W0041

Computational and Database Studies on Differential Binding of Ligands to Metal Centers. R.F. See, M.L. Goodbread, G.J. Jancy and S.M. McCollester, Departments of Chemistry, Indiana University of Pennsylvania, Indiana, PA 15705.

The bond order sum (BOS) of a ligand to a 2⁺ metal center has been shown (Inorg. Chem. (1998) 37, 5369) to be a function of the specific ligand, with values ranging from 1.88 (water) to 2.56 (isothiocyanate ion). A strongly correlated relationship (R² = 0.98) has been found between the ligand-specific BOS and the total bonding to the coordinating nitrogen atom in the free ligands isothiocyanate, acetonitrile, imidazole and pyridine. This relationship holds both for molecules that follow the Aufbau principle, and for non-Aufbau species such as low-spin octahedral and square-planar Ni(II) complexes. Computational studies at the B3YLP / LACVP* level have been undertaken to help determine the physical basis for this relationship. The implications of these results on ligands containing other binding atoms, such as oxygen, carbon or phosphorus, will also be discussed.