Molecular mechanics calculations of beta-diketonate, aqua, and aqua-beta-diketonate complexes of lanthanide ions using Gillespie-Kepert model

A version of molecular mechanics based on the Gillespie-Kepert model of coo rdination bonds "repulsion" is applied to lanthanide complexes. The force f ield parameters are developed that describe the structure of beta -diketona te-, aqua-, and mixed aqua-beta -diketonate complexes with good accuracy; t he same parameters are applicable to various coordination numbers/polyhedra For the aqua complexes, typical root-mean-square deviation (calculated vs. X-ray experimental values) is 0.02 Angstrom in Ln-O bond lengths and 2.0 d egrees in O-Ln-O valence angles. For most of the other compounds, the same precision is achieved in coordination bond lengths, while 3.5 degrees is a typical precision for coordination bond angles. Calculations successfully r eproduce the puckering of the beta -diketonate chelate rings, as well as th e relative stability of isomers for a representative example. (C) 2000 John Wiley & Sons, Inc.