Speciation of Mixtures of Copper (I) and Copper (II) Mixed Ligand Complexes by X-Ray Absorption Fine Structure Spectroscopy

Studies on speciation have been done in the mixtures of mixed ligand copper complexes. Three heterogeneous mixtures have been studied, each having one Cu(I) complex and one Cu(II) complex. The Cu(I) complex is Cu(thu)Cl 0.5H₂O] (1) and the Cu(II) complexes are Cu(L-phen)(bpy) H₂O] (2), Cu(L-tyr)(phn) 2.5H₂O] (3), and Cu(dien)(ina) 4H₂O.1/2SO₄] (4) (where thu = thiourea, phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine, tyr = tyrosine, dien = diethylenetriamine, and ina = isonicotinate anion). The mixtures have been prepared by mixing the Cu(I) complex with each of the Cu(II) complexes in the ratio of 1:1 by mole percentage. The X-ray absorption fine structure (XAFS) spectra have been recorded at the K-edge of copper in the mixtures as well as in the complexes, separately. The aim of the present work is to make a study of the different methods of speciation using XAFS, viz., principal component analysis (PCA) and the target transformation (TT) method, the linear combination fitting (LCF) method, derivative spectra methods, and normalized difference absorption edge spectra (NDAES) analysis. It has been shown that these methods can be used to determine the relative quantity of the mixed ligand complexes in their mixtures.