Microwave synthesis, characterization and biological activities of transition metal complexes with novel SNSN donor Schiff base ligand

A novel Schiff base (E)-N-(pyridine-2-yl)thiophen-2-ylmethylene)hydrazine carbothioamide (L), has been synthesised by the condensation of thiophen-2-carbaldehyde and 4-(pyridin-2-yl)-thiosemicarbazide, using solvent free microwave synthesis. The Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base are also prepared. They are characterised by elemental analysis, EI-mass spectrum, H-1 & C-13-NMR spectrum, F'TIR, UV-vis spectra, magnetic, EPR spectra and thermal analysis. The "SINIS7q" donor ligand binds the metal ion in tetradentate mode through thiophenyl and thioenolic sulphur atoms and imino and pyridine nitrogen atoms. The electronic spectra along with magnetic measurements demonstrate tetrahedral geometry for Co(II), Ni(II) and Zn(II) complexes, and square planar geometry for Cu(II) complex. All the complexes are found to be thermally stable from thermogravimetric studies. The complexes show enhanced antibacterial activity than the ligand against various bacterial strains. The BSA binding activity of the complexes shows that the affinity for binding is greater towards copper complex. The cytotoxicity of the ligand and its complexes are tested on HT29 colon cancer cells using MTT assay.