Ammonium hexachloroiridate(IV)

Olive Green Crystals

Iridium complexes are generated from ammonium hexachloroiridate.

Ammonium Hexachloroiridate(IV) is a reagent used for research applications and is used for catalytic production on hydrogen.
It is a key intermediate in the isolation of iridium from ores. Most other metals form insoluble sulfides when aqueous solutions of their chlorides are treated with hydrogen sulfide, but [IrCl6]2 resists ligand substitution. Upon heating under hydrogen, the solid salt converts to the metal:
(NH4)2[IrCl6] + 2 H2→ Ir + 6 HCl + 2 NH3

ChEBI: Ammonium hexachloroiridate is a salt comprising separate ammonium cations and octahedral [IrCl6](2-) anions. It contains a hexachloroiridate(2-).

Non flammable

It is precipitated several times from aqueous solution by saturation with ammonium chloride. This removes any palladium and rhodium. It is then washed with ice-cold water and dried over conc H2SO4 in a vacuum desiccator. If osmium or ruthenium is present, it can be removed as the tetroxide by heating with conc HNO3, followed by conc HClO4, until most of the acid has been driven off. (This treatment is repeated. ) The near-dry residue is dissolved in a small amount of water and added to excess NaHCO3 solution and bromine water. On boiling, iridic (but not platinic) hydroxide is precipitated. It is dissolved in HCl and precipitated several times, then dissolved in HBr and treated with HNO3 and HCl to convert the bromides to chlorides. Saturation with ammonium chloride and cooling precipitates ammonium hexachloroiridate which is filtered off and purified as above [Woo & Yost J Am Chem Soc 53 884 1931].