EFFECTS OF RELATIVITY ON THE NI-CO, PD-CO, AND PT-CO BONDING MECHANISM - A CONSTRAINED SPACE ORBITAL VARIATION ANALYSIS OF DENSITY-FUNCTIONAL RESULTS

Using a density functional based constrained space orbital variation t echnique, we have analyzed the importance of relativistic effects on t he various mechanisms which affect the metal-CO bond in Ni, Pd, and Pt monocarbonyls. The bonding is dominated by the rr back-donation mecha nism which, for Pd and Pt, is considerably reinforced by relativistic effects. The weaker Pd-CO bonding is rationalized by reduced back-dona tion. The combined effect of relativistic bond length contraction and of the atomic d orbital energies determines the trend in the metal-CO bond strengths, This trend is different from the one found for the coo rdinatively saturated M(CO)(4) tetracarbonyls.