Ionic motions and phase transitions in solid trimethylethylammonium tetrafluroberate studied by by¹H, ¹⁹F, and¹⁴N NMR, powder X-ray diffraction and differential scanning calorimetry

¹H, ¹⁹F, and ¹⁴N NMR, powder X-ray diffraction, and differential scanning calorimetry (DSC) were studied for trimethylethylammonium tetrafluoroborate, (CH₃)₃NC₂H₅BF₄. Five solid phases, named I, II, III, IV, and V in the order of decreasing temperature, were obtained in the temperature range 77-630 K. The transition temperatures and the corresponding enthalpy changes determined by DSC were 222K (0.16kj moi^-1), 239K (1.8 kJ mol^-1), 293 K (2.1 kJ mol^-1), and 362 K (4.5 kJ mol^-1). X-ray powder patterns showed that Phase I and II form an NaCl-type cubic lattice (a = 10.14 Å, Z = 4) and a tetragonal lattice (a = 8.59, c = 6,24 Å, Z = 2), respectively. The NMR study revealed that the canonic orientation in Phase I and II is dynamically disordered. Moreover, since the self-diffusion of anions and the Isotropie rotation of cations were observed in Phase I, this phase can be considered as a mesophase very close to the plastic phase. In Phases II, III, IV, and V we have detected the isotropic reorientation of anions, the anisotropic tumbling of cations, the C′₃ reorientation of the whoie (CH₃)₃N group about C-N bond axis, and the C₃ reorientation of the CH₃ groups. The motional parameters were evaluated for these cationic and anionic motions.