Electronic Structure of Small Isolated and Supported Manganese Oxide Clusters

In the present work, possible molecular models of the isolated manganese oxides and supported Mn₃O/Al₂O₃ structures were built based on small clusters of passivated MnO. The support was represented as a simplified model of the alumina tetramer cluster based on small fragments of AlOH. Combinations of MnOH and AlOH clusters were made to form both the isolated and supported manganese oxides clusters. The electronic structure of these systems was characterized by ab initio methods (DFT and CASPT2). It was observed that the vertical excitation energy of the isolated and supported Mn₃OH clusters is significantly lower than that of the alumina cluster model, while both the isolated and supported Mn₃OH wave function characters are qualitatively similar with respect to the ground state and electronic transition processes, suggesting that the alumina cluster behaves as an inert support, since there is little contribution of this component in the description of the low-lying electronic states. The present study also reports for the first time the spectroscopic parameters of several clusters containing the manganese transition metal atom.