Indium structural stability

The structure of the few indium(II) compounds identified by early workers is one of the classical problems in group III chemistry, (cf. gallium, Section 25,3.3.3). It is now clear that both M—M-bonded compounds and ionic mixed valence species exist, but the factors which govern the relative stability of these species still remain to be elucidated. 

Given the structure of InF3-3H20 (see above) and the tendency of indium(III) to be six-coordinate with hard ligands, it is reasonable that the mixed fluoro/aqua anionic complexes should also be [InF4(H20)2] and [InF5(H20)]2. This is compatible with the evidence from aqueous solution chemistry, where stability constants and thermochemical results indicate a series of [In(H20)6-nFn]l3 n)+ species.9 These complexes still await detailed systematic structural investigation. 

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