Gallium, indium and thallium

Since 1980, interest in organometallic compounds of Ga, In and T1 has grown, mainly because of their potential use as precursors to semiconducting materials such as GaAs and InP. Volatile compounds can be used in the growth of thin films by MOCVD metal organic chemical vapour deposition) or MOVPE metal organic vapour phase epitaxy) 

A technician handling a gallium arsenide wafer in a clean-room facility in the semiconductor industry. 

TriorganogaUium, indium and thallium compounds are air-and moisture-sensitive. Hydrolysis initially yields the linear [R2M]+ imi (which can be further hydrolysed), in contrast to the inertness of R3B towards water and the formation of 

6-dimesitylphenyl substituent is also extremely steri-cally demanding, and reduction of (2,6-Mes2C6H3)GaCl2 with Na yields Na2[(2,6-Mes2C6H3)3Ga3]. The [(2,6-Mes2C6H3)3Ga3] anion possesses the cyclic stmcture (23.23) and is a 27r-electron aromatic system. 

we illustrated the use of the metastable GaBr as a precursor to multinuclear Ga-containing species. Gallium(I) bromide has also been used as a precursor to a number of organogallium clusters. For example, one of the products of the reaction of GaBr with (Me3Si)3CLi in toluene at 195 K is 23.24. 

The reaction of the tetrahedral cluster (Me3Si)3C 4Ga4 with I2 in boiling hexane results in the formation of (Mc3Si)3CGaI 2 and (Me3Si)3CGal2 2. In each compound 

I2 oxidizes this compound and possible oxidation states are Ga(II) (e.g. in a compound of type R2Ga—GaR2) and Ga(III). (Me3Si)3CGaI 2 is related to compounds of type R2Ga—GaR2 steric factors may contribute towards a non-planar conformation  

Further oxidation by I2 results in the formation of the Ga(III) compound (Me3Si)3CGal2 2 and a structure consistent with equivalent Ga centres is  

Species of type [E2R4] (single E—E bond) and [E2R4] (E—E bond order 1.5) can be prepared for Ga and In provided that R is especially bulky (e.g. R = (Me3Si)2CH, 

Discovery In 1875 Paul-Emile Lecoq de Boisbaudran in Paris found the new element gallium. After the discovery it was shown that gallium is Mendelev s eka-aluminum. 

Most important mineral Gallium follows aluminum and zinc in minerals and is contained in flue dusts from coal burning, which may contain up to 1.5% gallium. The element is obtained as a by-product in the production of aluminum, zinc and copper. 

Mean content in an adult human body Content in a man s body (weight 701%)  

Oxidation states Ionization energy (k) moH) Electron affinity (k) moh )  

Density Molar volume Melting point Boiling point Specific heat c at 298 K 

The elements of group lllb—gallium, indium, and thallium —are rare and have little practical importance. Their principal compounds represent oxidation state +3 thallium also forms compounds in which it has oxidation number-t-1. Gallium is liquid from 29°C, its melting point, to 1700°C, its boiling point. It has found use as the liquid in quartz-tube thermometers, which can be used to above 1200°C. 

The oxidation state -1-2, corresponding to the loss of two electrons, is an important one for all of these elements. In particular, the elements in 

Electronic Structures of Titanium, Vanadium, Chromium, and Manganese and Their Congeners 

From boron to aluminium, there is the usual drop from the second row to the third row of the Group, but thereafter, the values remain unexpectedly high, most notably at thallium whose first ionization energy exceeds that of aluminium. In Section 8, you saw that there is a steep drop in ionization energy when a new Period begins, followed by an overall increase across a Period as the nuclear charge builds up. 

The first ionization energies of the Group II and Group III elements. There is a marked decrease between magnesium and barium, which is not matched by that between aluminium and thallium. 

In the lithium and sodium Periods, no intervening subshells are filled between Groups II and III in the potassium and rubidium Periods, however, the 3d and 4d subshells must be filled between these Groups, and in the caesium Period, both the 4f and 5d subshells are filled. 

Unexpectedly high ionization energies for gallium, indium and thallium make conversion of the metals into ions more difficult. They are a major contribution to the greater resistance to oxidation revealed in Table 9.3. 

Such effects, however, do not obliterate the strong resemblance of gallium, indium and thallium to aluminium that their presence in the same Group implies. All three elements are metals, which react with fluorine or chlorine to form trihalides, all of which are solids at room temperature. The metals also dissolve in dilute acids, evolving hydrogen and forming aqueous ions. With gallium and indium, these ions are Ga +(aq) and In (aq) we return to thallium in a moment. Addition of alkali precipitates colourless Ga(OH)3, which is amphoteric, and In(OH)3, which is not. 

Transition Metal Bond Lengths to Gallium, Indium, and Thallium 

Two further points of interest are (1) the apparently facile heterolysis of the E—M bonds in donor solvents (8,8a) suggesting considerable ionic character 

The thallium complex 8 is available by two general routes involving the use of either T1(I) or Tl(III) salts. The former involves a disproportionation reaction [Eq. (1)] presumably via a 

T1(I)—manganese intermediate (15-17), which has not been isolated, whereas the latter involves direct substitution at a Tl(IIl) center [Eq. (2)] (18). 

A number of reactivity studies have been performed on 6 and 8 and indicate a strongly polar (if not ionic) Mn—E bond Mn —E,+ (E = In, Tl). Thus heterolytic bond dissociation occurs in polar ligating solvents such as MeCN or DMF, and halogens, hydrogen halides, and alkyl halides readily add across the metal-metal bond in a manner consistent with the polarity described above (13,13a,18). In the thallium example, however, the reactions are generally more complicated and result in T1(I) salts [e.g., Eq. (3)], and metal exchange reactions are also more facile, e.g., the synthesis of 6 from 8 and indium metal. In general, therefore, the chemistry of 6 and 8 is consistent with predominantly ionic behavior. 

The existence of dimeric and polymeric species in aqueous solutions of indium(m) and thallium(iii) has an effect on kinetics of systems which include these reactants. A T-jump study of indium(iii) perchlorate solution has yielded a value for the rate constant for dimerisation of [InOH] +. Due to ion-pairing complications, it has not proved possible to determine unequivocally, by comparison of rate constants of this and of the indium(m)-sulphate system, whether the rate-determining step in dimerisation of [InOH] + is loss of a solvating water molecule from the indium. The situation is entirely similar for gallium(iii) in perchlorate solution.  

An AlFe octahedron has been found in strontium aluminium penta-fluoride, but it has very distorted geometry, with Al-F distances ranging from 1.60 to 1.92 A. 

Structure determinations for compounds containing these three elements are still rather rare. Ga04 tetrahedra feature in three mixed oxide systems, namely CaGa407, and a- and j8-Li5Ga04. The Ga-O distances are very similar in each case, ranging from 1.78 to 1.86 A, but in general the tetrahedra are quite distorted (O-Ga-O is 102—120°). 

Both tetrahedral and octahedral geometry are found for gallium in cis-dichlorobis-(2,2 -bipyridyl)gallium(iii) tetrachlorogallate. The octahedral gallium atom occurs in the cation and is bonded to two chlorine and four 

Indium also occurs with tetrahedral and octahedral geometry. In the anion [dibromobis(tetracarbonylcobalt)indate(m)] the indium atom is bonded to two bromine atoms and two tetracarbonylcobalt groups via direct In-Co bonds. The structure contains two crystallographically independent anions and these are equivalent within the limits of experimental error. The In-Br and In-Co distances lie in the ranges 2.561— 2.582 A and 2.596— 2.644 A, respectively, and in both cases the distances are near the sum of the relevant covalent radii. 

Octahedral InSg geometry has been found in the tris-(l,2-dicyano-methylene-l,2-dithiolato)indate(iii) anion. The In-S distances, which range from 2.589 to 2.633 A, are probably normal for octahedral In. The InS octahedron is slightly distorted, and it is possible to correlate the small differences in In-S bond lengths with the deviations of the trams-S-In-S systems away from 180°. The shortest In-S bonds occur in the straightest S-In-S groups. 

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A. N. Nesmeyanov and R. A. SokoUk, The Organic Compounds of Boron, Aluminum, Gallium, Indium and Thallium, North-HoUand Publishing Co., Amsterdam, the Netherlands, 1967. 

Metal-halogen stretching vibrations in coordination complexes of gallium, indium and thallium. A. J. Carty, Coord. Chem. Rev., 1969,4, 29-39 (32). 

For a discussion of the atomic properties of the group 13 metals see Downs AJ (1993) In Downs AJ (eds) Chemistry of aluminum gallium, indium and thallium. Blackie, London, Chapter 1... 

Paver MA, Russell CA, Wright DS (1995) Gallium, Indium and Thallium excluding Transition Metal Derivatives. In Abel EW, Stone FGA, Wilkinson G (eds) Comprehensive Organometallic Chemistry II. Elsevier, Oxford UK, vol 1, chap Up 503... 

KT1 does not have the NaTl structure because the K+ ions are too large to fit into the interstices of the diamond-like Tl- framework. It is a cluster compound K6T16 with distorted octahedral Tig- ions. A Tig- ion could be formulated as an electron precise octahedral cluster, with 24 skeleton electrons and four 2c2e bonds per octahedron vertex. The thallium atoms then would have no lone electron pairs, the outside of the octahedron would have nearly no valence electron density, and there would be no reason for the distortion of the octahedron. Taken as a closo cluster with one lone electron pair per T1 atom, it should have two more electrons. If we assume bonding as in the B6Hg- ion (Fig. 13.11), but occupy the t2g orbitals with only four instead of six electrons, we can understand the observed compression of the octahedra as a Jahn-Teller distortion. Clusters of this kind, that have less electrons than expected according to the Wade rules, are known with gallium, indium and thallium. They are called hypoelectronic clusters their skeleton electron numbers often are 2n or 2n — 4. 

Metal-Nitrogen Bond Lengths and Torsion Angles between the Metal and Nitrogen Coordination Planes for Three-Coordinate Aluminum, Gallium, Indium, and Thallium Amides... 

Table VIII also includes a series of gallium, indium, and thallium compounds of the general formula Cp(CO)3M 3E (E,M = Ga,W In,Cr In,Mo ...

Grjotheim, K., Krohn, C., Malinovsky, M., Matiaskovsky, K., and Thonstad, J., Aluminium Electrolysis—Fundamentals of the Hall-Herault process, CRC Press, Boca Raton, FL, 1982, 17. Palmear, I. J., in The Chemistry of Aluminium, Gallium, Indium, and Thallium, Downs, A. J., Ed., Blackie, London, 1993, 87. 

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