Linear gallium compounds

Tabletr.1-57 Linear thermal expansion coefficient a of gallium compounds...

Recently the first compounds containing Si=Ga or Si=In double bonds, l,3-disila-2-gallata- and -indataallenic anions respectively, were obtained in the form of lithium salts as dark red crystals by the reaction of bis(Ai tert butylmethylsilyl)dilithiosilane, with the respective M(III) halide (Figure 18). X-ray crystallographic analysis of gallium and indium salt derivatives showed that the >SiMSi< frameworks (M = Ga, In) are not linear and the two Si=M... 

A range of compounds has been synthesized by double-salt metathesis in which a two-coordinate, substituent-free gallium atom sits in an essentially linear environment between two transition metals. Compounds of the form (q -CjRjjjdppejFeGaMjCO) (M = Fe, n = 4j M = Cr, W, = 5 R = H, Me) may be accessed via reactions of (q -CjRjjjdppejFeGaCl with carbonylmetallate dianions K2[M(C0) ] [186-188, 244]. In such complexes, the bridging gallium atom is formally sp-hybridized and hence has two vacant p-orbitals, which may accept electron density from metal d-orbitals... 

No monomeric alkali metal alkyls or aryls are known, as those crystal structures which have been determined indicate electron-deficient, e.g. (MeLi), or ionic (K Me ) constitutions. The dialkyls of the lighter second group metals are mostly electron-deficient dimers or polymers, but those of zinc, cadmium and mercury are monomers with a linear structure as expected from participation of one (metal) s and one p orbital (with or without dji participation). In the third group the pattern is more complex. Whereas the trialkylboranes are monomeric, boron hydrides (and alkyl hydrides) and polyboron compounds form electron-deficient structures. Aluminium alkyls and alkyl hydrides are normally electron-deficient dimers or trimers gallium trialkyls are monomeric though the trivinyl is a dimer trimethylindium is a weakly associated tetramer in the solid state, otherwise all indium and thallium trialkyls appear to be monomers. 

---