Ammonium Hexachlor-rhodite, 2(NH₄)₃RhCl₆

Ammonium Hexachlor-rhodite, 2(NH₄)₃RhCl₆.3H₂O, may be prepared by mixing solutions of rhodium trichloride and ammonium chloride, the latter in excess. On slow evaporation in the cold, long red needles crystallise out.

The same salt is formed when ammonium rhodochlornitrate, RhCl₃.3NH₄Cl.NH₄NO₃, is decomposed with water and allowed to stand. In fact this is a better method of preparing the compound than the previous one, since there is no danger of its being contaminated with crystals of ammonium chloride.

Further, it is obtained on warming ammonium rhodium nitrite with concentrated hydrochloric acid. It is readily soluble in water, but not in alcohol. The crystals do not effloresce. When heated to glowing, metallic rhodium is left. According to Gutbier and Htittlinger the salt may also be prepared by saturating an aqueous solution of potassium pentachlor-rhodite, K₂RhCl₅, with hydrogen chloride, which effects the precipitation of most of the potassium chloride, and subsequently adding ammonium chloride. The salt separates on standing as dark red crystals.