Ionic liquid crystal engineering of 3-carbamoyl-1-alkylpyridin-1-ium tetrachlorocuprate(II) and tetrachlorozincate(II) salts

Abstract

Two series of nicotinamide based ionic liquid crystalline compounds, 3-carbamoyl-1-alkylpyridin-1-ium salts ([Nia–Cn]₂X, X = CuCl₄²⁻ and ZnCl₄²⁻; n = 12, 14 and 16), have been synthesized and characterized by single crystal and powder X-ray diffraction, DSC and POM. Both series form interdigitated bilayers in the solid state and liquid crystalline phase. The ionic layers of the two salts are stabilized mainly by four N–H⋯Cl and six C–H⋯Cl hydrogen bonds per anion and has sacrificed the formation of strong N–H⋯OC hydrogen bonding in the solid state. However, the N–H⋯Cl and N–H⋯OC hydrogen bonds dominate in the mesophase at high temperature to cause a significant increase of the thickness of the ionic layer.