Synthesis and crystal structures of sterically tuned ether functionalized NHC–silver(I) complexes: antibacterial and nucleic acid interaction studies

<div><p>A series of new imidazolium salts (<b>1–4</b>) as <i>N</i>-heterocyclic carbene (NHC) precursors have been synthesized by successive N-alkylation method. Reactions of these salts with Ag₂O by varying the metal to salt ratio forms a series of new Ag(I)–NHC complexes (<b>5–8</b>). All compounds were characterized by physico-chemical and spectroscopic techniques. The molecular structures of <b>1</b> and <b>5</b> were characterized by single-crystal X-ray diffraction analysis. A comparative investigation of the bacterial growth inhibition potential of the salts and respective complexes indicates that <b>5–8</b> displayed good antibacterial activities on <i>Staphylococcus aureus</i> (ATCC 12600) and <i>Escherichia coli</i> (ATCC 11303) compared with the salts. Furthermore, it was observed that with increase in chain length at <i>N</i>-positions, the antibacterial activities also increased. Nuclease activity of the reported salts and Ag(I)–NHC complexes with nucleic acids (DNA and RNA) were also studied using agarose gel electrophoresis; the results show that the compounds do not have any apparent interaction with nucleic acids in the absence of hydrogen peroxide (H₂O₂). However, <b>5</b> and <b>8</b> were efficient in promoting the cleavage of nucleic acids in the presence of H₂O₂.</p></div

Triphenylphosphine-supported synthesis of two-dimensional silver(I) complex with (1,3,4-thiadiazole-2,5-diyldithio)diacetic acid

<p>The reaction of dicarboxylate ligand, (1,3,4-thiadiazole-2,5-diyldithio)diacetic acid (H₂tdza) with silver(I) acetate and triphenylphosphine (PPh₃) facilitate the formation of complex [Ag₂(tdza)(PPh₃)₂]<i>_n</i> <b>(1)</b>. The complex was characterized by elemental analysis, FT-IR spectroscopy, ¹H-NMR, ¹³C-NMR and ³¹P-NMR spectroscopy, and single crystal X-ray diffraction. Structural analysis revealed that complex <b>1</b> has a 2D topologically promising architecture as a result from the formation of 26-membered cyclic ring. The tdza2⁻ ligand in <b>1</b> displays unprecedented µ₄-bridging mode which is also the first example for this ligand. The interdigitating arrangement and π-π stacking between 2D arrays stabilized the formation of complex <b>1</b>.</p

Asymmetric <i>N</i>-heterocyclic carbene benzimidazolium salts and their silver(I) complexes: potential as ionic liquid crystals

<p>The synthesis and characterisation of a homologous series of monodentate benzimidazolium salts, <b>1</b>–<b>4</b> and their mononuclear silver(I)–NHC (where NHC = <i>N</i>-heterocyclic carbene) complexes, <b>5</b>–<b>8,</b> are reported. The benzimidazolium salts were prepared from the <i>N</i>-alkylation of 1-methyl-benzimidazole with alkyl halides of varying carbon chain lengths. The mono silver(I)-NHC complexes, <b>5</b>–<b>8,</b> were prepared by the reaction of the benzimidazolium salts with Ag₂O. All the synthesised compounds were fully characterised by ¹H-nuclear magnetic resonance (¹H-NMR), ¹³C-NMR and fourier-transform infrared (FTIR) spectroscopy. The molecular structures of compounds <b>3</b>·PF₆, <b>4</b>·PF₆, <b>7</b> and <b>8</b> were elucidated through single-crystal X-ray diffraction analyses. We postulate that the attachment of long alkyl chains to the heterocyclic core of 1-methyl benzimidazole could induce mesophase formation. The liquid crystalline behaviour of the benzimidazolium salts was investigated by polarised optical microscope and differential scanning calorimetry. Salts <b>3</b> and <b>4</b> were found to be thermotropic liquid crystals which exhibited a smectic A phase. However, upon complexation with silver(I) ions, all the Ag(I)–NHC complexes are found to be non-mesogenic.</p