Synthesis, Crystal Structure And Biological Activity Of 2-acetylpyridine /2-benzoylpyridine Schiff-bases Containing Sulfur And Their Metal Complexes

Recently, sulfur–nitrogen chelating agents derived from thiosemicarbazones and S-alkyl/aryl esters of dithiocarbazic acid have generated considerable interest due to varied coordination environments and marked biological activities, notable for antibacterial, antifungal and antitumor. In many cases, their biological properties are often related to the donor sequence of the ligands and metal ion coordination. So it is important to study the synthesis and biological activities of schiff-base compounds containing sulfur–nitrogen chelating agents in the finding of new drugs against bacteria and cancer.In this paper, we studied the synthesis, single-crystal structures and biological activities of a series of schiff-base ligands and their metal complexes. The text has divided into three Chapter which were introduced as follows:Chapter 1 Synthesis, characterization, crystal structures and biological activities of 2-acetylpyridine thiosemicarbazone and their metal complexesTransition metal complexes Mn(L1)2 (1), Mn(L2)2 (2), Ni(L2)2 (3), where HL1 = 2-acetylpyridine thiosemicarbazone, HL2 = 2-acetylpyridine N(4)-methylthiosemicarbazone, have been synthesized and characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction studies. Biological studies, carried out in vitro against bacteria, fungi and K562 leukemic cell line, respectively, have shown that the free ligands and their corresponding complexes show distinct difference in the biological properties.. In addition, the complexes all showed higher biological activity than their separate ligands.Chapter 2 Synthesis, characterization, crystal structure and biological activity of Co(II) complex from 2-benzoylpyridine N(4)-methylthiosemicarbazoneTransition metal complexes Co(HL3)2(ClO4)2·3H2O (4) where HL3 = 2-benzoylpyridine N(4)-methylthiosemicarbazone, has been synthesized and characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction studies. This complex consists of discrete monomeric molecules with octahedrally hexacoordinate cobalt(II) ions, where two 2-benzoylpyridine N(4)-methylthiosemicarbazone act as NNS tridentate ligands coordinated to the central cobalt atom via the pyridine nitrogen, azomethine nitrogen and sulfur atoms. Preliminary in vitro screening showed that cobalt(II) complex 4 exhibited lower antibacterial and antitumor activity, as compared to the free ligand.Chapter 3 Synthesis, characterization, crystal structure and biological activities of 2-benzoylpyridine S-methyl- and S-phenyldithiocarbazates and their metal complexesTwo NNS tridentate Schiff base ligands of 2-benzoylpyridine S-methyldithiocarbazate (HL4) and 2-benzoylpyridine S-phenyldithiocarbazate (HL5) and their transition metal complexes [Cu2(L4)2(CH3COO)](ClO4) (5), [Zn2(L4)2(ClO4)2] (6), [Zn(L5)2](7) have been prepared and characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction studies. In the solid state, each of two Schiff bases remains in its thione tautomeric form with the thione sulfur atom trans to the azomethine nitrogen atom. Under similar perpared conditions, three new complexes showed distinctly different coordination modes depending on their coordinating preferences. Each copper atom in S-bridged dinuclear complex [Cu2(L4)2(CH3COO)](ClO4) (5) is surrounded by five donor atoms in a square-pyramidal fashion (4 + 1). [Zn2(L4)2(ClO4)2] (6) is a dimer in which each zinc atom adopts a seven-coordinate distorted pentagonal bipyramidal geometry, while mononuclear [Zn(L5)2] (7) has octahedral coordination geometry. The Schiff base coordinates as a uninegatively charged tridentate ligand chelating via pyridyl nitrogen, azomethine nitrogen and the thiolato sulfur atoms. Biological studies, carried out in vitro against selected bacteria, fungi, and K562 leukemic cell line, respectively, have shown that different substituted groups attached at the dithiocarbazate moieties and metals showed distinctive differences in the biological property.