4 Aluminium, gallium, indium and thallium J. P. Maher School of Chemistry, University of Bristol, Bristol, UK BS8 1TS 1 Introduction This year’s review was compiled via an ISI Personal Alert. This resulted in over 9000 references, and illustrates just how di¶cult it has become to cover such a diverse subject. By comparison with previous years the searches gave a di§erent proportion of papers: Al: 39%; Ga: 24%; In: 12%; Tl : 25%.There has been a discernable shift in interest towards the heavier elements in the group. A microcosm of the current chemistry for Group 13 can be seen in the abstracts to papers relating to Group 13 presented at the 1998 meeting of the ACS.1 There have been Group 13 reviews on the distribution of the M–M distances in the oxides of the elements and their spinels and delafossites,2 and a new database of the thermodynamic properties of the nitrides and related species is available.3 2 Aluminium The health hazards associated with environmental Al3` continues to attract attention. The current medical situation concerning the possible role of aluminium in Alzheimer’s disease has been reviewed.4 For a healthy adult the (safe) daily dietary intake of aluminium can be up to 60 mg.The aluminium content of German foodstu§s has been investigated,5 and the oral exposure of adults to aluminium was the subject of a recent long term survey.6 A huge amount of beer is consumed from aluminium cans so that it is surprising that this source of aluminium has evaded investigation until now! It was shown that the aluminum cans are corroded over time by canned beer, but that the corrosion may be reduced through refrigeration; in any case the quantities are minute compared to the allowed intake of aluminium.7 Bentonite is often used for fining wines and thus is another possible aluminium source, however \3mgL~1 is contained in red or white wines.8 The pros and cons of the risk of exposure to aluminium from drinking water for the development of Alzheimer’s disease have been discussed.9 Aluminium salts are also the major constituent of many widely used antiperspirants, the use of which has been linked with the systematic in vivo accumulation of aluminium. 10 Whatever the risk for healthy people, for patients undergoing renal dialysis aluminum toxicity is a major clinical hazard associated with anaemia, disturbed lymphocyte function and immunosuppression–the e§ects can be lethal.11 Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 45–56 45The term ‘ultratrace element’ has been defined as an element with an ‘established, estimated, or suspected requirement generally indicated by lg day~1 for humans’. Whilst aluminium has been so classified since 1984, its possible beneficial role in biochemistry is still only suspected, and swamped by potentially hazardous e§ects.12 Neither is the molecular mechanism of aluminum neurotoxicity understood. Some synergic e§ects have recently been investigated.Thus an association with nitric oxide has been discovered. Major alterations in nitric oxide regulation in Altzheimer’s disease have been observed.13 Chronic exposure to aluminum impairs the neuronal glutamate-induced activation of nitric oxide synthase and nitric oxide-induced activation of guanylate cyclase, so that impairment of the glutamate–nitric oxide–cyclic guanosine monophosphate (GMP) pathway in neurons may contribute to aluminum neurotoxicity.14 Aluminium salts apparently have the capacity to promote prooxidant events in the central nervous system in rats, measured levels of nitric oxide synthase were increased.15 It is also possible that Al3` neurotoxicity may be related to an alteration of the intracellular calcium regulatory system.Thus Al3` modifies Ca2` uptake in the endoplasmic reticulum, accelerates Ca2` release from mitochondria and strongly inhibits Ca2`–ATPase activity with a consequent high-level calcium accumulation inside the cell.16 The e§ect of aluminum on acetyl–CoA and acetylcholine metabolism in nerve terminals has been studied.The ion [Al(PO 4 )(OH)]~ may be the active form of aluminium which interacts with the verapamil binding sites of Ca2` channels, so restricting the Ca2` influx to the synaptoplasm. MVerapamil is a class IV antiarrythmic drug which blocks voltage sensitive Ca2` channelsN.This may inhibit the provision of acetyl–CoA to the synaptoplasm as well as the Ca-evoked ACh release. The authors suggest that excessive accumulation of aluminium in some encephalopathic brains may, by this mechanism, suppress still-surviving cholinergic neurons and exacerbate cognitive deficits caused by already-existing structural losses in the cholinergic system.17 There may also be links between magnesium deficiency and aluminium, whereby the uptake of aluminium is accelerated by magnesium deficiency during age-related neurodegenerative processes.18 Aluminium at concentrations as low as 0.015mM has been found to induce changes in the rheological properties of mucin, the important glycoprotein which forms mucus in solution.Aluminium will cause precipitation of the mucin biopolymer. Considering the ubiquitous nature of mucin in plants and animals this observation may have wide ranging implications for biological systems.19 Aluminum tris(8-hydroxyquinoline) is presently considered to be one of the most reliable electron transporting and emitting materials for molecular-based organic light-emitting diodes.Intense blue colours can be obtained from devices constructed using the quinolines and related compounds.20 Doping the materials with laser dyes gives other colours, for example, red–orange and yellow.21 The reactions of AlMe 3 with di-2-pyridylamine gave three compounds, all emit an intense blue color in solution and the solid state when irradiated with UV light.22 Materials with similar properties based on the 7-azaindole anion,23 and 2-hydroxypyridine, 2-pyridinemethanol, 8-hydroxyquinoline and 8-quinolinemethanol,24 have been described.The fluorescence behavior of the aluminium quinolinates have been studied in reverse micellar systems and very large fluorescence enhancement factors observed.25 Aluminium tris(2,6-diphenylphenoxide) acts as an intriguing bowl-shaped Lewis acid host which can protect various substrates which would otherwise react and Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 45–56 46promote regio- and stereo-specific reactions for groups which can coordinate to the aluminium.26 Highly selective b-diketone type ligands have been designed for Group 13 metal ions, in which the complexation of the Al3` was found to be dependent on the inter-ligand contact.27 The reaction of 2,2@-(buta-1,3-diyne-1,4-diyl)bis[6-(1,1- dimethylethyl)-4-methylphenol] with AlBu* 3 gives the corresponding bis(di-isobutylaluminium phenoxide), this holds two strongly Lewis acidic atoms of aluminum in a potentially convergent orientation. A 1: 1 adduct is formed with dme.An X-ray crystallographic study showed that the adduct is a linear oligomer in which the two Lewis acidic sites each bind a basic oxygen atom from di§erent molecules of dme.However, low-temperatureNMR solution studies indicated that a discrete 1: 1 adduct is favored, in which the two Lewis acidic sites each bind one of the two basic sites in a single molecule of dme. Formation of this adduct provides an example of the recognition and binding of a multidentate Lewis base by a complementary multidentate Lewis acid.28 Reaction of AlBu5 3 with Bu5 3 Al[O(H)CH 2 CH 2 CH 2 NMe 2 ] yielded the Lewis acid-base complex [(Bu5 2 AlMl-OCH 2 CH 2 CH 2 N(Me) 2 AlBu5 3N] 2 A.Compound A is also formed directly when 2 equivalents of AlBu5 3 reacts with 1 equivalent of [Bu5 2 Al(l-OCH 2 CH 2 CH 2 NMe 2 )] 2 .In contrast, the reaction of 2 equivalents of AlBu5 3 with 1 equivalent of [Me 2 Al(l-OCH 2 CH 2 NMe 2 )] 2 yielded Me 2 Al(l- OCH 2 CH 2 NMe 2 )AlBu5 3 B. The molecular structure of B shows the AlMe 2 chelate moiety bound to the anionic bidentate ligand, while the AlBu5 3 moiety is bonded to the anionic terminus of the ligand. The formation of compound A may occur via the Bu5-analogue of compound B, i.e., Bu5 2 Al(l-OCH 2 CH 2 CH 2 NMe 2 )AlBu5 3 , which is unstable due to significant Bu5 · · · Bu5 interligand interactions.29 A theoretical investigation using ab initio methods concerning the nature of the Al-containing species present in dilute aqueous alkaline solution, together with associated IR spectra measurements, confirms that the dominant species present is the [Al(OH) 4 (H 2 O) 2 ]~ anion.At high concentrations of sodium aluminate it was predicted that dimerization to the doubly hydroxy-bridged species [(OH) 3 Al(OH) 2 Al(OH) 3 ]2~ can occur and that this is assisted by the coordination of two or more water molecules.30 X-Ray structural and IR spectral measurements were carried out on mitryaevaite, ideally Al 10 [(PO 4 ) 8.7 (SO 3 OH) 1.3 ]p10 AlF 3 ·30H 2 O, a new mineral species from a Cambrian formation and occurring in the weathered zone of a vanadium-bearing black shale in carbonaceous concretions containing clay and fluorapatite.The mineral comes from southern Kazakhstan, and its name honours Dr Nonna Mikhailovna Mitryaeva for her contributions to mineralogy in Kazakhstan.31 A new aluminium vanadium oxide hydroxide, [Al 2 (OH) 3 (VO 4 )], an analog of the mineral augelite has been prepared.The structure contains clusters of edge sharing AlO 6 octahedra and AlO 5 trigonal bipyramids joined together by VO 4 tetrahedra.32 A series of aluminophosphate-based tubular mesoporous molecular sieves with and without substituted Si have been synthesized and characterised by a variety of techniques.The incorporation of the Si appears to make the aluminophosphate framework more flexible and facilitates the formation of an aluminophosphate-based mesoporous structure.33 A new two-dimensional aluminophosphate layer [Al 2 P 3 O 10 (OH) 2 ]- [C 6 NH 8 ] with an Al 2 P 3 O 12 3~ stoichiometry has been prepared from an alcoholic system using 4-methylpyridine as a template.The structure has alternating aluminum units, AlO 4 and AlO 5 , and PO 4 , PO 3 (OH), PO 2 (––O)(OH) units with rows of edge- Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 45–56 47sharing bridged six-membered rings and zigzag four-membered rings. The layers are held together by strong H-bonds. The organic ammonium cations [C 6 NH 8 ]` are located in the large cavities between the interlayer regions.34 A novel type of tridecameric cation consisting only of interconnected AlO 6 units is found in [Al 13 (OH) 24 (H 2 O) 24 ]Cl 15 ·13H 2 O.35 Unusual Al–Si, Al–P and Al–As bonds have been stabilised by the bulky ligand 2,2,6,6-tetramethylpiperidine (tmp) in the compounds [(tmp) 2 AlY] [Y\OR, SR, NR 2 , PR 2 , AsR 2 , CR 3 , Si(SiMe 3 ) 3 ; R\organyl, H].In contrast to the situation in the analogous [(tmp) 2 BY] compounds, quantum mechanical calculations rule out aluminium to nitrogen p-p to p-p bonding.36 Mono-adducts between (tmp) 2 AlX, (X\Cl, Br, I) complexes and Lewis bases, (tmp) 2 AlX·L, (L\py,thf) were observed, subsequent reaction with AlX 3 formed the tricoordinate alane, [(tmp) 2 AlL][AlX 4 ].37 The unique cluster (2,6-mes 2 H 3 C 6 Al) 2 [As(H)Ph 2 ](l-PhAsAsPh), which has a basket-shaped Al 2 As 4 core, was prepared by heating (H 2 AlC 6 H 3 mes 2 -2,6) 2 with an excess of H 2 AsPh.38 The chemistry of low valent aluminium compounds is fascinating.The first tetrahedral aluminium clusters containing r-bonded alkyl groups such as [M(Me 3 Si) 3 CNAl] 4 and [Cp*Al] 4 has been reported.These compounds complete the Group 13 tetrahedrane series.39 Oxidative addition of (mes)N––CHCH––N(mes) to [Cp*Al] 4 results in the monomeric AlIII derivative, [(g5-Cp*)AlN(mes)CH––CHN(mes)], which was characterised by X-ray crystallography.40 Potential precursors for low-valent aluminum compounds, bulky alkylaluminum dihalogenides [(Me 3 Si) 3 CAlX 2 ·thf] (X\F, Cl, Br, I) and dialkylaluminum halogenides [(Me 3 Si) 3 CAl(Me)X·thf] (X\Cl, Br, I) have been prepared.41 Reaction of AlCl 3 or AlBr 3 with R*Na (R*\SiBu5 3 ) gave the rubycoloured dialane R* 2 Al–AlR* 2 .An X-ray structure determination showed an Si 2 Al–AlSi 2 unit with the longest Al–Al bond to date [275.1(2) pm].42 R 2 Al–AlR 2 [R\CH(SiMe 3 )] reacts with LiCH 2 SMe with insertion of a carbene CH 2 into the Al–Al single bond.The product has a central R 2 Al–CH 2 –AlR 2 group with two coordinatively unsaturated Al atoms.43 Disproportionation of metastable AlX-solutions (X\Cl, Br, I) generates donor-stabilized (DAlX 2 ) 2 species, the Al–Al bond lengths in these are significantly shorter than in the organometallicR 2 Al–AlR 2 species, being strongly influenced by the donor molecule as well as by the halogen ligands.44 Reaction of Cp*Al with Al 2 I 6 proceeds by insertion of three Cp*Al moieties into the bridging Al–I bonds to form a curious Cp* 3 Al 5 I 6 compound with a cage structure in which an Al 2 unit is bridge bonded to an Al 3 unit by iodines.The compound is important in that it demonstrates the potential ro� le ofAlII species during the reactions between aluminium metal and alkyl iodides.45 Cationic alkyl aluminiums based on monoanionic N,N,N-pyridyliminoamide ligands catalyse ethylene polymerization.46 H 2 AlMN(Et)C 2 H 4 NMe 2N, H 2 AlMN(Me)C 2 H 4 NMe 2N and H 2 AlMN(Et)C 2 H 4 NEt 2N have been proposed as new precursors for the deposition of Al films.47 Novel organoaluminium–antimony compounds such as [Et 2 AlSb(SiMe 3 ) 2 ] 2 and [Bu* 2 AlSb(SiMe 3 ) 2 ] 2 may also be useful as precursor compounds.48 3 Gallium Gallium–gallium bonding is a regular topic for gallium chemistry.In the gas phase Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 45–56 48mass spectrometry measurements of diatomic metal–metal dissociation energies give Ga 2 \110.8^4.9 kJ mol~1, GaIn\90.7^3.7 kJ mol~1, In2 \74.4^5.7 kJ mol~1.49 The stability of the Ga–Ga bond in R 2 Ga–GaR 2 [R\CH(SiMe 3 ) 2 ] is further demonstrated by the observation that it is cleaved by some protic reagents such as phenols and also by C–F containing compounds, but that reagents such as dibenzoylmethane and dicarboxylic acids release two bis(trimethylsilyl)methanes leaving the dimer intact. The dicarboxylic acid products [e.g. 1,4-benzenedi(methylcarboxylic) acid, 1,4-cyclohexanedicarboxylic acid, 1,6-hexanedicarboxylic acid, and 1,4-butanedicarboxylic acid) have very short Ga–Ga bonds (237.7pm average), with two carboxylates e§ectively connected in each compound by two ‘spacers’ (dimethylbenzene, cyclohexane, hexane or butane) to form macrocyclic compounds with up to 22 atoms in the resultant heteroatomic rings.50 Double reduction of (Trip) 2 GaGa(Trip) 2 with Na/Et 3 Ngave Na 2 [GaMGa(Trip) 2N3 ] C with a planar GaGa 3 moiety in which the average Ga–Ga distance is 238.9(1.7) pm.This is longer than in the radical anion [(Trip) 2 GaGa(Trip) 2 ]~, 234.3(2) pm, with a formal bond order of 1.5, but shorter than in cyclic materials such as Na 2 [Ga(2,6- mesC 6 H 3 ) 3 ], 244 pm, with a formal bond order of 1.33.Dry oxygen reacted with C to form Ga[Ga(Trip) 2 ] 3 , here the average Ga–Ga bond length is 247.6(7)pm consistent with a bond order of one.51a The indium analogue In[In(Trip) 2 ] 3 was discovered in 1996.51b The formation of gallium ‘triple bonds’ has recently been disputed.52 [Tp(Bu5 2 )]Ga reacts with sulfur to form [Tp(Bu5 2 )]GaS providing evidence for gallium forming a double bond to sulfur; the corresponding indium compound gave a tetrasul- fido compound [Tp(Bu5 2 )]In(g2-S 4 ).53 Several compounds with potential as CVD precursors (chemical vapour deposition) have been described: [Bu5 4 Ga 4 (l3 -Ex)(l3 -Te) 4~x] (x\0–4; E\S, Se);54 [MeGaMl- N(H)PhN] 4 ;55 Me 3 Ga·Sb(SiMe 3 ) 3 and [Me 2 GaSb(SiMe 3 ) 2 ] 3 ;56 [Pr/(Cl)GaAsBu5 2 ] 2 and [(PhCH 2 ) 2 InAsBu5 2 ] 2 .57 EPR studies were reported for various isotopomers of GaH 2 and HGaCH 3 .58 Stepwise dehydrogenatioof [H 2 GaNH 2 ] 3 in supercritical ammonia at 15 °C generated the poly(imidogallane), [HGaNH]n.59 Various cluster compounds have been prepared: [(tmp)GaS] 4 ;60 Ga 4 [XC(SiMe 2 - R) 3 ] 4 (R\Me, Et) heterocubanes by reaction of Ga 4 [C(SiMe 3 ) 3 ] 4 with X\S, Se and Te;61 the quasi double cubane, [Ga 4 (OH) 6 (3-Bu5pzH) 10 ]6`, but no discrete Ga 4 O 4 , as yet, has been identified;62 heterometallic derivatives of [Mo 3 S 4 (H 2 O) 9 ]4` such as [Mo 3 GaS 4 (H 2 O) 12 ]5`,63 the tungsten–gallium cluster [W 3 GaO 4 (O 2 CEt) 8 ] 2 2~;64 the dinitrogen complex trans,trans-[MWX(PMe 2 Ph) 4 (l3 -N 2 )N2 (GaX 2 ) 2 ] (X\Cl, Br);65 gallium–iron clusters such as [(CO) 4 Fe–Ga 3 (OH) 4MSi(SiMe 3 ) 3N3 ] and [M(CO) 3 FeN2MGaSi(SiMe 3 ) 3N2 Cl]~;66 a gallium(I) pyrazolylborate compound with a short, two-electron dative bond [Ga: Fe[HB(3,5-Me 2 pz) 3 ]GaFe(CO) 4 ];67 CN~ reacts with GaMe 3 to form polymers [CsMCN(GaMe 3 ) 2N]n and [Cs(C 6 H 5 Me) 2MCN(GaMe 3 ) 2N]n.68 A wide variety of organogalliums have been studied: the benzylgallium compounds M[Mg 3 Br 2.4 Cl 1.6 (OEt 2 ) 6 ][Ga(CH 2 Ph) 4 ] 2 ·0.5C 6 H 5 MeN and [(3,5-Me 2 C 6 H 3 CH 2 ) 2 GaBr] 2 ;69 [(mes* 2 C 6 H 3 )GaCl 2 ] 2 ;70 Bu5 3 SiGaX 2 and (Bu5 3 Si) 2 GaX, (X\halide);71 heterocycles with Ga 2 Si 2 and a Ga 3 Si frameworks;72 [(PhMe 2 CCH 2 ) 2 GaNH(Bu5)] 2 and [(H 4 C 6 )Me 2 CCH 2 ]Ga[NH(Bu5)] 2 Ga(CH 2 CMe 2 Ph) 2 ;73 various SalenBu5 ligand dervatives of GaMe 3 and GaEt 3 ;74 [R 2 AlM(SePPh 2 N)N (R\Me, Et, Bu*) and Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 45–56 49[Et 2 GaM(SePPh 2 ) 2 NN];75 [(Me 3 SiCH 2 ) 2 GaP(SiMe 3 ) 2 ] 2 ;76 (mes) 2 Ga(facac) and Me 2 Ga(facac)·py;77 chalcogenides of GaIII (and AlIII) derived from Lewis base adducts of gallane (and alane), [Ga(TePh) 3 (NMe 3 )], [Ga(SeEt) 3 ·NMe 3 ] and [Ga(TePh) 3MP(C 6 H 11 ) 3N], trans-[MGaCl(l-Se)[P(C 6 H 11 ) 3 ]N2 ].78 GaMe 3 induced trimerization of acetonitrile leads to a hexanuclear gallium complex [(Me 2 Ga) 4 (MeGa) 2MHNC(Me)C(CN)CH(NCMe) 2N2 ].79 Four-coordinate dimethylgallium complexes containing bidentate ligands with O,O; O,N and S,N donor atoms were evaluated for their stability toward decomplexation in water, this is a key property in determining their potential as radiopharmaceuticals. The most hydrolytically stable compounds were those based on an N-alkylsalicylaldimidate donor.80 Triethylenetetraminehexaacetic acid (H 6 ttha) forms a strong complex with Ga3`, [Ga 2 (OH) 2 (ttha)][Na 2 (H 2 O) 6 ]·2H 2 O.The ligand is a potential chelating agent relevant to radiopharmaceutical applications involving Al3`, Ga3`, and In3`.81 The gallium(III) and indium(III) complexes of tris(2-mercaptobenzyl) amine and tris(2-hydroxybenzyl)amine were investigated in solution and in the solid state to help interpret their contrasting in vivo behavior as diagnostic imaging probes.82 Molecular-seive-type gallium phosphates have been prepared: Ga 4 (PO 4 ) 5 HF·1.5(tmen)·H 2 O (or ULM-18) an oxyfluorinated gallium phosphate was obtained by hydrothermal template synthesis using tmen;83 an aza-crown ether 1,4,7,10,13,16-hexaazacyclooctadecane acted as a template for Ga 5 F 2 (HPO 4 ) 2 (PO 4 ) 4 , C 12 H 27 N 6 (MIL-1);84 a new gallophosphate containing a gallium organic complex macrocycle 1,4,8,11-tetraazacyclotetradecane as part of the framework;85 a 14-membered ring gallium oxyfluorophosphate, Ga 7 P 6 O 28 F 3 C 10 N 2 H 16 , has 4,4@-bipyridyl and pyridine in the 14-ring channels;86 [NH 3 (CH 2 ) 4 NH 3 ][Ga(PO 4 )(PO 3 OH)], is a one-dimensional gallophosphate;87 and a gallium phosphonate cluster (Bu5 7 Ga 3 P 3 O 8 )·Bu5OH.88 4 Indium The preparation of nanometer size isolated particles of semiconductor materials is of considerable current interest, these are particles small enough to show quantum confinement and electronic e§ects dependent on the size of the particles.Group III–V materials have been di¶cult to prepare until now. In(PBu5 2 ) 3 can be used to form quantum dot indium phosphide, and it is likely that the method can be applied to InAs and GaP.89 (C 6 H 11 )PH 2 with InMe 3 cleanly forms thin films of crystalline InP under pyrolytic CVD conditions.90 Thin films of CuInSe 2 for solar cell devices have been grown by low-pressure MOCVDusing In[Se 2 CNMe(n-C 6 H 13 )] 2 and Cu[Se 2 CNMe- (n-C 6 H 13 )] 2 as precursors.91 Complexes of general formulae In(S 2 CNMeR) 3 (R\ Bu/, n-C 6 H 13 ) are useful air-stable precursors for other materials such as In 2 S 3 .92 The syntheses and X-ray crystal structures of [PPh 4 ][In(SePh) 4 ] and [PPh 4 ]- [In(SePh) 3 (SeH)],93 and of the one-dimensional compound [Ph 4 P][In(P 2 Se 6 )] D have been reported.93 Compound D contains infinite [In(P 2 Se 6 )]n ~ chains with a structure related to that ofK 2 FeP 2 Se 6 .94 Indium tris(alkylthiolate) compounds,95 and the neutral species InM(SCH 2 CH 2 ) 3 NN were synthesized and structurally characterized. 96 Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 45–56 50The first examples of mixed valence thioindates have been prepared, KIn 5 S 6 and MIn 5 S 7 (M\Na, K), in these indium appears as In`, In3` and covalent pairs of [In 2 ]4` along with S2~ and M`.97 The InII–InII compound M2,6-(Me 2 NCH 2 ) 2 C 6 H 3N(Cl)In–In(Cl)M(2,6-Me 2 NCH 2 ) 2 - C 6 H 3N2 has been prepared and characterised by X-ray crystallography.98a The cyclodiphosph( III)azane complex [M(BuNP)Bu5N2M(BuN)Bu5N2 In] 2 is a dimer of mononuclear indium(II) cages that are connected by an In–In bond.98b The reaction of R 2 In–InR 2 [R\CH(SiMe 3 ) 2 ] E, with Bu5NC or PhNC results in the formation of adducts rather than scission of the In–In bond.The In–In bond length (average 284.8 pm) is only slightly lengthened compared with those for E (282.8 pm).99 KInBr 3 is the first ternary InII bromide.100 In 4 [C(SiMe 3 ) 3 ] 4 abstracts O from o-nitrosotoluene forming the extremely hygroscopic In 4 O 4 [C(SiMe 3 ) 3 ] 4 , the structure exhibits a distorted In 4 O 4 moiety with normal In–O bond lengths, but short intracage In to In and O to O distances.This preparation completes the tetramer series In 4 X 4 R 4 .101 Various cluster compounds have been prepared: [Mo 3 InS 4 (H 2 O) 12 ]5` and the double cube [Mo 6 InS 8 (H 2 O) 18 ]8`;63 as well as Na 2 [W 3 InO 4 (O 2 CEt) 8 ] 2 ;102 Ni[InMC(SiMe 3 ) 3N4 ] is another amazing compound from Uhl’s Oldenburg group, a tetrahedral compound analogous to Ni(CO) 4 but with Ni–In bonds.103 Monomeric InC 6 H 3 (Trip) 2 -2,6 forms an Mn complex [(g5-Cp)(CO) 2 Mn–InC 6 H 3 (Trip) 2 -2,6]; this has a one-coordinate indium in the solid state.104 Organometallics previously mentioned in the gallium section, and with In analogues are [(mes* 2 C 6 H 3 )InCl 2 ] 2 ,70 Bu5 3 SiGaX 2 and (Bu5 3 Si) 2 GaX (X\halide).71 Indium hydride generating reactions have been described.InCl 3 with HSnBu 3 in thf at[78 °C generated HInCl 2 which was stable up to ambient temperature.105 LiInH 4 with NMe 3 ·HCl gave [InH 3 (NMe 3 )] which, whilst it could not be isolated in the solid state, on reaction with the stable carbene :CN(Pr*)C 2 Me 2 N(Pr*) gave [InH 3M:CN(Pr*)C 2 Me 2 N(Pr*)N].Al and Ga analogues were also prepared.106 Either InMe 3 ·Et 2 O or InMe 2 Cl with a large excess of LiH gave [Li(tmen) 2 ]- [Me 3 InH·InMe 3 ].107 Complexes with In–N bonds have been described: Cs[FInMN(SiMe 3 ) 2N3 ];108 indium amides, In(NRR@) 3 (R\Ph, Bu5, R@\SiMe 3 ; R\Bu5, R@\SiHMe 2 ), Li[InMNMe(SiMe 3 )N4 ], Li[In(NPh 2 ) 3 Cl], In(NRR@) 3 (py) (R\R@\Ph; R\Me, R@\SiMe 3 ), In[N(Bu5)(SiHMe 2 )] 3 (p-Me 2 Npy) and In[NMe(SiMe 3 )] 3 (p-Me 2 Npy), X-ray crystallographic measurements were made on many of these compounds;109 [In 2 Cl 4 L 2 (dmf) 2 ]·2dmf [HL\3-(2-pyridyl)pyrazole];110 [Et 2 In(Htmtaa)], [EtIn(tmtaa)], [ClIn(tmtaa)] and [RIn(tmtaa)] [R\Cp, Me, N(SiMe 3 ) 2 or OSiMe 3 ];111 chloro(phthalocyaninato)indium(III) reacted with R@MgBr [R@\p-tri- fluoromethylphenyl, m-trifluoromethylphenyl, p-fluorophenyl, perfluorophenyl] to form r-bonded aryl(phthalocyaninato)indium(III) complexes.112 Reaction in thf of 1,2-bis(halomercurio)tetrafluorobenzene (halide\Cl, Br) with the corresponding indium(I) halide gave spontaneous ring closure with formation of tetrakis(thf) adducts of 9,10-dichloro-9,10-dihydro-9,10-diindaoctafluoroanthracene and 9,10-dibromo- 9,10-dihydro-9,10-diindaoctafluoroanthracene respectively.113 Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 45–56 515 Thallium The notorious toxicity of thallium compounds is demonstrated by four instances of poisoning: chronic occupational thallium poisoning in a glass factory;114 symptoms involving skin coloration;115 severe sensorimotor neuropathy;116 and retinal damage, 117 this latter was a case of malicious poisoning.Thallium toxicity has also been reviewed.118 A recent substantial review concerns thallium in the environment: the history, production and uses of thallium;119a the aqueous geochemistry of thallium;119b the analysis of thallium in biological samples;119c human thallium toxicity;119d reproductive and developmental toxicity of thallium;119e thallium transport in cellular membranes. 119f The hydrogeochemistry of thallium in natural waters has been reported, 120 and the environmental implications of some revised hydrolysis constants for TlI and TlIII discussed.121 The problems of thallium pollution associated with mining deposits have been discussed.122 In contrast, thallium-201 reinjection imaging and positron emission tomography (SPECT) is finding increasing use in medicine, particularly for cardiac studies.123 Various mixed metal thallium oxides have been studied. In a-Tl 2 Te 2 O 5 there is strong stereochemical activity of both Te and Tl lone pairs.124 The Tl` lone pair is also stereochemically active in Tl 2 CuAsO 4 ,125 and in Tl[CuAsO 4 ] and Tl[CuPO 4 ].126 A new type 2212 phase has been discovered in a Tl–Hg–Ba–Cu–Osuperconducting system.127 The pathway for the formation of the TlBa 2 Ca 2 Cu 3 O 9 (1223) superconductors was studied, the reaction path implies the double-layer Tl–O series, Tl 2 Ba 2 CuO 6 and Tl 2 Ba 2 CaCu 2 O 8 at 800 °C and Tl 2 Ba 2 Ca 2 Cu 3 O 10 at 875 °C.The Tl-1223 phase is formed above 905 °C.128 Enhanced superconductivity was found in the Tl 1~xBixBa 2 Ca 2 Cu 3 O 9 system with increased Bi concentration (T# \110K at x\0.0 to T# \116K at x\0.2).129 Small amounts of fluorine (x) also increase T# in the compounds (Tl 0.5 Pb 0.5 )Sr 1.6 Ba 0.4 Ca 2 Cu 3 O 9~xFx.130 Much work on thallium superconducting materials is now going into improving their preparation,131 fabrication132 and electrical properties.133 The six-coordinate thallium(III) porphyrin triflate [Tl(tpp)(OSO 2 CF 3 )(thf)·thf]134 and a polymeric complex of TlIII containing bis(semiquinone) bridging ligands have been prepared.135 The preparation of four heterometallic porphyrinate dimers containing Rh–Tl r-bonds enabled the magnitudes ofNMRspin–spin coupling constants between thallium and rhodium nuclei to be measured for the first time.136 A new class of oligonuclear direct metal–metal bonded Pt–Tl compounds with the formula [(NC) 5 Pt–Tl(CN)n~1 ](n~1)~ (n\1–4) have been described.The compounds have huge Pt195–Tl205 spin–spin coupling constants, 25–71 kHz, for [(NC) 5 Pt–Tl(CN)] this is 71 060 Hz, and is the largest reported coupling constant ever observed between two di§erent nuclei!137 The X-ray crystal structure of [Tl(OPPh 3 ) 2 ][Au(C 6 F 5 ) 2 ] provides evidence for unsupported Au–Tl bonds forming a polymeric linear chain.138 The double cube compound [Mo 6 TlS 8 (H 2 O) 18 ]8` can be prepared but there was no evidence for the single cube [Mo 3 TlS 4 (H 2 O) 12 ]5`.63 The anions Tl 2 E 2 2~ (E\Se and/or Te) were prepared by extraction of MTlE (M\Na, K; E\Se, Te), in en–liquid NH 3 in the presence of 2,2,2-crypt.139 Several novel thallium(I) compounds have been described.Thus [2,6- (Trip) 2 C 6 H 3 Tl] is a unique monomeric arylthallium(I) compound with a singly coor- Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 45–56 52dinated thallium. 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