Spectral, thermal and in vitro antimicrobial studies of cyclohexylamine-N-dithiocarbamate transition metal complexes

Transition metal complexes of the type [M(L)₂] and those containing monodentate phosphines of the type [M(L)₂(PPh ₃)] {M = Ni, Co, Cu and Zn; L = cyclohexylamine-N-dithiocarbamate; PPh₃ = triphenylphosphine} have been synthesized. The complexes were characterized using IR, UV-vis, NMR spectroscopy, and thermal analysis (TGA). The ¹H NMR, ¹³C NMR and ³¹P NMR showed the expected signals for the dithiocarbamate and triphenylphosphine moieties. The spectral studies in all compounds revealed that the coordination of metals occurs via the sulphur atom of the dithiocarbamate ligand in a bidentate fashion. Thermal behavior of the complexes showed that the complexes were more stable than their parent ligands. The ligand moiety is lost in the first step and the rest of the organic moiety decomposes in the subsequent steps. Furthermore, the ligand and their metal complexes were screened in vitro for their antibacterial activity against Escherichia coli, Staphylococcus aureus, Salmonella typhi, Enterococcus faecalis, Pseudomonas aeruginosa and Bacillus cereus and antifungal activities against Aspergillus flavus, Aspergillus carbonarius, Aspergillus niger and Aspergillus fumigatus. The metal complexes exhibited higher antimicrobial activity than the parent ligands. Generally, the zinc complexes were effective against the growth of bacteria with Zn(L) ₂ displaying broad spectrum bacteriocidal activity at concentrations of 50 μg/mL; and Ni(L)₂ was more effective against the growth of fungi at concentrations of 100-400 μg/mL under laboratory conditions.