Electronic Spectra of M(CO)6 (M = Cr, Mo, W) Revisited by a Relativistic TDDFT Approach

Abstract

Relativistic time dependent density functional calculations have been performed on the excited states of the M(CO)6 (M = Cr, Mo, W) series. Our results, in agreement with previous density functional1 and ab initio2 calculations on Cr(CO)6, indicate that in all members of the series the lowest excited states in the spectra do not correspond to ligand field (LF) excitations, as has been accepted in the past. Instead they correspond to charge transfer (CT) states. The LF excitations are calculated at much higher energy than suggested by the original assignment by Beach and Gray3 and at different energy along the M(CO)6 series, being much higher in the heavier carbonyls than in Cr(CO)6. These results lead to a definitive reassessment of the role of the LF states in the photochemical dissociation of the metal−CO bonds in the M(CO)6 series, suggesting that the experimentally observed photodissociation of the M−CO bond upon irradiation into the lowest energy bands occurs in the heavier carbonyls, as it does in C...