Iridium Tribromide, IrBr₃

Iridium Tribromide, IrBr₃.4H₂O, may be obtained by dissolving the hydrated dioxide, IrO₂.2H₂O, in hydrobromic acid, and evaporating to dryness to decompose the tetrabromide thus formed. Extraction with water and subsequent crystallisation yields olive-green prisms, very soluble in water, but insoluble in alcohol.

At 105-120° C. the water of crystallisation is removed.

An Acid Iridium Tribromide, IrBr₃.3HBr.3H₂O, is obtained as small, deliquescent, steely blue crystals on working the mother-liquor from the previous salt for a further crop of crystals. It decomposes at 120° C.

Like the trichloride, iridium tribromide unites with bromides of the alkali metals to form hromiridites, the most important of which are:

Potassium Bromiridite, K₃IrBr₆.3H₂O, long, olive-green needles; Sodium Bromiridite, Na₃IrBr₆.12H₂O, brownish green rhombohedra; Ammonium Bromiridite, [(NH₄)₃IrBr₆]₂H₂O, small olive-green crystals.