XAFS study of mixed ligand benzimidazole copper complexes having distorted coordination geometry.

• Cu benzimidazole complexes 1–6 studied by XANES fingerprinting, EXAFS fitting and XANES simulations. • XANES indicated Cu2+ nature in all complexes with square pyramidal geometry for 1–5. • EXAFS further showed presence of two independent Cu formula units in 1 and 2. • XANES and EXAFS showed that Cu has tetrahedrally distorted square planar structure in 6. • p-DOS and d-DOS were correlated to splitting of white line and intensity of pre-edge peak. X-ray absorption fine structure (XAFS) at the Cu K-edge in copper complexes, viz., [Cu(BzImH) 4 X 2 ], where BzImH= benzimidazole and X= ClO 4 (1), NO 3 (2), ½ SO 4 (3), Br (4), Cl (5) and their 'inner complex' [Cu(BzImH) 2 ] (6) have been investigated using synchrotron radiation. The crystal structures of 4, 5 and 6 are not available. From EXAFS analysis, the structures of 4 and 5 have been estimated to be distorted square pyramidal and that of 6 to be tetrahedrally distorted square planar. Though, the crystal structure of the complexes 1 and 2 have been studied earlier using X-ray crystallography and found to be distorted square pyramidal, these complexes have been included in the study because each of these complexes has two independent formula units having two Cu sites in a molecule. In 2 the axial bond lengths are not similar at Cu1 and Cu2 sites. The electronic nature of Cu metal center in the complexes has been studied using XANES. The XANES spectra have been simulated and p-DOS and d-DOS calculated simultaneously for the Cu center in the complexes. The splitting of Cu K-edge into two edges K 1 and K 2 has been correlated with the p-DOS and the occurrence of pre-edge has been correlated with d-DOS. [Display omitted] [ABSTRACT FROM AUTHOR]