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 angstrom 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 CuN4 and tetragonally elongated CuN6 complexes. In agreement with experiment, square-pyramidal coordination is marginally favoured over trigonal bipyramidal coordination for CuN5 species. However, if the ligand requirements dictate, the LFMM accommodates trigonal bipyramidal coordination for CuN5 species, tetrahedral distortions of CuN4 species and cis-elongated CuN6 species
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