16 Scandium, yttrium, the lanthanides and the actinides S. A. Cotton Uppingham School, Uppingham, Rutland, UK LE15 9QE 1 Introduction The available 1998 literature has been surveyed, together with late 1997 publications. A highlight is the discovery of the first dinitrogen complex of an actinide (Section 4.2). Another is the synthesis of 231Pu, the ‘missing’ isotope of plutonium.1 Attempts continue at the synthesis of elements 113 and 114 but so far without success.2 IUPAC has published their revised recommendations for the names of the transfermium elements.3 Molecular mechanics calculations have been applied to the extraction of lanthanides with organophosphates.4 Two new volumes of the Gmelin Handbook have appeared; one deals with the optical spectra of neodymium compounds, the other with alloys of uranium with transition metals of Groups 8–10.5,6 A volume on the organometallic chemistry of the lanthanides7 contains articles on general principles of organolanthanides,8a amides,8b complexes with heteroallylic ligands,8c monomeric alkoxides8d and metallocenes in homogeneous catalysis.8e More specifically, a review of the organometallic chemistry of the lanthanides and actinides for 1995 has appeared. 9 A review of ‘self-assembled’ rings and cages in organolanthanide chemistry has been published.10 A review on the lanthanide oxides has appeared.11 Structural aspects of lanthanide dipivaloylmethanides and their Lewis base adducts have been reviewed.12 A review on lanthanide amino acid complexes has appeared.13 Ternary and quaternary uranium and thorium chalcogenides have been reviewed.14 Interest grows in gadolinium-containing MRI agents, including Gadolite which is zeolite-based, used as a suspension for examination of the stomach and intestines (see also Section 3.7).15NMR biomedical applications of lanthanide(III) chelates have been reviewed.16 Reviews have appeared covering the co-ordination chemistry of scandium published in 199417a and 199517b and the co-ordination chemistry of yttrium for 1994,17c 199518 and 1996.19 An article has been published about the role of CeO 2 doped with ZrO 2 or lanthanide oxides in automobile exhaust complexes.20 A book on relativistic e§ects in chemistry includes a chapter on lanthanide and actinide compounds. 21 Kinetics of actinide complexation reactions have been reviewed.22 A review of sandwich-type phthalocyanine and porphyrin complexes includes a considerable number of lanthanide compounds.23 A short article on the bioinorganic chemistry of the actinides in blood has appeared.24 The proceedings of the 1994 Workshop on Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 239Actinide Solution Chemistry at Tokai, Japan includes material on both lanthanides and actinides.25 2 Scandium Laser-ablated Sc atoms react with O 2 in Ar matrices forming ScO, OScO (bent, 128°) and (O 2 )ScO with small amounts of ScOSc; on annealing, ScO 3 , (ScO) 2 and Sc(O 2 ) 2 also result.26 The new telluride Sc 8 Te 3 , isostructural with Y 8 Te 3 and Ti 8 Te 3 , has chains of trans-edge-sharing octahedra condensed into corrugated sheets.27 The new ternary phosphide ScNiP has Sc–Sc bonds.28 An X-ray and EXAFS study of aqueous solutions of scandium(III) salts indicates that around seven water molecules are bound to scandium, with a Sc–Odistance of 2.18Å, further indication that, compared with its transition metal successors, scandium does not form a hexaaqua ion.29 Thermal dehydration of ScCl 3 ·6H 2 O and various chloride complexes provided evidence for tetra- and di-hydrates, further heating being accompanied by hydrolysis.30 Reaction of lanthanide oxides with NH 4 Cl is a classic route to anhydrous lanthanide chlorides; DTA study of the reaction of Sc 2 O 3 with NH 4 Cl indicates that (NH 4 ) 3 ScCl 6 , (NH 4 ) 2 ScCl 5 (H 2 O) and (NH 4 ) 3 Sc 2 Cl 9 are formed as intermediates.31 A structural study of Ba 2 ScCl 7 shows it to be Ba 2 [ScCl 6 ]Cl.32 High-pressure studies of Na 3 ScF 6 (cryolite structure) indicate little change in the octahedral co-ordination of scandium up to 27.9 kbar.33 Cubic [Rb 3 Sc 2 (AsO 4 ) 3 ] is constructed of vertex-sharing ScO 6 and AsO 4 polyhedra.34 Sc 3 Ir 5 B 2 and quaternary derivatives Sc 2 MIr 5 B 2 (M\Be, Al, Si, Ti–Cu, Ga, Ge) have been synthesised.35 The new amide [ScMN(SiHMe 2 ) 2N3 (thf)] has distorted tetrahedral co-ordination of scandium, with short Sc · · · Si contacts in the solid state; this is in contrast to the five-co-ordinate [LnMN(SiHMe 2 ) 2N3 (thf) 2 ].36 A triamidoamine complex of scandium distils on heating the corresponding ‘ate’ complex [eqn. (1)].37 A mixture of scandium triflate and sodium dodecylsulfate catalyses three-component reactions of aldehydes, amines and allyltributylstannane in aqueous solution, giving good yields of homoallylic amines.38 Scandium triflate catalyses the Streckertype reactions of aldehydes, amines and tributyltin cyanide in both aqueous and organic solution; complete recovery of the tin compounds was achieved.39 In addition to the forest green triple-decker sandwich [(g5-Bu5 2 C 2 P 3 )Sc(l-g6:g6- Bu5 3 C 3 P 3 )Sc(g5-Bu5 2 C 2 P 3 )] described two years ago, co-condensation of Sc vapour with Me 3 CC–– –P also a§ords dark purple [Sc(g5-Bu5 3 C 3 P 2 ) 2 ] 1.It is the first stable scandocene complex to be characterised as well as being the first molecular scandium( II) compound. It is EPR active and has the expected magnetic characteristics for a d1 compound (k%&& \1.70 kB ).40 Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 2403 Yttrium and the lanthanides 3.1 Binary and related compounds with non-metals The reaction of S 8 (g) with Ln` ions in a mass spectrometer a§ords a range of products, whose stoichiometry depends upon the lanthanide.41 Cerium reacts with 2- methoxyethanol at 250 °C forming ultrafine CeO 2 particles.42 Structures have been reported for the pentaphosphides MP 5 (M\Y,43a Dy,43b Ho,43b Tm,43c Lu43c).C-Type Ln 2 S 3 (Ln\Gd, Tb) have a cation-deficient Th 3 P 4 structure with eight-coordinate lanthanides.44 Ho 2 Se 3 , synthesised from HoSe 2~x and Ho using transport with AlCl 3 , has the Sc 2 S 3 structure.45 Rare earth transition metal borides such as Y 2 Co 14 B, LnCo 4 B and YCo 3 B 2 have been synthesised by Ca reduction of the rare earth oxide followed by di§usion of the lanthanide with the cobalt and boron at 1000 °C.This route is especially suitable for the borides of volatile lanthanides.46 3.2 Halides and complexes Rb 4 TmI 6 , synthesised by heating a mixture of RbI, Tm and HgI 2 , has the K 4 CdCl 6 structure with trigonal antiprismatic co-ordination of Tm.47 RbYbI 3 has a structure based on edge-sharing [YbI 6 ] octahedra.48 Gadolinium is eight-co-ordinate in BaGdCl 5 .49 Ba 2 [EuCl 7 ] is isostructural with Ba 2 [LnCl 7 ] (Ln\Gd–Lu, Y), but not with Ba 2 [ScCl 6 ]Cl, containing capped trigonal prismatic [EuCl 7 ]2~ ions.50 MCl 3 (M\Tb, Dy) react with [PPh 4 ]Cl in MeCN forming [PPh 4 ][MCl 4 (NCMe)] which contain dimeric [(MeCN)Cl 3 M(l-Cl) 2 MCl 3 (NCMe)]2~ anions.51 LaI 3 reacts withM (M\Cu, Ni) forming La 2 IM 2 , which have a new type of metal-rich layered structure. 52 3.3 Aqua-ions and salts Information from hydration studies of lanthanide- and actinide-(III) ions by laserinduced fluorescence spectroscopy has been combined with other techniques to indicate a change in hydration number from nine to eight in the Eu–Tb and Bk–Es regions of the series.53,54 EXAFS studies of aqua complexes and polyaminepolycarboxylate complexes have also been used to obtain co-ordination numbers.55 Interest continues in the anhydrous perchlorates.They exist in high- and low-temperature forms, both with nine-co-ordinate lanthanides.56 Stepwise thermal decomposition of several lan- Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 241thanide triflates has been examined, with LnF 3 as the eventual product.57 Erbium is six-co-ordinate in Er 2 (SO 4 ) 3 , seven-co-ordinate in Er(SO 4 )(HSO 4 ) and eight-coordinate in Er(HSO 4 ) 3 .58 Other sulfate salts (H 5 O 2 )Ln(SO 4 ) 2 (Ln\Ho, Er, Y) contain lanthanides in dodecahedral co-ordination; on thermal decomposition [Ln(HSO 4 )(SO 4 )] and [Ln 2 (SO 4 ) 3 ] are successively formed.59 The oxamate [Ho(oxam) 3 (H 2 O) 3 ] 4 ·2.75H 2 O contains nine-co-ordinate holmium.60 [Ca(H 2 pic)(H 2 O) 3 ] [Ce(pic) 3 ] is a 1-D polymer with alternating CeN 3 O 6 and CaNO 7 polyhedra.61 Salts of 1-hydroxyethane-1,1-diphosphonic acid have been studied across the series.62 The heavier lanthanides (Tb–Lu, Y) are seven-co-ordinate, as in the chain structure of [Tb(H 3 hedp)(H 2 hedp)]·5H 2 O whilst lighter lanthanides are eightco- ordinate in [Nd(H 3 hedp)(H 2 hedp)]·7H 2 O and [H 3 O][Eu(H 2 hedp) 2 ]·12H 2 O. 3.4 Complexes The most comprehensive survey yet of complexes LnCl 3 (thf)x (e.g. x\2, 2.5, 3, 3.5, 4) has appeared. Structures have been determined for LnCl 3 (thf) 2 (Ln\La, Ce, Pr), LnCl 3 (thf) 3.5 (Ln\Gd, Er), YbCl 3 (thf) 3 and LaCl 3 (thf)(H 2 O).Most of these belong to known structural types, but LaCl 3 (thf) 2 represents a new type, a single-stranded polymer . . . (l-Cl) 3 (thf) 2 La(l-Cl) 3 . . . with cis thf molecules and square antiprismatic eight-co-ordinate lanthanum. Far-IR spectra of the complexes have been correlated with structural type.63 An independent report of the structure of ErCl 3 (thf) 3.5 showed64 it to be the expected salt [ErCl 2 (thf) 5 ][ErCl 4 (thf) 2 ]; the structure of [EuCl 3 (thf) 4 ] has been determined again.65 Two families of lactam complexes, [Ln(L1) 8 ][CF 3 SO 3 ] 3 (Ln\La–Eu, L1\e-caprolactam) and [Ln(L1) 7 ][CF 3 SO 3 ] 3 (Ln\Gd, Tb, Dy, Yb, Lu);66a [Ln(L2) 8 ][ReO 4 ] 3 (Ln\Pr, Nd, Sm and Eu, L2\d- valerolactam) and [Ln(L2) 7 ][ReO 4 ] 3 (Ln\Tb)66b whose stoichoiometries appear to reflect the lanthanide contraction have been synthesised.The cation in [Pr(L1) 8 ]- [CF 3 SO 3 ] 3 has slightly distorted dodecahedral geometry whilst in [Eu(L1) 8 ][ReO 4 ] 3 it is square antiprismatic. [Sm(NO 3 ) 3 (L3) 3 ] (L3\N-butylcaprolactam) contains samarium in a distorted tricapped trigonal prismatic environment.67 A number of lanthanide dithionate complexes have been studied.68 Nd 2 (S 2 O 6 ) 3 ·14H 2 O has each neodymium bound to six water molecules and to three oxygens from di§erent dithionates; in Nd 2 (S 2 O 6 ) 3 (OPPh 3 ) 4 ·8H 2 O, each neodymium is eight-co-ordinate, bound to two phosphine oxides, four water molecules and two dithionates (one monodentate, one a bridging ligand).Interest in lanthanide–transition metal heterometallics continues. [Ln 2 (dmf) 10MM(CN) 4N] = (Ln\Sm, Eu, Er, Yb; M\Ni, Pd, Pt), [Sm(dmf) 5MM(CN) 4NCl] = and [Yb(dma) 4MM(CN) 4NCl] = have 1-D chain structures where cyanide-bridged diamond-shaped Ln 2 M 2 cores are linked into infinite arrays through cyanide bridges by [M(CN) 4 ]2~ groups.69 Reaction of LnCl 3 and NiCl 2 with KNCO in dmf gives two di§erent complexes, depending upon crystallisation conditions.[Ln 2 (dmf) 6 Ni(NCO) 8 ] = (Ln\Sm, Eu) form 1-D extended arrays whilst [Ln 2 (dmf) 8 Ni(NCO) 8 ] are monomers with three bridging cyanates.70 The structure of [Gd(OSMe 2 ) 8 ][Fe(CN) 6 ] is reported.71 The 1,4-dioxane complex [Nd(C 4 H 8 O 2 )(NO 3 ) 3 (H 2 O) 2 ] contains zig-zag chains with bridging dioxanes.72 Ln(NO 3 ) 3 ·xH 2 O react with [Ni(en) 2 (NO 2 ) 2 ] in methanol forming [Ni(en) 2 (NO 2 )] 2 - [Ln(NO 3 ) 4 (MeOH) 2 ]NO 3 ·MeOH (Ln\La–Lu, Y) which contain chains of nickel ions with nitro–nitrito bridges and ten-co-ordinate lanthanides.73 LnI 2 (Ln\Sm, Yb) Annu. Rep.Prog. Chem., Sect.A, 1999, 95, 239–260 242reacts with substituted pyridines in thf forming [LnI 2 (py) 4 ]; the structures of [LnI 2 (3,5-dmpy) 4 ] (Ln\Sm, Yb) and [YbI 2 (4-Bu5py) 4 ] were determined, all have trans structures.74 [SmI 2 (thf) 2 ] recrystallises from py–dme as [SmI 2 (dme) 3 ], which occurs as two isomers in the same crystal;75 one has a linear I–Sm–I linkage, the other a bent I–Sm–I linkage.In contrast [but in keeping with the lower stability of Tm(II)] [TmI 2 (dme) 3 ] reacts with hmpa forming [TmI 3 (hmpa) 4 ]; this recrystallises from pyridine (depending on conditions) as [TmI 2 (hmpa) 4 ]I·5py or [TmI(py)(hmpa) 4 ]I 2 . Syntheses have been reported76 for MeCN complexes [Ln(NCMe)n]X 3 , as have the structures of [La(NCMe) 9 ][AsF 6 ] 3 ·MeCN, [Sm(NCMe) 9 ][AsF 6 ] 3 ·3MeCN, [Pr(NCMe) 9 ]- [AlCl 4 ] 3 ·MeCN and [Yb(NCMe) 8 ][AlCl 4 ] 3 .[Ce(phen) 4 (NCMe) 2 ][ClO 4 ] 3 ·3MeCN has ten-co-ordinate cerium in a bicapped square antiprismatic geometry.77 Solvothermal synthesis of [La(en) 4 Cl] In 2 Te 4 has been reported; the cation has monocapped square antiprismatic co-ordination.78 The 11-co-ordinate [Sm(terpy)(NO 3 ) 4 ]~ ion has been characterised79 as its [H 2 terpy]2` salt.Two reports show the tetradentate tripodal ligand ntb forming two strikingly di§erent types of complex. [Ln(ntb)(NO 3 ) 3 ]·H 2 O (Ln\La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Er) contains ten-co-ordinate monomers.80 With lanthanide perchlorates, the lanthanides bind two ntb ligands in a slightly distorted example of the rare cubic co-ordination geometry in [Ln(ntb) 2 ]3` ions (Ln\Pr, Eu) in 4,4@-bipyridyl adducts. 81 The complex [La(tbpa)(H 2 O)(g2-ClO 4 )][ClO 4 ] 2 ·MeOH contains ten-coordinate lanthanum.82 [Sm(OSCR) 3 (thf) 2 ] and [Na(thf) 4 ] [Sm(S 2 CR) 4 ] (R\4-MeC 6 H 4 ) are reported to be the first lanthanide chalcogenocarboxylate complexes.83 3.5 Diketonates A solid state synthesis has been reported84 for [Pr(acac) 3 ] from anhydrous PrCl 3 and Macac (M\Li, Na).Interest increases in glyme adducts of the lanthanide b-diketonates. La 2 O 3 and Hhfac react together with tetraglyme in hexane forming [La(hfac) 3MMe(OCH 2 CH 2 ) 4 OMeN] an air stable and volatile (95 °C, 10~4mmHg) potential MOCVD precursor.85 Similar compounds [La(hfac) 3 (MeOCH 2 CH 2 OMe)H 2 O], [La(hfac) 3MMe(OCH 2 CH 2 ) 2 OMeN] and [La(hfac) 3MMe(OCH 2 CH 2 ) 3 ] have also been prepared.86 A one-pot synthesis of [Eu(hfac) 3 L] (L\terpy, diglyme) from Eu 2 O 3 and Hhfac in the presence of L has been described,87a as has a one-step route87b to Ln(diketonate) 3 Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 243(e.g. diketonate\acac, tfa, tmhd, etc.) via methyllanthanides prepared in situ from LaCl 3 and MeLi.[Y(hfac) 3 ] reacts with monoglyme and diglyme forming monomeric adducts [Y(hfac) 3 (MeOCH 2 CH 2 OMe)] which are eight- and nine-co-ordinate respectively. 88 In contrast, triglyme and tetraglyme form the ionic substances [Y(hfac) 2MMe(OCH 2 CH 2 )nOMe][Y(hfac) 4 ]. Sublimation of the compound where n\3 in the presence of ‘adventitious’ water yields the outer-sphere glyme complex [MY(hfac) 3 (OH 2 ) 2NMMe(OCH 2 CH 2 ) 3 OMeN] which has an infinite chain structure. [M(tmhd) 3 (H 2 O)] (M\Y, Gd) reacts with hmteta forming dimeric [(tmhd) 3 M(l- hmteta)M(tmhd) 3 ] in which only three of the four nitrogen atoms in the amine are bound to yttrium.89 The adducts [Eu(btfa) 3 (bipy)] and [Eu(bzac) 3 (bipy)] have been reported, as well as the structure of [Eu(btfa) 3 (bipy)]; the fluorinated compound shows a higher quantum yield in fluorescence.90 A new b-diketonate ligand, 1,3–bis(2–furyl)propane-1,3–dione, has been used to make the complex [Eu(dfp) 3 (phen)], a red emitter fabricated into a double layer electroluminescent device.91 The co-ordination geometry in [Ln(acac) 3 (phen)] (Ln\Ce, Pr) is described as slightly distorted square antiprismatic.92 [Eu(tan) 3 (bipy)] crystallises in two forms with slightly di§erent co-ordination polyhedra, one bicapped trigonal prismatic, the other square antiprismatic.93 Na[Er(pta) 4 ] contains tetragonally antiprismatic coordination of erbium.94 The co-ordination geometries in the air-stable potential CVD precursors [Ce(tmhd) 4 ] and [Ce(pmhd) 4 ] are distorted dodecahedral and square antiprismatic respectively; the former sublimes unchanged whilst the latter is involatile.95 On the other hand, [NH 4 ][Ce(etbd) 4 ], with distorted square antiprismatic co-ordination of Ce, was obtained under conditions expected to result in a Ce(IV) species.A number of binuclear tetraglyme complexes [Ce 2 (diketonate) 6MMe(OCH 2 CH 2 ) 4 OMeN] (diketonate\etbd; 1,1,1,5,5,5-hexa- fluoropentane-2,5-dionate; 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dionate) have also been made.96 EXAFS measurements on [Ln(hfac) 3 (H 2 O) 2 ] (Ln\Pr, Eu) indicate a co-ordination number of about 11, suggesting that some Ln · · ·F interactions are present.97 Lanthanide b-diketonates of fluorinated ligands form 1: 1 complexes with amino acids, enabling their extraction, transport and chiral recognition.98 Heterobimetallic compounds have been studied lately on account of their structures and magnetic properties.They are also potential MOCVD single-source precursors. The series [Ni(salen)La(hfa) 3 ] (Ln\Y, La–Yb) which have similar structures to several of the known [Cu(salen)La(hfa) 3 ] compounds sublime without decomposition in vacuo.99 3.6 Alkoxides, alkylamides, phosphides and thiolates Alcohol exchange between [Ce 2 (OPr*) 8 (Pr*OH) 2 ] and Hhfip a§ords [Ce(hfip) 4 (thf) 2 (Pr*OH)x], convertible into the stable adducts [Ce(hfip) 4 L 2 ] (L 2 \bipy; tmen; diglyme).Reaction with pmdien results in [Ce(hfip) 3 (OPr*)(pmdien)] and [Hpmdien] 2 [Ce(hfip) 6 ], the latter having octahedrally co-ordinated Ce.100 [Ce 2 (OPr*) 8 (Pr*OH) 2 ] reacts with Hthd and barium isopropoxide forming [Ba 4 Ce 2 (l6 -O)(thd) 4 (l3 -OPr*) 8 (OPr*) 2 ].101 Eu reacts with 2-methoxyethanol102 forming the hydrocarbon-soluble oligomer [Eu(OCH 2 CH 2 OMe) 2 ]n (n[10 in toluene).This reacts with 2,6-dimethylphenol or 2,6–diisopropylphenol forming the tetrametallic H 4 [MEu(l3 -g2-OCH 2 CH 2 OMe)(g2-OCH 2 CH 2 OMe)(OC 6 H 3 R 2 - Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 2442,6)N4 ] (R\Me, Pr*). These have a tetrahedron of seven-co-ordinate europium atoms, each bound to one terminal bidentate alkoxide, one bridging bidentate alkoxide, a terminal aryloxide and two bridging oxygens from other aryloxides. [Eu(OCH 2 CH 2 OMe) 2 ]n reacts with AlMe 3 forming the hexametallic [MMe 3 Al(l-g2- OCH 2 CH 2 OMe)Eu(l-g2-OCH 2 CH 2 OMe) 2 (AlMe 2 )N2 ].[LnMN(SiMe 3 ) 2N3 ] (Ln\La, Sm, Y) have been studied as highly active catalysts for the Tischenko reaction, dimerizing aldehydes to esters, e.g. converting benzaldehyde to benzyl benzoate.103 The amides [LnMN(SiHMe 2 ) 2N3 (thf) 2 ] (Ln\Y, La–Lu) are isostructural, with trigonal bipyramidal co-ordination; structures have now been determined for the La and Lu compounds, in addition to the Nd and Y analogues previously reported.36 Polynuclear lanthanide amides including [Ln 2 Br 4 (l- NHPh) 2 (thf) 5 ] (Ln\Sm, Gd) and [Ln 4 (l4 -O)(NHPh) 3 (OSiMe 2 NPh) 6 Na 5 (thf) 7 ]·thf (Ln\Gd, Yb) have been reported.104 The structure of trans- [Eu(PPh 2 ) 2 (meim) 4 ] has been determined.105 The N-substituted guanidinates [MMCyNC[N(SiMe 3 ) 2 ]- NCyN2 (l-Cl) 2 LiS 2 ] (M\Sm, Yb: S\Et 2 O, 0.5 tmen) have been synthesised and o§er a route to solvent-free alkyls and amides, of which [SmMCyNC[N(SiMe 3 ) 2 ]- NCyN2MCH(SiMe 3 ) 2N] and [YbMCyNC[N(SiMe 3 ) 2 ]NCyN2MN(SiMe 3 ) 2N] have been characterised.106 The first Ln(II) pyrazolate, [Yb(Ph 2 pz) 2 (dme) 2 ] has two chelating dimethoxyethane ligands and two g2 3,5-diphenylpyrazolates.107 [YMCH(SiMe 3 ) 2N3 ] reacts with HP(SiMe 3 ) 2 forming the dimeric [M(Me 3 Si) 2 PN2 YMl-[P(SiMe 3 ) 2 ] 2N- YMP(SiMe 3 ) 2N2 ].108 [Ln(SBu5) 3 ] (Ln\La, Ce, Pr, Nd, Eu, Yb, Y), made109 from [LnMN(SiMe 3 ) 2N3 ] and HSBu5, are intensively reactive, doubtless owing to co-ordinative unsaturation, and the adducts [(SBu5) 2 (bipy)Ln(l-SBu5) 2 Ln(bipy)(SBu5) 2 ] (Ln\Y, Yb) have been isolated.A series of thiophenolates and their selenium analogues have been synthesised110 and examined. [Ln(SPh) 3 (py) 3 ] 2 (Ln\Ho, Tm) have two thiolate bridges with sevenco- ordinate lanthanides; [Sm(SPh) 3 (py) 2 ] 4 has a linear arrangement of four seven-coordinate samariums with 3, 2 and 3 l-bridging thiolates; [Sm(SPh) 3 (thf)] 4n is a polymer. [Ln(SePh) 3 (thf) 3 ] (Ln\Tm, Ho, Er) have monomeric fac octahedral structures; [Sm(SePh) 3 (py) 3 ] 2 has two selenolate bridges with seven-co-ordinate samarium; and [Ln 3 (SePh) 9 (thf) 4 ]n (La\Pr, Nd, Sm) are polymeric with three doubly bridging selenolates.thf solutions of thiolates [Ln(SPh) 3 ] (Ln\Pr, Nd, Gd) dissolve sulfur, a§ording crystalline clusters [Ln 8 S 6 (SPh) 12 (thf) 8 ]; their structure is based on a cube of lanthanides, edge-bridged by mercaptides and face-bridged by sulfur.111 Clusters are also found in [Yb 4 Se 4 (SePh) 4 (py) 8 ] and in [Yb 6 S 6 (SPh) 6 (py) 10 ].112 A number of pyridinethiolate (2-SNC 5 H 4 ) complexes have been characterised.113 Ce(SNC 5 H 4 ) 3 reacts with [PEt 4 ][SNC 5 H 4 ] forming [PEt 4 ][Ce(SNC 5 H 4 ) 4 ], in which cerium is eight-co-ordinate; [PEt 4 ][Ln(SNC 5 H 4 ) 4 ] (Ln\Ho, Tm) were also reported.[Yb(SNC 5 H 4 ) 2 ] and [Yb(SNC 5 H 4 ) 3 ] crystallise from pyridine as seven-co-ordinate [Yb(SNC 5 H 4 ) 2 (py) 3 ] and eight-co-ordinate [Yb(SNC 5 H 4 ) 3 (py) 2 ] respectively. 3.7 Complexes of polyamine polycarboxylates, related complexes and NMR imaging agents The Eu(II) complex Na 3 [Eu(edta)]Cl·7H 2 O is in fact polymeric in the solid state with europium bound to two nitrogens and six carboxylate oxygens.114 A XAFS study of [Gd(dota)(H 2 O)]~ and [Gd(dtpa)(H 2 O)]2~ in the solid state and solution permits Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 245comparison with existing solid-state di§raction data.115 When binding to Gd3`, the tripodal ligand H 6 ttaha has one leg free, acting as a heptadentate ligand; two water molecules also co-ordinate, giving it a high relaxivity compared to many MRI agents.116 A new neutral potential MRI contrast agent, [Gd(dtpa-bmea)(H 2 O)] has very similar properties to the existing [Gd(dtpa-bma)(H 2 O)].117 Spin–lattice relaxation data for the Gd3` complex of 3,6,10-tris(carboxymethyl)- 3,6,10-triazadodecanedioic acid (see below) indicate that there is probably one water molecule co-ordinated.118 The solid state structure of [Gd(dtma)(H 2 O)]3` is a capped square antiprism.119 In solution the complex has only limited stability (logK\12.8). In the solid state, [La(pedta)(H 2 O)]·2H 2 O adopts a polymeric structure, giving ten-co-ordinate La; in solution, luminescence results for the Eu complex indicate three co-ordinated water molecules.120 The stability constants of [Ce(dota)]~ and [Yb(dota)]~ are reported as 1024.6 and 1026.4 respectively.121 Complexes [Ln(hedtra)(H 2 O)n] (Ln\most lanthanides) fall into three series; [M(hedtra)(H 2 O) 2 ]· 3H 2 O (M\Ho, Tm) have eight-co-ordinate square antiprismatic co-ordination in which the acid is co-ordinating through the hydroxo oxygen in addition to the two nitrogens and three carboxylate oxygen atoms.122 3.8 Some applications of lanthanides in organic chemistry The application of lanthanide metallocenes to the synthesis of small organic molecules has been reviewed123 as has SmI 2 as a reagent in polymer chemistry.124 Solutions of SmI 2 in tetrahydropyran reduce allylic, benzylic and alkyl halides forming stable Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 246organosamarium species.125 The e§ects of co-solvents upon the reducing power of SmI 2 in thf has been discussed.126 SmI 2 catalyses the reductive intramolecular cyclisation of a-bromo silyl ethers.127 Lanthanide triflates catalyse the highly stereoselective addition of chiral 3-(p-tolylsulfinyl)furfural with silyl ketene acetal128 whilst ytterbium triflate catalyses the addition of trimethylsilyl cyanide to many carbonyl compounds in high yield under mild conditions.129 [Sm(O 3 SCF 3 ) 2 (thf) 1.5 ] has a 1-D polymeric structure in the solid state; [Sm(O 3 SCF 3 ) 2 (NCMe) 1.5 ] and [Sm(O 3 SCF 3 ) 2 (NCBu5) 1.5 ] have similarly been prepared, the former being an excellent reagent for pinacol coupling reactions.130 Cerium(IV) ammonium nitrate and cerium(IV) sulfate act as oxidants in coupling reactions producing a-linked hexadecithiophene and tetracosithiophene derivatives.131 3.9 Poly(pyrazolyl)borates and related compounds [SmCl(HBpz 3 )L] (L\Hpz, N-methylpyrazol-1-yl) react with sodium b-diketonates forming [Sm(HBpz 3 )(acac)], [Sm(HBpz 3 )(tfac)] and [Sm(HBpz 3 )(hfac)].[SmCl(HBpz 3 )(Hpz)] reacts with K[H 2 Bpz 2 ] forming the bicapped trigonal prismatic [SmCl(HBpz 3 )(H 2 Bpz 2 )] whilst [SmCl(HBpz 3 )(Hpz)] is square-antiprismatic.132 3.10 Complexes of crown ethers and related ligands Lanthanides are nine-co-ordinate in [LnL 3 ][ClO 4 ] 3 ·3H 2 O (Ln\Nd, Ho; L\diethylene glycol).133 Complexes of lanthanide triflates with polyethene glycol MHO(CH 2 CH 2 O)nH; n\2,3,4N and polyethene glycol dimethyl ether MMeO(CH 2 CH 2 O)nMe; n\2,3,4N are e§ective Lewis acid catalysts for the Diels–Alder reaction and for the allylation of aldehydes with allyltributyltin.Structures have been reported for [La(OTf) 3 (thf)MHO(CH 2 CH 2 O) 4 HN],134a [Dy(OTf) 2MMeO(CH 2 CH 2 O) 4 MeN(H 2 O) 2 ][OTf]134a and [Eu(OTf) 3MMeO- (CHPhCHPhCH 2 (OCH 2 CH 2 ) 2 OCHPhCHPhOMeN].134b 2,2@-Bipyridyl complexes of Eu3` and Tb3` bound to polyethene glycol are strongly luminescent.135 The out-of-cavity hydroxide-bridged cationic complex [MY(OH)(benzo-15-crown- 5)(NCMe)N2 ]I 4 results from the reaction of YI 3 with the crown ether in MeCN.136 Yttrium is not bound to the crown ether in [Y(NO 3 ) 3 (H 2 O) 3 ]·Me 2 -16-crown- 5·H 2 O137 nor in [Yb(H 2 O) 8 ]Cl 3 ·15-crown-5.138 New oxonium complexes [H 9 O 4 ]- [LaCl 2 (H 2 O)(18-crown-6)]Cl 2 and [H 3 O][EuCl(H 2 O) 2 (18-crown-6)]Cl 2 have been reported.138 3.11 Complexes of macrocyclic ligands, particularly calixarenes, porphyrins and phthalocyanines p-Butylcalix[5]arene (H 5 L) forms dimeric lanthanide complexes [Ln 2 (H 2 L) 2 (dmso) 2 ] (Ln\Eu, Gd, Tb).139 The larger p-butylcalix[8]arene and p-nitrocalix[8]arene(H 8 L) rings each incorporate two lanthanides, forming [Ln 2 (H 2 L)(dmf) 5 ] (Ln\Eu, Lu).The structures of europium complexes of both p-butylcalix[5]arene and p-nitrocalix[8]- arene contain eight-co-ordinate europium.140 Calix[4]arenes substituted by acetamidophosphine oxide groups at the rim show selectivity, not just to trivalent ions but Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 247also to light lanthanides and actinides.141 Calix[4]arene podands and barrelands incorporating bipy groups form lanthanide complexes; their Eu3` and Tb3` complexes have high metal luminescence quantum yields.142 New routes have been described to unsymmetrical [Ln(pc)(pc@)] and [Ln(pc)(por)] systems.143 Heteroleptic triple deckers [Eu 2 (pc) 2 (por)] and [Eu 2 (pc)(por) 2 ] have also been synthesised.144 Syntheses of lipophilic lanthanide(III) bis(tetrapyridylporphyrinates) and their conversion into water-soluble N-methylated systems are reported.145 Gadolinium is eightco- ordinate in [Gd(tpp)(acac)(H 2 O) 2 ]·6H 2 O·3tcb.146 Remarkably, porphyrinogen complexes of neodymium and praseodymium fixN 2 and reduce it to theN 2 2~ anion in dimeric l-N 2 complexes.147 Two texaphyrin complexes are undergoing clinical trials; a gadolinium compound 2 is an e§ective radiation sensitiser for tumour cells, whilst the corresponding lutetium compound that absorbs light in the far-red end of the visible spectrum is in Phase II trials for photodynamic therapy for brain tumours and breast cancer.148 Europium complexes with a pendant-arm cyclen-based ligand in two stages, first by forming an external complex prior to encapsulation.149 3.12 Some spectroscopic studies A review of developments in luminescent materials for lighting and displays features rare earths prominently.150 Other reviews cover applications of lanthanide luminescence spectroscopy to solution studies151 and the luminescent properties of divalent europium complexes of crown ethers and cryptands.152 Another article details the synthesis and luminescence of lanthanide ions in nanoscale insulating hosts.153 Timeresolved chiroptical luminescence studies of mixtures of the enantiomers of [Eu(dipic) 2 ]3~ show solvent dependence in the rate of interconversion between the enantiomers.154 The solution luminescence spectra of 13 Eu(III) chelates have been examined155 and considerable variation in the 7F 0 ]5F 0 excitation spectra observed, depending upon the denticity of the ligand and the number and nature of co-ordinated nitrogen atoms.With additional information from excited-state lifetimes, solution structures were evaluated.Although it cannot be isolated in a pure state, a 1: 3 Eu(III) Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 248complex with diethylpyridine-2,6-dicarboxylate exhibits a very high quantum yield in CH 3 CN solution.156 Europium(III) complexes of calix[4]arenes incorporating bipyridine-N,N@-dioxide ligands have very high absorption coe¶cients and high luminescence quantum yields.157 Europium complexes of diphthalimidodiethylamine exhibit temperatureindependent luminescence.158 [1,4-dmpyH][Eu(ttfa) 4 ] exhibits triboluminescence (i.e.luminescence under pressure); europium has square antiprismatic co-ordination.159 [Eu(ttfa) 3 (phen)] is also triboluminescent.160 Sr 2 CeO 4 contains 1-D chains of CeO 6 octahedra. It exhibits blue-white emission at 485nm with a quantum yield of 0.48 owing to luminescence from a ligand-to-metal Ce4` charge transfer.161 3.13 Organometallics The three-co-ordinate r-alkyl [YMCH(SiMe 3 ) 2N3 ] is pyramidal in the solid state.108 Other new alkyls [LnMCH(SiMe 3 ) 2N3 ] (Ln\Pr, Nd) have been synthesised and their single-crystal absorption spectra recorded, along with those of [SmMCH- (SiMe 3 ) 2N3 ].162 Ligand-field splittings are similar to those in the analogous threeco- ordinate silylamides and aryloxides.The structure of the thermally unstable methyl-bridged compound [NdM(l-CH 3 ) 2 Al(CH 3 ) 2N3 ]·0.5[Al 2 (CH 3 ) 6 ] has been determined by neutron di§raction at 100 K. Hydrogens were located and a ‘tipped’ trigonal bipyramidal geometry at the bridging carbons characterised.163 The allyl [La(diox) 1.5 (g3-C 3 H 5 ) 3 ] reacts with various ligands forming adducts [LaL(g3-C 3 - H 5 ) 3 ] (L\dme, tmed, 2hmpa).164 [Ln(g3-C 3 H 5 )Cp* 2 ] react with [NHEt 3 ][BPh 4 ] to form [Ln(BPh 4 )Cp* 2 ] (Ln\Sm, Nd, Tm); in the solid state, the Sm compound has a bent SmCp* 2 unit that is also bound to two of the phenyl groups.165 This reacts with LiCH(SiMe 3 ) 2 to form [SmMCH(SiMe 3 ) 2NCp* 2 ] in high yield.[Nd(BPh 4 )Cp* 2 ] reacts with KCp* to form [NdCp* 3 ], another of the previously inaccessible LnCp* 3 systems. This reaction o§ers the hope of preparing more of these rare compounds, for the earlier lanthanides at least. Another route to cationic base-free ‘[LnCp* 2 ]`’ systems, albeit restricted to those lanthanides with an accessible divalent state, involves the oxidation of [LnMC 5 H 3 (SiMe 3 ) 2 -1,3N2 ] (Ln\Sm, Yb) by AgY (Y\CB 11 Br 6 H 6 , BPh 4 ) forming [LnMC 5 H 3 (SiMe 3 ) 2 -1,3N2 ]Y.A more general route, involving halide abstraction rather than electron transfer (Ln\Sm, Er, Yb), is shown in eqn. (2).[MLn[C 5 H 3 (SiMe 3 ) 2 -1,3] 2 IN2 ]]2AgY]2[LnMC 5 H 3 (SiMe 3 ) 2 -1,3N2 ]Y]2AgI (2) The [CB 11 Br 6 H 6 ]~ salts are more reactive; on recrystallisation from thf, ring-opening occurs, whilst [ErMC 5 H 3 (SiMe 3 ) 2 -1,3N2 ]` will abstract bromine from [CB 11 Br 6 H 6 ]~ or chlorine from CH 2 Cl 2 to form [MErX[C 5 H 3 (SiMe 3 ) 2 -1,3] 2N2 ] (X\Cl, Br). Structures are reported for the adducts [Sm(dme)MC 5 H 3 (SiMe 3 ) 2 -1,3N2 ][BPh 4 ], [Sm(thf) 2MC 5 H 3 (SiMe 3 ) 2 -1,3N2 ][CB 11 Br 6 H 6 ], [Er(thf) 2MC 5 H 3 (SiMe 3 ) 2 -1,3N2 ]- [CB 11 Br 6 H 6 ] and [MErBr[C 5 H 3 (SiMe 3 ) 2 -1,3) 2N2 ].166 A crown ether causes a displacement reaction167 when added to [LnMC 5 H 3 (SiMe 3 ) 2 -1,3N2 ] (Ln\Sm, Yb); the products are the salts [Sm(18-crown- 6)MC 5 H 3 (SiMe 3 ) 2 -1,3N][SmMC 5 H 3 (SiMe 3 ) 2 -1,3) 3 ] and [Yb(18-crown- 6)MC 5 H 3 (SiMe 3 ) 2 -1,3N][MC 5 H 3 (SiMe 3 ) 2 -1,3) 3 ].The [SmMC 5 H 3 (SiMe 3 ) 2 -1,3N3 ]~ ion, has also been isolated as the [K(18-crown-6)(g2-PhMe) 2 ]` salt. [YbMC 5 H 3 (Bu5) 2 - Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 2491,3N2 ] and its mono-adducts with Et 2 Oand dme have been synthesized, the latter both having the expected bent sandwich structures.168 The alkyls [(C 5 H 4 Bu5) 2 Ln(l- Me) 2 Ln(C 5 H 4 Bu5) 2 ] (Ln\Nd, Sm) have been synthesised; the corresponding hydrides cannot be isolated, though the samarium compound can be observed in solution.169 Hydrogenolysis of alkyls [NdR(C 5 H 4 CH 2 CH 2 OMe) 2 ] a§ords a transient [NdH(C 5 H 4 CH 2 CH 2 OMe) 2 ] which rearranges into [Nd(C 5 H 4 CH 2 CH 2 OMe) 3 ].The pentamethylcyclopentadienyl ligand has been responsible for many of the advances in f-block organometallic chemistry. Now two papers have been concerned with complexes of the tetramethylisopropylcyclopentadienyl analogue. Syntheses and structures are reported170 for [Sm(thf)(C 5 Me 4 Pr*) 2 ] and [(C 5 Me 4 Pr*) 2 Sm(l- Cl)Sm(C 5 Me 4 Pr*) 2 ].LnCl 3 (Ln\Y, Sm, Lu) react with two moles of NaC 5 Me 4 Pr* in thf forming [Ln(thf)Cl(C 5 Me 4 Pr*) 2 ] which can be alkylated to yield [Ln(thf)Me(C 5 Me 4 Pr*) 2 ] and [Ln(thf)MCH(SiMe 3 ) 2N(C 5 Me 4 Pr*) 2 ] which are e§ective precatalysts for the hydrosilylation of alkenes and alkynes. Structures of [Lu(thf)Me(C 5 Me 4 Pr*) 2 ] and [Lu(thf)Cl(C 5 Me 4 Pr*) 2 ] were reported.171 The alkyls [LnMCH(SiMe 3 ) 2NCp* 2 ] (Ln\La, Sm, Y, Lu) catalyse the hydroamination/cyclisation of aminoallenes.172 Treatment of [Sm(thf) 3 Cl 2 Cp] with hot toluene, followed by removal of the thf by distillation yields173 [SmCl 2 Cp]·0.16C 6 H 5 Me; this is in fact a cluster, [Sm 12 Cl 24 Cp 12 ], containing an icosahedron of samarium atoms.The similarly prepared [YbCl 2 Cp]·0.33thf·0.22toluene is [Yb 3 (thf) 3 Cl 5 Cp 3 ][Yb 6 Cl 13 Cp 6 ].[Yb(dme)Cp 2 ] reacts with perfluorodecalin or with perfluoromethylcyclohexane forming [MYb(thf)FCp 2N2 ], the first example of C–F activation of a saturated perfluoro compound by a lanthanide organometallic.174 A number of adducts of [Ln(OPR 3 )Cp 3 ] (Ln\La, Nd, Sm, Yb; R\Ph, o-tolyl, Bu/, etc.) have been synthesised and the structures of [Yb(OPR 3 )Cp 3 ] and [Nd(OPR 3 )Cp 3 ] determined; the former is tetrahedral and the latter has a geometry more typical of TBPY co-ordination. 175 [MLn(g-C 5 H 4 Me) 3N4 ] (Ln\Pr) has a structure similar to its Ln\La, Ce, Nd analogues.176 LnCl 3 reacts with excess Na[1,3-(Me 3 Si) 2 C 5 H 3 ] forming two series of complexes, [LnMg5-(Me 3 Si) 2 C 5 H 3N3 ] (Ln\La, Sm, Nd, Gd, Dy) (whose structures show pseudo-trigonal co-ordination of the lanthanide) and [MLnCl[(Me 3 Si) 2 C 5 H 3 ]N2 ] (Ln\Gd, Dy, Er, Y, Yb).177 Syntheses and structures are reported178 for the ytterbium(II) p-arene complexes [Yb(AlCl 4 ) 2 (g6-C 6 H 6 )]·C 6 H 6 , [Yb(AlCl 4 ) 2 (g6-C 6 H 3 Me 3 )] and Na[Yb 2 (AlCl 4 ) 5 (g6- C 6 H 6 )].The samarium(II) complexes [SmM(g6-C 6 H 5 Me)Sm(AlCl 4 ) 3N2 ], [Sm(AlCl 4 ) 2 ], [Sm(AlCl 4 ) 2 (g6-C 6 H 6 )], [Sm(AlCl 4 ) 2 (g6-C 6 H 3 Me 3 )], Na[Sm(AlCl 4 ) 3 (g6-C 6 H 6 )] and Na[Sm(AlCl 4 ) 3 (g6-C 6 H 3 Me 3 )] have been synthesised.179 Structures have been reported for [Pr(thf)Cl(ind) 2 ]180 and [Ln(thf)(ind) 3 ] (Ln\La,180,181 Pr,181 Nd,181 Sm181).This year there are numerous reports on (cot) complexes.[Nd(thf) 3 (BH 4 ) 3 ] reacts with K 2 cot forming [MNd(thf)(BH 4 )(cotN] 2 ]; with [NHEt 3 ][BPh 4 ], this a§ords the novel cationic [Nd(thf) 4 (BH 4 )(cot)][BPh 4 ]. Both of these react with KCp* yielding [Nd(thf)Cp*(cot)].182MO calculations on [Ln(cot) 2 ] and [Ln(cot) 2 ]~ (Ln\Ce, Nd, Tb, Yb) suggest that the neutral complexes are best regarded as Ln(III) systems.183 Compounds [Lnn(cot)m] [(n,m\(n, n]1) for n\1–5)] produced by laser vaporisation and molecular beam methods probably have multiple decker sandwich structures. 184 The anion in [Li(thf) 4 ][Sm(cot) 2 ] has a sandwich structure.185 [MSm(l-I)- (thf) 2 (C 5 Me 4 R)N2 ] reacts with K 2 cot forming [MSm(thf) 2 (C 5 Me 4 R)N2 (l-g8: 8-cot)] Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 250(R\Me, Et); [MSm[Me(OCH 2 CH 2 ) 2 OMe](C 5 Me 5 )N2 (l-g8: g8-cot)] has a bent triple-decker structure,186 as do the unsolvated compounds [MSm(C 5 Me 4 R)N2 (l- g8:g8-cot)] (R\Me, Et).Samarium reacts with C 8 H 8 in the presence of RSSR187 (R\2-pyridyl, 2,4,6-triisopropylphenyl) to form [Sm(thf) 0.5 (RS)(cot)], [Sm(hmpa) 2 (RS)(cot)] (four-legged piano stool structure when R\2-pyridyl) and [Sm(hmpa) 2 (RS)(cot)] (three-legged piano stool structure when R\2,4,6-triisopropylphenyl).Other triple deckers,188 as yet uncharacterised structurally, are [Ln 2MC 8 H 6 (SiMe 3 ) 2 -1,4N3 ]. Samarium reacts with C 8 H 8 and I 2 in thf to form [Sm(thf)I(cot)] which a§ords [Sm(hmpa) 3 (cot)] I when treated with excess hmpa.189 With a catalytic amount of iodine, La and Sm react with C 8 H 8 in the presence of hmpa to form [La(hmpa) 4 (cot)]- [La(cot) 2 ] and [Sm(hmpa) 3 (cot)][Sm(cot) 2 ], the latter structure confirmed by X-ray di§raction.Room- and low-temperature absorption spectra are reported for [Ln(thf) 3 I(cot)] (Ln\Pr, Nd, Sm).190 A novel compound 3 is the first complex of the pyrene trianion. [Cp*ClLa(l-Cl) 2 Li(thf) 2 ] reacts with pyrene and potassium to form [(LaClCp*) 3 (C 16 H 10 )(thf)].This contains two lanthanums g6-bonded to two of the rings; the third lanthanum is g2 bound to one of the middle rings, though it additionally co-ordinates a thf molecule.191 4 Actinides 4.1 Binary compounds and complexes An earlier claim for the existence of the Th3`(aq) ion has been questioned.192 SrTh 2 Se 5 has a structure based on U 3 S 5 whilst semiconducting SrTh 2 Te 6 contains layers of 2 = [Th 2 Te 6 ~] double chains joined by Cu` ions.193 A synchrotron X-ray di§raction study of [Th(S 2 PMe 2 ) 4 ] indicates the bonding is largely ionic with some 5d-like involvement,194 in contradistinction to some ab initio calculations, suggesting that these may overestimate the covalent nature of actinide bonding.Another application of the useful synthon [UI 3 (thf) 4 ] lies in the synthesis of a rare U(III) complex of an amine ligand, [U(tbpa)I 2 ]I·py, which has nine-co-ordinate uranium.82 Syntheses are reported of new chlorouranate(III) complexes SrUCl 5 ,195 Ba 2 UCl 7 ,195 CsUCl 4 ,196 and Cs 2 LiUCl 6 ,196 the last having the elpasolite structure.UCl 4 and certain phases (KCl)x(UCl 4 )y are selectively deposited inside carbon nanotubes by capillary action. 197 The complex[UO 2 (NO 3 ) 2 (tbp) 2 ] is very soluble in supercriticalCO 2 , suggesting an alternative to organic solvents for nuclear fuel processing.198 EXAFS spectra have been reported for [UO 2 (NO 3 ) 2 (tbp) 2 ], [UO 2 (NO 3 ) 2 (tibp) 2 ], [UO 2 (NO 3 ) 2MOP(OMe) 3N2 ] and [UO 2 (NO 3 ) 2MOP(OPh) 3N2 ].There are small differences in the U–O(P) bond lengths which may relate to di§erences in extraction Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 251e¶ciency.199 Camphene-derived organophosphorus compounds have been studied as potential extractants of uranium and the structure of [UO 2 (NO 3 ) 2 (RPO 3 Me 2 ) 2 ] (R\endo-8-camphanyl) determined.200 Relativistic density functional calculations on [UO 2 (OH) 4 ]2~ indicate that a trans structure is only slightly more stable than a cis one; a suggested mechanism for intramolecular ligand exchange in [UO 2 (OH) 4 ]2~ between uranyl and hydroxide involves a cis isomer.201 Activation parameters for ligand substitution reactions in ternary complexes of the type UO 2 LF 3 and UO 2 L 2 F (e.g.L\pyridinecarboxylate, oxalate) have been determined.202 2-D sheet structures have been found in [NHEt 3 ][(UO 2 ) 2 (PO 4 )(HPO 4 )] and [NPr 4 ]- [(UO 2 ) 3 (PO 4 )(HPO 4 ) 2 ].203 In a remarkable example of metal-ion control, [UO 2 Cl 4 ]2~ reacts with tert-butylcalix[ 6]arene (H 6 L) only in the presence of Cs` to form a trimetallic inclusion complex204 Cs[Hpy] 3 [UO 2 Cl 2 ] 2 [H 2 L].The crown ether does not co-ordinate to uranium in [UO 2 (CH 3 CO 2 )(H 2 O)(OH)] 2 ·18-crown-6 and [UO 2 (CH 3 CO 2 ) 2 (H 2 O) 2 ]· 2(H 2 O)·18-crown-6.205 The crown ether does not co-ordinate in either [UO 2 (NCS) 2 (H 2 O) 3 ]·1.5(18-crown-6)·MeCN or in [Th(NCS) 4 (H 2 O)(HOCH 2 - CH 2 OH)]·18-crown-6.206 A convenient microscale preparation of [UO 2 Cl 2 (OPPh 3 ) 2 ] has been described.207 Calixarenes have been suggested as uranophiles, the larger rings may act as receptors for multinuclear U(VI) species.208 A calix[4]arene with an acid and an amide group attached to the ring (L) forms a dimeric complex with the uranyl ion, [(UO 2 ) 2 L 2 ].209 The synthesis and structure of a uranyl monooxasapphyrin complex 4 is reported.210 The ring exhibits less deviation from planarity than the corresponding pentaphyrin.Hydrothermal synthesis of a number of new layered uranium(IV) fluoride species from UO 2 , HF and H 3 PO 4 additionally uses alkanediamines as templating agents. [H 3 N(CH 2 ) 3 NH 3 ][U 2 F 10 ]·2H 2 O, [H 3 N(CH 2 ) 4 NH 3 ] [U2 F 10 ]·3H 2 O, [H 3 N(CH 2 ) 6 NH 3 ] [U2 F 10 ]·2H 2 O and [HN(CH 2 CH 2 NH 3 ) 3 ][U 5 F 24 ] all contain negatively charged layers of uranium fluoride polyhedra (containing eight- and nineco- ordinate uranium) separated by the positively charged cations; the latter can be exchanged for a wide range of Group 1, Group 2 and transition metals.211 [NO]- [MF 6 ] (M\Np, Pu) are reported,212 as in the synthesis and structure of the first transactinide crown ether complex, [NpO 2 (18-crown-6)][ClO 4 ].213 Some more 237Np Mo� ssbauer studies have been reported, several this time on Np(V) compounds. 214 Analysis of Mo� ssbauer isomer shifts for Np(III–VII) compounds has been reported.215 A XANES study of plutonium aqua ions indicates that spectra are dependent upon, and characteristic of, the oxidation state.216 [Pu(CO 3 ) 5 ]6~ has been Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 252identified by EXAFS as the Pu(IV) species in solution at high carbonate concentration; the structure of crystalline [Na 6 Pu(CO 3 ) 5 ] 2 [Na 2 CO 3 ]·33H 2 O has also been determined. 217 Information from hydration studies of Cm(III) ions by laser-induced fluorescence spectroscopy indicates a co-ordination number of nine; hydration numbers have been given for other Cm(III) complex species.53 Carboxylate-derived calix[4]arenes218 show high selectivity for Am3`.Laser ablation of AmO 2 in polyimide219 produces organometallic ions including AmCN`, AmC 2 H` and AmC 4 H` as well as larger AmCxHyNz ` species, with x up to [12. 4.2 Alkoxides, amides and thiolates The importance of the choice of starting material in synthetic work is nicely illustrated by a study of aryloxides.220 UCl 4 and [UX 4 (NCMe) 4 ] (X\Br, I) react with two moles of KOR (R\2,6-di-tert-butylphenoxide) forming respectively [K(thf) 4 ][UCl 3 (OR) 2 ] (TBPY), [UBr 2 (OR) 2 (thf)] and [UI 2 (OR) 2 ].[UI 2 (OR) 2 ] and [K(thf) 4 ][UCl 3 (OR) 2 ] will react with a further mole of KORforming [UX(OR) 3 ] (X\Cl, I) whilst UCl 4 and [UI 4 (NCMe) 4 ] react with 4.2 moles of KOR forming [U(OR) 4 ].As anticipated, [UMN(SiMe 3 ) 2N3 ] has a pyramidal three-co-ordinate structure in the solid state, like the lanthanide analogues.221 [UHMN(SiMe 3 ) 2N3 ] reacts with B(C 6 F 5 ) 3 forming H 2 and [UMN(SiMe 3 ) 2N2MN(SiMe 3 )[SiMe 2 B(C 6 F 5 ) 3 ]N]. [UMC(Ph)(NSiMe 3 ) 2N2 Cl 2 ] reacts with NaBH 4 forming [UMC(Ph)(NSiMe 3 ) 2N2Mg3-BH 4N2 ] 5.Hydrogen atoms were located in both X-ray and neutron-di§raction studies.222 [MU(L)(l-Cl)N2 ] ML\N(CH 2 CH 2 NSiMe 3 ) 3N reacts with LiOR [R\Bu5, C(CF 3 ) 3 , Ph, 2,6-Bu5 2 -4- MeC 6 H 2 ] forming alkoxides and aryloxides [U(L)(OR)].223 Ate complexes [U(L)(OR)(OR@)Li(thf)n] (R, R@\Bu5, Ph), which have capped trigonal bipyramidal co-ordination of uranium, can be oxidized to neutral U(V) complexes [U(L)(OR) (OR@)].Potassium film reduction of [U(L@)Cl] [L@\N(CH 2 CH 2 NSiMe 2 Bu5) 3 ] gives [MU(L@)N2 (l-Cl)] and [U(L@)], separable on fractional sublimation. The latter reacts224 reversibly with N 2 forming the remarkable dinitrogen complex [MU(L@)N2 - (l-g2: g2-N 2 )].Density function calculations on the model compound [MU(NH 3 )- (NH 2 ) 3N2 (l-g2: g2-N 2 )] indicate significant U]N 2 p backbonding.225 On reduction in thf, [UI(NRR@) 3 ] (R@\3,5-dimethylphenyl; R\N-tert-butylanil- Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 253ide) forms [U(thf)(NRR@) 3 ] which reacts with [MoMNPh(Bu5)N3 ] underN 2 forming the end-on bridged compound [(NRR@) 3 U(l-N 2 )MoMNPh(Bu5)N3 ].[(NRR@) 3 U(l- N 2 )MoMNPh(Ad)N3 ] has also been synthesised.226 4.3 Organometallics Reductive coupling of acetone occurs in the presence of UCl 4 and Li–Hg. The carbon-based radical [UCl 3 (Me 2 C0 O)] dimerises to [MUCl 3 (thf) 2N2 (l- OCMe 2 CMe 2 O)] which reacted with LiCl forming [Li 2 (thf)][MUCl 4 (thf)N2 (l- OCMe 2 CMe 2 O)]; the last reacts with Li–Hg to form UCl 3 and [Li 2 (thf)]- [UCl 4 (OCMe 2 CMe 2 O)].The structure of [MUCl 3 (hmpa) 2N2 (l-OCMe 2 CMe 2 O)] was reported.227 A rare EPR study of U(V) compounds, including [U(NEt 2 ) 3 (cot)], [U(NEt 2 ) 3 Cp* 2 ][BPh 4 ] and [U(thf)(NEt 2 ) 2 (cot)][BPh 4 ] has been reported.228 An EPR and ENDOR study229 of [U(g7-C 7 H 7 ) 2 ]~ indicates an f1 ground state, largely made up of 5fn and 5fp uranium orbitals, with some admixture of 5f/.The cationic amide [U(thf)(NMe 2 )Cp* 2 ] [BPh 4 ] reacts with catalytic amounts of NR 2 H (R\Me, Et) forming a heterocyclic metallacycle 6.230 The amide forms an isocyanide adduct [U(CNBu5) 2 (NMe 2 )Cp* 2 ][BPh 4 ] with Bu5NC, but inserts MeCN, CO 2 and CO, forming [U(thf)MNC(Me)NMe 2NCp* 2 ][BPh 4 ], [U(thf)(O 2 CNMe 2 )Cp* 2 ] [BPh 4 ] and [U(thf)(g2-CONMe 2 )Cp* 2 ][BPh 4 ] respectively.The first uranium(IV) triflates, [U(OTf) 2 Cp* 2 ], [U(py)(OTf) 2 Cp* 2 ], [U(OTf)Cp* 3 ] and [U(py)(OTf) 2 (cot)] have been reported,231 as well as [U(py)(OTf) 4 ]. Structures have been determined for [U(H 2 O)(OTf) 2 Cp* 2 ] and [U(OTf)(CNBu5)Cp* 3 ]. A new route has been reported to the remarkable U(VI) imides232 [U(NR) 2 Cp* 2 ] (R\Ph, Ad) together with the structure of the adamantyl compound. MO calculations on [An(cot) 2 ] (An\Th, U) support the view that they are actinide(IV) systems.183 4.4 Chemistry of the post-actinides Although the synthesis of elements 113 and 114 is so far unsuccessful (see Section 1), there have been plenty of developments.Attempts of theoreticians to predict the future chemistry of the transactinides,233 suggest particular stability not just for elements around the Z\114 ‘magic island’ but also neutron-rich isotopes of element 110.Relativistic calculations continue to increase in importance, for example enabling prediction that the transactinide oxyhalides like DbOX 3 (X\Cl, Br), SgO 2 Cl 2 and SgOCl 4 will be less volatile than the halides of these elements.The volatility order RfCl 4[HfCl 4[ZrCl 4 has similarly been predicted. Supercomputer-facilitated calculations predict a Sg–Br bond length of 2.6Å for SgBr 6 . Fluoride complexation of Rf Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 239–260 254is very similar to Hf, with a complex ion [RfF 6 ]2~ proposed.234 Theoretical and experimental study of RfCl 4 has been reported.235 The increased volatility of RfCl 4 compared to HfCl 4 is ascribed to relativistic e§ects.Transport experiments suggest that RfOCl 2 only exists in the condensed phase. A comparative study of the extraction of Zr, Hf and Rf from HCl with tributylphosphate leads to an extraction order Zr[Rf[Hf, at variance with earlier studies.236 Study of the sorption of Rf from HF–HCl-containing aqueous solution indicates that its behaviour resembles Th rather than Hf.237MOcalculations have been applied238 to the electronic structure of hydrated and hydrolysed complexes of Nb, Ta, Pa and Db to obtain values for free energy changes aonstants of hydrolysis reactions, predicting hydrolysis to decrease in the order Nb[Ta[DbAPa.Calculations for the chloro complexes239 of these elements gives an order of complex formation (for [HCl][4M) of PaANb[Db[Ta; the hydrolysis order is the reverse, Ta[Db[NbAPa, significantly di§erent to that for the aqua ions. Study of the extraction of fluoro, chloro and bromo complexes of Nb, Ta, Pa and Db into aliphatic amines has been reported. 240 Dubrium shows a distribution coe¶cient in 6MHCl similar to Nb leading to an extraction sequence Pa[Nb[\Db[Ta.Gas phase and solution studies on seaborgium using 265Sg(t "[7 s) and 266Sg(t "[21 s) indicate that it behaves similarly to Mo and W.241 Oxychlorination is believed to produce SgO 2 Cl 2 . It is suggested that volatile species of Bh and Hs, HBhO 4 and HsO 4 , are potentially separable. Oxychlorination of 263Sg enabled its separation242 from Rf, Db and from heavy actinides, probably as [SgO 2 Cl 2 ].Separations of Sg in aqueous solution243 indicate ]6 to be the most stable oxidation state and that it forms neutral or ionic oxo and oxohalide compounds, possibly [SgO 4 ]2~, [SgO 3 F]~, [SgO 2 F 3 ]~ or [SgO 2 F 4 ]2~. There is evidence for strong complexation with F~. 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