Stannic Fluoride, SnF₄

Stannic Fluoride, SnF₄, has been prepared by the interaction of stannic chloride and anhydrous hydrogen fluoride at high temperature. It is a snow-white, crystalline, hygroscopic substance, which has a density of 4.78 at 19° C., and boils at 705° C., but sublimes below this temperature. It dissolves in water with evolution of heat, forming a solution from which hydrated stannic oxide separates on heating or allowing to stand. A solution, which decomposes similarly, is obtained by dissolving the hydrated oxide in hydrofluoric acid. Stannic fluoride combines with ammonia and other bases, and also with alkali and other fluorides to form stannifluorides of the type M'₂SnF₆.

Stannic fluoride forms with ammonia at 43° C. the white solid SnF₄.NH₃, which can be heated to 400° C. with loss of very little ammonia; the compound SnF₄.2NH₃ is formed when stannic fluoride and ammonia are heated in a sealed tube at 120°-130° C. Both compounds dissolve in water, but their solutions gradually decompose. Aniline, pyridine, and quinoline also form additive compounds with stannic fluoride.

The stannifluorides were first investigated by Marignac. They are isomorphous with the corresponding complex fluorides of silicon, titanium, germanium, and zirconium.