[en] Extended X-ray absorption fine structure (EXAFS) spectra have been studied at the K-edge of copper in some of its biologically important complexes, viz., [Cu(BzImH)₄X₂] and [Cu(BzIm)₂], where X= Cl, Br, 1/2SO₄, ClO₄, NO₃, and BzIm = Benzimidazolato anion. The spectra have been recorded using a bent crystal 0.4 m Cauchois-type transmission spectrograph. The positions of EXAFS maxima and minima have been used to determine the bond lengths in the complexes with the help of three different methods, namely, Levy's, Lytle's and Lytle, Sayers and Stern's (L.S.S.) methods. The phase uncorrected bond lengths have also been determined from Fourier transforms of the experimental spectra. The results obtained from these methods have been discussed and it has been found that the results obtained by L.S.S. method are comparable with the results obtained by Fourier transformation method and that these two methods give phase uncorrected bond lengths.

[en] Highlights: • Distorted octahedral Ni complexes have been studied using EXAFS as well as XANES. • Simulated XANES spectra show different features depending on metal p- and s-DOS. • s-DOS contribution to rising part of edge has been found to vary among complexes. • Constant p-DOS over 0–10 eV give rise to weak and split while line in complex 1. - Abstract: Distortion in mononuclear Schiff base nickel (II) complexes having pyridine and related N-containing heterocyclic derivatives has been studied using X-ray absorption spectroscopy. Extended X-ray absorption fine structure (EXAFS) analysis has been used to confirm the octahedral nature of Ni center and obtain a simple cluster of atoms around this metal ion. Ab-initio X-ray absorption near edge structure (XANES) simulations have been performed using FEFF9 for almost similar coordination around nickel metal in these complexes. The study supports variation in the order of distorted octahedral nature of Ni complexes with O and N atoms around the metal ions, with respect to changing nature of ligand. Theoretical XANES spectra generated for clusters of atoms around the metal ion have been correlated to corresponding p-DOS and s-DOS of the metal.