Mixed Stannic Halides

Stannic chlorobromide, SnCl₂Br₂, was described by Ladenburg, and the three compounds, SnCl₃Br, SnCl₂Br₂, and SnClBr₃, by Besson; whilst Lenormand supposed that he had obtained SnCl₃I, SnCl₂I₂, SnClI₃, SnBr₃I, SnBr₂I₂, SnBrI₃ by the interaction of stannous halides and appropriate halogens or halogen hydracids; but it has been shown by Auger, by reference to their physical behaviour, that all these supposed compounds are probably mixtures.

Thus, mixtures of SnBr₄ and SnI₄ show a normal freezing-point curve, with a eutectie point at the composition SnBr_3.2I_0.8; and the supposed compound SnBr₂I₂, which melts at 54° C., is identical with an equimolecular mixture of SnBr₄ and SnI₄, and may be separated by ten fractional crystallisations into fractions melting at 88° C. and 27°C., having the compositions SnBr_1.2I_2.8 and SnBr_2.7I_1.3 respectively.

Similarly the supposed compounds SnBrI₃ and SnBr₃I may be partly resolved by crystallisation. Moreover, it is suggested that in all molten mixtures of the composition SnBr_αI_4-α the halogen atoms are perfectly mobile, and that the same is true for the chlorobromides and chloroiodides.