Synthesis, spectral properties, DNA binding interactions and DNA cleavage studies of lanthanide (III) complexes of 2-acetylpyridine acetoylhydrazone: the X-ray crystal structure of 10-coordinate Ce (III) and Sm (III) complexes

The lanthanide (III) complexes of general formula of [Ln(APAH)2(NO3)(H2O)2]·2NO3·nH2O (where Ln = La, Ce, Pr, Nd, Sm, and APAH = 2-acetylpyridine acetylhydrazone) have been synthesized and characterized by elemental analysis, molar conductance, spectroscopic (UV, IR), electro-chemical, thermal studies and single crystal X-ray diffraction studies. The coordination mode of the ligands and the geometry of [Ce(APAH)2(NO3)(H2O)2]·2NO3·H2O and [Sm(APAH)2(NO3)(H2O)2]·2NO3·2H2O confirmed by single crystal X-ray studies. The crystals are triclinic with P1bar crystallographic symmetry. The central metal is deca-coordinate in both the Ce and Sm complexes. The coordination polyhedron around the cerium atom can be described as a distorted bicapped square antiprism. The results explain that the central lantanide (III) ions in each complex are coordinated through pyridine nitrogen, azomethine nitrogen atom and amide carbonyl oxygen donor atoms. The hydrazone acts as neutral tridentate ligand. The binding properties of these complexes with calf-thymus DNA have been investigated using absorption spectrophotometry. The changes in absorption spectra complexes upon addition of DNA suggest strong π-stacking interaction between the complexes and DNA base pairs. The complexes show nuclease activity via oxidative path way.