Chlorostannates

Chlorostannic acid, H₂SnCl₆, exists, and from it are derived a number of salts, the stannichlorides.

Chlorostannic Acid, H₂SnCl₆.6H₂O, is formed when the solid pentahydrate SnCl₄.5H₂O, or a concentrated solution of the chloride is saturated with hydrogen chloride gas. It separates on cooling the liquid to 0° C. in thin plates, which melt at about 20° C. There is a marked similarity between this acid and its salts and chloroplatinic acid, H₂PtCl₆.6H₂O, and its salts, though the latter acid and its salts are the more stable.

Sodium Stannichloride, Na₂SnCl₆.5H₂O, crystallises in prisms when the concentrated solutions of the constituent salts are mixed together, the potassium salt K₂SnCl₆ crystallises in anhydrous regular octahedra, with which the ammonium salt (NH₄)₂SnCl₆ is isomorphous. This latter salt was formerly used by dyers, and was named pink salt, because of its use as a mordant for madder-red colours; it dissolves in 3 parts of water at 14.5° C., and from its dilute solution stannic hydroxide separates on boiling. A large number of stannichlorides have been prepared containing various amounts of water of crystallisation; the chlorides of barium, cadmium, copper, silver, lead, and thallium, however, appear not to combine with stannic chloride.