Impurity Atoms on Small Transition Metal Clusters. Insights from Density Functional Model Studies

Abstract

We review our computational studies at the DFT level on small isolated metal clusters of late transition metals that contain atomic (H, C, O) or diatomic (CO, N2) ligands. These investigations were initiated by the clarification of the structure of iridium and rhodium clusters, as characterized by EXAFS, and then were extended to clusters of other transition metals (Ni, Ru, Pd, Os, Pt). The results suggest that a single H atom hardly changes the structure of a small metal cluster, while the presence of O and C impurity atoms causes large variations in the metal–metal distances. The adsorption of single atoms results in a partial oxidation of the metal moiety, yet addition of an atomic impurity only moderately modifies the electronic properties of small clusters, whereas stronger modifications of the properties are caused when the charge of the metal cluster is varied. The dissociative adsorption of larger amounts of hydrogen, up to 6 H2 molecules, on metal tetramers causes an elongation of the (average) inter-metallic distances, bringing them close to the experimental values. This body of computational results can be helpful for elucidating the structures of experimentally observed species and for rationalizing their electronic and catalytic properties.