Structural, spectral studies and antimicrobial activity of Zinc(II), Cadmium(II) and Nickel(II) complexes of 2-acetylbenzothiophene-3-thiosemicarbazone and 2-acetylbenzothiophene-4-ethyl-3-thiosemicarbazone

Abstract

• Two thiosemicarbazone ligands and their Zinc(II), Cadmium(II) and Nickel(II) complexes were synthesized and characterized. • Single crystal X-ray studies confirmed the structure of Zinc(II) and Nickel(II) complexes. • The complexes displayed enhanced antimicrobial activity in comparison to the ligands. Zn(II), Cd(II) and Ni(II) complexes of 2-acetylbenzothiophene-3-thiosemicarbazone (HL 1 ) and 2-acetylbenzothiophene-4-ethyl-3-thiosemicarbazone (HL 2 ) have been prepared. The new complexes [Zn(L 1 ) 2 ] ( 1 ), [Cd(L 1 ) 2 ] ( 2 ), [Ni(L 1 ) 2 ].0.5CH 3 CN ( 3 ), [Zn(L 2 ) 2 ] ( 4 ), [Cd(L 2 ) 2 ] ( 5 ) and [Ni(L 2 ) 2 ] ( 6 ) have been characterized by elemental analysis and spectroscopic methods. The crystal structures of 1 , 3 and 4 are also reported. Density functional theory (DFT) computations have been conducted to study electronic structures of the ligands and complexes. The spectroscopic results obtained for the complexes indicated that the ligands coordinate in the thiole form and the X-ray crystal structures confirm the spectroscopic data. The crystal structures show that the ligands coordinate to the metal centers as a bidentate N, S-donors. The coordination geometry of the zinc complexes is distorted tetrahedral while that of the nickel complex is distorted square planar. In vitro tests of antibacterial activity show that the Cd complexes 2 and 5 have strong inhibitory actions, compared to Tobramycin, against G(+) Bacillus subtilis, while the Ni complex 3 showed strong activity against G(+) Staphylococcus aureus . In comparison to Nystatin, the cadmium complexes show strong activity against Aspergillus fumigatus and complexes 2 and 3 were effective against Aspergillus niger .