Iridium tetroxide
Iridium tetroxide is a binary compound of oxygen and iridium in oxidation state +8. This compound was formed by photochemical rearrangement of IrO2 in solid argon at a temperature of. At higher temperatures, the oxide is unstable. 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 salt such as IrO4SbF6 did not result in anything.