Syntheses, crystal structures, spectral and DFT studies of copper(II) and nickel(II) complexes with N'-(pyridine-2-ylmethylene) acetohydrazide

Three new metal(II) complexes (copper(II)/nickel(II)) with N'-(pyridine-2-ylmethylene) acetohydrazide [Cu(HL)(2)]center dot(ClO4)(2) 1, [Ni(HL)(2)]center dot NO3 center dot ClO4 center dot 0.5H(2)O 2 and [Cu(mu-CH3COO)(L)](2)center dot 4H(2)O 3 have been synthesized form N'-(pyridine-2-ylmethylene) acetohydrazide (HL/L). The synthesized complexes were characterized by means of elemental analysis, spectroscopic, magnetic susceptibility and cyclic voltammetric measurements. Single crystal X-ray analysis of complexes has revealed the presence of a distorted octahedral geometry around mononuclear copper(II) and nickel(II) complex (1 and 2) and distorted square pyramidal geometry around copper(II) centers of complex 3. In the solid state Schiff base remains in its keto-tautomeric form. On complexation with Cu(II)/Ni(II) ions in natural or slightly acidic medium it coordinates through ketonic oxygen (keto form, HL) whereas in basic medium it acts as monoprotic (enol form, L) ligand. Variable-temperature magnetic susceptibility data of the compound 3 indicates the presence of weak antiferromagnetic interaction with J = -123 cm(-1). The cyclic voltammograms of homobinuclear complex 3 in DMSO gave two irreversible waves which correspond to the Cu(II,II)/Cu(II,I) and Cu(II,I)/Cu(I,I) redox processes. On the other hand, the mononuclear complex 1 exhibited M(II)/M(I) quasireversible wave E-1/2 = 0.06 V vs Ag/AgCl. X-band electron paramagnetic resonance (epr) data of copper(II) mononuclear and binuclear complexes 1 and 3 have been collected to investigate magnetic properties of the complexes in detail. The electronic structures, spectral properties of the ligands and the complexes have been explained by DFT and TD-DFT calculations. In addition, biological activity ranking of present complexes 1-3 are investigated theoretically. Complexes catalyzed the dismutation of superoxide (O-2(square-)) at biological pH in alkaline nitroblue tetrazolium chloride assay and IC50 values were evaluated. (C) 2017 Elsevier B.V. All rights reserved.