Structural and Electronic Investigation of Copper(II) Complexes of Salicylaldehyde Benzoyl Hydrazine Derivatives via DFT and XAFS Analysis

In this work, two Copper(II) complexes that were produced and structurally studied were obtained from salicylaldehyde benzoyl hydrazine ligands. These complexes are (1) Cu(L1)2Cl2·2H2O, and (2) Cu(L2)2Cl2·2H2O. L1 stands for Salicylaldehyde Benzoyl Hydrazine (SBH), and L2 for 3-nitro salicylaldehyde benzoyl hydrazine (3NSBH). Calculations using density functional theory (DFT) were used to predict bond properties, examine electronic structures, and optimize geometries. EXAFS and XANES, two types of experimental X-ray absorption fine structure (XAFS) spectroscopy, were used to examine the oxidation state and local coordination environment of the copper centers. To examine and confirm the different coordination geometries of two Copper(II) complexes, a combined DFT and XAFS investigation was conducted. The results showed a distorted square pyramidal structure and a distorted square planar structure, respectively. Copper in both complexes is confirmed to be in a +2 oxidation state by XANES and Mulliken charge studies, which also point out variations in metal–ligand covalency depending on electron density delocalization. Moreover, two Copper(II) complexes exhibit clear structural rigidity as revealed by DFT and EXAFS investigations using vibrational modes and Debye–Waller factors. For in-depth understanding of the structural and electrical characteristics of transition metal complexes, this integrated approach shows that both computational and spectroscopic methods may be used.