Journal of Physical Chemistry A, Vol.117, No.46, 12116-12124, 2013
Shift from Covalent to Ionic Bonding in Al2MoOy (y=2-4) Anion and Neutral Clusters
The electronic and molecular structures of Al2MoOy (y = 2-4) anion and neutral complexes were studied using anion photoelectron spectroscopy and density functional theory calculations. The spectra are broad, reflecting significant structural changes in the transition from anion to neutral, and the neutral electron affinities determined from the spectra are similar for all three species. The calculations suggest that the lowest energy isomers of the neutral clusters can be described as predominantly (Al+)(2)[MoOy-2] ionic complexes, in which the Al+ cations bond with O2- anions in a way that minimizes repulsion with the positively charged Mo center. The anion structures for all three complexes favor closer Mo-Al and Al-Al internuclear distances, with the extra negative charge distributed more evenly among all three metal centers. Energetically, the fully occupied 3s orbitals on the Al centers are lower than the Mo-local 4d-like orbitals and above the O-local 2p-like orbitals. In the case of Al2MoO2-, there is direct Al-Al covalent bonding. The calculated spectroscopic parameters for these species are consistent with the observed spectra, though definitive assignments are not possible due to the broad, unresolved spectra observed and predicted.