Synthesis of two new symmetrical macroacyclic Schiff base ligands containing homopiperazine moiety and their mononuclear complexes: Spectral characterization, X-ray crystal structural, antibacterial activities, antioxidant effects and theoretical studies

Abstract

Two new symmetrical macroacyclic Schiff base ligands, L1 and H2L2 have been prepared from the condensation of 2-((4-(2-aminobenzyl)-1,4-diazepan-1-yl)methyl) benzenamine (A) with 2-formylpyridine and 2-hydroxy-3-methoxybenzaldehyde, respectively. Metal complexes were synthesized by the reaction of the ligands with Ni(ClO4)2·6H2O, Cu(ClO4)2·6H2O, Mn(ClO4)2·6H2O and Co(ClO4)2·6H2O in methanol and the resulting products were characterized by elemental analyses, IR, ESI-MS, 1H and 13C NMR spectra and conductivity measurements. The structure of the complex [CoL2](ClO4) has also been determined by a single crystal X-ray structural analysis, showing that the Co(III) atom is in an almost regular trans-O2N4 octahedral environment, coordinated by all six donor atoms of the macroacyclic ligand. As well, the nature of metal–ligand bonding in the complexes was analyzed by NBO, EDA and EDA-NOCV analyses. The antioxidant and antibacterial activities of the synthesized compounds were in vitro screened by 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging and disc diffusion methods, respectively. The results reveal that the synthesized complexes possess excellent antioxidant (IC50; 0.325–1.303 mg/ml) and antibacterial activities in comparison to ascorbic acid and antibiotics as positive controls, respectively. In view of their biological activities, it is possible that these complexes may have future applications as biological agents.