Valence-to-Core X-ray Emission Spectroscopy as a Probe of O-O Bond Activation in Cu2 O2 Complexes.

Valence-to-Core (VtC) X-ray emission spectroscopy (XES) was used to directly detect the presence of an O-O bond in a complex comprising the [CuII 2 (μ-η2 :η2 -O2 )]2+ core relative to its isomer with a cleaved O-O bond having a [CuIII 2 (μ-O)2 ]2+ unit. The experimental studies are complemented by DFT calculations, which show that the unique VtC XES feature of the [CuII 2 (μ-η2 :η2 -O2 )]2+ core corresponds to the copper stabilized in-plane 2p π peroxo molecular orbital. These calculations illustrate the sensitivity of VtC XES for probing the extent of O-O bond activation in μ-η2 :η2 -O2 species and highlight the potential of this method for time-resolved studies of reaction mechanisms.