Mono-, bi- and multi-nuclear silver complexes constructed from bis(benzimidazole)-2-oxapropane ligands and methacrylate: syntheses, crystal structures, DNA-binding properties and antioxidant activities

Abstract

The reactions of AgNO₃ with sodium methacrylate and three structurally related ligands in the absence of light gave three new silver coordination complexes, namely, [Ag₂(methacrylate)₂(Etobb)₂]·CH₃CN 1, [Ag(methacrylate)(Bobb)] 2 and [Ag₂(methacrylate)₂(Aobb)]_n 3, where Etobb = 1,3-bis(1-ethylbenzimidazol-2-yl)-2-oxapropane, Bobb = 1,3-bis(1-benzylbenzimidazol-2-yl)-2-oxapropane, Aobb = 1,3-bis(1-allylbenzimidazol-2-yl)-2-oxapropane. All three complexes have been characterized by elemental analysis, UV-visible and infrared spectroscopy, and single-crystal X-ray diffraction. Complex 1 is binuclear and tri-coordinated by two N atoms to two Etobb ligands, while complex 2 is mononuclear. Complex 3 is a unique metal–organic compound that has a diamond-like multinuclear silver center, with each Ag bridged by two Aobb ligands and two methacrylate ions to form 1-D single-coordination polymer chain structures that extend into 2-D frameworks through π–π interactions. The X-ray structures show a wide range of Ag–Ag distances in the polymers, which are dependent on the conformation of the bridging ligand. The DNA-binding properties of the three Ag(I) complexes have been investigated by electronic absorption, fluorescence, and viscosity measurements. The results suggest that the three complexes bind to DNA via an intercalative mode, and their binding affinity for DNA follows the order 1 > 2 > 3. Moreover, the antioxidant activity experiment shows that complex 2 has the potential ability to scavenge hydroxyl radicals in in vitro studies.