Identification of an iridium-containing compound with a formal oxidation state of IX

The tetrahedral iridium tetroxide cation [IrO4]+, which has an iridium 5d0 valence electron configuration and a formal oxidation state of IX, is generated in the gas phase, identified by infrared photodissociation spectroscopy, and predicted, by quantum chemical calculations, to be the most stable of all possible [IrO4]+ isomers.