Biological activities of pyridine-2-carbaldehyde Schiff bases derived from S-methyl- and S-benzyldithiocarbazate and their zinc(II) and manganese(II) complexes. Crystal Structure of the Manganese(II) complex of pyridine-2-carbaldehyde S-benzyldithiocarbazate

Transition metal complexes [Zn(L1)2] (I) and [Mn(L2)2] (II), where HL1 = pyridine-2-carboxaldehyde S-methyldithiocarbazate, HL2 = pyridine-2-carboxaldehyde S-benzyldithiocarbazate, have been synthesized. Complex II was characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction studies. The manganese(II) atom in complex II adopts a distorted octahedral geometry with the Schiff base coordinated to it as a uninegatively charged tridentate chelating agent via the pyridine and azomethine nitrogen atoms and the thiolate sulfur atom. Biological studies carried out in vitro against selected bacteria, fungi, and K562 leukemia cell line, respectively, have shown that the free ligands and their metal complexes exhibited distinctive differences in the biological properties. Ligand HL1 and complex I have the marked and broad antimicrobial activities compared to HL2 and complex II while only HL1 and complex II show significant antitumor activity against K562 leukemia cell line, since they exhibit IC50 values in the μM range.