Indium trichloride, InCl₃

Indium trichloride, InCl₃, is prepared by the action of excess of chlorine upon indium, the lower chlorides, or a mixture of indium sesqui-oxide and carbon, the product being purified by distillation in a stream of carbon dioxide. It forms white, lustrous tablets, which do not volatilise appreciably at 440°. Volatilisation occurs slowly at 600.° The vapour density is 7.8, referred to air as unity, at 600° to 850°, corresponding to the molecular formula InCl₃; but at higher temperatures dissociation occurs.

The density of the solid chloride is 4.0. The chloride is very deliquescent and dissolves readily in water, in which it is slightly hydrolysed; but the solution loses very little hydrogen chloride when evaporated at 100°.

The equivalent conductivities of aqueous solutions of indium trichloride at 25° are, according to Thiel, as follows (η = conc. in gram-equivalents per c.c.; v = dilution, in litres per gram equivalent: -

v	0.33	3.33	33.3	333	3333
1000η	3.0	0.30	0.03	0.003	0.0003
λ	10.2	30.5	50.6	101.0	225.0

Indium trichloride forms double salts with the chlorides of the alkali metals, ammonium, and platinum. The salt K₃InCl₆.2H₂O crystallises in the ditetragonal, bipyramidal class of the tetragonal system; and the ammonium, rubidium, and caesium salts of the type X₂InCl₅.H₂O are isomorphous with one another, crystallising in the bipyramidal class of the rhombic system. The platinum salt has the composition 2InCl₃.5PtCl₄.36H₂O. Indium trichloride also forms an addition-product with ammonia, and with pyridine forms the compound InCl₃.3C₅H₅N, m.p. 253°.