Synthesis, X-ray crystal structural, antioxidant and antibacterial studies of new Cu(II) macroacyclic Schiff base complex with a ligand containing homopiperazine moiety

Abstract

A symmetrical macroacyclic Schiff base ligand, L, has been prepared from the condensation of 2-((4-(2-aminobenzyl)-1,4-diazepan-1-yl)methyl) benzenamine (A) with 2-formylpyridine. Its copper complex was synthesized by the reaction of ligand with Cu(ClO4)2·6H2O in methanol. The characterization of the product by elemental analyses, IR, EI–MS, 1H and 13C NMR spectra, however, indicated that due to the structural preference of metal ion during the Schiff base formation equilibrium reaction, the metal was not coordinated by the expected N6 donor ligand, but only by an N5 donor ligand, where one of the azomethine groups of free ligand has been cleavaged to an NH2 group. This was also confirmed by a crystal X-ray structural analysis of the mono-Shiff base complex [CuL](ClO4)2·H2O showing the copper atom to be in a distorted square pyramidal geometry, coordinated by all 5 nitrogen donor atoms of this N5 donor ligand. The antioxidant and antibacterial activities of the synthesized compounds were studied in vitro, screened by 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging and disc diffusion methods, respectively. Results revealed that the synthesized complex possess an excellent antioxidant (IC50; 0.325–1.303 mg/ml) and antibacterial activity in comparison to ascorbic acid and antibiotics as positive controls, respectively. The biological activities of this complex suggest it may be useful as a biological agent.