Study on synthesis, crystal structure, antioxidant and DNA-binding of mono-, di- and poly-nuclear lanthanides complexes with bis(N-salicylidene)-3-oxapentane-1,5-diamine

A Schiff base ligand bis(N-salicylidene)-3-oxapentane-1,5-diamine H2L have been prepared. Reaction of the shape-specific designed ligand with Ln(NO3)3⋅6H2O afforded three novel complexes, namely, Sm(L)(NO3)(DMF)(H2O) 1, [Eu(H2L)2(NO3)3]n 2 and Tb2(L)2(NO3)2 3. The ligand and complexes were characterized by elemental analysis, UV–Vis, IR, NMR spectroscopy and X-ray crystallography. It is noteworthy that the complexes demonstrate three different types of the structure which changed according to the charge density and acidity of the lanthanide. Complex 1 is a discrete mononuclear species that Sm(III) ion is nine-coordinated in the structure and forming a distorted tricapped trigonal prism geometry. Complex 2 is possessed a 1-D ribbon framework constructed from an extended array of ten-coordinated Eu3+ centers and the Schiff base ligands. Complex 3 is revealed as a centrosymmetric binuclear neutral entity, in which Tb(III) ion is eight-coordinated with the coordination surround of distorted square antiprism geometry. In order to explore the relationship between the structure and biological properties, the DNA-binding properties have been investigated by electronic absorption, fluorescence, and viscosity measurements. The results suggest that the ligand and complexes bind to DNA via groove modes. The intrinsic binding constants Kb of the complexes 1–3 are (1.19 ± 0.112) × 105, (4.22 ± 0.086) × 104 and (3.89 ± 0.104) × 104 M−1 respectively. Moreover, the antioxidant activity experiments show that these compounds also exhibit good antioxidant activities against OH and O2− in vitro studies.