Theoretical studies of the transition metal–carbonyl systems MCO and M(CO)2, M=Ti, Sc, and V

Abstract

A b initio calculations on the transition metal–carbonyl systems MCO and M(CO)2, M=Ti, Sc, and V, have been carried out using large Gaussian basis sets and an extensive treatment of electron correlation. The dissociation energies (De) and geometries of these molecules are given, and the bonding mechanisms are discussed. High-spin ground states are favored for the monocarbonyl molecules, whereas for the dicarbonyl molecules there is a competition between high-, intermediate-, and low-spin states, which are found to be very close in energy. The computed De(Ti–CO) is 0.62 eV whereas for Ti(CO)2 it is 1.02 eV, relative to the ground state Ti atomic asymptote and CO(1Σ+). This suggests that the recent experiment giving a value of ≊1.75 eV for De[Ti–(CO)x] should be interpreted as giving the De for Ti(CO)x, x≥2. For the three metal atoms the binding energy per carbonyl is found to be significantly lower for the dicarbonyl than the monocarbonyl molecules. This is in contrast to the Ni(CO)x molecules, where each CO is bound with approximately the same energy.