ChemInform Abstract: Metal-Metal Interactions in Transition-Metal Clusters with π-Donor Ligands

A variety of structural types of transition metal clusters containing mainly π-donor ligands are reviewed. Their structure and bonding are analyzed using a simple and unified molecular orbital approach based on the consideration of metal-metal bonding as arising from the interaction of the frontier orbitals of individual metal fragments derived from their local MLn coordination. This kind of “local metal frontier orbital” approach allows us to construct metal-metal orbital interaction diagrams in a convenient way. Using these molecular orbital diagrams, relevant optimal electron counts for major structural types are discussed. It is emphasized that the “t2g” set fragment orbitals, which are non-bonding in carbonyl clusters, play the crucial role in metal-metal bonding for clusters with π-donor ligands. Bonding characteristics for Mo(W)-Fe-S, Ni-S(Se) and related clusters are also discussed.