Potassium Chloriridite, K₃IrCl₆

Potassium Chloriridite, K₃IrCl₆.3H₂O, results (1) when potassium carbonate and chloriridate are heated to redness; (2) on heating potassium chloriridate in hydrogen chloride at 440° C. Some insoluble iridium trichloride is simultaneously produced; (3) it is also formed by reducing a suspension of chloriridate in water with sulphur dioxide, hydrogen sulphide, or nitric oxide. The salt crystallises in olive prisms, which effloresce in the air, and are readily soluble in water, although insoluble in alcohol.

The monohydrate, K₃IrCl₆.H₂O, was prepared by Duffour by the action of hydrochloric acid upon the double oxalates of iridium and potassium at boiling temperature. It yields greenish brown orthorhombic crystals, isomorphous with its rhodium analogue, K₃RhCl₆.H₂O.

The aqueous solution on prolonged boiling deposits an oxychloride in the form of a green powder. Chlorine water or aqua regia converts the salt into the chloriridate. Addition of excess of alkali to a solution of the chloriridite in water does not cause a precipitate to form, since the sesquioxide dissolves as rapidly as formed (vide infra), yielding an olive-green solution.