Abstract / Summary
Three new zirconium(IV) complexes with thione ligands 2-mercaptobenzothiazole (MBT), 2-mercaptobenzimidazole (MBI) and 1-methyl-1H-tetrazole-5-thiol (HMtzS) have been synthesized and characterized by FT-IR, 1H NMR, molar conductance, PXRD, SEM and EDX analysis. The analytical data were consistent with the formation of complexes of general formula [ZrO(thione)2], where each thione ligand coordinates to the Zr(IV) ion in a bidentate (S,N) fashion through the deprotonated thiolate sulfur and the heterocyclic ring nitrogen atom. The molar conductance measurements showed that all complexes are non-electrolytes. PXRD analysis showed that [ZrO(MBT)2] has a relatively well-defined crystalline structure with an average crystalline size of ~35.7 nm, while [ZrO(MBI)2] and [ZrO(MtzS)2] were predominantly amorphous or poorly crystalline. SEM images revealed different morphologies, [ZrO(MBT)2] exhibited a dense layered fibrous structure whereas [ZrO(MBI)2] and [ZrO(MtzS)2] presented a highly agglomerated cauliflower-like granular morphology with particle sizes in the range of 38-230 nm. EDX analysis confirmed the presence of Zr, S, C, O and N in the complexes. Antibacterial activity of free ligands and their Zr(IV) complexes were evaluated against Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli. All the complexes exhibited higher antibacterial activity than their corresponding free ligands and [ZrO(MBI)₂] possessed the most balanced and potent activity against all three strains (19, 17 and 18 mm, respectively) while [ZrO(MtzS)₂] showed the highest activity against S. epidermidis (21 mm). The complexes were not superior than the standard antibiotic tetracycline but comparable to it which indicates their potential as promising antibacterial agents.