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

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.