Study on synthesis, structure, and DNA-binding of lanthanide complexes with 2-carboxylbenzaldiehyde thiosemicarbazone

2-Carboxylbenzaldehyde thiosemicarbazone (HL), and its three lanthanide (III) complexes, LnL(3).4H(2)O [Ln(III) = La, Sm, Eu], have been synthesized in water. The complexes were characterized by elemental analyses, molar conductivity and I R spectra. The crystal structure of [Sm2L6(CH3OH)(4)].7.5CH(3)OH.0.5H(2)O obtained from methanol solution was determined by X-ray diffraction analysis, crystallized in the triclinic system, space group P - 1, Z = 1, a = 12.217 (2) angstrom, b = 14.706 (2) angstrom, c = 15.035 (2) angstrom, alpha = 11 1.84(1)degrees, beta = 103.47(1)degrees, gamma = 104.24(1)degrees, R-1 = 0.0290. It has symmetrical (mu-OCO)(2), (mu-O)(2) and disamarium(III) units. The coordination geometry of each Sm(III) ion is a distorted tetradecahedron with nine oxygen atoms. In addition, the DNA-binding properties of the ligand and its complexes have been investigated by absorption, fluorescence, and viscosity measurements. The experimental results indicate that the ligand and the Sm-complex can bind to DNA, but the other two complexes cannot; the binding affinity of the Sm-complex is higher than that of the ligand and the intrinsic binding constant K-b of the complex is 3.22 x 10(5) M-1. (c) 2007 Published by Elsevier Ltd.