Hexachlorosmites, M₃OsCl₆

Osmium trichloride yields a series of double salts known as osmo-chlorides or chlorosmites, M₃OsCl₆. Of these the most important are the potassium and ammonium salts.

Potassium Chlorosmite, K₃OsCl₆.3H₂O, is obtained as dark red crystals, along with the colourless crystals of potassium and ammonium chloride by addition of ammonia to a solution of osmium tetroxide in aqueous potassium hydroxide, and subsequent saturation with hydrogen chloride.

The crystals effloresce in air. They dissolve in water to a red solution which possesses an astringent taste, but which becomes sweet and unpleasant upon standing.

The crystals dissolve in alcohol, but not in ether. Alkalies and alkali peroxides precipitate the hydrated sesquioxide from the aqueous solution.

Ammonium Chlorosmite, (NH₄)₃OsCl₆.3H₂O, results when hydrogen chloride is passed into a solution of osmium tetroxide in hydrochloric acid. The red liquid is evaporated with ammonium chloride, when crystals of the same colour are obtained.