ESR Studies of the Copper(II) Complexes of Ammo Acids

Abstract

Abstract The X-band and K-band ESR spectra of the trans-planar copper(II) complexes of amino acids, whose crystal structures are now known, were measured in a polycrystalline state at room temperature and in frozen aqueous-methanolic solutions at the temperature of liquid nitrogen. The polycrystalline samples showed a variety of ESR line shapes, most of which had three different principal g values; g1=2.04–2.07, g2=2.08–2.12, and g3=2.16–2.29. On the other hand, all the ESR line shapes observed for the frozen solutions were quite similar, and they indicate a normal tetragonal copper (II)-ion environment. There was, moreover, a remarkable difference in the g values between the complexes in the two states. The correlation among the g values, the d-d band energies, the bonding parameters (a measure of the degree of covalency of the copper-ligand bondings), and the geometrical configurations of the coordinating atoms for the complexes in a crystal is discussed in some detail.