Iridium tetroxide explained

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 6K. At higher temperatures, the oxide is unstable.^[1] The detection of the iridium tetroxide cation 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.

Notes and References

1. 10.1021/jp990388o. Reactions of Laser-Ablated Iridium Atoms with O₂. Infrared Spectra and DFT Calculations for Iridium Dioxide and Peroxoiridium(VI) Dioxide in Solid Argon. 1999. Citra. Angelo. Andrew. Lester. J. Phys. Chem. A. 103. 21. 4182–4190. 1999JPCA..103.4182C.