Synthesis, crystal structures, and biological evaluation of Cu(II) and Zn(II) complexes of 2-benzoylpyridine Schiff bases derived from S-methyl- and S-phenyldithiocarbazates.

Two NNS tridentate Schiff base ligands of 2-benzoylpyridine S-methyldithiocarbazate (HL1) and 2-benzoylpyridine S-phenyldithiocarbazate (HL2) and their transition metal complexes [Cu2(L1)2(CH3COO)](ClO4) (1), [Zn2(L1)2(ClO4)2] (2), [Zn(L2)2](3) have been prepared and characterized by elemental analysis, IR, MS, NMR 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 prepared conditions, three new complexes showed distinctly different coordination modes depending on their coordinating preferences. Each copper atom in S-bridged dinuclear complex [Cu2(L1)2(CH3COO)](ClO4) (1) is surrounded by five donor atoms in a square-pyramidal fashion (4+1). [Zn2(L1)2(ClO4)2] (2) is a dimer in which each zinc atom adopts a seven-coordinate distorted pentagonal bipyramidal geometry, while mononuclear [Zn(L2)2] (3) has octahedral coordination geometry. Biological studies, carried out in vitro against selected bacteria, fungi, and K562 leukaemia cell line, respectively, have shown that different substituted groups attached at the dithiocarbazate moieties and metals showed distinctive differences in the biological property. Zinc(II) complexes 2 and 3 could distinguish K562 leukaemia cell line from normal hepatocyte QSG7701 cell line. Effect of the title compounds on Mitochondria membrane potential (MMP) and PI-associated fluorescence intensity in K562 leukaemia cell line are also studied. The title compounds may exert their cytotoxicity activity via induced loss of MMP.