GEOMETRY OPTIMIZATION OF ORGANOMETALLIC COMPOUNDS USING A MODIFIED EXTENDED-HUCKEL FORMALISM

The modified extended-Huckel method suggested recently by Calzaferri and co-workers has been parametrized for organometallic compounds in order to have at hand a semiempirical tool allowing for rapid optimization of their geometries. The model is based on (i) the introduction of an approximate two-body repulsive electrostatic energy term and (ii) the use of a distance-dependent Wolfsberg-Helmholz formula, K = 1 + kappae(-delta)(R(LAMBDAB)-d0), for 1-2 and 1-3 interactions. The optimum values for the kappa, delta parameters determined for given classes of metal-ligand interactions have been found to be transposable to systems exhibiting several types of ligands such as aromatic rings, carbonyls, phosphines, etc. The overall performance of the model is satisfactory, as it leads for a series of more than 30 organometallic compounds to average error bars of 0.058 and 0.039 angstrom on metal-ring and metal-carbonyl bond distances, respectively, and of 2.6-degrees on bond angles.