The electronic structure of transition metal carbonyl complexes

Abstract

Discrete variational X _α calculations are reported on the neutral carbonyl complexes Ni(CO)₄, Fe(CO)₅ and Cr(CO)₆, as well as on the ions Co(CO)₄ ^-, Fe(CO)₄ ^-, Mn(CO)₅ ^-, Mn(CO)₆ ⁺ and V(CO)₆ ^-. Valence electron ionization potentials are predicted very well by transition-state calculations. The description of complex binding in Ni(CO)₄ according to these calculations differs markedly from the one obtained in MSX_α and Hartree-Fock calculations, which contradicted each other. The relative magnitude of σ-donation and π-back-donation is found to be roughly equal in the three neutral complexes (0·2–0·3 and 0·5 e respectively). Large changes occur in the ionic complexes, notably in the π-back-donation. These changes are correlated with the observed shifts in C-O stretching frequencies and force constants.