X-ray absorption studies of copper(II) mixed ligand complexes with tetramethylethylenediamine as primary ligands

Abstract

X-ray absorption near edge structure (XANES) measurements have been made on the K-edge of copper in some of its biologically important complexes involving tetramethylethylenediamine (tmen) as primary ligand. Other inorganic anionic ligands are oxalate anion (ox), acetylacetonate anion(acac), glycinate(gly) anion and ethylenediamine(en). Various X-ray absorption parameters in the near edge region, e.g., chemical shift, i.e., shift of K-edge of copper in complex with respect to K-edge of copper metal, energy position of the principal absorption maximum and edge-width have been determined. The K-edge has been found to split into two components, i.e., K1 and K2 in the complexes. This feature suggests square planar geometry for the complexes. The chemical shift data suggests that in the complexes copper is in oxidation state +2 and that the relative ionic character of the complexes is in the following sequence: Cu(tmen)(ox).4H2O < Cu(tmen)(acac)(ClO4) < Cu(tmen)(gly)ClO4 < Cu(tmen)(en)SO4.4H2O. For these four complexes, we observe that the sequence of variation of chemical shifts follows the same trend as obtained in the available spectrochemical series, i.e., oxalate < glycinate < ethylenediamine. The effective nuclear charge has been estimated from the chemical shift data.