Hiroshi Ono

New mesophases in ionic crystals: piperidinium perchlorate and nitrate studied by 1H, 2H, 14N and 35Cl NMR

Abstract Measurements of 1H, 2H, 14N and 35Cl NMR, differential thermal analysis, differential scanning calorimetry and powder X-ray diffraction were carried out in solid piperidinium perchlorate and nitrate above room temperature. Two and one solid-solid phase transitions were observed for the perchlorate and nitrate, respectively. The crystal structure in the highest-temperature phase of the perchlorate is CsCl-type cubic ( a = 6.02(6) A and Z = 1 ) while that of the nitrate is NaCl-type cubic ( a = 9.35(5) A and Z = 4 ). In this phase of the perchlorate self-diffusion of the cation and isotropic rotation of both cation and anion were revealed. In the highest-temperature phase of the nitrate, the isotropic rotation of both ions was detected. These phases are highly disordered and especially the phase of the perchlorate can be assigned to an anionic plastic phase.

1H and 19F NMR studies on molecular motions and phase transitions in solid triethylammonium tetrafluoroborate

Abstract Measurements by differential thermal analysis and differential scanning calorimetry and of the spin-lattice relaxation time (T1), the spin-spin relaxation time (T2), and the second moment (M2) of 1H and 19F NMR were carried out in the three solid phases of (CH3CH2)3NHBF4. X-ray powder patterns were taken in the highest-temperature phase (Phase I) existing above 367 K and the room-temperature phase (Phase II) stable between 220 and 367 K. Phase I formed a NaCl-type cubic structure with a = 11.65(3) A , Z = 4, V = 1581(13) A 3 , and Dx = 0.794 g cm−3, and was expected to be an ionic plastic phase. In this phase, the self-diffusion of anions and the isotropic reorientation of cations were observed. Phase II formed a tetragonal structure with a = 12.47(1) and c = 9.47(3) A , Z = 4, V = 1473(6) A 3 , and Dx = 0.852 g cm−3. From the present DSC and NMR results in this phase, the cations and/or anions were considered to be dynamically disordered states. The C3 reorientation of the cation about the Nue5f8H bond axis was detected and, in addition, the onset of nutation of the cations and local diffusion of the anions was suggested. In the low-temperature phase (Phase III) stable below 219 K, the C3 reorientations of the three methyl groups of cations and the isotropic reorientation of anions were observed. The motional parameters for these modes were evaluated.

Ionic plastic phases in trimethylammonium trifluoroacetate studied by 1H and 19F NMR spectroscopy, X-ray diffraction and thermal measurements

1H and 19F NMR, differential scanning calorimetric and X-ray powder diffraction measurements were carried out in solid trimethylammonium trifluoroacetate, (CH3)3NHCOOCF3. Two solid–solid phase transitions were observed at 307 and 330 K. The structures of the solid phases obtained above 330 K and between 307 and 330 K are CsCl-type cubic and tetragonal, respectively. In the two phases, both cations and anions perform self-diffusion and isotropic rotation. From the dynamic behaviour of the ions together with thermal data, both phases are assignable as ionic plastic phases.

CATIONIC SELF-DIFFUSION IN SOLID CHOLINE PERCHLORATE STUDIED BY 1H NMR

Abstract The 1H spin-lattice and spin-spin relaxation times, and the second moment of the 1H NMR linewidth of choline Perchlorate, [(CH3)3NCH2CH2OH]ClO4, were measured in its highest-temperature solid phase, i. e. above 275 K. X-ray powder patterns taken at ca. 380 K revealed that in this phase the crystal has a CsCl-type cubic structure (a = 6.326(4) Å and Z = 1). From 1H NMR experiments it was found that the cations in this phase undergo isotropic rotation and translational self-diffusion. From the 1H T1, measurements, the activation energies of the cationic rotation and self-diffusion were evaluated to be 21.4 ± 0.4 and 62 ± 3 kJ mol-1 , respectively.

Crystal Structure of the High-temperature Solid Phases of Choline Tetrafluoroborate and Iodide

Abstract The crystal structure of the highest-and second highest-temperature solid phases of choline tetrafluoroborate and iodide was determined by X-ray powder diffraction. The structure in the highest-temperature phase of both salts is NaCl-type cubic (a = 10.16(2) Å, Z = 4 for tetrafluorobo-rate; a = 10.08(2) Å, Z = 4 for iodide). The second highest-temperature phase of tetrafluoroborate and iodide is CsCl-type cubic (a = 6.198(6) Å and Z = 1) and tetragonal (a = 8.706(2) Å, c = 6.144(6) Å, and Z = 2), respectively. DSC was carried out for the iodide, where the presence of three solid-solid phase transitions was confirmed. Enthalpy and entropy changes of these transitions were evaluated.