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 [Au-2(RIme-(CH2)(3)-ImR)(2)](X)(2) (X = Br, PF6, BF4) have been synthesised and thermally characterised. All the compounds are stable up to 200 degrees C and the bis(imidazolium) salts [H-2(RIm-(CH2)(3)-ImR)](X)(2) (X = Br, PF6) behave as thermotropic liquid crystals in the temperature range 100-200 degrees 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 AueAu distances, as indicated by solid state emission properties. (C) 2015 Elsevier B.V. All rights reserved.