XAFS Study of Mixed Ligand Ethylenediamine Copper Complexes Having Distorted Octahedral Coordination Geometry

Abstract

X-ray absorption fine structure (XAFS) at the Cu K-edge in copper complexes, viz., Cu(en)₂Br₂.H₂O (1), Cu(en)₂Cl₂.H₂O (2), Cu(en)₂(ClO₄)₂ (3), Cu(en)₂SO₄ (4), where en= ethylenediamine, have been investigated using synchrotron radiation. For the analysis of EXAFS, theoretical models have been generated for each complex using their available crystal structure data. The theoretical models have been fitted to the respective experimental data by two methods. In the first method, the coordination number N has been varied and amplitude reduction factor  has been fixed. In the second method, N has been fixed and  has been varied. The results obtained by the two methods have been compared with each other. Ab-initio XANES calculations have been performed to obtain simulated XANES spectra as well as p-DOS and d-DOS for the absorbing Cu metal center. The XANES calculations reproduce well the absorption edge in the experimental XANES spectra. The splitting of Cu K-edge into two edges K₁ and K₂ has been correlated with the p-DOS. The separation of the K₁ and K­₂ peaks in the derivative experimental spectra agree well with the derivative simulated spectra. The occurrence of pre-edge has been correlated with d-DOS.