Molecular modelling for coordination compounds: Cu(II)-amine complexes.

The Ligand Field Molecular Mechanics (LFMM) method has been applied to 85 Cu(II)-amine complexes, eighteen of which were selected to form a training set. A single set of parameters yields Cu-N bond lengths for four-, five- and six-coordinate systems generally within 0.04 A of their X-ray crystallographic values. Larger deviations are indicative of counterion effects and/or crystallographic artefacts arising from Jahn-Teller averaging. The LFMM treatment is flexible and unbiased and for simple ligands, automatically gives planar CuN(4) and tetragonally elongated CuN(6) complexes. In agreement with experiment, square-pyramidal coordination is marginally favoured over trigonal bipyramidal coordination for CuN(5) species. However, if the ligand requirements dictate, the LFMM accommodates trigonal bipyramidal coordination for CuN(5) species, tetrahedral distortions of CuN(4) species and cis-elongated CuN(6) species.