Synthesis, characterization and SOD activity of bisbenzimidazole-based copper(II) complexes

•Three mononuclear copper (II) coordination complexes were synthesized as SOD mimics.•SOD activities of three complexes were measured using the NBT method.•Hirshfeld surfaces and 2D fingerprint analysis were performed for copper complexes.•DFT calculation of copper(II) complex was performed and compared with its X-ray structures. Three bisbenzimidazole-copper(II) coordination complexes, [Cu(MIDB)(NO3)(CH3OH)](NO3) (1), [Cu(MIDB)(H2O)2](NO3)2 (2), and [Cu(ODB)2](ClO4)2 (3) (MIDB =N-methyl bis(benzimidazol-2-ylmethyl) amine; ODB = bis(2-benzimidazolylmethyl) ether), were synthesized and characterized. The component ions in their crystals are linked by N-H...O, O-H...O, C-H...π and π...π interactions into three-dimensional networks which are quantitatively manifested by the Hirshfeld surface analysis. Their frontier molecular orbital compositions and natural charge population were conducted theoretically at the DFT/(UB3LYP)/6-31G+(d, p) level for the copper coordination units, indicating that the HOMO and LUMO orbitals are mainly contributed by the benzimidazole groups and the coordination bonds are stabilized by the delocalized stabilization energy between the lone-pair bonding orbitals from N and/or O atoms and the lone-pair anti bond orbitals of the copper center. The cyclic voltammetry showed irreversible one-electron redox reactions for the three complexes in DMF solutions. SOD activity of 1 (IC50=1.34 µM) was slightly better than that of 3 (IC50=1.36 µM) by using the NBT method. [Display omitted]