FT-Raman, FT-IR, NMR structural characterization and antimicrobial activities of 1,6-bis(benzimidazol-2-yl)-3,4-dithiahexane ligand and its Hg(II) halide complexes

Abstract

1,6-Bis(benzimidaz-2-yi)-3,4-dithiahexane ligand (L) and its mercury halide complexes were prepared and characterised. The elemental analysis, molecular conductivity, FT-Raman, FT-IR (mid, far), H-1, C-13 NMR and geometry optimization in MOPAC using MNDOd parameter on CACHE, prove the existence of neutral, mononuclear and the distorted tetrahedral [Hg(L)X-2] complexes. In all the three complexes, the ligand acts as a chelating bidentate, through two of the bridging sulphur atoms and together with the monodentate coordination of the two anionic halide ligands to the metal centre forming a possible 4-coordinate compounds. The antimicrobial activities of free ligand, its hydrochlorinated salt, mercury halides and the complexes are evaluated using disk diffusion method in dimethyl sulfoxide (DMSO) as well as the minimal inhibitory concentration (MIC) dilution method, against 10 bacteria. The obtained results from disk diffusion method are assessed in side-by-side comparison with those of Penicillin-g, Ampicillin, Cefotaxime, Vancomycin, onaxacin and Tetracyclin well-known antibacterial agents. The results from dilution procedure are compared with Gentamycin as antibacterial and Nystatin as antifungal. The antifungal activities are reported on five yeast cultures namely Candida albicans, Kluyveromyces fragilis, Rhodotorula rubra, Debaryomyces hansenii and Hanseniaspora guillierinondii, and the results are referenced with Nystatin, Ketaconazole and Clotrimazole, commercial antifungal agents. In most cases, the compounds show broad-spectrum (Gram(+) & Gram(-) bacteria) activities that are comparatively, slightly less active or equipotent to the antibiotic and antifungal agents in the comparison tests.