Metal Complexes of Multidentate N2S2 Heterocyclic Schiff-base Ligands;Formation, Structural Characterisation and Biological Activity

Abstract

Abstract The synthesis of ligands with N2S2 donor sets that include imine, an amide, thioether, thiolate moieties and their metal complexes were achieved. The new Schiff-base ligands; N-(2-((2,4-diphenyl-3-azabicyclo[3.3.1]nonan-9-ylidene)amino)ethyl)-2-((2-mercaptoethyl)thio)-acetamide (H2L1) and N-(2-((2,4-di-p-tolyl-3-azabicyclo[3.3.1]nonan-9-ylidene)amino)ethyl)-2-((2-mercaptoethyl)thio) acetamide (H2L2) were obtained from the reaction of amine precursors with 1,4-dithian-2-one in the presence of triethylamine as a base in the CHCl3 medium. Complexes of the general formula K2[M(Ln)Cl2], (where: M = Mn (II), Co(II) and Ni(II)) and [M(Ln)], (where: M = Cu(II), Zn(II) and Cd(II); n =1-2, expect [Cu(HL2)Cl]) were isolated. The entity of ligands and complexes including their purity were confirmed using elemental microanalysis (C.H.N.S), atomic absorption (A.A), chloride content, conductivity measurement’s, melting point and thermal analysis technique. The molecular structures were elucidated with FT-IR, UV-Vis, magnetic susceptibility, 1H-and 13C-NMR and mass spectroscopy. The synthesised compounds were evaluated for their activity against bacterial strains (G+ and G-) and fungi species. The tested compounds indicated that; the ligands have not shown any antimicrobial activity against Escherichia coli. The Cd(II) complexes, for ligands H2L1 and H2L2, display the higher antimicrobial activity, compared with the other complexes. The H2L1 and H2L2 have not shown any activity against Candida albicans. All complexes for ligands (H2L1 and H2L2) exhibited less activity against Candida albicans, compared with other types of fungi.