Rhodium Ammonium Chlornitrate, (NH₄)₃RhCl₆(NH₄)NO₃

Rhodium Ammonium Chlornitrate or Ammonium Rhodichlor-nitrate, RhCl₃.3NH₄Cl.NH₄NO₃ or (NH₄)₃RhCl₆(NH₄)NO₃, may be obtained by adding a considerable excess of ammonium chloride and some nitric acid to a strongly acid solution of rhodium trichloride. It may also be prepared by addition of ammonium nitrate to an acid solution of ammonium chlor-rhodite.

On evaporation in a warm place the salt crystallises out in reddish violet scales, resembling chromium trichloride. It was apparently first prepared by Claus as the result of crystallising a solution of ammonium chlor-rhodite in nitric acid. Claus, however, thought it was simply the chlor-rhodite in a second crystalline form. Wilm obtained the same salt, but overlooked its nitrate content, regarding it as a new double chloride, until Leidie drew attention to it.

Ammonium rhodochlornitrate may be dried at 100-105° C. without decomposition. It is very soluble in water, being decomposed by the same. The solution on standing deposits crystals of ammonium chlor- rhodite, and this is a useful method of preparing the latter salt free from excess of ammonium chloride. The rhodochlornitrate is stable in solution or in the presence of aqua regia. It is but slightly soluble in nitric acid.

The formation of this salt, Leidie points out, may be taken advantage of in separating rhodium from other metals accompanying it during the treatment of platinum ores.