Synthesis and structure of new tetracopper(II) complexes bridged by 2-{N′-[2-(dimethylamino)ethyl]oxamido}benzoate: DNA-binding and anticancer activity

Tetranuclear complexes constructed from asymmetrical N,N′-bis(substituted)oxamide have been synthesized and characterized by X-ray single-crystal diffraction. The cytotoxicities and reactivities towards DNA of the two complexes have been investigated. [Display omitted] ► Two tetranuclear complexes have been synthesized and characterized. ► The two complexes exhibit cytotoxicities against SMMC-7721 and A549 cell lines. ► The DNA-binding abilities are consistent with cytotoxicities in the order 2>1. ► The terminal ligands are very important in the DNA-binding and cytotoxic properties. Two new circular tetranuclear copper(II) complexes, [Cu4(dmoxba)2(bpy)2(CH3OH)2](pic)2·2H2O (1) and [Cu4(dmoxba)2(phen)2](pic)2·2CH3OH (2), where dmoxba, pic, bpy and phen stand for the anion of 2-{N′-[2-(dimethylamino)ethyl]oxamido}benzoate, picrate, 2,2′-bipyridine and 1,10-phenanthroline, respectively, have been synthesized and structurally characterized by X-ray single-crystal diffraction. Both the complexes have embedded inversion centers and similar complex cations assembled by the oxamide-bridges and carboxylate-bridges of two cis-dmoxba3− ligands. The Cu⋯Cu separations through the oxamide-bridge and the carboxylato-bridge are 5.1991(4) and 5.4674(4)Å in 1 and 5.1843(5) and 5.2138(5)Å in 2, respectively. Both copper(II) ions are in square-pyramidal environments in 1. While in complex 2, the inner and exo copper(II) ions have square-planar and square-pyramidal coordination geometries, respectively. In both the crystals, three-dimensional supramolecular structures are formed by hydrogen bonds and π–π stacking interactions. The DNA-binding properties and anticancer activities of the two complexes were investigated. The results suggest that the two complexes interact with HS-DNA in the mode of intercalation with the intrinsic binding constants 5.0×104M−1 (1) and 6.7×104M−1 (2). The influence of structural variation of the terminal ligands in the tetranuclear complexes on DNA-binding properties is preliminarily discussed.