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

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.