Co(III) N,N′‐diarylformamidine dithiocarbamate complexes: Synthesis, characterization, crystal structures and biological studies

Abstract

Three symmetric N,N‐diarylformamidine dithiocarbamates, N,N′‐bis(2,6‐dimethylphenyl)formamidine dithiocarbamate (DTL1), N,N′‐bis(2,6‐disopropylphenyl)formamidine dithiocarbamate (DTL2) and N,N′‐dimesitylformamidine dithiocarbamate (DTL3), and three unsymmetric ones, N′‐(2,6‐dichlorophenyl‐N‐(2,6‐dimethylphenyl)formamidine dithiocarbamate (DTL4), N′‐(2,6‐dichlorophenyl)‐N‐(2,6‐diisopropylphenyl)formamidine dithiocarbamate (DTL5) and N′‐(2,6‐dichlorophenyl)‐N‐mesitylformamidine dithiocarbamate (DLT6), were reacted with chloridocobalt(III) in water to give Co‐(DTL1)3 (1), Co‐(DTL2)3 (2), Co‐(DTL3)3 (3), Co‐(DTL4)3 (4), Co‐(DTL5)3 (5) and Co‐(DTL6)3 (6). All the dithiocarbamates and complexes were characterized using 1H NMR, 13C NMR, Fourier transform infrared, UV–visible and mass spectra and the purity confirmed by elemental analysis. In addition, crystal structures of complexes 1, 2, 4 and 5 were determined, confirming the formation of mononuclear species in which the Co(III) centers coordinated to six sulfur atoms from three dithiocarbamate ligands resulting in distorted octahedral geometries. All complexes showed moderate to good antibacterial activities against Gram‐negative bacteria Escherichia coli, Salmonella typhimurium, Klebsiella pneumoniae and Pseudomonas aeruginosa even at low concentrations. None of the six were active against Gram‐positive bacterium methicillin‐resistant Staphylococcus aureus and only active against S. aureus at high concentrations. Complexes 5 and 6 were found to be more active than ciprofloxacin against S. typhimurium, E. coli, P. aeruginosa and K. pneumoniae and complexes with chloro‐substituted ligands generally had enhanced activities. Antioxidant activities of the dithiocarbamate salts and their Co(III) complexes were also investigated using DPPH assay and the complexes were found to be more efficient. Complex 2 with an IC50 value of 2.84 × 10−4 mM displayed the highest activity of all compounds tested, even outdoing ascorbic acid. The radical scavenging ability of the complexes followed the order 2 > 1 > ascorbic acid >3 > 4 > 6 > 5.