APPLICATION OF A UNIVERSAL FORCE-FIELD TO MAIN GROUP COMPOUNDS

The ability of a Universal force field (UFF) to reproduce the structures of a variety of main group molecules is examined. The magnitude of bond distance errors for main group compounds are somewhat larger than for organic compounds, though X-C bond distances are well reproduced. Bond distance errors for X-Y polar covalent bonds are generally less than 0.05 angstrom. Comparable bond length errors are observed for hypervalent X-O and X-N bonds (errors on the order of 0.05 angstrom) and dative bonds (errors as large as 0.04 angstrom). The error in bond length for bonds involving centers with multiple electronegative substituents bound to an electropositive center approaches 0.1 angstrom. Bond angle errors are generally less than 5-degrees, although larger errors (up to 14-degrees) are frequently observed for hypervalent complexes and in centers with multiple electronegative substituents. UFF gives very large bond angle errors (up to 44-degrees) for some heavy atom maingroup compounds such as the C-Tl-C bond in diethyldithiocarbamatodiphenylthallium(III), where the electronic structure is incorrectly described.