Molecular structures, spectral, electrochemical, DFT and antioxidant activities of copper(II) complexes with NNO donor Schiff base ligand

Abstract

The synthesis and solid state structural, spectral and electrochemical solution characterization of [Cu(L)(acpy)]ClO41 and [Cu(L)(NO3)] 2 [where L = N'-[(E)-phenyl(pyridin-2-yl)methylidene]thiophene-2-carbohydrazide and acpy = 2,6-Diacetylpyridine] have been done by elemental analysis, UV–vis, FTIR, electrochemical techniques (CV and DPV) and electron paramagnetic resonance (epr) spectroscopy. The single crystal structures were solved by the X-ray diffraction technique. In complex 1, copper ion is in a distorted octahedral environment. The geometry of copper(II) in complex 2 is distorted square pyramidal (τ = 0.201). The mono deprotonated, HL ligand act as a tridentate to a copper(II) ion. On the basis of density functional theory (DFT) calculation, the electronic excitations involve transitions mainly from metal ligand bonding mostly the α-LUMO within the dominant Cu dxy character and to α-LUMO+1. Epr spectra for polycrystalline samples showed the copper(II) hyperfine features as well as half-field signal which are appropriate for ΔMs = ±2 of dimers. Presence of half-field signal in 1 is due to solid-solid interaction (intra-molecular) where as in 2 the nature of interaction is intra-molecular. The antioxidant superoxide measurements show that the both complexes 1 and 2 behave as superoxide mimic in alkaline nitro blue tetrazolium chloride assay.