Tuning the structure of mercury (II) complexes as antibacterial agents by varying the halogen atoms (Cl and Br) and extending the spacer length of the imidazole-2-thione ligands

Abstract

A series of mercury(II) complexes with empirical formula of Hg2LX4 (L = ligand and X = halogen) namely [Hg2(mbit)Cl4]n(1), {[Hg₂(mbit)Br₄]·CH3CN}n (2) [mbit = bis(1-methyl-imidazole-2-thione)methan], [Hg2(prbit)Br4]n (3), [Hg2(prbit)Cl4]n (4) [prbit = 1,3-bis(1-methyl-imidazole-2-thione) propane], [Hg2(pbit)Cl4]n (5) and [Hg2(pbit)Br4]n (6) [pbit = 1,5-bis (1-methyl-imidazole-2-thione) pentane] were designed and synthesized by a branched tube method. The complexes 2 to 5 have been fully characterized by single crystal X-ray diffraction, elemental chemical analysis (CHNS), infrared spectroscopy (IR), powder X-ray diffraction (PXRD), UV–Vis spectroscopy, thermogravimetric analysis (TGA) and photoluminescence spectroscopy (PL). On the base of PXRD patterns, the compounds 1 and 6 are not isostructural with the complexes 2 to 5. In the 2D structure of 2, the central atoms adopt distorted tetrahedral and octahedral geometries with HgBr4 and HgS2Br4 donor sets, respectively. Interestingly, by increasing the number of methylene groups in the ligand spacer from one in the mbit to three in the prbit, dimension of the polymer was increased from the 2D in 2 to the 3D in the structure of 3 with distorted HgBr4 trigonal pyramidal and HgS2Br2 seesaw environments. Further increasing the ligand flexibility and number of methylene moieties to five in the pbit, the structure of complex 5 was unexpectedly turned into a dinuclear species with distorted HgS2Cl2 seesaw and ideal HgCl4 trigonal pyramidal geometries. The polymers 3 and 4 with the same organic ligands and different halogen anions are isostructural. As a common feature, the complexes 2 and 5 were further stabilized by the intermolecular interactions to form a 3D non-covalent supramolecular structure. The in vitro bioefficacy of the complexes 2 to 5 were assessed against some Gram-positive and -negative bacteria and the results confirmed their substantial antimicrobial potential.