Synthesis, characterization, DFT calculations and antimicrobial studies of cadmium(II) sulfate complexes of thioureas and 2-mercaptopyridine; X-ray structures of polymeric diaqua(N,N′-dimethylthiourea) sulfatocadmium(II) and bis(2-mercaptopyridine)sulfatocadmium(II)

Abstract

Cadmium(II) complexes of thioureas, [Cd(Tu)(SO4)(H2O)2]n (1), [Cd(Dmtu)(SO4)(H2O)2]n (2) and [Cd(Mpy)2(SO4)]n (3) (Tu = thiourea, Dmtu = N,N′-dimethylthiourea and Mpy = 2-mercaptopyridine) were prepared and characterized by IR and NMR spectroscopy, and thermal analysis. While the solid state structure of 1 is known in the literature, the structures of 2 and 3 were determined by single crystal X-ray crystallography. Complexes 2 and 3 exist in the form of one-dimensional polymers. In 2, each cadmium atom is octahedrally coordinated by two doubly bridging Dmtu ligands, two sulfate ions and two water molecules. In 3, the octahedral coordination at the cadmium atom is attained by four bridging Mpy ligands and two sulfate ions. The results of the thermal analyses of 1 and 2 indicate a good correlation between the calculated and found weight loss values. The IR spectra of 1–3 were simulated and interpreted by means of periodic DFT calculations of their modelled polymeric solid state structures. The IR and NMR spectroscopic data are consistent with sulfur coordination of the thiones and oxygen coordination of the bridging sulfato group to the cadmium(II) ions. The antimicrobial activities of the complexes were evaluated by their minimum inhibitory concentrations and the results showed that the complexes exhibit moderate activities against gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). The activities against molds (Aspergillus niger and Penicillium citrinum) were poor, while the complexes were almost ineffective against yeasts (Candida albicans and Saccharomyces cerevisiae).