Liquid crystals based on halogold(I) complexes with 4-isocyano-4′alkoxybiphenyl derivatives

Abstract

Rod-like complexes [AuCl(CNC₆H₄C₆H₄OC_nH_2n+1-p)](n= 4, 6, 8, 10, 12) have been prepared by reaction of [AuCl(tht)](tht= tetrahydrothiophene) with the isonitriles CNC₆H₄C₆H₄OC_nH_2n+1-p. Metathetical reactions with KBr or KI afford the corresponding [AuX(CNC₆H₄C₆H₄OC_nH_2n+1-p)](X = Br, I). While the free isonitriles are liquid crystals displaying nematic and (some of them) smectic A phases with a short range of existence at moderate temperatures (40–85 °C), their coordination to AuX (X = Cl, Br, I) produces a marked increase in the melting points of the materials, and also an enormous expansion of the range of existence of the mesophase. The order in the mesophase also increases and only the smectic A phase is formed in most of the complexes (for X = Cl, Br and n= 4 a nematic phase is also formed). All the biphenyl halogold(I) derivatives are mesogenic (except for X = I and n= 4) and their melting points decrease in the order I > Br > Cl. Ranges of mesophase of nearly 140 °C are attained. Most of the complexes decompose to the isotropic state (above 220 °C), but seem thermally stable below 200 °C.