Synthesis, characterization, thermal, and antimicrobial studies of binuclear metal complexes of sulfa-guanidine Schiff bases

A series of metal complexes of Schiff bases derived from condensation of sulfa-guanidine with 1-benzoylacetone (H2L1), 2-hydroxybenzophenol (H2L2), dibenzoylmethane (H2L3), 5-methylisatine (H2L4), and 1-methylisatine (H2L5) have been synthesized. The complexes are characterized by elemental analysis, molar conductance, magnetic moment measurements, IR, UV-Vis, 1H NMR, and ESR spectra, as well as thermogravimetric analysis. The low molar conductance values indicate the complexes are nonelectrolytes. IR and 1H NMR spectra show that H2L1-H2L5 are coordinated to metal ions by two bidentate centers. Mn(II), Co(II), Ni(II), and Cu(II) complexes display paramagnetic behavior, whereas the Zn(II)-complex was diamagnetic. All studies confirm the formation of an octahedral geometry for [Cu2L1(AcO)2(H2O)6] 3H2O (1), [Mn2L4(AcO)2(H2O)6] 2H2O (6), [Ni2L4(AcO)2(H2O)6] 2H2O (8), a tetrahedral geometry for [Cu2L2(AcO)2(H2O)2] (2), [Cu2(L4)2] (4), [Co2(L4)2] 2H2O (7) and [ZnHL4(AcO)(H2O)] 2H2O (9) and a trigonal bipyramid geometry for [Cu2L3(AcO)2(H2O)4] (3) and [Cu2HL5(AcO)3(H2O)3] H2O (5). H2L4 was most effective on Gram negative, Gram positive bacteria, and fungi (diameters inhibition zone ranged between 10.5-27.5 mm) after 24 and 48 h, respectively. Complex 8 showed moderate antimicrobial activity. Its minimum inhibitory concentration (MIC) against Escherichia coli, Bacillus subtilis, Candida albicans and Aspargllus flavas was 20 mg L-1. The compound proved to be of moderate toxicity and its LD50 was 20 mg L-1.