New Chemical Family of [n-CxH(2x+1)NEt3][BEt3Me] Showing Ionic Plastic-Crystal (x = 4, 5), Rotator-Crystal (x = 6, 7) and Liquid-Crystal Phases (x = 8–16)

Abstract

Abstract New ionic liquid crystals of [n-CxH(2x+1)NEt3][BEt3Me] (abbreviated to [CxNEt3][BEt3Me]) were detected for species with even numbers of 8 ≤ x ≤ 16. In contrast, plastic- and rotator-crystal phases were obtained for [CxNEt3][BEt3Me] species with lower x values of x = 4, 5, and 6, 7, respectively. Because we previously documented plastic phases for the [CxNEt3][BEt3Me] (x = 1–3) species, [CxNEt3][BEt3Me] can be classified as a novel chemical family adopting the entire range of states (mesophases) between solid and isotropic liquid phases (plastic, rotator, and liquid crystals) as a function of the alkyl chain length. Polarized optical microscope (POM) and X-ray diffraction (XRD) measurements revealed that these liquid crystals (x = 8–16 with even numbers of x) form smectic B (x = 8) and A (x = 10), and nematic phases (x ≥ 12) in the liquid-crystal phases. In the case of x = 4, 5, XRD analysis showed that the salts form cubic crystal structures. Furthermore, the NMR line shapes revealed that both the cation and anion underwent isotropic reorientation. In contrast, the NMR spectra showed that the cations rotated about their long axis in the [C6NEt3][BEt3Me] and [C7NEt3][BEt3Me] crystals.