Electronic aspects of dioxygen binding to cobalt-schiff-base-complexes: Anab initio calculation

It is shown that there are four possible electronic configurations for the ground-state of the dioxygen complex of Co(acacen)L (with the fifth ligand L = none, H₂ O, Imidazole, CN^? and CO). Fromab-initio calculations with a minimal basis set, close energy values are indeed computed for these four configurations with the lowest one (ground state configuration) corresponding to a charge-transfer configuration Co(III)-O ₂ ^? ₂, in agreement with the results of ESR spectroscopy from the literature. The enthalpy of oxygenation is related to the σ-donor ability of the fifth ligand and to the ease of oxydation of Co(II) to Co(III).