Asymmetric <i>N</i>-heterocyclic carbene benzimidazolium salts and their silver(I) complexes: potential as ionic liquid crystals
收藏资源简介：
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 Ag<sub>2</sub>O. All the synthesised compounds were fully characterised by <sup>1</sup>H-nuclear magnetic resonance (<sup>1</sup>H-NMR), <sup>13</sup>C-NMR and fourier-transform infrared (FTIR) spectroscopy. The molecular structures of compounds <b>3</b>·PF<sub>6</sub>, <b>4</b>·PF<sub>6</sub>, <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.
