Cobalt(II), nickel(II), palladium(II) and zinc(II) metallothiosemicarbazones: Synthesis, characterization, X-ray structures and biological activity

Abstract

Metal(II) complexes of the type [Co(S-HL)2Cl2] and [Ni(N,S-L)2], [Pd(N,S-L)2], [Zn(N,S-L)2], were synthesized from the reaction of HL with metal(II) chlorides. All complexes were characterized by spectroscopic methods, such as elemental analysis, FT-IR, 1H NMR, and single crystal X-ray diffraction. In the [Co(S-HL)2Cl2] complex, the cobalt atom adopts a distorted tetrahedral geometry around the cobalt(II) ion, with two neutral monodentate S-thiosemicarbazone ligands coordinating via one of the thiocarbonyl sulfur atom and two chlorides. In the [Ni(N,S-L)2] and [Pd(N,S-L)2] complexes, HL ligand is coordinated with the metal center, as a mono anionic bidentate N,S donors which are in trans position and that metal(II) ions adopt square planar coordination. [Zn(N,S-L)2] indicates that the anionic thiosemicarbazone ligands bind to the metal in a distorted tetrahedral arrangement with N,S donor atoms. The antimicrobial activity of the ligand and metal(II) complexes were studied against bacterial strains and fungal stain. It was observed that the ligand showed weaker activity than the metal complexes. The Zn(II) complex had the best antibacterial activity against E. faecalis, while the Co(II) complex showed the best activity against S. aureus bacteria. Co(II) and Pd(II) complexes were relatively more effective against Gram-negative bacteria. It was determined that metal complexes were less effective against gram negative bacteria compared to gram positive bacteria. A little antifungal activity was observed in Zn(II) and Co(II) complexes.