β-Stannyl Chloride, Sn₅O₉Cl₂

β-Stannyl Chloride, Sn₅O₉Cl₂.4H₂O, is related to β-stannic acid, which may be written Sn₅O₉(OH)₂.4H₂O; and it may, therefore, be regarded as the chloride of this acid. An alternative view is to consider the hydroxide as amphoteric, and as behaving as a diacid base, of which β-stannyl chloride is a salt. Because of the mode of formation and properties of the chloride this latter view is perhaps to be preferred; thus it is a basic stannic chloride.

β-stannyl chloride is prepared by first acting on tin with nitric acid of density 1.3 to 1.4, the temperature being kept low to prevent the formation of parastannic acid; hydrochloric acid is then added to the resulting β-stannic acid, and the gelatinous mass produced is diluted with water and filtered. The filtrate is precipitated with hydrochloric acid, the precipitate washed with the acid diluted with an equal volume of water, and the product dried in a vacuum over sulphuric acid and potash. The β-stannyl chloride thus obtained is a transparent, glassy mass which contains nine or four molecules of water to one molecule of Sn₅O₉Cl₂, according to whether it has been dried in air or in a vacuum. It is soluble in dilute hydrochloric acid, and unlike stannic chloride is reprecipitated by the strong acid. This compound is also formed by hydrolysis when dilute solutions of stannic chloride are kept.