Synthesis and structural studies of nickel(II)- and copper(II)-N,N′-diarylformamidine dithiocarbamate complexes as antimicrobial and antioxidant agents

Abstract

A series of six N′N-diarylformamidine dithiocarbamate ligands and their metal complexes of Cu(II) and Ni(II) chloride salts have been synthesized. Three symmetrical, N,N′-bis(2,6-dimethylphenyl)formamidine dithiocarbamate (DL1), N,N′-bis(2,6-disopropylphenyl)formamidine dithiocarbamate (DL2), N,N′-mesityl formamidine dithiocarbamate (DL3) and three unsymmetrical N′-(2,6-dichlorophenyl-N-(2,6-dimethylphenyl)formamidine dithiocarbamate (DL4), N′-(2,6-dichlorophenyl)-N-(2,6-diisopropylphenyl)formamidine dithiocarbamate (DL5) and N′-(2,6-dichlorophenyl)-N-mesityl formamidine dithiocarbamate (DL6) dithiocarbamate ligands were reacted with CuCl2 and NiCl2 to give [Ni-(DL1)2] (1), [Ni-(DL2)2]·H2O (2), [Ni-(DL3)2] (3), [Ni-(DL4)2]·3H2O (4), [Ni-(DL5)2]·H2O (5), [Ni-(DL6)2] (6), [Cu-(DL1)2]·3H2O (7), [Cu-(DL2)2] (8), [Cu-(DL3)2]·2H2O (9), [Cu-(DL4)2]·3H2O (10), [Cu-(DL5)2]·3H2O (11) and [Cu-(DL6)2] (12). All ligands and the complexes were characterized using FT-IR, UV–Vis, 1H and 13C NMR, mass spectrometry and by elemental analysis. In addition, the structures of complexes 1, 5, 8 and 11 were confirmed by single crystal X-ray diffraction analysis as mononuclear neutral species in which the geometry around the metal centers is distorted square planar. In this coordination manner, the metal centers bound to four sulfur atoms from two dithiocarbamate ligand in a bidentate fashion. All complexes showed moderate to good antibacterial activities against Gram-negative, Salmonella typhimurium, Pseudomonas aeruginosa, Escherichia coli and Klebsiella pneumoniae and gram-positive, Staphylococcus aureus (methicillin resistant) and Staphylococcus aureus bacteria. Complexes 4 and 5 were found to be more active than ciprofloxacin against E. coli and K. pneumoniae. In addition, complexes with chloro substituted ligands displayed higher activities. Antioxidant activities of complexes with symmetrical formamidine ligands were generally high compared to the ones with the unsymmetrical formamidine moieties, with 2 having an IC50 value of 1.10 × 10−3 mM and 12 had 2.91 mM.