MOLECULAR MODELLING OF DIMETAL SYSTEMS. J. Bacsa, J. C. A. Boeyens, Centre for Molecular Design, Department of Chemistry, University of the Witwatersrand, Private Bag 3, Johannesburg 2050, South Africa

A significant feature of the dinuclear metal cluster complexes with multiple metal-metal bonds are their geometries; typically very short metal-metal bonds and eclipsing ligand atoms. These features have been modelled by Boeyens using Molecular Mechanics [1]. This study extends the techniques developed by Boeyens to dinuclear clusters where the bond order is uncertain and to clusters containing mixed metal atoms. This allows for the electronic effects in the metal-metal bond to be studied by quantifying and hence subtracting contributions made by steric effects to the overall metal-metal bond interaction. Thus the electronic nature of the dimetal bond can be studied in greater detail.

The force field for metal-metal bonds is not well established in the literature. Therefore suitable values of the force constant, k and and the undistorted bond length, r_o of the metal-metal bond are chosen empirically. A likely value of r_o is assumed and k is adjusted until a combination (k, r_o) is found to reproduce the observed structure after refinement. The transferable force field parameters for the dimetal bond are determined by identifying a unique pair (k, r_o) for the metal-metal bond occuring in two different steric environments.

1. J. C. A. Boeyens, Inorganic Chemistry, 1985, 24, 4149.