Synthesis, spectroscopic identification, thermal, potentiometric and antibacterial activity studies of 4-amino-5-mercapto-S-triazole Schiff’s base complexes

• Novel Schiff’s base complexes were synthesized.
• The complexes are characterized by different spectroscopic techniques.
• Thermogravimetric parameters of metal(II) complexes were calculated in different methods.
• Complexes were found more biologically sensitive than ligand.

Complexes of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) of general composition [M(L)2] have been synthesized [L = 4-pyridin-2-yl-methylene amino-4H-1,2,4-triazole-3-thiol]. The elemental analyses, molar conductance, spectral (IR, UV–Vis, 1H NMR, mass), magnetic moment and thermal measurements studies of the compounds led to the conclusion that the ligand acts as a tridentate manner (SNN). The molar conductance of the metal complexes in fresh solution of DMSO lies in the range of 8.34–10.46 Ω−1 cm2 mol−1 indicating their non-electrolytic behavior. On the basis of analytical and spectroscopic techniques, octahedral geometry of the complexes was proposed. The Schiff base acts as tridentate ligand coordinated through deprotonated thiolic sulfur, azomethine nitrogen and pyridine nitrogen atoms. The ligand field parameters were calculated for Co(II), Ni(II) and Cu(II) complexes and their values were found in the range reported for a octahedral structure. The data show that the complexes have composition of ML2 type. The activation of thermodynamic parameters are calculated using Coast–Redfern, Horowitz–Metzger (HM), Piloyan–Novikova (PN) and Broido’s equations. Protonation constants of Schiff base and stability constants of their binary metal complexes have been determined potentiometrically in 50% DMSO–water media at 25 °C and ionic strength 0.10 M potassium nitrate. Both the Schiff’s base ligand and its complexes have been screened for antibacterial activities.

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