An X-ray absorption near edge spectroscopy (XANES) study on organochromium complexes at the Cr K-edge Original Research Article

A XANES study on a series of chromium carbene complexes reveals that the white line energies are influenced rather by the coligand sphere than by the carbene substitution pattern. Nevertheless, energy shifts arising from a modification of the carbene ligand are significant and can be explained in terms of π-donor/σ-acceptor properties of the carbene ligand which are coined by the heteroatom next to the carbene carbon atom. As observed for a limited number of compounds the energy shift of the white line correlates with the 53Cr-NMR shift which both reflect the effective charge at the metal. Surprisingly, the white line energies of the carbene complexes bearing a formally zerovalent metal resemble those observed for chromium(III) and -(IV) oxides Cr2O3 and CrO2, indicating a similar effective charge of the metal in these quite different types of compounds. All spectra exhibit a characteristic pre-edge structure which can be assigned to transitions into orbitals bearing d-character. An analysis of the shape resonances indicates a reciprocal correlation between the average Cr–C bond length and the energy position in the XANES spectra.