X-ray absorption studies of copper (II) mixed ligand complexes with benzimidazole as one of the ligands

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 benzimidazole (BzImH) and other inorganic anionic ligands (X), viz; [Cu(BzImH)4X2] and [Cu(BzIm)2],where X= Cl, Br, 1/2SO4, ClO4, NO3, and BzIm = benzimidazolato anion. Various X-ray absorption parameters in the near edge region, such as., 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 estimated. All the complexes have been found to have copper in oxidation state +2. The shape of the K-edge has been found to show splitting of the K-edge into two components, i.e., K1 and K2 in all of these complexes. This feature suggests elongated octahedral and distorted tetrahedral geometries for the complexes which have also been proposed from the earlier studies. Further, the values of the chemical shift suggest the relative ionic character of the complexes in the following sequence: Cu(BzImH)4Br2 < Cu(BzImH)4Cl2< Cu(BzImH)4SO4 < Cu(BzImH)4(ClO4)2 < Cu(BzImH)4(NO3)2. The edgewidths of the K-edge also support this relative ionic character.