A VALENCE FORCE-FIELD FOR ZIRCONOCENE DICHLORIDES

In this study valence force field parametrizations for zirconocene dichloride complexes are reported. The three models developed and investigated provide complete sets of parameters that can be used either in standard force fields without software extensions for the treatment of pi-ligands or in force fields that can handle the multiple-reference problem encountered in highly symmetric coordination compounds as well as in force fields where a distributed-forces model for the treatment of centrosymmetric ligands is available. The new parameters have been tested with a series of 21 nonbridged and 12 ansa-metallocene complexes. The agreement between X-ray structural data and the results of the three model calculations is excellent. On the average, bond lengths are reproduced to better than 2 pm, bond angles to 1-degrees, and the torsion angles defining the relative orientations of the ligands in the bent-metallocene conformers to about 60 for complexes exhibiting no significant intermolecular interaction in the solid state. Additionally, the new series of parameter sets presented allows for a good reproduction of the experimental vibrational data.