Iridium Disulphide, IrS₂

Iridium Disulphide, IrS₂, has been prepared in a variety of ways, chief among which are:

1. Heating ammonium chloriridate with sulphur.
2. Acting on finely divided iridium with an alkali polysulphide.
3. Passing hydrogen sulphide over lithium chloriridite at 4.7° C. No action takes place below 0° C., whilst above 10° C. the salt is rapidly attacked, free sulphur separating. The product is repeatedly extracted with absolute alcohol and dried at 90-100° C. in carbon dioxide.

Iridium disulphide is a brown powder. Moist air has no action on it. Heated to 300° C. in air, sulphur is expelled, metallic iridium remaining behind. Hydrochloric and nitric acids do not affect it although fuming nitric acid and aqua regia effect its decomposition. It is reduced to a lower sulphide at red heat in a current of carbon dioxide.