13 Fe Co and Ni By S.A. COTTON Felixstowe College Felixstowe Suffolk IP11 7NQ UK 1 Introduction Organometallic compounds are dealt with elsewhere in this volume and receive only a passing glance here. Similarly coverage of complexes of macrocyclic ligands has been limited. Particular trends discernible this year include continued interest in binuclear iron 0x0-species and in nickel complexes with sulfur ligands. 2 Simple Binary and Coordination Compounds of Oxygen Nitrogen and Halogen Donors An important new book' covers the synthesis and structures of the various iron oxides hydroxides and basic iron salts. The synthesis has been described of a y-Fe,O,/polymer nanocomposite as a magnetic material with appreciable transmission in the visible region of the spectrum.Barium surface doped iron(Ir1) oxide particles for high-density magnetic recording have been studied. Photo-oxidation of matrix-isolated iron pentacarbonyl at 20 K leads to the identification of two binary iron oxides one believed to be the peroxide Fe(q2-0,) and the other the planar (or neatly so) trioxide FeO, rather than O=Fe=O as previously ~uggested.~ The hydride CaMgNiH, synthesized by sintering ternary metal alloy powders under dihydrogen has tetrahedral [NiH4I4- anions present (Ni-D distances in the corresponding deuteride are 1S97-1.602 A).' The electron affinity of FeCl has been reported' to be 4.3 & 0.2eV. 0-donors.-A report7 concerning higher oxidation states involves iron(v1) with the observation of sharp-line near-IR luminescence in FeOi-.A ferryl(v) intermediate has been invoked' in a study of DNA cleavage with a system involving an iron(r1) complex and dioxygen or H20,. [For some other iron(1v) complexes see pages 180 and 183.1 Among the aqua-complexes of metal halides both cis and trans-stereuchemistries U. Schwertmann and R. M. Cornell 'Iron Oxides in the Laboratory. Preparation and Characterization'. VCH Weinheim New York 1991. R.F. Ziolo E. P. Giannelis B. A. Weinstein. M. P. O'Horo. B. N. Gangulq. V. Mehrotra. M. W. Russell. and D. R. Huffmann Science 1992. 257. 219. ' C. Sarda C. Bonino P. Mollard and A. Rousset. 1.Moyn. Muyn. Murer.. 1992 109 127. M. Fanfarillo A. J. Downs. T. M. Greene and M. J. Almond Inory. Chem.. 1992. 31. 2973. ' B. Huang. K. Yvon and P.Fischer 1.Allo~.~ Compd.. 1992. 178. 173. ' M. M. Koborov. Y. V. Pervova and L. N. Sidorov Mendelerr Commun. 1992 41. M. Herren and H. U. Gudel. Itiory. Chcm. IY92. 31 3683. " R.E. Shepherd. T.J. Lomis. and R. R. Koepsel J. Cheni. Soc.. Chem. Conimun.. 1992. 222. 169 170 S. A. Cotton are known for MX2.4H20 units (Table 1 lists those whose structures have been determined). The structures of FeBr2-4H,O CoBr;4H20 and NiCI,-4H20 all involve' octahedral coordination of the metal; the first two are truns but the nickel complex is cis. Steric repulsions between bromines may favour the adoption of the trans-isomer though hydrogen-bonding and the effects of electron configuration may also be important. Table 1 Stereochemistry in MX2.nH20(n = 2 4 6) Fe co Ni n CI Br C1 Br c1 Br 2 t ~ t t t ~ 4 t t C t c - 6 ~ t t t t (c = cis; t = trans) The two crystalline forms of FeF,.3H20 have been reinvestigated lo and it is suggested that a previously reported structure of FeF2.4H,0 was in fact that of a-FeF,.3H,0.Reports on halogenoferrates include the syntheses' ' from iron bromine and the appropriate bromide of several AFeBr (A = alkali metal NH, Ag). Detailed magnetic studies have been made on two tetrach1oroferrates.l2.' The novel [Fe,C1,I2~ ion has a structure based on edge-sharing tetrahedra.I4 Like the corresponding chloride FeBr,.2Ph,PO has been shown" to be rrans-[FeBr,(OPPh,),][FeBrJ and [COI,(ONM~,)~] is pseudotetrahedral whilst [CoCI (ONMe,),] is similar." FeCl reacts with CIOTeF to form [Fe(OTeF,),] which readily reacts with bases and is believed to have a three-coordinate trigonal planar structure; it forms a distorted octahedral trjs(adduct) with S0,ClF.' ' Iron(m) is well known to form complexes with polyols and sugars; magnetic susceptibility and ESR studies suggest that the iron exists in mononuclear (presumably aqua) species with normal magnetic moments at pH 1-2 polynuclear species with lowered moments at pH 3-10 and mononuclear complexes where the iron is probably coordinated to the alcoholic OH groups at higher pH." Further investigations have been reported' 9,20 in the complex area of iron(1rr)-nitrilotriacetate complexes; it is K.Waizumi H. Masuda and H. Ohtaki. Inory. Chirn. Actu. 1992 192. 173. D.G. Karraker and P. K. Smith. fnorg. Chem. 1992. 31 11 19. I' G. Thiele. D. Honert and H. Rotter. Z. Anorg. Allgem. Chrm.. 1992. 616. 195. R. Shaviv C. B. Lowe. J. A. Zors. C. B. Aakeroy. P. B. Hitchcock. K. R. Seddon. and R. L. Carlin Inory. Chirn. Acta 1992 198-200. 613. l3 R. Shaviv K. E. Merabet. D. P. Shum C. 9. Lowe. I). Gonzalez. R. Burriel. and R. L. Carlin. Inorg. Chem.. 1992 31 1724. 14 K. Ruhlandt-Senge and U. Muller. 2.Narurforsch Teil B. 1992. 47. 1075. l5 E. Durcanska T. Glowiak E. Gyepes I. Ondrejkovicova. and G. Ondrejovic. Actci Fnc. Rerum Nut. Unit.. Comeniunae Chim.. 1991. 39. 3 (Chem. Ahsrr. 1992. 117. 80521). S. Jin M. Nieuwenhuyien W. T. Robinson and C.J. Wilkins. Actci Crystcilloyr. Sect. C. 1992. 48. 274. " T. Drews and K. Seppelt.Z. Anorg. Allgem. Chem. 1991 606 201. H. Yokoi. Y. Mori T. Mitani. and S. Kawata Bull. Chem. Sot. Jpn.. 1992. 65 1x98. 19 S. L. Heath. A. K. Powell H. L. Utting. and M. Helliwell. J. Chrm. Sot,.. Dcilfori 7rans.. 1992. 305. 2" Y. Nishida. K. Yoshirawa and T. Akamatsu. Chem. Lett. 1991. 1521. FP Co and Ni concluded that a mononuclear species is obtained at low pH which dimerizes to [(Fe(nta)(H20))20]2- at higher pI3. The structure of the barium salt of the latter (1) has been reported.’ 0 \\ 0 Octahedral six-coordinate iron has been confirmed for a bis(dipico1inato) ferrate iron(iii) complex;21 such iron(m) complexes catalyze the oxidation of saturated hydrocarbons by H202 in pyridine-acetic acid and the high-spin ion cis-[FeCl,(picolinate),] -has been characterized as a model for one-iron non-haem enzymatic oxidations.22 The reactive intermediates for this and a number of other intermediates for the metal-induced activation of H202 have been investigated kineti~ally.~~ Iron carboxylates investigated include24 [Fe(la~tate)~(H,O),] and the iron(iI1) oxydiacetate species [Fe{O(CH2C02)2}(H20)2X] (X = C1 Br) in which the car- boxylate occupies meridional positions with the two water molecules trans.25Two different kinds of trinuclear carboxylates have attracted attention.Inelastic neutron scattering shows 11 transitions in the region between 2-25 cm-’ in a ‘traditional’ p,-0x0-centred mixed-valence carboxylate,26 [Fe30(02CCD3),(C,D,N)3]* (C,D,N). These transitions disappear on dilution in a host lattice indicating that they originate in intermolecular electronic transitions.Iron(i1) acetate reacts with a bidentate N-donor BIPhMe [2,2’-bis( 1-methylimidazolyl)phenylmethoxymethane]to give an unusual trinuclear complex [Fe,(OAc),(BIPhMe),] (2) in which the three irons have a linear rather than triangular arrangement featuring one monodentate and two bidentate bridging acetates. Magnetic susceptibility studies indicate ferromag- netic exchange co~pling.~’ Several iron carboxylate complexes featuring bridging ligands have been postulated as models for iron sites in proteins. These are discussed together with a number of p-0x0 complexes in Section 7. I A. Cousson F. Nectoux and E. N. Rizkalla Acru Crj,stul[ogr.,Sec,r.C. 1992 48.1354. 22 J. Chem., D. H. R. Barton. S.D. Beviere W. Chavasiri. D. Doller W.-D. Liu and J. H. Reibenspies N~N 1992 16. 1019. 23 H.-C. Tung. C. Kang. and D.T. Sawyer J. Am. Chem. Sot,.. 1992 114. 3445. 24 P. Liu and M. Hong Jiegou Huuxue 1992. 11. 44 (Chem.Ahstr.. 1992. 117 101 459). 2s A. K. Powell J. M. Charnock A. C. Flood C. D. Garner. M. J. Ware and W. Clegg J. Chem. Soc. Dulton Trans.. 1992. 203. 2h U. A. Jayasooriya R. D. Cannon C. E. Anson. S. K. arapKoske. R. P. White and G.J. Kearley. J. Chem. So(..,Chem. Commun. 1992 379. 21 R. L. Rardin. P. Poganiuch. A. Bino. D. P Goldberg W. B. Tolman S. Liu and S.J. Lippard J. Am. Chem. Soc.. 1992. 114. 5240. 172 S. A. Cotton (2) R=CH3 The iron(1rI) complex of N,N'-bis(2-hydroxyphenyl)ethylenediamine-N,N'-diacetic acid28 (H,edda) has a very high stability constant (log K = 40.l) though not as high as a new hexadentate ligand which has an affinity for iron exceeding that of enterobac- tin29 at phyological pH.Iron catecholate complexes with cubane-like Fe,O cores3' (others are dimeric) have been synthesized whilst monomeric bis(catecho1ate) complexes have likewise been characterized3' and the redox properties of the iron(II)/(III) redox couples investigated. Metal complex ferrimagnets [NBu,] [M"Fe"'(ox),] with three-dimensional network structures of alternating Fe"' and MI' ions have been prepared.32 Several papers have appeared concerning the effect of high pressure on kinetics. The reaction of the iron(II1) aqua ion with azide has been studied by stopped-flow methods33 and shown to involve predominantly the reactions of [Fe(H2O),(OH)I2 + with N; and HN,; the corresponding reaction with thiocyanate has been reinves- tigated.The [Fe(CN),] -/[Fe(CN),I4 self-exchange reaction involves a very high positive volume of activation.34 The redox exchange of [Co(edta)] -and [Co(hedta)(H,O)] -has been described in terms of a non-adiabatic outer-sphere mechanism in which ring-closure and elimination of water precede electron transfer.35 The pressure dependencies of the electrode potentials of [Fe(H20),l2+I3+ [Fe(phen)3]2fi3+ [Fe(CN),]3-/4p and [Co(~epulchrate)]~+'~+ have been re-ported .3 Several alkali metal tetra-alkoxo and aryloxo cobaltates of the general type M,[Co(OR),]-xTHF have been synthesized; from spectroscopic data they seem generally to have tetrahedrally coordinated cobalt.37 Six-coordination is general for solvated species including those of cobalt(II) in most 0-donor solvents such as water dmso and dmf but an EXAFS of cobalt(1r) 28 J.F. Gibson and 0.J. Vaughan. J. Chem. Soc. Dulton Truns. 1992 1375. 29 R. J. Motekaitis Y. Sun and A. E. Martell Inorg. Chim. Actu 1992 198-200 421. 30 S.C. Shoner and P.P. Power Inory. Chem. 1992 31 1001. 31 D. Zirong S. Bhattacharaya J. K. McCusker P. M. Hagen D. N. Hendrickson and C. G. Pierpoint Inorg. Chem. 1992 31 870. 32 H. Tarnaki M. Mitsumi K. Nakarnura N. Matsumoto S. Kida H. Okawa. and S. Iijima. Chem. Lett. 1992 1975. 33 M. R. Grace and T. W. Swaddle. Inory.Chem.. 1992 31 4674. 34 H. Takagi and T.W. Swaddle Inory. Chrm. 1992 31 4669. 35 W. H. Jolly D. R. Stranks and T.W. Swaddle Inory. Chem. 1992. 31. 507. 36 H. Doine T.W. Whitcornbe and T.W. Swaddle Can. J. Chem.. 1992 70 81. 37 A.I. Ibrahim W. Gaube W. Kalies. and B. Witt J. Prakt. Chem. 1992 333 397. Fe Co. and Ni 173 and its chloro complexes in hmpa indicates that four-coordination is general in species [C~(hmpa),-~Cl,](~-”)+. Co-0 and Co-Cl bond lengths are shorter in the four- coordinate species than in corresponding ions like [CO(H,O),]~’. Among other complexes of simple 0-donors several cobalt complexes of pyridine N-oxide (PyO) and trimethylamine oxide have been studied39 with structures determined for [co(opy161[cocl4] 7 [cO(opy)& [Co(ONMe )4]12 and [Co(ONMe )2x2] (X = C1 I); as indicated by the formulae six-coordination is general for pyridine N-oxide and tetrahedral four-coordination for trimethylamine oxide.Six-coordination also occurs4o in [Co(hfac),(OPPh,),]. A modified electrolytic process for the synthesis of cobalt(I1r) acetate has been de~cribed.~’ N-donors.-Coordination numbers between 3 and 8 are known for iron(m) complexes. What appears to be a new geometry for four-coordination is the trigonal mono- pyramid rather than the usual tetrahedron for the brown high-spin pentane-soluble triamide complex (3),where the bulky trialkysilyl groups inhibit access to the vacant axial position.42 ,NSiMe2Bu‘ Bu‘Me$iN.-Fe’ ) ciaiMe2But (3) The crystal structure of [Fe(4-F-bipy),][PF63 shows four of the eight possible isomers;43 electronic spectra of iron(r1) complexes of phen bipy terpy and other ligands and their reduction products have been examined.44 FeN coordination has been crystallographically characterized for an iron(I1) tris(diimine) complex and its dissociation in the presence of hydroxide examined in a number of different solvents;45 the kinetics of reactions of diimine-cyanide complexes with various oxidizing agents have been analyzed.46 A convenient synthesis47 has been reported for the high-spin iron(I1r) poly(pyrazoly1)borate complex [NEt,][FeCl,{ HB(pz),)].The syntheses have been rep~rted~**~~ of a large number of [Co(N,),L,] complexes = pyridine or substituted pyridines) as well as the structures of two examples (L = py 4-Mepy); all appear to have rner geometry.Cobalt(II1) ammines are a hardy 3X K. Omtsumi. K. Tohji. Y. Abe. and S. Ishiguro. Inorq. Chim. Actu 1982. 191. 183. 34 (a) S. Jin M. Nieuwenhuyzen. and C.J. Wilkins J. Chem. Soc. Dalton Truns.. 1992 2071 ; (h) S.Jin M. Niewenhuyzen W. T. Robinson and C. J. Wilkins Actu Crj~.stulloyr.Sect. C. 1992 48 274. 40 J. R. Polam and L. C. Porter. Acra Crj~srulloqr.. Sect. C 1992 48 1761. 41 U. B. Ogutveren R. E. Plirnley. and 1. Nieve J. Appl. Electrochem. 1992 22 351 42 C.C. Curnmins J. Lee R. R. Schrock and W. D. Davis. Anqew. Chem.. Int. Ed. Enql.. 1992 31 1501. 43 C. K. Cho and A. S. Secco Actu Crystalloqr. Sect. C. 1992 48. 165. 44 P.S. Braterman J.-I. Song and R.D. Peacock. Inorg. Chem. 1992 31. 555. 45 M.J. Blandarner. J. Burgess J. Fawcett P. Guardado C. D. Hubbard. S. Nuttali L.J.S. Prouse S. Radulovic. and D. R. Russell Inory. Cheni. 1992 31 1383. 4h J. Burgess and B. Shraydeh Polyhedron. 1992. 11. 2015. 4-S. Cho D. Whang K. Han and K. Kim. Inorq. Chem. 1992. 31 519. 4H M. A. S.Goher. R. J. Wang and T. C. W. Mak. Polyhedron. 1991. 11 829. 44 F.A. Mautner Cryst. Res. Tc.chnol. 1991 26. 883. 174 S.A. Cotton perennial. The structure of [CO(NH,),][cUCI,] has been determined5’ above and below the transition temperature of 281 K. Thermal analyses have been carried oUt51-53 on a number of hexaammine salts with and without the presence of added potassium halides. A classic photoisomerization in [Co(NH,),(NO,)] C1 (nitro to nitrito) has been rein~estigated,~ together with the reverse thermal isomerization by single crystal diffraction.Kinetic studies have been carried out5 on the spontaneous isomerization of [Co(NH,),(SCN)I2 + ; the synthesis and hydrolysis (showing first order dependence on OH-) of the [Co(NH,),(SMe,)13+ ion has been reported.s6 [Co(NH,),(CO,)]CI reacts in the solid state with NH,SCN to give trans-[Co(NH,),(NCS),]Cl whilst in the analogous reaction with [Co(en),(CO,)]Cl cis-[Co(en),(NCS),]CI is formed first subsequently isomerizing into the tr~ns-isomer.~~ The structure of [Co(NH,),{ (S)-alaninate}]SO has been reported.58 The structure of [Co(CO,)(phen),] shows59 that Co-N bonds trans to 0are slightly longer than the cis-Co-N bonds; cis-[Co(glycine)(phen),] C1 has also been syn- thesized and crystallographically characterized.“ A series of paper~~l-~, reports syntheses structures and configurations of [CoX(dien)(dapo)] (X = halide pseudohalide NO, ONO) complexes and their + base hydrolysis.Other amine complexes reported include [Co(medien)(dien)] 3+ (medien = 3-methyl-1,5-diamin0-3-azapentane), where both the fuc and mer-isomers have been isolated and subjected to molecular mechanics analysis,, and isomers65 of + . [C~(trien)(salicylate)]~ Quinquepyridine ligands form mono-helical 1 1 and double-helical 2 2 cobalt(r1) c~mplexes;~~,~~ the crystal structure (4)of the complex [Co(cp,qpy)(MeoH)(H,o)][PF,] [cp,qpy = 4’,4”’-bis(4-~hlorophenyl)-2,2’ 6‘,2“ 6f’,2fff shows pentagonal bipyramidal seven-coordination.6”’,2””-quinquepyridine] The structure of tetragonal [NiCl,(Py),] has been redetermined,68 whilst the structures of planar trans-[NiCl,L,] (L = 2,6-Me2Py 2,3,6-Me3py) have also been T. Aoyama S. Ohba Y. Saito. and I. Bernal Acra Crystullogr. Sect. C. 1992 48 246. L. Zheng L. Dai and X. Xin Thermochim. Acta 1992. 196 437. 52 M.D. Patil G.N. Natu and S.B. Kulkarni Buli. Chem. Soc. Jpn. 1992 65 1026. 53 L. H. Khalil N.A. Moussa and S. Mikhail J. Muter. Sci.. 1992. 27 557. 54 M. Kubota and S. Ohba Actu Crystullogr. Sect. C. 1992 48 627. 55 A. Ellis A. Fultz R. Hicks,T. Morgan L. Parsons M. J. Saderholm L.A. Smith M. Stabb J. K. Starnes L. J. Sun and L. Roecker Aust. J. Chem. 1992 45 2049. 56 D.A. Buckingham C. R. Clark and G. F. Liddell Inorg. C‘hem. 1992 31 2909. ” J. Zhuang Q. Cheng. X. Xin and L. Zheng Yingyong Huaxue 1992. 9. 33 (Chem. Ahstr.. 1992. 117 102997). 58 B. Prelesnik K. Andjelkovic and N. Juraanic Acta Crystullogr. Sect. C. 1992 48 427. 59 C. A. McAuliffe R. G. Pritchard M. R. Bermejo A. Garcia-Vazquez A. Macias J. Sanmartin J. Romero. and A. Sousa Acfa Crystullogr. Sect. C 1992 48 1841. 60 B. Ye T. Zheng L. Ji and H. Zhuang Chin. Cheni. Lett. 1991,2 529 (Chem. Abstr. 1992,116.206613). 61 P. Comba D. A. House W.G. Jackson W. Marty. H. Stoeckli-Evans and L. Zipper. Helc. Chim. Actu 1992 75 1130. 62 P. Comba W.G. Jackson W. Marty and L. Zipper Helc. Chim. Actu 1992 75 1147. 63 P. Comba W. G. Jackson W. Marty and L.Zipper Htdc. Chim. Acta. 1992 75 1172. 64 I. M. Atkinson F. R. Keene J. M. Gu1bis.G. H. Searle,and E. R. T.Tiekink,J. Mol. Struct. 1992,265.189. 65 Y. Yamomoto E. Toyota T. Kumon and H. Sekizaki Bull. Chem. Soc. Jpn 1992 65 283. 66 E. C. Constable J. V. Walker D. A. Tocher and M. A. M. Daniels. J. Chem. Soc,..Chem. Commun.. 1992 768. ” E.C. Constable and J.V. Walker. J. Chem. Soc. Chem. Commun. 1992 884. “ R. E. Bachman. K. H. Whitmire. S. Mandal. and P. K. Bharadwaj. Acta Crvstalloyr.. Sect. C 1992. 48. 1836. Fe Co and Ni in~estigated.~~ Tetragonal pyramidal five-coordination occurs7o in [Ni(3,5-dimethyl- piperidine),(NCS),] and the structures of five dimeric adducts of substituted pyridines with nickel(I1) carboxylates likewise display five coordinate sp geometries with Ni-Ni distances of 2.708-2.765 (Reproduced with permission from J.(‘hem. Soc. Chem. Commun. 1992 768) The structure of tr~ns-[Ni(en)~(NCS),] has been redetermined.72 EXAFS has been used to provide comparative structural data on nickel(I1) and (HI) bis(diamine) complexes; both Ni-N and Ni-halogen distances shorten on increasing the oxidation state the former proving perhaps surprisingly the more sensitive.’ Ethanol solutions of the nickel(r1) diamine complex [Ni(N,N-Me,en),][C1O4] absorb and fix CO in air to give a trinuclear carbonato complex [Ni3(H20)4(C0,)(Me,en),lCCI0,1 (5). The transformation can be reversed by passing N through the solution whilst the presence of perchlorate seems to be important as only slight fixation is observed with other counter-ions (e.y.halide nitrate ~ulfate).’~ (Reproduced with permission from Inoty. Chem. 1992 31 1060) 69 W. L. Darby R. J. Butcher and L. M. Vallarino Inorq. Chim. Acta. 1992. 194 113. ’() M. Koman E. Jona and E. Durcanska Acta Crys~alloqr.,Sect. C 1992. 48 1652. M. Morooka S.Ohba M. Nakashima.T. Tokii. Y. Muto M. Kato and 0.M. Steward Acru Cry.sralloqr.. Sect. C 1992 48 1888. 12 N. V. Podberezskaya T. P. Shakhtshneider. A. V. Virovets and P. A. Stabnikov Zh. Srruct. Khim. 1991 32. 96 (Chem.Ahstr.. 1992. 116 140593). 73 J. Evans W. Levason. and R. J. Perry J. Chrm. SOC.,Dalton 7ratis.. 1992. 1497. 74 T. Tanase. S. Nitta. S. Yoshikawa. K. Kobayashi T. Sakurai and S. Yano Itiary. Chem. 1992,31 1058. 176 s.A.Cotton A double helical complex [Ni,(spy),][PF,] of the hexadentate ligand 2,2‘ 6’,2”:6“,2“‘:6’1’,21‘’’ :6””,2””’-sexipyridine (spy) has been synthesizedT5 (6). (Reproduced with permission from J. Chem. Soc. Chem. Commun. 1992 65) Both tetrahedral monomeric and binuclear five-coordinate nickel(I1) tris(pyra- zo1yl)borate complexes have been characterized .?‘ Using a tripodal ligand nickel(I1) complexes with NiN,S,O and NiN,S chromophores have been obtained;77 for five-coordinate complexes with NiN,S2 chromophores related to hydrogenase see Section 9. 3 Complexes of Tertiary Phosphines Two groups have ah initio calculations on c~s-[F~H(H,)(PR,)~] + . The properties of [FeXY(dmpp),] [X,Y = H C1; dmpp = Me,P(CH,),PMe,] and the structure of the dichloro compound (trans-,unlike the others) have been reported,*’ as has that of trans-[FeBr,(depe),] which is a catalyst for the Kharasch reaction between MgEtBr and alkyl halides to give alkanes and alkenes.The two proposed mechanisms involve iron(1) and iron(m) species. The structure of trans-[FeBrH(depe),][BPh4] has also been determined.8 The preparation of the symmetrically bridged alkynide [C1Fe(dmpe),(C~CC,H4C~C)(dmpe),FeCl] and the redox properties of this and other dmpe complexes [Fe(dmpe),(X)(Y)] (X Y = C1 or CCPh) have been reported.82 The cation in [Fe(NCMe),(dppe),][BF,1 is Iron(r1) complexes of a new bulky chelating phosphine 1,2-bis(di-n-butylphosphino)ethane (dbpe) have been reported [FeCl,(dbpe),] a precursor for a series of alkyne complexes is paramagnetic in solution but diamagnetic in the solid state.*“ 75 E.C. Constable and R. Chotalia. J. Chem. Soc,..Chern. Commun. 1992 64. 76 S. Trofimenko J. C. Calabrese. J. K. Kochi. S. Wolowiec. F B. Hulsbergen. and J. Reedijk. Inor6q. Chern.. 1992 31 3943. 7 K.G. Ragunathan and P.K. Bharadwaj. J. Chrm. Sor... Dulfon 7runh.. 1992. 2417. 78 J.-F. Riehl. M. Pelissier. and 0. Eisenstein. Inory. Chem. 1992 31. 3344. 79 F. Maseras M. Duran. A. Lledos. and J. Bertran. J. Am Chem. Soc,.. 1992. 114. 1922. 80 N. Bampos L. D. Field. and T. W. Harnbley Polyhedron. 1992. 11 1213. 81 D. J. Evans R. A. Henderson. A. Hills. D. L. Hughes and K. E. Ogilvie. J. Chern.SOC,.. Dulfon 7’run.s..1992 125Y. 82 L.D. Field A. V. Goerge F. Laschi. E. Y. Malouf. and P. Zanello J. Oryunorner. Chern. 1992,435 347. H\ A. J. Blake. A. J. Atkins R.O. Gould and M. Schroder Z.Krisrulloyr.. 1992. 199 287. x4 J. Lewis M. S. Khan A. K. Kakkar. P. R. Raithby. K. Fuhrmann. and R. H. Friend. J. Oryunomef. Chmi. 1992,433 135. Fe Co and Ni The non-classical hydride [FeH(H,)(pp,)] is8’ rigid in solution at low tem- + peratures with the hydride and dihydrogen ligands cis. The related cation [FeH(pp,) (N,)] + reacts with 4-pentynoic acid to give the octahedral pentynoate + [Fe(pp,)(O,C(CH,),C-CH}] in which the carboxylate acts as a chelate.8h Comparison of the analogous iron and ruthenium compounds indicates that the barrier to rotation of the dihydrogen ligand is higher in the former indicating rather surprisingly that Fe is a better back-donor than RU.~’ An extension of earlier synthetic work on reactions between metal powders and halophosphoranes has led to the synthesis of tbp [CoI,(PMe,),] from cobalt and Me,PI,.The corresponding reaction using Bu,PI gives an unusual metal phosphane complex88 (7). (Reproduced with permission from Angew. Chem. In?. Ed. Engl. 1992 31 919) The solid cobalt(r) dinitrogen complex of the tripodal ligand pp3 [Co(pp3)(N2)] [BPh,] is transformed by gaseous H into a white dihydride (the addition can be reversed under a dinitrogen atmosphere) which has a classical dihydride structure. In contrast if the reaction is carried out with the hexafluorophosphate salt of the N complex the resulting red dihydrogen complex has a non-classical structure (Scheme 1).The white tetraphenylborate salt dissolves in various solvents to give red solutions containing the q2-complex; on adding ethanol the white classical dihydride precipi- tates. Similar ethanol precipitation with solutions of the hexafluorophosphate gives the x5 C. Bianchini M. Peruzzini. A. Pola. A. Vacca. and F. Zanobini. Gnzz. Chirn. Irul.. 1991. 121. 543. Hh K. Linn D. Masi C. Mealli C. Bianchini and M. Peruuini Acru Cry.sta/loyr..Sucr. C. 1992 48. 2220. J. Eckert. A. Albinati R. P. White C. Bianchini and M. Peruzzmi Inory. Chmm. 1992 31. 4241. HX C. A. McAuliffe S. M. Godfrey A.G. Mackie. and R. G. Pritchard. Anyuw. Churn. Inr. Ed. Engl. 1992.31. 919. 178 S.A.Cotton q2-dihydride. This is therefore an example of a solid-state/solution tautomerization as well as a counter-ion influenced isomeri~ation.~’ Scheme 1 (Reproduced with permission from J. Am. Chem. Soc. 1992 114 5906) Several new nickel(0) complexes of bulky diphosphines have been reported.9o [NiBr,(PEtPh,),] has pseudotetrahedral coordination” whilst [Ni(N,),( PEt ,),I has a trans-planar geometry;’ charge-transfer photolysis of the latter gives dimeric [(Ni(N,),(PEt,)),]. Several mono- bi- and tri-nuclear Ni(PMePh,) fluoroalkyl complexes have been reported.93 Square planar NiCl and NiBr complexes of 3,4-dimethyl-3’,4’-bis(diphenylphosphino)tetrathiafulvalene have been synthesized and structurally ~haracterized.’~The results of force-constant calculations for [Ni(PX,),] (X = F C1 Br Me) have been ~ornpared.’~ Elemental S reacts with [NiX,(PPh,),] (X =halide NO, NCS) to afford NIX and Ph,PS whilst the corresponding reaction with [NiX(S,CNR,)(PPh,),] gives NIX and [Ni(S,CNR,),] by disprop~rtionation.’~ The new ylid complex [Ni(CH,PPh,CH,PPh,),]Br fea-tures square-planar coordination of nickel.97 .The influence of coligands on sulfur dioxide binding in Ni(PR3),(S02) complexes has been investigated by MO calcula- tion~;~~ small phosphines which are strong donors are expected to favour the q1 pyramidal mode of bonding.Various nickel(o) diphosphine complexes bind CO .99 89 C. Bianchini C. Mealli M. Peruzzini and F. Zanobini. J. Am. Chem. Soc.. 1992 114 5905. 90 P. Mastrorilli G.Moro C.F. Nobile and M. Latronico Inorq. Chim. Actu 1992 192 183. 9’ J.0. Malm V. Alfredsson G. Svensson and J. Albertsson Actu Crystallogr. Sect. C. 1992 48 406. 92 A. Becalska R. J. Batchelor F. W. B. Einstein R. H. Hill and B. J. Palmer. Inorg. Chrm. 1992 31 31 18. 93 R. McDonald K. C. Sturge A. D. Hunter and L. Shilliday Orgunometallics. 1992 11 893. 94 M. Fourmigue and P. Batail Bull. Soc. Chim. Fr. 1992. 129. 29. 9s H.G. M. Edwards and V. Fawcett. Inorg. Chim. Acra . 1992 197. 89. 96 J. Darkwa W. A. A. Ddamba. and L. M. Koczon. Bull. Chem. Sots. Erhiop.. 1991.5.73 (Chem. Ahsrr. 1992 116 222 285). 97 J. K. Gong. T. B. Peters P. E. Fanwick and C. P. Kubiak Orgunornr~rullics.1992. 11. 1392. J. Reinhold M. Schuler T. Hoffmann and E. Wenschuh Inorq.Chrm. 1992 31 559. O9 P. Mastrorelli G. Moro C.F. Nobile and M. Latronico Inorq. Chim. Actu 1992. 192 189. Fe Co and Ni 179 Some five-coordinate bis(triarsine) complexes of nickel show 'O0 an extensive nickel- centred redox chemistry with all oxidation states from 0 to +4 observed by cyclic voltammetry. 4 Complexes with S and Se Donors The bulky thiol2,4,6-triphenylthiophenol(HSTriph) has been synthesized; its reaction with [Fe(N(SiMe,),),] involves reduction to the iron(I1) compound [Fe(STriph),] a dimer (8) like the analogous silylamide with three-coordinate iron. O' R I S RS-Fe' 'Fe-SR 'S' I R Several investigations have concerned simple complexes of monomeric mercapto ligands. A general synthesis has been reported for stable [Fe"'(SR),]- models for oxidized rubredoxin with crystallographically characterized examples for R = Me Et and Ph.'" The structure of [NMe,],[Fe(SePh),] has been determined;" the Fe-Se bond is reported to be more ionic than that between Fe and S.Several iron(i1) thiolates are reversible CO carrier~.''~ Syntheses have been reported for [Fe,(SMe),(NO),] a known tumorigenic promoter and related systems.' OS Electronic spectra and crystal-field calculations have been carried out for [Ni- (SR),I2- and some solvolysis has been shown to occur;'06 mass spectra have been reported for several Ni and Ni thiolates along with the crystal structure of [Ni6(SPr)l,].'07 Use of the bulky thiolate S-2,4,6-Pr\C6H (SR) gives a binuclear species [Ni,(SR),] which is based on face-sharing bitetrahedra with three bridging thiolates."' Mixed-valence nickel thiolates [Ni,(SPr),X] (X = Br,I) have chain structures (related to those of [Ni,(SR),]) with individual [NI,(SR),X]' molecules joined by halogen bridges.The halogen bridges are symmetrical in the iodide but not in the bromide.'" Single-crystal ESR electronic spectra and magnetic susceptibility data have been reported' lo for [PPh,],[Co(SPh),:] whilst [Co,(SPr'),] -is the first complex to have face-sharing MS tetrahedra.' '' 100 J. Downard L. R. Hanton. and R. L. Paul. J. Chem. Soc. Chem. Commun. 1992 235. I"' K.-Ruhlandt-Senge and P. P. Power Bull. Soc. Chim. Fr. 1992 129 594. L. E. Maelia M. Millar and S.A. Koch. Inorq. Chem. 1992 31 4594. N. Ueyama H.Oku W. Y. Sun. A. Nakiimura. and K. Fukuyama Phosph.. Sulph. Silicon Relar. Elrm.. 1992 67 151. '04 A. Szakacs J. Kresz L. Marko Z. Nagy-Magos and J. Takacs Inorg. Chim. Acto 1992 198-200 401. A. R. Butler C. Glidewell and S. M. Glidewell J. Chem. Soc. Chem. Commun. 1992 141 Polyhedron 1992 11. 591. 'Oh T. Yamamura and H. Arai Bull. Chem. Soc. Jpn. 1992 65 1799. 107 H. Feld A. Leute. D. Rading A. Benninghoven. G. Henkel T. Krueger. and B. Krebs,Z. Narurforsch. Teil B 1992 47 929. ion A. Silver and M. Millrear. J. Chem. Soc. Chem. Commun. 1992. 948. 10') T. Kruger B. Krebs and G. Henkel. Angew. Chrm. Int. Ed. Engl.. 1992. 31 54. K. Fukui N. Kojima H. Ohya-Nishiguchi and N. Hirota. Inorg. Chrm.. 1992 31. 1338. 180 S. A. Cotton The reaction of NiCl, PPh, and Na,(edt) (edt = ethane-1,2-dithiolate) in meth- anol causes cleavage of a C-S bond and the isolation of square-planar [Ni(PPh,),{ S(CH2)2S(CH,),S)].1 ' The octahedral anion [Ni(thioxanthate),] is ~ oxidized electrochemically to the Ni"' analogue; it does however decompose at room temperature to the dimer [Ni2(SEt),(CS3),l2- which has thiolato bridges and one CS group chelated to each nickel.' ' Among dithiocarbamates [Fe(S,CN(CH,CH,OH),),] and solvates have been reinvestigated' l4 and previous studies re-evaluated.Tris(dially1dit hiocarbamato)co bal t is isomorphous with the iron analogue with trigonally distorted octahedral coordination. ' ' 5 Complexes of Porphyrins and other Macrocycles Porphyrins.-There has again been intense activity in this field.Of interest are 0x0-iron(1v) chlorin and porphyrin n-cation radical complexes prepared by rn-chloroperoxybenzoic acid oxidation of iron(r1r) species.' l6 ' l9 In contrast NMR evidence has been adduced to support the assignment of n-anion radical character in two-electron reduced iron(1tr) meso(P)-substituted porphyrins. ' 2o Resonance Raman and magnetic resonance' ,' have been used to compare iron porphyrin complexes in the oxidation states (I) through (iv); electronic and Resonance Raman spectra have been used to characterize bis(imidazo1e) model complexes of iron(protoporphyrin).' 22 Other applications of Resonance Raman spectroscopy to the study of iron porphyrins include' 23 examination of Fe-OH bond strengths in high- and low-spin bis(hydrox- ides) of co-condensation products' 24 of [Fe(tpp)] with ethene and oxygen in matrices at 25 K and of iron hydroporphyrins.' 25 A structurally characterized five-coordinate iron(Ir1) 'picket-fence' porphyrin com- plex affords on reduction a five-coordinate iron(ir ) complex with unusually large quadrupole splitting in the Mossbauer spectra.' 26 Other structures reported' 27 include those of two salts of [Fe(tpp)(EtOH),] + of an iron(oep) cation radical,' 28 and of a five-coordinate high-spin iron(rrr) oxophlorin complex.' 29 The structure of [FeLCl] (L = dioxobacteriochlorin) a model for heme d, I" G. Henkel and S. Weissgraber Angw Chrm.. Irir. Ed. Etiyl. 1992 31. 1368. R. Cao X. Lei Z. Huang M. Hong. and H. Liu J. Coord. Chrm. 1992 25.165. S.B. Choudhury and A. Chakravorty Inorg. Chun.. 1992. 31. 1055. I I4 D. L. Boyd N. V. Duffy A. Felczan E. Gelinterer. D. L. Uhrich. G.A. Katsoulos and J. B. Zimmerrnan Inory. Chim. Acta 1992 191. 39. E. Kello J. Lokaj and V. Vrabel Coll. Cxch. Chern. Cornmuti.. 1992. 57 332. IJh A. L. Balch. C. R. Corman. L. Latos-Grazynski. and M. W. Renner. J. Am. Chrm. Soc,.. 1992. 114 2230. S.Ozawa Y. Watanabe and I. Morishima Inorg. Chrm.. 1992 31. 4042. 'In H. Fujii and K. Ichikawa. Inorg. Chem.. 1992. 31 I1 10. 'I9 K. Yamaguchi. Y. Watanabe and I. Morishirna Inory. Chrm.. 1992 31. 156. I2O K. Yamaguchi and I. Morishima. Inorg. Chrm.. 1992 31. 3216. K. R. Rodgers. R.A. Reed. Y.O. Su and T.G. Spiro Inorg. Chrm. 1992. 31. 2688. 122 A. Desbois and M.Lutz Eur. Biophys. J.. 1992. 20 321. K. H. Rogers R. A. Reed T.G. Spiro. and Y. 0.Su Nrw J. C'hrm.. 1992. 16 533. A. Weselucha-Birczynska I. R. Paeng A. A. Shabana. and K. Nakamoto Nrw J. Chrm.. 1992. 16. 563. L. A. Anderson M. My1rajan.T. M. Loehr E. P. Sullivan. and S. H. Straws Nw J. Chrni.,1992,16,569. E. L. Bominaar X.-D. Ding A. Gimelseed. E. Rill. H. Winkler A. X. Trautwein H. Nasri J. Fischer. and R. Weiss Itiory. Chrm.. 1992 31 1845. 12' W. R. Scheidt D. K. Geiger. Y. J. Lee. P. Gans and J. C. Marchon. Inory. Chrm.. 1992 31 2660. IZR W. R. Scheidt H. Song. K. J. Hailer M. K. Safo. R. D. Orosz. c'.A. Reed. P.G. Debrunnerand. and C. E. Schulz. Inorgq. Chrm.. 1992 31. 939. 12V A. L.Ralch. L. Latos-Grazynski. B. c'. Noll. M. M. Olrnstead. and E.P. Zovinka /nor$/.Chrm. 1992.31 2248. Fe Co and Ni shows'30 significantly longer Fe-N bonds to the saturated pyrroline rings (2.1 1 A) compared with those to the unsaturated pyrrole rings (2.04A); binuclear [(Fe(tpp)},O] has been suggested as a model for cytochrome P-450 mono-oxygenase.' 31 [(Fe(oep)},O] can be protonated to give a p-hydroxo complex ion [(Fe(oep)},OH]+ whose crystal structure (9) shows a large Fe-0-Fe angle (146.2.) owing to ring-ring interactions.' 3' (Reproduced with permission from J. Am. Chern. Soc. 1992 114 4420) A modified picket fence iron(iir) porphyrin has been suggested as a model for haemoglobin mutants.' 33 Reaction of the picket-fence species [Fe(NO,),(TpivPP)] -( HzTpivPP = r,r,r,~-mt.so-tetrakis-o-pivalamidophenyl)porphyrin) with mercaptans gives iron(t1) NO complexes but on reaction with KSR anionic iron(ir1) complexes [Fe(NO,)(SR)(TpivPP)]-are obtained; structures are reported for both types.' 34 Several low-spin bis-ligated (porphinato)iron(tir ) complexes of the type [Fe( tmp)L,] + (tmp = tetramesitylporphinato; L = 2-MeHim substituted pyridine) have been syn- thesized.Structures of several examples have been determined' 35;the axial ligands are perpendicularly aligned leading to the 'large y max' type of ESR spectra characteristic of cytochromes b. The effect of substitutent size on free rotation of the axial bases of cytochrome b models has been studied.'36 and 'H COSY has been used to determine ' "I K. M. Barkigia. C. K. Chang. J. Fager. and M.W.Renner. J. Am. Chrni. Soc... 1992 114. 1701. I.'' C. Guo. S. Zhu. and M. Gui. HMU.YUK Xuehuo. 1992. 50. 129 (Chrm. Ahsrr.. 116. 206669). 13' W. R. Scheidt. B. Cheng. M. K. Safo. F. Cukiernik. J.-C. Marchon. and P.G. Debrunner. J. Am. Chmi. Soc.. 1992. 114. 4420 H. Imai S. Nakagawa. and E. Kyuno. Inory. C'hini. Ac,ru 1992. 193. 105. H. Nasri. K. J. Haller. Y. Wang. B. H. ltuynh. and W. R. Scheidt. fnory. Chrni. 1992. 31. 3459. M. K. Safo. Ci.P. Gupta. C. T. Watson. U. Simonis. F. A. Walker. and W. R. Scheidt. J. .4m. Cliem. SOC,.. ' 1492. 114. 7066. F A. Walker. L. Simonis. H. Zhang. J. M. Walker. T. McDonald Ruscitti. C. Kipp. M. S.A. Arnputch. B.V. Castilio. S. H. Cody. D. L. Wilson. R. E. Graul. G.J. Yong. K. Tobin. J.T. West. and R.A. 182 S.A. Cotton spin densities at the pyrrole fi-positions of unsubstituted low-spin iron(r1r) tpp complexes.' EXAFS studies on iron(I1) and (111) 'basket-handle' porphyrins include' 38 the assignment of an Fe"(0,) rather than an Fe"'(0;) formulation to a dioxygen adduct; '7ONMR and FTIR studies of oxygenated 'hybrid' haemoprotein models with axial hindered bases indicate considerable polarizability of the Fe-0 moiety; there is however no hydrogen bonding between the dioxygen and the NH groups of the picket fence in contrast to the results with unhindered bases.' 39 Syntheses have been reported' 40 for several octaethyltetraazaporphyrin complexes of iron; the ligand is a stronger a-donor and n-acceptor than porphyrins and therefore stabilizes the unusual 'intermediate' spin state of 3/2 for iron(r1r) in FeLCl.Pyr~lysis'~' of [Fe(tpp)Cl] has been studied by FTIR and Mossbauer spectroscopy; Fe(tpp) complexes have been investigated as surface-polymer coupling reagents and as corrosion inhibitors. 142 Iodine oxidation of (tetrabenzoporphyrinato)cobalt(Ir) Co(tbp) affords Co(tbp)I a macrocycle-oxidized molecular conductor. '43 One-electron reduction of methyl- cobalamin adds an electron to an antibonding orbital considerably weakening the Co-C bond resulting in a > 1015 enhancement of bond hom~lysis.'~~ The structure of a dicobalt cofacial porphyrin 145 and the characterization of a p-superoxo complex have been reported whilst the ground states of [Co(tpp)] and [Co(oep)] cation radicals have been probed by ESR.'46 A simple synthesis of aquacobalamin has been de~cribed,'~~ as has a new B, model system using a ligand with a pendant pyridyl group.14' The structures of several nickel(i1) b-halogenated pyrrole porphyrins have been determined,149 as well as a nickel ~hlorin,'~' whilst the first chlorophin has been obtained from oxidative ring-opening of an (octadehydrocorrinato)nickel(II)salt.' ' The nickel(1) octaethylisobacteriochlorin anion is being investigated as an F 430 m0de1.l~~ Other Macrocyc1es.-This area is reviewed elsewhere in this volume; a selection of Barichivich New J.Chem.1992 16 609. 13' Q. Lin U. Simonis A. R. Tipton C. J. Norvell. and F.A. Walker Inorg. Chem. 1992 31 4216. 13' C. Cartier M. Momenteau E. Dartyge. A. Fontaine G.Tourillon. A. Michalowicz and M. Verdaguer J. Chem. SOC.,Dalton Trans. 1992 609. 139 I. P. Gerpothanassis B. Loock and M. Momenteau J. Chem. SOC.,Chem. Commun. 1992. 598. I4O J. P. Fitzgerald B.S. Hafferty A. L. Rheingold L. May and G.A. Brewer Inorg. Chem. 1992,31 2006. (a) T. Sheng B. Rebenstorf A. Widoloev and R. Larsson J.Chem.Soc. Faraday Trans.. 1992,88,477,;(h) J. Blomquist H. Laang R. Larsson and A. Wideloev J. Chem. SOC.,Faraday Trans. 1992 88 2007. 14' B. Meyer-Roscher T. Siemens and H. Brockmann Ado. Muter. 1992 4 496. 143 K. Liou T. P. Newcomb M. D. Heagy J. A. Thompson W. B. Heuer R. L. Musselman C. S. Jacobsen B. M. Hoffmann and J. A. Ibers Inorg. Chem. 1992 31 4517. 144 B. D. Martin and R.G. Finke J. Am. Chem. SOC.. 1992 114 585.145 J. P. Collman J. E. Hutchison M. A. Lopez,A. Tabard R. Guilard W. K. Seok J. A. Ibers and M. L'Her J. Am. Chem. SOC. 1992 114 9869. 146 M. Satoh Y. Ohba S. Yamaguchi. and M. Iwaizumi Inorg. Chem. 1992 31 298. 14' R. Bieganowski and G. Klar J. Chem. Res. (S) 1992 116. I48 A. Gerli M. Sabat and L.G. Marzilli. J. Am. Chem. Soc. 1992 114 671 I. D. Mandon P. Ochenbein J. Fischer R.Weiss. K. Jayaraj R. N. Austin A. Gold P.S. White.0. Brigaud P. Battioni and D. Mansuy Inorg. Chem. 1992. 31 2044. 150 K. M. Barkigia M. A. Thompson J. Fajer R. K. Pandey K. M. Smith and M.G. H. Vicente New J. Chem. 1992 16 599. 15' C. K. Chang W. Wu. S. Chern and S. Peng Angew. Chem. Inf. Edn. EnqI. 1992. 31 70. 15' G. K. Lahiri L,. J. Schussel and A. M. Stoltzenberg Itiorg.Chem. 1992 31 4991 Fe Co and Ni 183 papers is discussed here where the interest lies principally in the metal centre. A macrocyclic tetraanionic ligand has been used to stabilize iron(Iv) as a six-coordinate bis(buty1isocyanide) adduct (lo).'53 The five-coordinate(SP) iron(1rr) complex of a tetraimidazole ligand [FeLCl] loses the chloride in methanol solution to become a six-coordinate bis(Me0H) solvate whose properties model the lipoxygenase binding site.' 54 Non-octahedral cobalt(II1) complexes are still relatively rare as are paramagnetic cobalt(u1) compounds; several five-coordinate tropocoronands (1 1) with both square pyramidal and the more unusual trigonal bipyramidal geometries have been syn- thesized with the larger macrocycle ring favouring the latter geometry.' 55 Complexation of CoCI with the pentadentate crown ether 15-crown-5 has led to the isolation' 56*157 of several complexes which are generally pentagonal bipyramidal + [Co(15-crown-5)L2l2 (L = MeCN H,O).Polymer-supported cobalt(i1) complexes of tetraazamacrocycles form dioxygen adducts with considerably greater lifetimes than the same complexes in solution.' 58 The effect of ring size upon ligand field strength and redox potential has been studied for cobalt(m) complexes of some N macrocycles.' 59 The crystal structure and electron density distribution are reportedt6' for trigonally compressed meso-[Co(hexaen)]Cl at 106K (hexaen = 1,4,7,10,13,16-hexaazacyc-looctadecane). The effects of the donor atoms and their position and spacing and of the ring size have been examined for a number of cobalt and nickel(I1) complexes of mixed-donor macrocycles.' Nickel(]) and (III) complexes continue to attract interest. The N donor hexaclen (1,4,7,10,13,16-hexaazacyclooctadecane) forms'62 stable [Ni(hexaclen)][AsF,] on reduction of the Ni" analogue. The structure of the tetragonal nickel(II1) complex [Ni([13]aneN4)Br2]Br ([13]aneN4 = 1,4,7,10-tetraazacyclotridecane) has been de- terrnined.l6 Oxidation of [Ni((9)aneS,)J2 + affords the isolable Ni"'analogue which has significantly shorter Ni-S distances than the Ni" c~mpound.'"~ Complexes of cyclam-type ligands continue to be popular. Kinetic studies show'65 that the formation of such complexes consists of a fast second-order reaction [first order in both nickel(1I) and ligand] followed by a slower first-order rearrangement of the intermedi- ate.Studies of nickel(I1) complexes of sterically congested substituted cyclams indicate the substituents affect the magnetic behaviour with less congested complexes more Is3 T. J. Collins B. G. Fox,Z.G. Hu K. L. Kostka,E. Munck,C. E. F. Rickard,and L.J. Wright,J. Am. Chem. Soc.. 1992 114 8725. IS4 E. Mulliez G. Guillot-Edelheit P. Leduc. J. C.Ch0ttard.C. Bois A. Bousseksou. and W. Nitschke. New 1. Chem. 1992 16 435. lS5 B.S. Jaynes. T. Ren S. Liu. and S.J. Lippard. J. Am. Chem. Soc,.. 1992. 114. 9670. 156 0.K. Kireeva B. M. Bulychev N. R. Streltsova V. K. Balsky and A. G. Duniun. Polyhedron 1992 14 1801. IS7 B. M. Bulychev 0.K.Kireeva. V. K. Bzlsky and N. R. Streltsova Polyhedron 1992. 11. 1809. J. H. Cameron and S. Graham J. Cheni. Soc. Dalton Trans.. 1992 385. Is9 M. Tsuchimoto and J. Fujita Bull. Chem. Soc. Jpn. 1992 65 191. I ti0 M. Morooka S. Ohba and K. Toriumi. Acta Crystallogr.. Sect. 8,1992 48 459. Ih' K. R. Adam M. Antolovich D. S. Balduin L. G. Brigden P.A. Duckworth. L. F. Lindoy A. Bashall M. McPartlin and P. A. Tasker J. Chem. Soc. Dalton Trans.. 1992 1869. lb2 G. Gencheva M. Miteva E. Zhecheva and P. R. Bonchev 7eor. Eksp. Khim 1991.27.339 (Chrm.Ahstr.. 116 50 267). H. Miyamae K. Yamauchi and M. Yamashita. J. Chem. Soc. Dalton Trans. 1992 2921. lh4A. J. Blake. R. 0.Gould M. A. Halcrow. A. J. Holder T. I. Hyde and M. Schroder,J. Chem. Soc. Dalton Trans..1992 3427. 165 J. R. Roeper and H. Elias Inorg. Cheni. 1992. 31. 1202. 184 S.A. Cotton But N N But (1 1) (Reproduced with permission from J. Am. Chem. Soc. 1992 114 9670) Fe. Co urid Ni 185 likely to be high-spin.' h6 cis-[Ni(isocyclam)(H2O),]C1,~2H,O(isocyclam = 1,4,7,11-tetraazacyclotetradecane) has six-coordinate geometry with cis-water molecules more distorted than that in the corresponding cyclam complex. On heating it undergoes deaquation-anation to give c~is-[NiCl,(isocyclam)] and on further heating isomerizes irreversibly to the trans-isomer with concomitant configurational change in the ligand. In contrast ci.~-[Ni(cyc1am)(H20),]C1,~2H,0 does not isomerize on heating.lh7 Some new asymmetric tetraaza macrocyclic complexes of nickel have been preparedlh8 and their binding to synthetic polymer supports examined.The study of nickel complexes of ligands with pendant arms added to the cyclic 1,5-diazacyclooc- tane has shown that metal-ligand bonding can influence the adoption of the unfavourable chair/chair configuration of the fused metallacycle rings.' 69 6 Schiff Base and Related Complexes Trends in the UV/visible and EPR spectra and in the redox potentials of mononuclear iron(w) complexes of Schiff bases derived from salicylaldehyde have been examined resulting in a correlation between the frequency of a ligand-metal CT band and the FellI/I1 redox potentia1.17' The p-0x0 complex [(Fe(salophen)},O] forms a dmso adduct that has a square-pyramidal structure linked by a bent Fe-0-Fe bridge,' 71 whilst octahedrally coordinated iron is found in low-spin K[Fe(acacen)(CN),].2H20.Structures have also been for [Fe(acacen)X] (X = CI NO,) and [{Fe(acacen)),O]. [acacen = N,N'-ethylenebis(acetylacetonylideneiminate)]. Another binuclear com-plex features a terephthalate bridge.' 73 Electrochemical oxidation of the oxygen carrier [Co(salen)] has been in a range of solvents. Solid-state 15NNMR studies on NO adducts ofcobalt N-substituted salicylideneiminate complexes suggest that the shift tensor may be used as a criterion of bond angle; the structure of the bent [Co(NO)(esal),](Co-N-0 129' ) (esal = o-OC,H,CH=NEt) was determined.' 7s In the field of reduced Schiff base complexes acetone solutions of the nickel tetrahydrosalen complex (12a) add 0 at low temperatures changing in colour from cherry-red to yellow-orange with dehydrogenation only as far as a dihydrosalen complex (12b); the reaction has been shown in one case to be first order in both 0 and the nickel complex.[No such dehydrogenation reaction is observed with correspond- ing Felrr and Cu" complexes]. The reaction is inhibited by adduct formation (e.y. with 166 K. Kaobiro. A. Nakyama. T. Hiro. and Y. Tobe. Inory. Chem.. 1992. 31 676. 1 h7 Y. Satake Y. Ihara H. Senda. M. Suruki. and A. Uehara. Inory. Chem.. 1992. 31. 3248. 1 hH J. H. Cameron. H. B. Harvey. and I. Sourar. Inory. Chim. ktu. 1992. 192,253:J. Chrm. Soc.. Dulfori 7i.un.s.. 1992. 597. lhy M. Y. Darensbourg. I. Font. D. K. Mills.M. Pala. and J. H. Reibenspies. Itwry. Ch~m..1992. 31. 4965. I" K. Ramesh and R. Mukherjee. J. Chem. Soc.. Dultori Truns.. 1992 83. 1'1 F. M. Ashmawy A. R. Ujaimi C.A. Mc4ulitTe. R. V. Parish. and R.G. Pritchard. Inory. Chirn. .4ctu. 1991. 187. 155. I'' X. Wang W.T. Pennington. D. L. Anhers. and J.C. Fanning. Polyhrdron 1992. 11. 2253. M. Dusek. V. Petricek. J. Kamenicek. and Z. Sindelar. Actu Cr>stulloyr.. Sec,r. C. 1992. 48. 1579. E. Eichhorn A. Rieker and B. Spciser. Anyc9c.. Chem.. fnr Ed. Enyl.. 1992. 31. 1214. C.J. Groombridge. L. F. Larkworthy. A. Marecaux. D. C. Povey G. W. Smith. and J. Mason. J. Chum. Soc.. Dulton Truns.. 1992. 3125. 186 S.A. Cotton py); nickel complexes of either the corresponding salen or dihydrosalen ligands do not form such adducts.' 76 Me Schiff base complexes of Ni" are of course noted for their interesting magnetic properties.It is generally assumed that diamagnetic tetracoordinate complexes are square planar and paramagnetic complexes are tetrahedral; equilibria between the two are often observed in solution depending upon solvent and temperature. Some complexes with NiN,S2 chromophores exhibit similar behaviour. The characteriz- ation of a square-planar paramagnetic complex (13) of a related ligand but with N202 Pi Pi coordination of nickel rather shatters this comfortable illusion.' 78 Nickel complexes of unsymmetrical quadridentate Schiff bases with a pendant N-acetyl or trifluoroacetyl substituent have been synthesized; the crystal structure of one of the latter shows'79 that a 'non-bonding' Ni-F interaction may be responsible for inhibited enantiomer interconversion.Crystal structures have been reported for two nickel complexes.'8o [Fe(acac),(NO,)] has been synthesized from [Fe(acac),] and used to make the binuclear heterometallic [Cu(saIen)Fe(acac) (NO,)]. "'A. Bottcher H. Elias L. Muller and H. Paulus. Anyew'. Chem. Int. Ed. Engl. 1992 31 623. D. Laroque I. Morgenstern-Badarau H. Winkler E. Bill A. X. Trautwein and M. Julve Inorg. Chim. Acta 1992 192 107. ''' T. Frommel W. Peters H. Wunderlich and W. Kuchern Angew. Chem. Inr. Ed. Engl. 1992 31. 612. 179 M. Kwiatkowski and G. Bandoli J. Chem. Soc. Dalton Trans. 1992. 379. Y. Elerman. H. Paulus I. Svoboda and H. Fuess Z. Krist..1992. 198. (a)129; (h) 132. Fe Co and Ni 7 Oxo-bridged Species and Models for Oxygen-containing Proteins There have been two reviews relevant to this area which includes such important iron-containing biological systems as haemerythrin and ferritin. One' discusses synthetic models for iron-oxygen aggregation and biomineralization the other' 82 binuclear iron centres in proteins. Dicobalt substitution of iron in haemerythrin has been carried out; EXAFS measurements indicate a dicobalt site (Co-Co 3.54 A) with histidine 1igati0n.l~~ Ah initio Hartree-Fock calculations reported'84 on the well-known binuclear ion [Fe,0CI,12-indicate the coupling between the irons to be sensitive to the Fe-0 distance but less so to the Fe-O-Fe angle; the bromide analogue [Fe20Br,12 has a ~ similar structure.lS5 Many structurally characterized iron complexes have been reported.A di-iron(I1) complex [Fe,(p,-OAc),(tpa),][BPh,l [tpa = tris(2-pyridylmethy1)aminel has been suggested as a model for the core of ribonucleotide reductase. The iron atoms are some 4.29 8 apart consonant with the very weak observed antiferromagnetic interaction. On oxidation it converts to a p-0x0 species [Fe2(p-O)(OAc)2(tpa)2][BPh,l (14)with (Reproduced with permission from J. .4m. Chem. SOC.,1992 114 7788) the advent of the p-0x0 bridge accompanied by a switch to monodentate terminal behaviour by the acetates.'' Diferrous complexes with two OH bridges [Fe,L,(OH),] [L = HB(3,5-Pri),] or alternatively with one OH and one carboxylate bridge.181 K.S. Hagen. Angew. Chem. Int. Ed. Engl. 1992. 31 1010. R.G. Wilkins Chem. SOC.Re[:.,1992 21 171. J. Zhang D. M. Kurtz M. J. Maroney md J. P. Whitehead Inorg. Chem. 1992 31 1359. I 84 J. R. Hart A. K. Rappe S. M. Gorun and T. H. Upton Inorg. Chem. 1992 31. 5254. Ins P. J. M. Evans B. W. Fitzsimmons W. G. Marshall A. J. Golder L. F. Larkworthy D. C. Povey and G. W. Smith. J. Chem. SOC.,Dalton Trans. 1992 1065. I 86 S. Menage Y. Zang M. P. Hendrich and L. Que J. Am. Chem. Soc.. 1992. 114. 7786. 188 S. A. Cotton (Reproduced with permission from Inorg. Chem.. 1992 31 3342.) [Fe,L,(OH)(O,CPh)] (15) have been characterized and suggested as haemerythrin A m0de1s.l~~ different type of bridging system in a di-iron(1r) complex (16) is provided"' by two benzoates and a water molecule in [Fe,(H,O)(O,CPh),(tmen),].Bridging by two carboxylates and a p-0x0 group has been reported this year in models for the di-iron 0x0 centres in haemerythrin and the B2 subunit of ribonucleotide (16) (Reproduced with permission from J. Am. Chrm. Soc. 1992 114 8741) "' N. Kitajima N. Tamura. M. Tanaka and Y. Moro-oka Inorg. Chem.. 1992. 31. 3342. K.S. Hagen and R. Lachicotte J. Am. Chem. Soc. 1992 114. 8741. Fe Co and IVi + reductase (RRB2). For [Fe20(bmima)2(02CR)2]2 [bmima = bis(( l-methyl- imidazole-2-y1)methyl)amine;R := Me Ph] (17) magnetic data are fitted with temperature-dependent J values and interpreted in terms of a weakening of the hydrogen bond between a solvate water molecule and the 0x0 bridge.'89 Complexes such as [Fe20(H,0)2(02CCH,Cl)2(bipy)2][N03]2 have been made by a new route from the parent iron carboxyiate ferric nitrate and bipy.''' Mixed-metal p-oxobis(acetato) dimers where one metal may be iron have been the subject of detailed magnetic study."' (Reproduced with permission from Inclrg.Chenz.. 1992 31 1126) Among spectroscopic measurements. the first detailed 2D NMR study of paramag- netic di-iron complexes both ferrous and mixed valence has been made.'92 Electron transfer in Fe"Fe"' complexes with both phenoxo and carboxylate bridges and high-spin FeN,O chromophores has been studied by NMR and ESR.'93 The first iron(i1r) complex e~hibiting'~ a nematic mesophase believed to involve an oxo- bridge is reported (1 8).A hexanuclear cluster [Fe,(p,-C)) (p2-OMe) (OMe ),( tren )2] ' has been sugges- ted'95 as a soluble model for the core of ferritin. Possibly the most interesting report of the year concerns the trapping of quite large iron hydroxide units containing hydroxo(oxo) iron clusters with 17 and 19 iron atoms. K. J. Oberhausen J. F. Richardson R. J. O'Brien. R. M. Ruchanan. J. K. McCusker R. J. Webb and D. N. Hendrickson Inorg. Chmn.. 1992 31 1123. K. L. Tdft. A. Masschelein. S. Liu. S.J. Lippard. D. Garfinkel-Shweky. and A. Bino. Inory. C'hitn. ,.lc,to. 1992 198-200. 627. R. Hotzelmann. K. Wieghatdt J. Ensling. H. Romstedt P. Gutlich E. Bill IJ. Florke. and H.-J. Haupt. J. Am. Chem. Soc.. 1992 114 9470. L.-J. Ming H.G.Jang and I-. Que Inorg. Chrm. 1992. 31 359. M. S. Mashuta R. J. Webb. J. K. McCusker. E.A. Schmitt K. J. Oberhausen. J. F. Richardson R. M. Buchanan and D. N. Hendrickson J. Atn. Chern. Soc.. 1992 114. 3815. Y. Galyametdinov. G. Ivanova. K. Griesar. A. Prosvirin. I. Ovchinnikov. and W. Haase. Adr. Marer.. 1992. 4. 739. V. S. Nair and K. S. Hagen Inory. Chrm.. 1992 31. 4048. 190 S. A. Cotton Their structures have a common core (19) confirmed by X-ray diffraction and have important implications for biomineralization processes. 96 (Reproduced with permission from Angew. Chem. Int. Ed. Engl. 1992 31 192) 8 Cluster Complexes Including Iron-Sulfur Proteins An extensive volume'97 containing 10 reviews devoted to iron-sulfur proteins has appeared.Articles discuss trinuclear cuboidal and heterometallic cubane-type clus- the replacement of S by Se,198b the EPR spectra,'98c and the structural and ter~;~~~' functional diversity198d of iron-sulfur proteins; and Fe-S clusters in enzymes. 98e An iron(I1) complex with a tetradentate peptide has been proposed199 as a model for the reduced form of rubredoxin. Iron-sulfur dimers have been synthesized as models for Rieske-type proteins; the ESR spectra of the reduced forms indicate oxygen coordination.200 S.L. Heath and A.K. Powell Angew. Chem. Int. Ed. Engl. 1992 31 191. ly7 'Adv. Inorg. Cheni.' Vol. 38. ed. R. Cammack Academic Press 1991. lY8 (a)R. H. Holm in ref. 197 p. 1; (h)J. Meyer J.-M. Moulis J. Gaillard and M. Lutz in ref. 197 p. 74; (c) W.R. Hagen in ref. 197 p. 165; (d)H. Matsubara and K. Saeki in ref. 197 p. 223; (e) R. Cammack. in ref. 197 p. 281. '9y W. Sun A. Kajiwara N. Ueyama. and A. Nakamura J. Chrm. Soc. Dulton Truns. 1992 3255. P. Beardwood and J. F. Gibson J. Chem. SOC..Dulton Trans. 1992 2457. Fe Co and Ni 191 FAB MS has been applied to four-iron clusters.201 Crystal structures reported include [AsPh,],[Fe,S,(SAd),] (SAd = l-adamantanethiolate),20zand Fe,S clus-ters where both thiolates and thiourea are the terminal ligand~.~' An oxidative conver~ion~'~ of an Fe,S core into an Fe,S centre has been reported whilst clusters [MFe,S,] (M = Mo W) that are structurally and electronically analogous to the reduced three-iron centres in ferredoxins have been ~haracterized,~' as have cubane clusters with NiFe,E (E = S Se) cores.2o6 The characterization of high nuclearity clusters [P-Na,Fe 8S30]8- and [Na,Fe20Se,,]9 -has been reported.207 Notable selenium and tellurium-containing clusters are [Fe,Te,(PEt,),][PF,] (cubane) [Fe,Se,(PEt,)][PF,] (stellated octahedron)208 and [Fe,Te,(PEt,),] (c~bane).''~ Single-crystal ESR spectra" have been obtained at 4.2 K of [Co6(p3- S),(PEt,),][BPh,] whilst CoBr, Na,S and dppm give a cluster2' with a distorted Co core [CO,(,U,-S)~{ Ph,PCH P(O)Ph,),].On the other hand [CoCl(PPh,),] reacts with excess Li,S to give [C~,(,U,-S),(,U~-S),(PP~,),B~~,,C~~~,] which has a capped prismane core. l2 A range of clusters with between 4 and 21 nickels results from the reactions of Se(SiMe,) with [NiC12L2] (L = R,P) e.g.[Ni7Se,(PPr\)6].2l3 9 Other Metalloproteins Reviews have appeared on the electronic structures of the active sites in non-haem iron enzymes,2 and of multiple weak forces in ion-binding molecules such as enterobac-tins.2'' Two families of synthetic chiral enterobactin analogues have been made one catechoylamide being the most efficient iron(II1) binder yet synthesized with a stability constant for the Fe3+ complex within three orders of magnitude of enterobactin itself;" two structures have been determined of simple iron(Ir1) complexes that relate to that of enterobactin.2' A comparison of the X-ray absorption spectra of nickel complexes with NiN,S2 chromophores,e.g. [Ni(terpy)(2,6-Me,C6H,S),I with those of a [FeNi] hydrogenase indicate the latter to have a distorted tbp nickel centre with a mixed N/O and S donor ESR spectroscopy has been used to probe the redox behaviour of '"' W.L. Lee D.A. Gage Z. H. Huang C. K. Chang M. G. Kanatzidis and J. Allison J. Am. Chem. So(,. 1992. 114 7132. '02 H. Kambayashi M. Nakamoto S. M. F'eng H. Nagao and K. Tanaka Chem. Lett. 1992. 919. '03 U. Bierbach W. Saak D. Haase and S. Pohl Z. Naturforsch. Teil B. 1991 46,1629. '04 E. K. H. Roth and J. Jordanov Jnorg. C'hem.. 1992 31 240. 'OS D. Coucouvanis S.A. Al-Ahmad A. Salifoglou V. Papaefthymiou A. Kostikas and A. Simopoulos J. Am. Chem. Soc. 1992 114 2472. '06 S. Ciurli P. K. Ross M. J. Scott. B.-B. Yu and R. H. Holm J. Am. Chem. Soc. 1992 114 5415. 207 J. F. You G.C. Papaefthymiou and R.H. Holm J. Am. Chem. Soc. 1992 114 2697. 208 F. Cecconi C. A. Ghilardi S. Midollini and A. Orlandini J. Chem. Soc.. Chem. Comrnun. 1992 910. 'OY M. L. Steigerwald T. Siegrist S. M. Stuczynski and Y. U. Kwon J. Am. Chem. Soc. 1992 114 3155. A. Bencini S. Midollini and C. Zanchini Inory. Chem. 1992 31 2132. M. Hong Z. Huang X. Lei B. Kang. F. Jiang and H. Liu Chin. J. Chem. 1992 9 425. 212 F. Jiang L. Huang X. Lei H. Liu B. Kang. Z. Huang and M. Hong Polyhedron 1992 11 361. 'I3 D. Fenske H. Krautscheid and M. Mueller Angew. Chem. Int. Ed. Engl. 1992 31 321. '14 E. 1. Solomon and Y. Zhang Ace. Chem. Rus. 1992 25 343. 215 A. Shanzer J. Libman and S. Lifson Pure Appl. Chum. 1992,64 1421. 'I6 Y.Tor. J. Libman A. Shanzer C. Felder and S. Lifson J. Am.Chem. Soc. 1992 114 6661. T. D. P. Stack T. B. Karpishin and K. N. Raymond. J. Am. Chem. Soc. 1992 114. 1512. 'I" M. M. Olmstead J. P. Whitehead C. Bagyinka M.J. Maroney and P. K. Mascharak Inorg. Chem. 1992. 31. 3612. 192 S. A. Cotton related species with both Nil and Ni"' compounds identifiable.,l Compounds with [NiN,Se,] chromophores have also been explored.220 A nickel macrocyclic complex catalyses the reduction of protons to H under electrochemical conditions.22' The electronic and NMR spectra of nickel(]])-substituted carboxypeptidase have been measured and its reactivity with D-and L-phenylalanine investigated.,,' 10 Complexes with Unusual Magnetic Properties including Spin-equilibrium Compounds Reviews in this area have covered intersystem crossing in iron(i1) complexes,223 spin-fr~stration~~~ complexes .,' in iron(1ir) complexes and electronic spin crossovers in cobalt(1r) Among iron(1r) complexes the effect of substituents on the spin state of iron(]]) tris-complexes of substituted bipyridyls has been examined.226 Magnetism of the crossover compound227 [Fe(NCS),(5,6-dmp),] (dmp = dimethylphenanthroline) has been examined including LIESST studies below 70 K.The crystal structure ofthe 'non- spin-crossover' 2,9-dmp analogue has been determined ; comparison with the parent [Fe(NCS),(phen),] suggests that steric hindrance is responsible for high-spin behaviour down to 6 K. Specific heat anomalies in spin-transition systems [Fe(NCS),(bts),] and [Fe(2-pic),]C12 [bts = 2,2'-bis(4,S-dihydro-S-methyl-l,3-thiazole; 2-pic = 2-picolylamine] have been studied by microcalorimetry and thermal conductivity.228 A structural comparison of the spin-crossover compounds [Fe(NCS),L,] (L = 2,2'-4,5-dihydrothiazine or phen) which exhibit rather different crossover behaviour has been made the former showing a gradual singlet-quintet transition the latter an abrupt transition.Whilst the overall molecular changes are broadly similar in terms of bond-shortening and a trend towards a more regular FeN octahedron the rapidity of changes in the lattice parameters differs mirroring the susceptibility changes. while there are also differences in structural anisotropy.229 The first two-step spin crossover (at 164 and 197K) to be observed in a polynuclear complex has been detected in dinuclear [(Fe(bt)(NCS) 1 ,bipym] (bt = 2,2'-bithiazoline) by magnetic susceptibility and Mossbauer rneas~rernents.~~~ Sub-picosecond AS = 2 intersystem crossing has been observed in the low-spin state of a spin-crossover compound.231 A kinetic study of the high-spin -+ low-spin relaxation in [Fe(ptz),][BF,] 'Iy N.Baidya M. M. Olmstead. and P. K. Mascharak. J. An7. Chrm. Soc.. 1992 114 9666. 220 N. Baidya B.C. Noll M. M. Olmstead. and P. K. Mascharak. It70ry. Chrm.. 1992 31. 2999. 12' L. L. Efros. H. H. Thorp. G. W. Brudvig. and K. H. Crabtree. Itzorgq. C'hem.. 1992. 31 1722. 222 I. Bertini A. Donaire. R. Monnanni. J.-M. Moratal. and J. Salgado. J. Chrm. Soc,..Dolron ?'r~itn.,1992. 1443. 223 A. Hauser. C'oord. Chcw. Rtw..1992 111. 275. 224 J. K. McCusker. E.A. Schmitt and D.N. :lendrickson. NATO AS/ Su.. Srr. E. 1991. 198. 297 (Chem. Ahsrr.. 1992. 116 226 404). lZ5 J. A. Zarembowitch. New. J. C'hmi.. I%)?, 16. 255. 22h D. Onggo and H. A. Goodwin. Ausr. J. Chern. 1991. 44. 1539. 22 7 D. C. Figg. R. H. Herber. and J. A. Potenm. Inory. Chrv77.. 1992 31 21 I I. R. Jakobi H. Romstedt. H. Spiering and P. Gutlich Anyrw. Chrm.. It7f. Ed. Enyl.. 1992. 31. 178. J.-A. Real. 9. Gallois. T. Granicr. F. Suez-Panama. and J. Zarembowitch fiiorq. Chmi.. 1992. 31. 4972. 230 J.-A. Real. H.Rolvin A. Bousseksou. A. Dworkin. 0.Kahn F. Varret. and J. Zarembowitch J. .4m. Chem. Soc. 1992. 114. 4650. "' J. K. McCusker. K. K,Walda. R. C. Dunn. J D. Simon. D. Magde. and I>. N. Hendrickson.J Am Chrm. Soc.. 1992 114. 6919. Fe Co and Ni (ptz = propyltetrazole) has shown the kinetics to deviate from first order because of cooperative effects of elastic origin.232 Iron(rrr) complexes.-The ability of the octaethyltetraazaporphyrin ligand to stabilize the S = 3/2 state for iron(i1i) has already been mentioned (p. 182). The complex [Fe(sal,trien)][BPh,] acetone (sa1,trien is a hexadentate ligand derived from salicylaldehyde and triethylenetetraamine) has been isolated in two crystalline forms; the monoclinic form is a spin-crossover system whilst twin crystals are high-~pin.,~~ The crystal structure of the monoclinic form at 290 K reveals bond lengths intermediate between those expected for pure high and low-spin systems.Another Schiff-base type complex with a pentadentate ligand (mbpN) forms a six-coordinate lutidine adduct [Fe(mbpN)(lut)][BPh4] (20)that undergoes spin-state interconversion faster than the lifetime of the 57Fe excited state.234 (Reproduced with permission from Bull. Chem. Soc. .lap. 1992 65 1825) Two studies examining equilibria between 312 and 1/2 states may be noted. One paper23 examined nitrosyl-iron complexes of a Jager-type ligand whilst the complex [Fe(bipy),{ONC(CN),j ,][ONC(CN),] has magnetic moments of 3.63 pB at 378 K and 2.56 pB at 80 K.236 Several paramagnetic cobalt(ii1) tropocoronands have already been mentioned in Section 5. The complex [C~(tripyam),][ClO,]~ (tripyam = tri-2-pyridylamine) when freshly prepared contains some low-spin isomer with the ’E ground state frozen into the solid; this reverts to the high-spin 4T form over some months.On ion-exchange 232 A. Hauser Chem. Phjs. Lett. 1992. 192 65. 2x Y. Maeda H. Oshio Y. Tanigawa T. Oniki. and Y. Takashima. Hxperfine Interucr. 1991. 68. 157. ’j4 Y. Maeda Y. Noda H. Oshio and Y. Takashima Bull. Chem. Soc. Jpn. 1992 65 1825. ’-”E. Konig G. Ritter. J. Dengler. and L. F. Larkworth). Inorcq. Cherii. 1992. 31 1196. ”’ K. N. Gerasimchuk. N. Laslo and V.V. Skopenko. Dokl. .4kud. Xuuk. Ckr. SSR. 1991. 7. I IX (Chrm. Ahstr. 1992. 116. 142 644). 194 S. A. Cotton onto laponite it is absorbed as a pink aqua complex [C~(tripyam)~(H~O),]’+ with bidentate ligands but if microwave-accelerated the orange [C~(tripyam)~]~ + species is absorbed.Iron(I1) complexes of this ligand have likewise been The first paramagnetic planar Ni” complex to be characterized has already been mentioned in Section 6 and the effect of ring substituents on nickel cyclam complexes in section 5. Some binuclear nickel(r1) complexes with thiolate bridges (21) have been synthesized and studied; these are unusual in that one nickel site has square planar N2S2coordination of low-spin Ni” and the other has a square pyramidal N3S2 donor set yielding high-spin nicke1(11).’~* C14 C13 (21) (Reproduced with permission from Bull. Chem. SOC.Jup. 1992 65 512) ’”S. P. Bond C. E. Hall C.J. McNerlin W. R. McWhinnie and D.J. Walton J. Muter. Chem. 1992,2 37. 238 M. Mikuriya M. Handa S. Shigematsu S. Funaki F.Adachi,and H. Okawa Bull. Chem.Soc.Jpn. 1992 65 512.