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

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 × 104 M−1 (1) and 6.7 × 104 M−1 (2). The influence of structural variation of the terminal ligands in the tetranuclear complexes on DNA-binding properties is preliminarily discussed.