BIMETALLIC THERMOCHEMISTRY - PERTURBATIONS IN M-H AND M-C BONDS DUE TO THE PRESENCE OF M'

The effect of perturbing the environment of a transition metal-ligand (M-L) complex by the addition of another metal atom, M', was investiga ted by ab initio generalized valence bond/correlation-consistent confi guration interaction methods. We have examined the properties of low-l ying states of Pt-X, Zr-X, and (PtZr)-X, where X = {H, CH3}. The bondi ng trends of the transition metal diatomic-ligand complexes have been compared to their monometallic analogs. We find that Zr acts as an ele ctron donor in all the diatomic complexes and that in these complexes the hydride-diatomic bond strengths are increased much more on average than the methyl-diatomic bonds relative to the monometallic complexes . For example, the PtZr-H bond strength is increased by over 14 kcal/m ol relative to Zr-H, while the Zr-CH3 bond strength increases only by 4 kcal/mol in the bimetallic complex. The Pt-ligand bond strengths als o both increase upon ''alloying'' the transition metal, but the magnit ude of the changes are more similar-8 kcal/mol for the hydride versus 6 kcal/mol in the methyl complex. We comment on the implications of th ese results for the potential use of Pt Zr alloys as dehydrogenation c atalysts.