Chelates of copper(II) with N-alkylated amino acids: distortion of coordination polyhedron and apical bond length

Abstract

The length of the bond between copper(II) and an apically situated water molecule varies for six N-alkylated α-amino acid chelates with distorted coordination geometry from 2.206 to 2.464 Å. This is attributed to differences in distortion of the copper(II) coordination polyhedron. Apical bond lengths of six distorted and one strictly planar copper(II) complexes (with proline, Cu OH 2 = 2.52 A ̊ ) were correlated with ten measures of distortion (various combinations of valence angles defining the copper coordination geometry, distortion vectors and their components in the (CuOH 2) direction) yielding an r value typically in the range 0.80–0.93; multiple correlation yielded an R value up to 0.96. The ability of molecular mechanics models to reproduce the apical bond length is briefly discussed and an approach based on the use of regression functions for estimation of CuOH 2 bond lengths from the calculated distortion of the coordination polyhedron is proposed.