Iridium tetroxide

Iridium tetroxide (IrO₄, Iridium(VIII) oxide) is a binary compound of oxygen and iridium in oxidation state +8. This compound was formed by photochemical rearrangement of [(η¹-O₂)IrO₂] in solid argon at a temperature of 6 K (−267.15 °C; −448.87 °F). At higher temperatures, the oxide is unstable. The detection of the iridium tetroxide cation IrO⁺
₄ by infrared photodissociation spectroscopy with formal oxidation state +9 has been reported, the highest currently known of any element. However no salts are known, as attempted production of an Ir(IX) salt such as IrO₄SbF₆ did not result in anything.

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