Geometry prediction of bridged zirconocene dichlorides by quantum chemicalmethods

The ab initio Hartree-Fock theory has been demonstrated to give accurate ge ometry predictions for bridged zirconocene dichlorides. Equilibrium geometr ies of crystallographically characterized bridged zirconocene dichlorides w ere optimized by Hartree-Fock, MP2, BLYP, and B3LYP methods, with basis set s ranging from 3-21G* to 6-311G**. Selected geometrical parameters were com pared with experimental crystal structures. The least expensive HF/3-21G* m ethod proved to be notably accurate. The accuracy of HF/3-21G* was verified by a comprehensive data set of 62 bridged zirconocene dichlorides. Further more, experimental corrections were applied to the optimized geometry param eters to eliminate systematic deviations. Corrections resulted in considera bly improved accuracy for systematically overestimated metal-ligand distanc es, with maximum deviation falling from 0.081 to 0.039 Angstrom, and absolu te average deviations from 0.048 to 0.012 Angstrom. Ligand-metal-ligand ang les were predicted accurately with absolute average deviations of 0.7-1.3 d egrees. Zirconium-chlorine distances and chlorine-zirconium-chlorine angles are relatively constant in the studied molecules. Zirconium-cyclopentadien yl distances can be influenced mainly by modifying the ligand structure, wh ereas cyclopentadienyl-zirconium-cyclopentadienyl angles and cyclopentadien yl-cyclopentadienyl plane angles can be controlled by bridge modifications. The HF/3-21G* method can be applied for the estimation of steric effects i n zirconocene catalyzed polymerization reactions, therefore being suitable for the construction of structure-polymerization property correlations. (C) 2000 John Wiley & Sons, Inc.