Theoretical and solid-state structures of three new macroacyclic Schiff base complexes and the investigation of their anticancer, antioxidant and antibacterial properties

Three symmetrical macroacyclic Schiff base complexes were prepared from a ligand derived from the condensation reaction of 1,4-bis(2-aminophenyl)piperazine and salicylaldehyde (L) with Cu(ii), Ni(ii) and Co(ii) perchlorates. The ligand and the Schiff base complexes were characterized by elemental analyses, UV-vis, FT-IR and mass spectrometry, with the structure of [CoL] being determined by a single crystal X-ray structural analysis. In this complex, the cobalt is in a distorted trigonal prismatic coordination environment, surrounded by the six donor atoms of the deprotonated hexadentate ligand. In order to compare the experimental and theoretical data and determine structure parameters in all complexes, Density Functional Theory (DFT) calculations at the B3lyp and BP86 levels with Def2-TZVP basis set have been carried out. NBO and QTAIM analyses have been used to describe the nature of M–O and M–N bonding in these complexes. The synthesized complexes were screened for their antioxidant activities using the DPPH free radical scavenging assay while their bactericidal activity was evaluated by the paper disc diffusion method against both Gram-negative and Gram-positive bacteria, revealing strong antioxidant activities and moderate effectiveness against all bacteria tested. The cytotoxicity of the metal complexes was also investigated against AGS (gastric) and A549 (lung) adenocarcinoma cells.