Potassium Iridicyanide, K₃Ir(CN)₆

Pure iridium, when heated in a finely divided condition to a dull glow with potassium cyanide, yields a double cyanide.

The yield, however, is poor. A better method is to heat ammonium chloriridate with a slight excess of potassium cyanide for ten to fifteen minutes. Extraction of the melt with boiling water and subsequent evaporation yields crystals of the potassium iridicyanide, the other constituents, namely, potassium chloride and cyanide, being more soluble and remaining in solution.

Potassium iridicyanide yields hexagonal crystals (a: с = 1: 1.3319) which are colourless, transparent, and stable in air. The crystals dissolve in water easily, but only with difficulty in alcohol. The solution yields precipitates of various colours with salts of the heavy metals. With ferrous salts a white precipitate is obtained; with ferric, a bright yellow. Acetic acid is without action on potassium iridicyanide, although it decomposes the corresponding rhodicyanide. This affords, therefore, a useful method of separating rhodium from iridium.