Cu^II Pyrazolyl‐Benzimidazole Dinuclear Complexes with Remarkable Antioxidant Activity

Abstract

Abstract Three dinuclear coordination complexes generated from 1‐ n ‐butyl‐2‐((5‐methyl‐1 H ‐pyrazole‐3‐yl)methyl)‐1 H ‐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(NO 3 )(μ‐Cl)( L’ )] 2 ( C 1 ) and 22 % of [Cu(NO 3 )(μ‐NO 3 )( 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)(μ‐Cl)( L) ] 2 ( C 3 ). The presence of N−H⋅⋅⋅O and C−H⋅⋅⋅O intermolecular interactions in the crystal structure of C 1 and C 2 , and C−H⋅⋅⋅N and C−H⋅⋅⋅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.