Direct Spectroscopic Confirmation of the Oxygen‐Centered Diradical Character of the Tetraoxidorhenium(VII) Cation [Re(O)4]

Mononuclear inorganic diradical species are scarce. Here, we confirm, via X‐ray absorption spectroscopy in the gas phase combined with computational studies, the oxygen‐centered diradical character of the tetraoxidorhenium(VII) cation. A dioxido‐superoxido isomer, close in energy to the diradical, is also found, where rhenium appears in its rare oxidation state of +6. Addition of one or two hydrogen atoms to [Re,O4]+ forms hydroxido ligands, and strongly disfavors isomers with any oxygen‐oxygen bond. This adds spectroscopic characterization of the rhenium oxidation state and the nature of ligands to the known ability of [Re,O4]+ to perform two consecutive hydrogen‐atom ion reactions from methane, and demonstrates that pentaatomic [Re,O4]+ combines a metal center in its highest oxidation state with two oxygen‐centered radical ligands in a highly reactive species. Highly reactive [ReO4]+ combines rhenium in its highest oxidation state with oxygen‐centered diradical character of its oxygen ligands in the small volume of only one pentaatomic entity.