Synthesis, spectroscopy and X-ray crystal structures of some zinc(II) and cadmium(II) complexes of the 2-pyridinecarboxaldehyde Schiff bases of S-methyl- and S-benzyldithiocarbazates

Abstract

The Schiff bases formed by condensation of S-methyl- and S-benzyldithiocarbazate with 2-pyridinecarboxaldehyde react with zinc(II) and cadmium(II) acetates to form stable metal complexes of general formulas, [Zn(NNS)(CH3COO)]2 and [M(NNS)2] (M=Zn2+, Cd2+; NNS−=anionic forms of the 2-pyridinecarboxaldenhdye Schiff bases of S-methyl- and S-benzyldithiocarbazate, respectively) which have been characterized by a variety of physico-chemical techniques and X-ray crystallographic structure analysis. The complexes, [Zn(NNS)(CH3COO)]2 are acetate anion-bridged centrosymmetric dimers in which each of the Schiff bases is coordinated to the zinc(II) ions as a uninegatively charged NNS tridentate chelating agent coordinating via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom. The acetate anion acts as a bridging bidentate ligand coordinating with the two zinc atoms in a syn–syn manner. Each zinc(II) ion in the dimer adopts an approximately square-pyramidal geometry. The bis-ligand complexes, [M(NNS)2] (M=Zn2+, Cd2+) have distorted octahedral structures in which the two anionic Schiff bases are coordinated to the metal ions meridionally as NNS tridentate chelating agents via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom.Both the mono- and bis-ligand zinc(II) complexes exhibit strong cytotoxic activity against the HELA (human cervical cancer) cell lines. Some of these compounds exhibit stronger cytotoxicity against HELA than the commercially important anticancer drug, Tamoxifen.