L. Anderson R. Faust Y. Rubin and F. Diederich Angew. Chem. Int. Ed. Engl. 1994 33 1366. l1 A. B. Smith R. M. Strongin L. Brard G. T. Furst W. J. Romanow K. G.Owens and R. J. Goldschmidt J. Chem. SOC. Chem. Commun. 1994 2187. 'I2 S. Kuwashima M. Kubota K. Kushida T. Ishida T. Ishida M. Ohoshi and T. Nogami Tetrahedron Lett. 1994 35 4371. 'I3 C. J. Hawker P. M. Saville and J. W. White J. Org. Chem. 1994 59 3503. 'I4 T. Ishida K. Tanaka and T. Nogami Chem. Lett. 1994 561. 'I5 M. R. Banks J. I. G. Cadogan I. Gosney P.K. G. Hodgson P. R. R. Langridge-Smith and D. W.H. Rankin J. Chem. SOC.,Chem. Commun. 1994 1365. C. J. Hawker K. L. Wooley and J. M. J. Frechet J. Chem. SOC.,Chem. Commun. 1994 925. Fullerene Chemistry 6-6 closed 5-6 open 6-6 open 5-6 closed R = Ph R = 3,4-(MeO),Ph (a) P Figure 5 (a) The possible structures of a rnethanofullerene; (b) The crystal structure of [(3,4-dimethyoxypheny1)-phenylmethano]C,,.2CHC13.Relevant bond lengths are C(lkC(2)= 161.4(7)pm C(lFC(61) = 151.0(7)pm and C(2kC(61) = 151.5(7)pm. The angles C(61)-C(2)-C(l) = 57.6" C(61)-C(l)-C(2) = 57.9(3)" C(l)-C(61rC(2) = 64.5(3)" and C(62)-C(61FC(68) = 115.4(4)O (Reproduced from J. Chern. Soc. Chern. Cornrnun. 1994 1607) derivatives are readily synthesized by addition of diazoamides both ring-closed and ring-opened isomers are formed and are separable by HPLC." Calix[8]arene may be attached to C, via polyether chain azide addition to yield the azafullerene."' Racemic and enantiopure fullero-3,4-prolines have been prepared and converted into the protonated amino acids."' 1,2 and 1,4 isomers of C, azacrown ethers have been prepared.' 2o N-acylated fulleropyrrolidines including a perfluorinated deriva- 11' A.Skiebe and A. Hirsch J. Chem. SOC.,Chem. Commun. 1994 335. 'IR M. Takeshita T. Suzuki and S. Shinkai J. Chem. SOC.,Chem. Commun. 1994 2587. 'I9 M. Maggini G. Scorrano A. Bianco C. Toniolo R. P. Sijbesma F. Wudl and M. Prato J. Chern. Soc. Chem. Commun. 1994 305. l2O S. N. Davey D. A. Leigh A. E. Moody L. W. Tetler and F.A. Wade J. Chem. Soc. Chem. Commun. 1994 391. M. J. Rosseinsky ) ) folc, i,Bu"Li,OoC,C0Cl2 lW% 1 2 ii NaN (2 equ.) wet acetone (0.05%),reflux 100% I 3 Scheme 1 \L 4 5 6 7 Figure 6 Reaction of the azidoformate 3 with C, yields the aziridine 4.which is thermally converted into the isomeric oxazole 5 (Reproduced from J. Chem. Soc. Chem. Commun. 1994 1365) tive have been prepared from the previously known N-H compound.121 The perfluorinated material forms monomolecular Langmuir-Blodgett films by spreading toluene solutions on water.' 22 Similar azomethine ylid addition chemistry affords 12' M. Maggini A. Karlsson L. Pasimeni G.Scorrano M. Prato and L. Valli Tetrahedron Lett. 1994,35 2985. lZ2 M. Maggini L. Pasimeni M. Prato G. Scorrano and L. Valli Langrnuir 1994 10 4164. Fullerene Chemistry 591 -N2 + -heat i 170.0 150.0 130.0 110.0 60.0 70.0 50.0 6 148.0 146.0 1u.a 1420 140.0 13.0 136.0 134.0 6 Figure 7 Synthetic scheme for a dendritic fullerene.The 13C NMR spectrum of the product (a) is shown together with an expanded section (6 133-149) showing resonances due to the fullerene moiety (b) (Reproduced from J. Chem. SOC. Chem. Commun. 1994 925) 592 M.J. Rosseinsky ferrocenyl fulleropyrrolidines as does reaction with the acyl chloride of ferrocene with the unfunctionalied pyrr01idine.l~~ The reaction of c60 with the tertiary amine 1,8-diazabicyclo [5.4.0]undec-7-ene gives a diamagnetic DBU c60 addition product via radical recombination of the ions formed in an initial electron-transfer step.' 24 Electrospray ionization mass spec- trometry shows that reaction of c60 with isobutylamine in air results in formation of oxygenated C6,0,(RNH2), with rn = 6 dominant while no oxygen is incorporated in a slower amine-only addition reaction under an inert atmosphere.' 25 1,3-diphenylnit-rilinine undergoes 1,3-dipolar cycloaddition with C, to form a pyrazoline dia- dduct.'26 The monoadduct of piperazine with c60 forms Langmuir-Blodgett films at the air-water interface with weak SHG (Second Harmonic Generation) activity.' 27 Nitrile oxides form 1,3-dipolar adducts to the 6:6 ring fusions of C7, and three separable isomers are formed.'28 Diels-Alder chemistry of c60 was well developed before 1994; the first use of the related ene reaction in functionalizing the molecule was reported this year producing a monoadduct with 3,5-di-t-butyl-4-(trimethylsiloxy)allylben~ene'~~ and 4-ally1 an- isole.' 30 8-methoxyheptafulvene has been reported to undergo [8 + 2) cycloaddition with c60 across a 6 :6 bond to give a tetrahydroazulenofullerene.'31 Ring-opened benzocyclobutenol undergoes Diels-Alder addition across the 6 :6 bond to give monosubstituted 1,9-dihydrofullerenes and the resulting alcohol is readily functional- ized.' 32 Diels-Alder adducts with tropones' 33 and ~ycloheptatriene'~~ are formed under high pressure and hydroquinone functionalized c6o's have been prepared.' The use of a remote tether to promote regiospecific functionalization of C, was demonstrated using multiple Diels-Alder additions of 1,3 butadienes attached via a methanofullerene carboxylic acid to give tris adducts across the 6 :6 bonds.136Mono Diels-Alder adducts of o-quinodimethane with C, and c76 have been isolated.' 37 (Trimethylsily1)ethynyl and phenylethynyl-fullerenes have been prepared by reac- tion with the lithium acetylide salts in refluxing toluene followed by acid addition yielding mono- and bis-adducts which have similar electrochemistry to C, itself.' 38 The compounds HC,,CH,SiMe,Y and C6,(CH2SiMe2Y) (Y = Me H CH=CH,,Ph,O'Pr) have been prepared from the Grignard reagents in THF and 123 M.Maggini A. Karlsson G. Scorrano G. Sandona G. Farnia and M. Prato J. Chem. SOC. Chem. Commun. 1994,647. 124 A. Skiebe A. Hirsch H. Klos and B. Gotschy Chem. Phys. Lett. 1994 220 138. 125 S. R. Wilson and Y. Wu Org. Mass Spectr. 1994 29 186. 126 S. Muthu P. Marutharnuthu R. Ragunathan P. R.Rao and C. K. Mathews Tetrahedron Lett. 1994,35 1763. 127 L. B. Can D. J. Zhou C. P. Luo C. H. Huang T. K. Li J. Bai X. S. Zhao and X. H. Xai J. Phys. Chem. 1994 98 12459. 128 M. S. Meier M. Poplawska A. L. Cornpton J. P. Shaw J. P. Selegue and T.F. Guarr J.Am. Chem. Soc. 1994 116 7044. 129 K. Kornatsu Y. Murata N. Sugita and T.S. M. Wan Chem. Lett. 1994 635. 130 S. Wu L. H. Shu and K.N. Fan Tetrahedron Lett. 1994 35 919. 131 E. Beer M. Feuerer A. Knorr A. Miclach and J. Daub Angew. Chem. Int. Ed. Engl. 1994 33 1087. 132 X. Zhang and C.S. Foote J. Org. Chem. 1994 59 5235. 133 H. Takeshita J.-F. Liu N. Kato A. Mori and R. Isobe J. Chem. SOC. Perkin Trans. 1 1994 1433. 134 J.-F. Liu N. Kato A. Mori H. Takeshita and R. Isobe Bu//.Chem. Soc. Jpn. 1994 67 1507.135 W. Bidell R. E. Douthwaite M. L. H. Green A. H. H. Stephens and J. F. C. Turner J. Chem. SOC. Chem. Commun. 1994 1641. 136 L. Isaacs R.F. Haldimann and F. Diederich Angew. Chem. Int. Ed. Engl. 1994 33 2339. 137 A. Herrrnann F. Diederich,C. Thilgen,H. U.Terrneer,and W.H. Muller Helu. Chim. Acta. 1994,77,1689. 138 K. Kornatsu Y. Murata N. Takirnoto S. Mori N. Sugita and T. S.M. Wan J.Org. Chem.,1994,59,6101. F ullerene Chemistry 593 toluene respectively :the unexpected formation of the latter suggests that the addition reactions may have radical as well as simply nucleophilic character.' 39 EPR has been used to study the regiochemistry of radical addition to C,,140 and 141 GO-Hydrolysis of polycyclosulfated fullerenes (see section on Molecular Chemistry) yields polyhydroxylated fullerenes (C,,(OH), n z 10-1 2)14 and hydrolysis of the product obtained on treating c60 with an excess of BH,-THF complex yields water soluble fullerols.143 Organometallic Chemistry.-C,,O has been shown to react with Ir(CO)Cl(PPh,) to afford a monoadduct in which the iridium complex adds to the C-C bond at one of the 6:6 ring junctions adjacent to the epoxide (Figure S).144 Treatment of Rh(acac)(C,H,) successively with c60 and pyridine affords Rh(acac)(C,H,N) q2C60.145c60 platinum and iridium organometallics may be prepared by elimination of HCl from species such as PtHCl(PPh,) in the presence of c60 to yield PtC,o(PPh,),.146 Electronic structure calculations have been used to rationalize the reactivity of C, with organometallics.147 A review of the organometallic chemistry of the fullerenes has been p~b1ished.l~' Reaction of a mixture of the D, and D isomers of C, with Ir(CO)Cl(PPh,) affords ~2-C,,IrCOC1(PPh,),.4c6H6 with the D, isomer of C, found predominantly in the product. The CS4 is bound via a 6 6 junction connecting two pentagons (Figure 9)-the selective crystallization of the less abundant D, isomer is ascribed to its increased tendency to adduct formation due to its more localized .n bonding.'49 The reaction of a tenfold excess of Ir(CO)Cl(PMe,) with c60 affords the bis adduct q2C,o[Ir(CO)Cl(PMe,)2]2 where the two iridium groups are 'para' at opposite ends of the fullerene.'50 4 Polymers High pressure polymerization of c60 and the formation of alkali metal fulleride polymers is covered in Section 2 and under Alkali Metal Fullerides Diels-Alder addition of a cyclopentadiene functionalized polymer to c60 allows reversible attachment of c6 to a polymer support.' Polychlorostyrene doped with 10% c60 undergoes a thousand-fold conductivity enhancement when the fullerene is partly reduced to C;0.152 Problems of multiple addition and subsequent cross-linking in c60 139 H.Nagashima H. Terasaki E. Kimura K. Nakajima and K. Itoh J. Org. Chem. 1994 59 1246. 140 J. R. Morton F. Negri and K. F. Preston Can. J. Chem. 1994 72 776. 14' R. Borghi L. Lunazzi G. Placucci P. J. Krusic D. A. Dixon and L. B. Knights Jr. J. Phys. Chem. 1994 98 5395. 14' L. Y. Chiang L.-Y. Wang J. W. Swirczewski S.Soleel and S. Cameron J. Org. Chem. 1994 59 3960. 143 N.S. Schneider A.D. Darwish H. W. Kroto R. Taylor and D. R. M. Walton J. Chem. SOC.. Chem. Commun. 1994,463. 144 A.L. Balch D.A. Costa J. W. Lee B.C. Noll and M.M. Olmstead Inorg. Chem. 1994 33 2071. 145 Y. Ishii H. Hoshi Y. Hamada and M. Hidai Chem. Lett. 1994 801. 146 S. Schreiner T.N. Gallaher and H. K. Parsons Inorg. Chem. 1994 33 3021. 14' (a)D. L. Lichtenberger L. J. Wright N. E. Gruhn and M. E. Rempe J.Organomet. Chem. 1994,478,213; (h)J.A. Lopez and C. Mealli J. Organomet. Chem. 1994 478 161. 148 J.R. Bowser Adv.Organomet. Chem. 1994 36 57. 149 A. L. Balch A. S. Ginwalla J. W. Lee B. C. Noll and M. M. Olmstead J.Am. Chem. SOC.,1994,116,2227. 150 A. L. Balch J. W. Lee B.C. Noll and M. M.Olmstead Inorg. Chem. 1994 33 5238. 15' K. I. Guhr M. D. Greaves and V. M. Rotello J. Am. Chem. SOC.,1994 116 5997. 15' S. E. Down D. R. Rosseinsky and R. S. Whitehouse J. Electroanal. Chem. 1994 365 311. M.J. Rosseinsky Figure 8 Crystal structure of q2-C,,01r(CO)Cl(PPh,) 50% thermal contours are shown for all atoms and only lhe ips0 carbons of the phenyl rings are shown. Relevant bond lengths are O(1tC(3) 1.445( 12)A O(1 bC(4) 1.462( 12)A C(3)-C(4) 1.480( 1 1)A Ir-C( 1) 2.168(7)A Ir-C(2) 2.174(7)A C(lbC(2) lSOO(1l)A. Bond angles of interest are C(3)-0(1)-C(4) 61.6(6)’ 0(1kC(3)-C(4) 59.9(6)” O(l)-C(4)-C(3) 58.8(6)0 C(l)-Ir-C(2) 40.4(3)0 (Reproduced by permission from Znorg. Chem. 1994 33 2071) copolymer formation can be overcome by cycloaddition of azido-substituted polysty- renes to c60 to give polymers which retain the electronic properties of the fullerene and the solubility and processability of the polystyrene.’ 53 Five mole percent c60doping of poly(0-trimethylsily1)phenylacetyleneenhances the photoconductivity.’54 Thermal breaking of the intermolecular C-C bonds in photopolymerized c60 proceeds with an activation energy of 1.25eV.”’ C, is also photopolymerizable albeit with greater difficulty this is ascribed to a reduction in the number of reactive double bonds to the five in each polar cap of the C, molecule.’56 The C,,(OH) (n = 10-12) fullerols (see under Organic Chemistry) derived from hydrolysis of sulfonation products of c60 may be condensed with excess diisocyanate (to prevent cross-linking) to give a dendritic polymer with six linear urethane connected polyether arms.’ s7 Soluble polyarylamine sulfone polymers with the c61 fulleroid pendant group have been prepared.58 5 Electrochemistry Electrochemical studies in o-dichlorobenzene show that the C; anion is a weak base while reduction to the dianion results in a marked increase in basicity (pK 153 C. J. Hawker Macromolecules 1994 27 4836. 154 K. Yoshino T. Akashi K. Yoshimoto S. Morita R. Sugimoto and A. A. Zakhidov Solid State Commun. 1990 90 41. 155 Y. Wang J. M. Holden X.-X. Bi and P.C. Eklund Chem. Phys. Lett. 1994 217 413. 156 A. M. Rao M. Menon K.-A. Wang P. C. Eklund K. R. Subbaswamy D. S. Cornet M. A. Duncan and I. J. Amster Chem. Phys. Lett. 1994 224 106. 157 L.Y. Chiang L. Y. Wang S. M. Tseng J. S. Wu and K. H. Hsich J. Chem. Soc. Chem. Commun. 1994 2675. 158 M. Berrada Y. Hashimoto and S. Miyata Chem. Muter. 1994 6 2023. Fullerene Chemistry Figure 9 The structure of (q2-C,,)Ir(CO)Cl(PPh,),. The principal twofold axis of an ideal D, symmetry molecule bisects the C(32bC(53)and C(42kC(43)bonds while the other twofold axes pass through the midpoints of the C-C bonds between the other hatched carbons. The C(32)-C(53) bond (1.455(6)A),which coordinates the iridium is considerably longer than the C(42bC(43)bond (1.332(11)A)at the opposite pole of the fullerene (Reproduced by permission from J. Am. Chem. SOC. 1994 116 2227) HC60 s 3.4 fO.1).I5' Electrochemical and EPR studies have indicated that the C& anion is diamagnetic while dynamic Jahn-Teller distortions are suggested for the Ci0 and (22; anions.' 6o X-Ray diffraction evidence exists for electrochemical intercalation of Bu,N+ cations into c60 films from acetonitrile solutions.'" Up to five reversible electrochemical reductions may be observed in c60trapped in electropolymerized films on Pt or C disk electrodes.162 The electrochemistry of methanofullerenes and [4 + 21 cycloaddition products have been studied.63 The effect of substituent electronegativ- ity on the electrochemistry of monosubstituted fullerenes is in accord with their electronegativity implying that inductive rather than resonance effects are important and more electronegative systems can be prepared simply by adding electron- withdrawing groups to the m01ecule.l~~ 6 Endohedral Fullerenes A considerable amount of progress has been made towards the bulk isolation and structural characterization of these molecules.A review of theory and experiment to the end of 1993 is available.' 65 The mechanism of endohedral metallofullerene formation in the gas-phase has been proposed to be the nucleation of polycyclic polyne 159 D. E. Cliffel and A. J. Bard J. Phys. Chem. 1994 98 8140. 160 M. M. Khaled R. T. Carlin P. C. Trulove G. R.Eaton,and S. S. Eaton,J. Am. Chem. SOC.,1994,116,3465. 161 K. Tomura M. Nishizawa D. Takemura T. Matsue and I. Uchida Chem. Lett. 1994 1365. A. Deronzier J.-C. Moutet and P. Seta J. Am. Chem. SOC. 1994 116 5019. 163 F. Arias Q. Xie L. Echegoyen Y. Wu Q. Lu and S.R.Wilson J. Am. Chem. SOC. 1994 116 6388. 164 T. Suzuki Y. Maruyama T. Akasaka W. Ando K. Kobayashi and S. Nagase J. Am. Chem. SOC.,1994 116 1359. 16' D.S. Bethune R.D. Johnson J.R. Salen M.S. De Vries and C.S. Yannoni Nature 1993 366 123. 596 M.J. Rosseinsky rings around a metal atom followed by conversion into the metallofullerene on the basis of quadrupole mass spectrometry studies.' Formation of endohedral species by insertion of the guest into the pre-formed fullerene via low energy formation of a nine-membered ring 'window' through breaking a pentagon-hexagon bond has been suggested by theoretical ~alculations,'~~ and exposing c60 to 2000 atmosphere of He Ne Ar Kr and Xe at 620 "C leads to formation of 0.1YOof endohedral species such as Xe@C, (and C70) consistent with such a mechanism.'68 The 3He NMR spectra indicate diamagnetic ring currents in c60and C70 from the 6 ppm and 29 ppm shielding of He in He(@C6 and He@C7 relative to the free atom.'69 The chemical shift of the 3He in He@C6 can be accurately cal~ulated.'~~ This NMR technique has also been used to follow organic reactions of fullerenes,'71 and mass spectrometry has been used to show helium encapsulation by derivatized fullerenes.' 72 Laser ablation of C6,/La203 mixtures gives evidence for formation of La@C, by a 'window' mechani~m.'~~ Ion drift tube techniques have indicated that NbC (n = 28-50) species with even values of n are endohedral but n odd species are fullerenes with metal atoms as part of the cage structure showing that networked metallofullerenes are a stable third class of f~l1erene.I~~ The separation and extraction of endohedral species from soot generated by arc erosion of metal oxide impregnated rods is a key aspect of endohedral fullerene chemistry-250 "C extraction with toluene under high pressure (16.5atm) produces 0.3% mass yield of a species rich in La@C (n = 82 is d~minant).'~~ Single stage HPLC allows the isolation of one isomer of La@C, whose near infrared spectrum is consistent with the formulation La3fC823-.176 Spark erosion of rods with a 1 :100 ratio of Y203 to C followed by HPLC on polystyrene and 'buckyclutcher' columns allows isolation of Y@c82 whose cyclic voltammetry shows one oxidation and three + reduction waves indicating a charge distribution Y3 (@jC; .'77 Automated anaerobic HPLC with polystyrene columns can be used for large-scale separation of Sc@C2 and Y@2 from the faster running empty cage fullerenes (200mg in 16hrs) while on-line EPR monitoring allows identification of paramagnetic Y @C, and sc3@c82 to mark the metallofullerene fraction; Y@c82 and Sc3@& can be isolated from the M@C2 metallogullerene fraction using a 'buckyclutcher' HPLC column.' 78 D.E. Clemmer K. B. Shelimov and M. F. Jarrold Nature 1994 367 718. 16' R. L. Murray and G. E. Scuseria Science 1994 263 791. M. Saunders H. A. Jimenez-Vazquez R. J. Cross S. Mroczkowski M. L. Cross D. E. Giblin and R. J. Poreda J. Am. Chem. Soc. 1994 116 2193. 16' M. Saunders H.A. Jimenez-Vazquez R.J. Cross S.Mroczkowski M.L. Cross D.E. Giblin R.J. Poredan D. I. Freedberg and F. A. L. Anet Nature 1994 367 256. J. Cioslowski J. Am. Chem. SOC. 1994 116 3619. 17' M. Saunders H. A. Jimenez-Vazquez B. W. Bangerter R. J. Cross S. Mroczkowski D. I. Freedberg and F.A. L. Anet J. Am. Chem. SOC. 1994 116 3621. 172 S.N. Davey D.A. Leigh A. E. Moody and L. W. Tetler J. Chem. Soc. Chem. Commun. 1994 I. 173 R. Huang H. Li W. Lu and S. Yang Chem. Phys. Lett. 1994 228 111. 174 D. E. Clemmer J. M. Hunter K. B. Shelimov and M. F. Jarrold Nature 1994 372 2488. 175 C. Capp T.D. Wood A.G. Marshall and J.V. Coe J. Am. Chem. Soc. 1994 116 4987. 17' K. Yamamoto H. Funasaka T. Takahashi and T. Akasaka J. Phys. Chem. 1994 98 2008. 177 K. Kikuchi Y. Nakao S. Suzuki Y. Achiba T. Suzuki and Y.Maruyama J. Am. Chem. Soc. 1994,116 9367(10). (a)S. Stevenson H. C. Dorn P. Burbank K. Harich J. Haynes Jr. C. H. Kiang J. R. Salem M. S. De Vries P. H. M. van Loosdrecht R. D. Johnson C.S. Yannoni and D. S. Bethune Anal. Chem. 1994,66 2675; (b)S. Stevenson H. C.Dorn P. Burbank K. Harich J. Haynes Jr. C. H. Kiang J. R. Salem M. S. De Vries P. H. M. van Loosdrecht R. D. Johnson C. S. Yannoni and D. S. Bethune Anal. Chem. 1994 66 2680. Fullerene Chemistry I I I I I 1 1 1 I I 3280 3300 3320 33LO 3360 3380 3-500 31.20 31.1.0 3460 H/G LD-TOF-MS (355 nm) L. 600 800 1000 1200 1400 m/ Figure 10 (a) EPR spectrum and (h) laser desorption time-ofjight mass spectrum of Sc,(u C, (Reproduced by permission from J. Phys. Chem.1994 98 8597) Improved separation techniques have allowed more detailed physical characteriz- ation of these species. PES studies of La@C, solid films indicate that the lanthanide is in the +3 state (though electronic structure calculations predict strong covalency and 1.49 8 displacement of the lanthanide from the centre of the cage) but the solid is non-metallic despite the radical nature of the molecule.'79 An EPR study of Sc3(uC,2 revealed 22 symmetric hyperfine lines about g = 1.9985 consistent with an equilateral triangle of Sc atoms within the C, isomer ofC, (EPR and mass spectra shown Figure lo).' 8o The first crystallographic information concerning endohedral fullerenes comes from an electron diffraction and lattice imaging study of SC~(~C,~ which is hexagonal close packed with c/a = 1.63 (the ideal value) and the intermolecular separation in the close packed layer is 11.2 A equal to that of hollow C,,.I8' (Figure 11).A simple model for the bonding in endohedral fullerenes has been devised and used to predict stable endohedral species.Is2 D. M. Pokier M. Knupfer J.H. Weaver W. Andreoni. K. Laasonen M. Parincllo D. S. Bethune K. Kikuchi and Y. Achiba Phys. Rev. B 1994 49 11403. H. Shimohara M. Inakuma N. Hayashi H. Sato Y. Saito and S. Bandow,J. Phys. Chem. 1994,98,8597. '*'R. Beyers C.H. Kiang R.D. Johnson J.R. Salem M.S. de Vries C.S. Yannoni D. S. Bethune H.C. Dorn P. Burbank K. Harich and S. Stevenson Nature 1994 370 196. K. Jackson E. Kaxiras and M. R. Pederson J. Phys. Chem. 1994 98 7805.M. J. Rosseinsky Figure 11 (a) High resolution TEM lattice image of Sc2(dC,,; (b) is a Fourierfiltered image to bring out the periodicities in the original image; c and d are simulated images of 6.78 thick Sc,iu C, and C, crystals at 5008 deforus. In c and d three different orientations of the molecules are superimposed to simulate the orientational disorder present in the crystals (Reproduced by permission from Nature 1994 370 196) 7 Carbon Nanotubes Following the many studies reported in 1993 preparative work has concentrated on the synthesis ofhigh purity monodisperse tube samples to allow the unambiguous study of chemical and physical properties. Chemical opening and filling of the tubes has been achieved. A review of the area has been published in 1994.183 The carbon nanoparticles which typically compose 1/3 of the sample under all-carbon rod erosion can be burnt off in air or oxygen at 750 "C over 30 minutes leaving 1% by mass of the sample as pure open nan0t~bes.l~~ Perfect tubes longer than 40pm can be grown using a water cooled copper cathode together with the graphite anode preventing defect formation due to sintering together of the tubes at high temperat~re."~ The outside of closed tubes can be wet and the inside of open tubes filled by substances with low surface tension (<200 mNm- ')-this allows the interior of the tubes to be wetted by water and organic solvents.'86 Transition metal la3 T.W. Ebbesen Annu. Rev. Mater. Sci. 1994 24 235. T. W. Ebbesen P. M. Ajayan H.Hiura and K. Tanigaki Nature 1993 367,519. D.T. Colbert J. Zhang S. M. McClure P. Niklaev. Z. Chen J.H. Hafner D. W. Owens P.G. Kotula. C. B. Carter J. H. Weaver A.G. Rinzler and R. E. Smalley. Science 1994 266 1218. E. Dujardin T. W. Ebbesen. H. Hiura and K. Tanigaki Science 1994 265 1850. Fullerene Chemistry 599 catalysts co-evaporated from the anode increase the density of single-walled tubes this was first demonstrated using Co :C composite rods.'87 The single-walled tubes occur both as web-like deposits in the chamber when a mixed Co/Pt catalyst is used,'" and in the soot with Fe/Ni and Co/Ni catalysts.'89 Arc evaporation of Sc-C composite rods allows encapsulation of Sc,5C19 crystallites within the nanot~bes."~ The composition of the soot as well as the cathode carbon is a sensitive function of the catalytic metal-palladium and enhances the percentage of C70 and other higher fullerenes formed in comparison with pure graphite while platinum produces a high nanotube density in the cathode carbon.lgl The quenching of hot carbon vapour onto a -30 "C flat graphite substrate produces carbon cones up to 24 nm long which all have the same 19"cone angle shown to be the smallest of the five possible opening angles for graphitic cones.lg2 An important development is the chemical opening and filling193 of the nanotubes by nitric acid oxidation-pitaxially grown crystals of nickel can be formed and there is much scope for future development.Intercalation by potassium and rubidium into nanotubes can be achieved by vapour phase reaction-the results imply a highly defective structure for the tubes resembling turbostratic graphite rather than concentric hollow ~y1inders.l~~ 0.2 wt% Ruthenium particles (3-7 nm) supported on the external surfaces of the tubes are highly selective in catalysing the reduction of cinnamaldehyde to cinnamyl alcohol.' 95 Magnetic and electron transport measurements on 'as made' tubes seem to imply that the microscopic electronic structure is similar to that of graphite.The diamagnetic susceptibility is larger than that of graphite,' and quite isotropic when measured parallel or perpendicular to the axis of an aligned bundle of tubes.' 97 The semi-metallic nature of the tubes was quantitatively addressed by transport and magnetotransport measurements using contacts made to individual bundles of tubes with an STM198-a fit to p(r)indicates that the band overlap (3.7 meV) is ten times smaller than in graphite (40meV) resulting in fewer carriers and a larger low-temperature resistivity.The Hall voltage is always positive indicating p-type carriers. '99 EPR measurements indicate that neither potassium nor iodine 'doping' can introduce carriers,200 in contrast to graphite. The 1580cmp1 E, vibrational mode of graphite also appears in the Raman spectrum of the nanotubes.200 Mixing of the cr* and n* states of a flat graphite sheet on IK7C.H. Kiang W.A. Goddard R. Beyers J. R. Salem and D. S. Bethune J. Phys. Chem. 1994,98,6612. J. M. Lambert P. M. Ajayan P.Bernier J. M. Planeix V. Brotons B. Coq and J. Castaing Chem. Phys. Lett. 1994 226 364. lS9 S. Seraphin and D. Zhou Appl. Phys. Lett. 1994 64 2087. 190 Y. Saito M. Okuda T. Yoshikawa S. Bandow S. Yamamuro K. Wakoh. K. Sumiyama and K. Suzuki Jpn. J. Appl. Phys. 2 Lett. 1994 33 L186. 19' S. Seraphin D. Zhou J. Jias M. A. Minke S. Wang T. Yadav and J. C. Withers Chem. Phys. Lett. 1994 217 191. 19' M. Ge and K. Sattler Chem. Phys. Lett. 1994 220 192. 193 M. L. H. Green P. J. F. Harris and S.C. Tsang Nuture 1994 372 159. 194 0.Zhou R. M. Fleming D. W. Murphy C. H. Chen R.C. Haddon A. P. Ramirez and S. H. Glarum Science 1994 265 84. 195 J. M. Planeix N. Coustel B. Coq V. Brotons P. S. Krumbhar R. Dutarte P. Geneste P. Bernier and P. M. Ajayan J. Am. Chem.Soc. 1994 116 7935. 19' J. Heremans C.H. Olk and D. T. Morelli Phys. Rea. B 1994 49. 15 122. 197 X. K. Wang R. P.H. Chang A. Patashinski and J.B. Ketterson J. Muter. Res. 1994 9 1578. 19' L. Langer L. Stockman J. P. Heremans V. Bayot C. H. Olk C. Van Haesendonck Y. Bruynseraede and J.-P. Issi J. Muter. Res. 1994 9 927. 199 S.N. Song. X. K. Wang. R. P. H. Chang and J. B. Ketterson Phys. Ret.. Lett. 1994 72 697. K. Tanaka,T. Sato,T. Yamabe K. Okahara,K. Uchida M. Yumura H. Niino,S. Ohshima Y. Kuriki K. Yase. and F. Ikazaku Chem. Phys. Lett. 1994 223 65. M. J. Rosseinsky folding into a tube in the LDA can significantly reduce the gaps predicted for small radius tubes by tight-binding calculations.201 BN also displays a tendency to curl and form onion-like structures under electron beam irradiation; however complete closure of the spheres does not occur.2o2 '"' X.Blase L. X. Benedict E. L. Shirley and S.G. Louie,.Phys. Rev. Lett. 1994 72 1878. '02 F. Banhart M. Zwanger and H.J. Muhr Chem. Phys. Lett. 1994 231 98.

ISSN:0260-1818    

DOI:10.1039/IC9949100577

出版商:RSC    

年代:1994

数据来源: RSC