The electronic structure of transition metal tricarbonyl derivatives in the ground state and the cationic hole-states. a semiempirical INDO MO investigation based on the green's function formalism

Abstract

The electronic structures of benzene chromium tricarbonyl (1), cyclopentadienyl manganese tricarbonyl (2), trimethylenemethane iron tricarbonyl (3), cyclobutadiene iron tricarbonyl (4) and butadiene iron tricarbonyl (5) have been studied in the ground state and in the cationic hole-states by means of semiempirical INDO calculations and many-body perturbation theory based on the Green's function formalism. The vertical ionization potentials of 1–5 in the outer valence region have been calculated with the inclusion of electron correlation and relaxation. In the cases of 1 and 2 it is found that the sequence of the ionization events corresponds to the ordering of the molecular orbitals (MO's) in the electronic ground state. The breakdown of Koopmans' theorem is demonstrated for the iron complexes 3–5 where the highest occupied MO'S are of ligand type while the first ionization potentials are due to MO's with predominant metal 3 d character. The different behaviour of the Cr, Mn and Fe tricarbonyl complexes is analyzed as a function of the localization properties of the orbital wavefunction and as a function of the corresponding two-electron integrals. The different bonding schemes in the series 1–5 are discussed.