Experimentally Calibrated Analysis of the Electronic Structure of CuO+ : Implications for Reactivity.

The CuO+ core is a central motif of reactive intermediates in copper-catalysed oxidations occurring in nature. The high reactivity of CuO+ stems from a weak bonding between the atoms, which cannot be described by a simple classical model. To obtain the correct picture, we have investigated the acetonitrile-ligated CuO+ ion using neon-tagging photodissociation spectroscopy at 5 K. The spectra feature complex vibronic absorption progressions in NIR and visible regions. Employing Franck-Condon analyses, we derived low-lying triplet potential energy surfaces that were further correlated with multireference calculations. This provided insight into the ground and low-lying excited electronic states of the CuO+ unit and elucidated how these states are perturbed by the change in ligation. Thus, we show that the bare CuO+ ion has prevailingly a copper(I)-biradical oxygen character. Increasing the number of ligands coordinated to copper changes the CuO+ character towards the copper(II)-oxyl radical structure.