Synthesis, Characterization and Antibacterial Studies of Some Metal Complexes of N-DI (Pyridin-2-YL) Thiourea Derivatives

N-(di (pyridin-2-yl) carbamothioyl)-3-nitrobenzamide (L1) and N-(di(pyridin-2-yl) carbamothioyl)-4-nitrobenzamide (L2)) and their copper (II), nickel (II), cobalt (II) and zinc (II) complexes have been synthesized, characterized and tested for antibacterial activity. The ligands were synthesized under reflux and characterized with some spectroscopic techniques. FTIR studies of these two nitro-substituted-N-di (pyridin-2-yl) thiourea derivatives showed the presence of >N-H and >C=S groups. The 1HNMR spectra of these compounds, L1 and L2 revealed chemical shifts for dipyridyl-protons at 7.13 - 8.37 ppm and 6.89 - 8.03 ppm respectively. The 13CNMR spectra, in support, appeared downfield around ~154 ppm for pyridyl-carbon atoms. Mass spectrum of these compounds showed molecular ion peaks at m/z, 383. Each of these ligands reacted with Cu (II), Ni (II), Co (II) and Zn (II) salts to give eight corresponding metal complexes [MLCl2]. Majority of the complexes showed no >N-H band but the >C=S band, as appeared on the FTIR spectra. The absorption bands at 519 - 579 cm-1 revealed the presence of (M-S) and confirmed the metal to thiocarbonyl-sulphur bonding in the complex. The UV-VIS absorption spectra showed intraligand n→π* transition absorption band, and for some complexes, metal → ligand charge transfer (MLCT) transition. The 1HNMR spectra of the two zinc complexes [ZnLCl2], revealed peaks similar to the corresponding ligands. The ligands and the complexes were biologically active when tested against seven bacteria strains. The significant inhibitory activity of the ligands was recorded against Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus, Klebsiella Pneumoniae and Escherichia coli Resistant. The complexes showed enhanced and significant antibacterial activities against all the bacterial strains, more than their corresponding ligands.