Synthesis, characterization and biological study of 2-acetylbenzothiophene 4-cyclohexyl-3-thiosemicarbazone ligand and its transition metal complexes

Abstract

Considerable interest has been aroused for thiosemicarbazones and their transition metal complexes because of their wide variety of biological activity. A 2-acetylbenzothiophene 4-cyclohexyl-3-thiosemicarbazone ligand 1 was successfully synthesized. The ligand formed complexes namely [ZnL₂] 2, [CdL₂] 3, [NiL₂] 4, [PdCl₂HL] 5 and [CuL₂H₂O]₂ 6, where HL is the corresponding ligand. The ligand and its complexes were characterized by elemental analyses, Fourier transform infrared (FTIR) spectra, ultraviolet–visible spectroscopy (UV/VIS), nuclear magnetic resonance (¹H & ¹³C NMR) spectra, single crystal X-ray diffraction analysis, molar conductivity and magnetic moment measurements. The single crystal X-ray diffraction analysis indicated that in the solid state the free ligand exists in the thione form with C=S bond distance 1.74 Å. The elemental analysis results for the complexes are in good agreement with the values calculated for the predicted molecular formulas. The spectroscopic analysis of the zinc(II) 2, cadmium(II) 3 and nickel(II) 4 complex of 1 indicated that the ligand coordinated to the metal centers as a bidentate ligand through the thiolate sulfur and the azomethine nitrogen to give a distorted square planar arrangement around nickel(II) center and a distorted tetrahedral arrangement around zinc(II) and cadmium(II) center. The Zn–S bond distance is 2.28 Å; while, the Zn–N bond distance is 2.05 Å. Palladium(II) complex 5 showed preference for the thione form of the thiosemicarbazone ligand and the structure of the complex is close to a distorted square planar. The ligand 1 was coordinated with copper(II) ions in the thiol form. The complex 6 was dimeric and the geometry surrounding the copper centers is close to a distorted octahedral. In vitro antimicrobial tests showed that some of the prepared complexes had strong inhibitory effect. The cytotoxic activity was evaluated against human hepatocellular carcinoma cells and Chang liver cells.