Cu-II Pyrazolyl-Benzimidazole Dinuclear Complexes with Remarkable Antioxidant Activity

Three dinuclear coordination complexes generated from 1-nbutyl-2-((5-methyl-1H-pyrazole-3-yl)methyl)-1H-benzimidazole (L), have been synthesized and characterized spectroscopically and structurally by single crystal X-ray diffraction analysis. Reaction with iron(II) chloride and then copper(II) nitrate led to a co-crystal containing 78% of [Cu(NO3)(mu-Cl)(L')] (2) (C-1) and 22% of [Cu(NO3)(mu-NO3)(L')] (2) (C-2), where L was oxidized to a new ligand L'. A mechanism is provided. Reaction with copper chloride led to the dinuclear complex [Cu(Cl)(mu-Cl)(L)] (2) (C-3). The presence of N H center dot center dot center dot O and C H center dot center dot center dot O intermolecular interactions in the crystal structure of C-1 and C-2, and C H center dot center dot center dot N and C H center dot center dot center dot Cl hydrogen bonding in the crystal structure of C-3 led to supramolecular structures that were confirmed by Hirshfeld surface analysis. The ligands and their complexes were tested for free radical scavenging activity and ferric reducing antioxidant power. The complex C-1/C-2 shows remarkable antioxidant activities as compared to the ligand L and reference compounds.

Automated summary

Three dinuclear coordination complexes were synthesized and characterized by spectroscopic and X-ray diffraction analysis. The complexes showed supramolecular structures confirmed by Hirshfeld surface analysis. The ligands and their complexes exhibited significant antioxidant activities.