Valence-to-Core X-ray Emission Spectroscopy as a Probe of O-O Bond Activation in Cu2O2 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 [Cu-2(II)(mu-eta(2):eta(2)-O-2)](2+) core relative to its isomer with a cleaved O-O bond having a [Cu-2(III)(mu-O)(2)](2+) unit. The experimental studies are complemented by DFT calculations, which show that the unique VtC XES feature of the [Cu-2(II)(mu-eta(2):eta(2)-O-2)](2+) core corresponds to the copper stabilized in-plane 2p pi peroxo molecular orbital. These calculations illustrate the sensitivity of VtC XES for probing the extent of O-O bond activation in mu-eta(2):eta(2)-O-2 species and highlight the potential of this method for time-resolved studies of reaction mechanisms.