Electronic and geometric structure of the 3d-transition metal monocarbonyls MCO, M=Sc, Ti, V, and Cr

摘要

The electronic and geometric structure of the 3d-transition metal monocarbonyls MCO, M=Sc, Ti, V, and Cr was investigated through coupled cluster (CC) and multireference variational methods (MRCI) combined with large basis sets. For the ground and a few low-lying excited states complete potential energy profiles were constructed at the CC-level of theory. The M-CO dissociation energies of the ground states (X) over tilde (4)Sigma(-),(X) over tilde (5)Delta,(X) over tilde (6)Sigma(+), and (X) over tilde (7)A(') are calculated to be 36, 27, 18, and 2 kcal/mol for ScCO, TiCO, VCO, and CrCO, with respect to Sc(F-4),Ti(F-5),V(D-6),Cr(S-7)+CO(X (1)Sigma(+)). The bonding is rather complicated and could be attributed mainly to pi-conjugation effects between the M and CO pi-electrons, along with weak sigma-charge transfer from CO to M atoms. Almost in all cases the metal atoms appear to be slightly positively charged, at least according to the direction of the dipole moment vectors and the MRCI population densities.