Exposing the Oxygen‐Centered Radical Character of the Tetraoxido Ruthenium(VIII) Cation [RuO₄]⁺

Abstract

The tetraoxido ruthenium(VIII) radical cation, [RuO4]+, should be a strong oxidizing agent, but has been difficult to produce and investigate so far. In our X‐ray absorption spectroscopy study, in combination with quantum‐chemical calculations, we show that [RuO4]+, produced via oxidation of ruthenium cations by ozone in the gas phase, forms the oxygen‐centered radical ground state. The oxygen‐centered radical character of [RuO4]+ is identified by the chemical shift at the ruthenium M3 edge, indicative of ruthenium(VIII), and by the presence of a characteristic low‐energy transition at the oxygen K edge, involving an oxygen‐centered singly‐occupied molecular orbital, which is suppressed when the oxygen‐centered radical is quenched by hydrogenation of [RuO4]+ to the closed‐shell [RuO4H]+ ion. Hydrogen‐atom abstraction from methane is calculated to be only slightly less exothermic for [RuO4]+ than for [OsO4]+.

Direct spectroscopic evidence for the high-spin state of dioxidomanganese(v)

“…Furthermore, we want to emphasize that neither in the oxygen K-edge spectrum of [OMn V O] + nor in [OMn IV OH] + the molecular orbital contributing to the energetically lowest lying excitation of the spectrum has a prominent 3d character. This is in contrast to the case of oxygen centered radicals, 63 which can therefore be excluded here.…”