Synthesis, biological activities and theoretical studies of a new macroacyclic Schiff base ligand and its related Co(II), Ni(II), and Cu(II) complexes: The X-ray crystal structure of the Co(II) complex

•synthesized of macroacyclic Schiff base complexes.•characterized the synthesized compounds by elemental analysis, IR, ESI-MS and, NMR spectroscopy.•Investigation of a cytotoxicity and antioxidant activities by in vitro.•NBO, EDA, and EDA-NOCV studies. A new symmetrical macroacyclic Schiff base ligand (H2L) was prepared by the condensation reaction of 2-(4-(2-aminophenyl)piperazin-1-yl)benzeneamine and 2-hydroxy-5-nitro-benzaldehyde which was then used to synthesize the Co(II), Ni(II) and Cu(II) complexes. The new compounds were characterized by Mass spectrometry, IR, 1H NMR and 13C NMR spectroscopy and elemental analyses. The single crystal X-ray structural analysis of [CoL] showed that the Cobalt atom was in a slightly distorted trigonal prismatic environment coordinated by the four amine nitrogen atoms and two phenol oxygen atoms of the ligand; the nitro groups are not coordinating to the metal atom. The in vitro antioxidant attributes of the synthesized compounds were evaluated, using DPPH free radical scavenging with the lowest IC50 reported for [CuL]. The cytotoxicity of the compounds was also evaluated against A-549 lung adenocarcinoma cells, which showed the H2L and [CuL] were more effective than the other two compounds. NBO, EDA, and EDA-NOCV studies were used to look at the type of metal–ligand interactions in these complexes. [Display omitted]