Stannic Iodide, SnI₄

Stannic Iodide, SnI₄, is formed from its elements, and is conveniently prepared by bringing together a carbon disulphide solution of iodine and metallic tin. Carbon tetrachloride may, however, be advantageously substituted for carbon disulphide, owing to the fact that stannic iodide is much more soluble in this solvent at its boiling-point than at ordinary temperature, and, therefore, separates on cooling. The iodide may also be obtained by precipitating a concentrated solution of stannic chloride with potassium iodide. It is a bright red, crystalline powder consisting of regular octahedra; after sublimation, however, it appears in yellowish red needles. This compound melts at 143.5° C., and boils at 340° C., though it is said to sublime at 180° C. It may be dissolved in carbon disulphide, alcohol, ether, chloroform, benzene, and arsenic tribromide. Cryoscopic determinations of the molecular weight of stannic iodide in the last-named solvent yield abnormal results, of which various explanations have been given.

Stannic iodide does not give a clear solution with water on account of hydrolysis; it forms with ammonia three additive compounds: SnI₄.3NH₃, SnI₄.4NH₃, SnI₄.6NH₃ (Personne), which are produced by the action of ammonia on a solution of the iodide in carbon disulphide or ether. The first compound is yellow; the other two are white. They are all volatile and are decomposed by water into ammonia, ammonium iodide, and stannic oxide. The compound SnI₄.8NH₃ has also been prepared.

Iodostannic Acid cannot be formed in aqueous solution on account of the hydrolysis of stannic iodide, which is much more complete than that of the chloride. Pyridine stanni-iodide, (C₅H₅NH)₂SnI₆, is formed in bluish black needles when an alcoholic solution of pyridine hydriodide is added to a solution of stannic iodide in alcoholic hydrogen iodide. The quinoline salt is similarly obtained.