In this project in the Theoretical and Computational Physical Chemistry Program of the Chemistry Division, Prof. Ondrechen will test models for bridged-valence dimers of ruthenium and back-bonded complexes of transition metal systems. The near-coincidence of infrared and Raman frequencies in the Creutz-Taube ion is treated with inclusion of electron-electron repulsion and hybrid terms. The model will be extended to polymeric one-dimensional chains and two-dimensional nets, and tested to see if the hybrid terms give rise to a novel purely electronic mechanism for superconductivity. A model for systems with dimeric bridges will be used to study complexes with both pi-bonding and back-bonding interactions between the metal ion and a conjugated bridging ligand.