Electronic Structure of the [Cu(Salen)] Complex and the Chemical State of Its Atoms Studied by Photoelectron Spectroscopy and Quantum-Chemical Calculations

The electronic structure of the [Cu(Salen)] complex was studied and the chemical state of its atoms was characterized by X-ray and ultraviolet photoelectron spectroscopy combined with density functional theory calculations. It was found that the presence of a complexing Cu atom leads to the electron density redistribution not only on the nitrogen and oxygen atoms involved in the CuO₂N₂ coordination center but also on the carbon atoms of the salen ligand. The valence orbitals of the atoms of the CuO₂N₂ coordination center were found to make the predominant contribution to the highest occupied molecular orbital, and the 3d atomic orbitals of Cu were shown to be distributed over molecular orbitals in the binding energy ranges of 2–4 and 6–11 eV.