Insights into structural and spectral properties of cobalt (II) complexes bearing asymmetric thiourea ligands and their remarkable bioactivities against Gram negative bacteria

A major number of sulfur compounds including derivatives of thiourea is medicinally important agents and metal complexes of thioureas are often more medicinally active. Monoisopropylamine and m-toluidine, as aliphatic and aromatic amines, were used to prepare monodentate thiourea ligands [1-isopropyl-3-phenylthiourea (L 1 ) and 1-phenyl-3-m-tolylthiourea (L 2 ), respectively] and single crystals of cobalt complexes incorporating these ligands were also isolated. These tetrahedral complexes, [Co(L 1 ) 2 Cl 2 ] and [Co(L 2 ) 2 Cl 2 ], were demonstrated in different lattice packings (orthorhombic and monoclinic, respectively). To characterize the antibacterial patterns (percent growth inhibitions and percent viability inhibitions) of these compounds, the activities of dimethyl sulfoxide solutions (50–200 μg/ml) of them against Gram negative bacterial strains (i.e., Klebsiella pneumoniae, Pseudomonas aeruginosa and Serratia marcescens ) were determined. Chloramphenicol (CHL) was used as the commercial standard. At 200 μg/ml, the complex Co-L 1 inhibited these bacteria by 94.9, 92.2 and 69.8 % and Co-L 2 inhibited them by 86.0, 87.0 and 78.3 % (92.1, 86.6 and 72.3 % by CHL), respectively. Furthermore, [Co(L 1 ) 2 Cl 2 ] and [Co(L 2 ) 2 Cl 2 ] offered bactericidal action with 100 % viability inhibition against Klebsiella pneumoniae , but the action was bacteriostatic with 72.3–96.2 % and 84.4–96.9 % viability inhibitions against Pseudomonas aeruginosa and Serratia marcescens , respectively. • Two tetrahedral cobalt(II) complexes bearing asymmetric thiourea ligands were prepared. • The bioactivity of them was studied against K. pneumoniae, P. aeruginosa and S. marcescens . • Some activities given by the complexes exceeded those of chloramphenicol standard.