Theoretical analysis of apical bonding in copper(II) chelates with N-substituted amino acids

The interdependence between the side of apical coordination of H₂O and steric crowding at the apical positions was investigated on a set of 34 copper(II) bis-complexes with N- and N,N-substituted amino acids. As a measure of steric crowding, overlapping volumes V* were used, calculated using a modified overlapping spheres method. Steric crowding around the apically bonded ligand was the same for this set of complexes as for the copper(II) bis-complexes with naturally occurring amino acids, with the optimal occupied volume values between 1 and 1.5 Å³. The interdependence between the length of the apical bond and distortion of the coordination polyhedron was also studied. The apical bond length showed sigmoidal dependence on the magnitude of distortion.