title: Electronic structure of coordinatively unsaturated molybdenum and molybdenum oxide carbonyls.
abstract: Results of density functional theory calculations on coordinatively unsaturated molybdenum carbonyl and molybdenum oxide carbonyl anion and neutral complexes observed in previous experimental studies [Wyrwas, Robertson, and Jarrold, J. Chem. Phys. 126, 214309 (2007)] and extended to related complexes are reported. The ground and low-lying electronic states were calculated for the most stable structures predicted for Mo(CO)(n)/Mo(CO)(n) (-) (n=1-3, 5 and 6), MoO(CO)(n)/MoO(CO)(n) (-) (n=0-3), and MoO(2)(CO)(n)/MoO(2)(CO)(n) (-) (n=0-2). Interesting trends are predicted with CO addition, electron addition, and oxidation of the Mo center. In all cases, anions have stronger Mo-CO bond energies, which is attributed to enhanced pi(CO) ( *) backdonation. This enhancement is more dramatic for the molybdenum oxo complexes because the highest occupied molecular orbitals shift from Mo to the pi(CO) ( *) backbonds with the addition of oxygen to the Mo center. Sequential addition of CO for all species results in a sequential stabilization of low spin states and a destabilization of higher spin states. Further, average Mo-CO bond lengths increase as carbonyls are sequentially added. This effect is attributed to fewer electrons per Mo-CO pi(CO) ( *) backbond. Finally, addition of O to Mo(CO)(n) appears to weaken the Mo-CO bonds, and addition of CO to MoO(n) appears to weaken Mo-O bonds. The calculations are validated by favorable agreement between the available measured anion photoelectron spectra and simulated spectra based only on calculated spectroscopic parameters (vibrational frequencies and normal coordinate displacements).
authors.affiliation: Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, USA.
authors.forename: Ekram
authors.initials: E
authors.lastname: Hossain
authors.forename: Caroline Chick
authors.initials: CC
authors.lastname: Jarrold