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

2-Carboxylbenzaldehyde thiosemicarbazone (HL), and its three lanthanide (III) complexes, LnL3•4H2O [Ln(III) = La, Sm, Eu], have been synthesized in water. The complexes were characterized by elemental analyses, molar conductivity and IR spectra. The crystal structure of [Sm2L6(CH3OH)4]•7.5CH3OH•0.5H2O 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) Å, b = 14.706 (2) Å, c = 15.035 (2) Å, α = 111.84(1)°, β = 103.47(1)°, γ = 104.24(1)°, R1 = 0.0290. It has symmetrical (μ-OCO)2, (μ-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 Kb of the complex is 3.22 × 105 M−1.