Molecular Motions in Highly Disordered Solid Phases of [(CH3)3NCH2CH3]X (X = ClO4, PF6, NO3) Studied by 1H, 19F, and 14N NMR, Powder X-Ray Diffraction, and Differential Scanning Calorimetry

Abstract 1H, 19F, and 14N NMR, powder X-ray diffraction, and differential scanning calorimetry (DSC) were measured in trimethylethylammonium perchlorate, hexafluorophosphate and nitrate, [(CH3)3NCH2CH3]X (X = ClO4, PF6, NO3). Three, four and four solid phases were obtained for perchlorate, hexafluorophosphate, and nitrate, respectively, in the temperature ranges from 77 K to their decomposition temperatures. X-Ray powder patterns showed that the highest-temperature solid phases of perchlorate and hexafluorophosphate are CsCl-type cubic, while that of nitrate is NaCl-type cubic. The second highest-temperature phases of perchlorate and hexafluorophosphate form tetragonal lattices. The NMR study revealed that the cations perform isotropic rotation as well as self-diffusion in the CsCl-type cubic and tetragonal phases of perchlorate. In the cubic phase of hexafluorophosphate, isotropic rotation and self-diffusion of both anion and cation were observed. In the NaCl-type cubic phase of nitrate, isotropic rotation of both ions was detected. The structures in the highest- and second highest-temperature phases of the three salts were found to be dynamically disordered. Especially, the highest-temperature phases of perchlorate and hexafluorophosphate can be classified into the ionic plastic phase of the CsCl-type structure. Activation energies of the ionic motions in these phases were evaluated. Motional modes of the ions in the lower temperature phases were also deduced.