Analysis of the coordination geometry in copper complexes

Abstract

Geometrical parameters associated with a metal coordinated system have been analysed using data from 75 structures of copper complexes involving 370 coordination bonds. Coordination bond length and coordination bond angle, and deviation of the metal atom from the plane of equatorial ligand atoms have been analysed in detail for both oxygen and nitrogen ligand atoms. At the ligand end, the parameters defined closely follow that of the hydrogen bonded system and are related to the lone pair orbital directions. We find that (1) for oxygen ligands, the axial bond lengths are distinctly longer than the equatorial ones in octahedral (OCT) and square pyramidal (PY) geometries. The situation is reversed for trigonal bi-pyramidal (TBP) geometry with nitrogen ligands. (2) The coordinnation bond angle involving axial atoms varies between 130 and 180° for the OCT case and 170 and 180° for TBP geometry. Angles lying around 90° range from 75-105° with a few exceptions in OCT geometry. (3) The metal atom lies very nearly in the equatorial plane in TBP, while it deviates significantly in others. The extent of deviation can be explained qualitatively with the pull of the metal atom by the axial atoms. (4) The distribution of the ligand end parameters indicate that the bond direction strongly tends to cling to the associated orbital. When the ligand atom has two orbitals, the influence of the non-associated orbital is not significant and is far less as compared to hydrogen bonding.