COMPARATIVE MOLECULAR MECHANICS STUDY OF THE HIGH-SPIN NICKEL(II) COMPLEXES OF AN EXTENDED SERIES OF TETRAAZA MACROCYCLES

Force field parameters for modeling tetraaza macrocyclic ligand complexes of high-spin Ni(II) are reported. The MM2 force field has been modified and extended to include systems containing a tetraaza macrocyclic ligand coordinated around four positions of an octahedral nickel ion (that contains halide or other monodentate ligands in the remaining coordination sites). X-ray structural data for twenty-one such high-spin complexes have been used in the calibration of an extended force field which is capable of modeling the geometries of complexes within the above category. However, it was found that relatively minor changes in particular force field parameters may lead to considerable variation in the relative strain energies for different stereoisomers of a given complex type. Comparative strain energies for metal complexes obtained in this manner should be considered, at best, to be only semiquantitative.