| Sumario: | Four new ionic rotator-crystals of [NEtMeR][BEt] (R = Pr, Bu; x = 1, 2) were observed. Rotator crystals (two-dimensional plastic crystals) are mesophases between solid and isotropic liquid phases. Solid-state H and C nuclear magnetic resonance (NMR) measurements revealed that the ellipsoidal cations of [NEtMeR] undergo uniaxial rotation about their N–R axis and libration motion of the axis, and the anions perform isotropic reorientations in the highest-temperature solid-phase (rotator phase). Differential scanning calorimetry (DSC) measurements showed small entropy changes of 8–11 J K mol at the melting point of the compounds. These results suggest that the cations and anions have large degrees of freedom of motion in the rotator phase. The diffraction patterns of X-ray diffraction (XRD) could be indexed to the trigonal structure (space group of P31c). Compared with the reported data for [NEtMePr][BEtMe] (x = 1, 2) compounds, which also have rotator-crystal phases and transform to a plastic crystalline phase, a model that explains why the cations of [BEt] salts hardly perform isotropic reorientation in the solid phases was proposed.
|
|---|