Synthesis, crystal structure and superoxide dismutase activity of two new bis(μ-acetato/μ-nitrato) bridged copper(II) complexes with N′-[phenyl(pyridin-2-yl)methylidene]benzohydrazone

Two homodinuclear copper(II) end-on bis(μ-acetato/μ-nitrato) bridged complexes with two NNO donor ligands, viz., [(L)Cu(μ-CH3COO)2Cu(L)] (1) and [(L)Cu(μ-NO3)2Cu(L)] (2) (where L = N′-[phenyl(pyridin-2-yl)methylidene]benzohydrazone) are reported. Both complexes are structurally characterized using single crystal X-ray diffraction studies and belong to monoclinic crystal system having space group P21/n. The distance between two copper centers is 3.344(8) and 3.406(7) Å respectively for 1 and 2. On the basis of density function theory (DFT) calculations, the electronic excitations involve transitions mainly from metal–ligand bonding MOs to the β-LUMO within the dominant Cu dxy character and to β-LUMO+1. Epr spectra for polycrystalline samples exhibited the copper(II) hyperfine structures as well as zero-field splitting which are appropriate for triplet state of such a dimmers. Complexes effectively catalyze the dismutation of superoxide (O2−) in alkaline nitro blue tetrazolium chloride assay and IC50 values were determined.