Design, Synthesis, and Antibacterial Assessment of Silver(I)-Based Coordination Polymers with Variable Counterions and Unprecedented Structures by the Tuning Spacer Length and Binding Mode of Flexible Bis(imidazole-2-thiones) Ligands

An investigation of the impact of alkyl spacer length of the flexible ligands and influence of shape and coordination ability of the counterions has been done on a series of five silver(I)-bis(imidazole-2-thione) coordination polymers. The five compounds, namely, [Ag2L4(NO3)(2)](n), {[AgL4](2)[CF3SO3](2)}(n), [Ag2L6(CF3SO3)(2)](n), [Ag2L6(NO3)(ClO4)](n), and [(Ag2LBr2)-Br-6](n) (L-4 = 1,1'-(butane-1,4-diyl)-bis(3-methylimidazoline-2-thione) and L-6 = 1,1'-(hexane-1,4-diyl)-bis(3-methylimidazoline-2-thione) have been characterized by elemental analysis, IR spectra, thermogravimetric analysis (TGA), powder X-ray diffraction, and single crystal X-ray diffraction. In the title polymers, the L-4 and L-6 ligands exhibit unprecedented coordination modes, and the Ag(I) centers adopt a range of coordination geometries. The single crystal structural analysis of the title compounds shows that polymers based on the L-4 ligand predominately adopt AgS4 core structure which does not appear in the polymers containing L-6 ligand. The TGA experimental data reveal that these compounds start to decompose in the temperature range of 240-341 degrees C. All of the synthesized compounds, in particular, polymer 2, possess antibacterial activity against the selected strain of Gram-negative (Escherichia coli, Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus, Bacillus subtilis) bacteria.