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.