Synthesis and thermotropic behaviour of bis(imidazolium) salts bearing long-chain alkyl-substituents and of the corresponding dinuclear gold carbene complexes

New propylene bridged bis(imidazolium) salts bearing at the wingtip positions a benzyl group functionalised with one or two long alkyl chains, as well as the corresponding dinuclear N-heterocyclic dicarbene gold(I) complexes of general formula [Au2(RIm-(CH2)3-ImR)2](X)2 (X = Br, PF6, BF4) have been synthesised and thermally characterised. All the compounds are stable up to 200 °C and the bis(imidazolium) salts [H2(RIm-(CH2)3-ImR)](X)2 (X = Br, PF6) behave as thermotropic liquid crystals in the temperature range 100-200 °C. By contrast, only the gold(I) diNHC complexes with eight aliphatic chains present mesomorphism, whereas those with four chains show numerous crystalline phases with structural disorder and presumably modified Au-Au distances, as indicated by solid state emission properties.