Iridium Dichloride, IrCl₂

Iridium Dichloride, IrCl₂, was stated to result as an olive-green powder when spongy iridium is heated in a current of chlorine, although Claus regarded the product as a mixture of the free metal and its trichloride. A similar substance is obtained by the action of chlorine on iridium sulphide.

Wohler and Streicher, however, have prepared the dichloride by ignition of iridium trichloride in chlorine at 770° C., and thus placed its existence beyond all doubt. It is a crystalline substance, brown in colour, and insoluble alike in acids and bases. Its limits of stability are 763° to 773° C. in an atmosphere of chlorine. Above 773° C. it dissociates into the monochloride and free chlorine.

For many years, however, it has been known that iridium dichloride can exist in combination with certain other stable salts. Thus, the following complexes have been described: IrCl₂.H₂SO₃.4NH₄Cl, IrCl₂.(NH₄)₂SO₃.2NH₄Cl + 4H₂O, and IrCl₂.K₂SO₃.2NH₄Cl + 4H₂O.