Synthesis, crystal structures, antimicrobial properties and enzyme inhibition studies of zinc(II) complexes of thiones

Zinc(II) complexes of thiones having the general formula [ZnL2Cl2] where L = N-methylthiourea (Metu), N,N′-dimethylthiourea (Dmtu), tetramethylthiourea (Tmtu), N,N′-diethylthiourea (Detu), and diazinane-2-thione (Diaz), were prepared by reacting ZnCl2 with the corresponding thiones. They were characterized by elemental analysis, IR and NMR spectroscopy and two of them {[(Tmtu)2ZnCl2] (1) and [(Diaz)2ZnCl2] (2)} using X-ray crystallography. The spectral data suggests that the coordination of thiones to zinc(II) occurs through the sulfur atom as indicated by an up field shift in the CS resonance of thiones in 13C NMR and downfield shift in N–H resonance in 1H NMR. The crystal structures of the complexes show a tetrahedral coordination environment around the zinc atoms with the bond angles ranging from 99.33(5)° to 116.81(7)°. Antimicrobial activities of the complexes were evaluated by minimum inhibitory concentration and the results showed that the complexes exhibited significant activities against gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa) and yeasts (Candida albicans, Saccharomyces cerevisiae). However, moderate activity was observed against molds (Aspergillus niger, Penicillium citrinum). The complexes were also tested for inhibition activity against an enzyme, Alkaline Phosphatase EC 3.1.3.1 and were found to be active inhibitors.