Nuclear Magnetic and Quadrupole Resonance Studies of Phase Transitions in Crystalline (NH4)2SbF5 and (ND4)2SbF5

1988 ◽  
Vol 43 (3) ◽  
pp. 233-238 ◽  
Author(s):  
Ataru Kobayashi ◽  
Yoshichika Yoshioka ◽  
Nobuo Nakamura ◽  
Hideaki Chihara
Keyword(s):  
Activation Energy ◽  
Phase Transitions ◽  
Transition Point ◽  
Spin Lattice Relaxation ◽  
Ammonium Ion ◽  
Temperature Phase ◽  
Lower Phase ◽  
Resonance Frequencies ◽  
Quadrupole Resonance ◽  
Lower Transition

(NH4)2SbF5 undergoes two successive phase transitions at 169 and 292 K, both of which are of typical lambda-type and without thermal hysteresis. Proton and fluorine spin-lattice relaxation time measurements showed that the isotropic reorientation of the NH4+ ions is highly excited below the lower transition point with an activation energy of 15.5 kJ mol-1 and that the uniaxial reorientation of the square pyramidal SbF52- anion is excited above about 200 K with an activation energy of 42.0 kJ mol-1. There is strong cross relaxation between the proton and the fluorine over the whole temperature range of the measurements. The 121Sb and 123Sb nuclear quadrupole resonance frequencies show an anomalous temperature dependence; each resonance frequency assumes a minimum at around 100 K and increases on heating, reaches a maximum at the lower transition point, decreases drastically in the middle temperature phase and then fades out just below the upper transition point. The anomalous increase in the resonance frequencies stems from the reorganization of the N - H ... F type hydrogen bonds with the progress of the lower phase transition. The lower and the upper transition temperatures shift to 173.0 and 290.1 K, respectively, on deuteration of the ammonium ion.

Incommensurability and Domain Structure of K2SbF5

2002 ◽  
Vol 57 (6-7) ◽  
pp. 456-460
Author(s):  
A. M. Panich ◽  
L. A. Zemnukhova ◽  
R. L. Davidovich
Keyword(s):  
Relaxation Time ◽  
Phase Transitions ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Spin Lattice ◽  
Relaxation Measurements ◽  
Increasing Temperature

Phase transitions and incommensurability in K2SbF5 have been studied by means of 123Sb NQR spectra and spin-lattice relaxation measurements. The phase transitions occur at 117, 135 and 260 K. The line shape and temperature dependence of the spin-lattice relaxation time T1 at 135 to 260 K are characteristic for an incommensurate state with a plane wave modulation regime. At 117 to 135 K a distinct fine structure of the NQR spectra has been observed. The X-ray diffraction pattern of this phase is interpreted as a coexistence of two modulation waves along the a and b axis with wave vectors (a*/6 + b*/6) and (a*/2 + b*/2), respectively. The best interpretation that fits our NQR data is a coexistence of two domains, the structures of which are modulated with different periods in such a manner that each domain exhibits only one of the aforementioned modulation waves. Redistribution of line intensities with the variation of temperature shows that one of the domains becomes energetically preferable on cooling and is transformed into the low temperature phase at 117 K. The 123SbNQR measurements in K2SbF5 show unusually short values of T1, which become close to the spin-spin relaxation time T2 with increasing temperature. - Pacs: 61.44.Fw, 64.60, 64.70, 64.70.Rh, 76.60

2H and 195 Pt NMR Studies of Molecular and Electron Spin Dynamics in Paramagnetic [Cu(H2O)6][PtCl 6]

1998 ◽  
Vol 53 (6-7) ◽  
pp. 447-452
Author(s):  
Takahiro Iijima ◽  
Kengo Orii ◽  
Motohiro Mizuno ◽  
Masahiko Suhara
Keyword(s):  
Activation Energy ◽  
Electron Spin ◽  
Nmr Spectra ◽  
Chemical Shift Anisotropy ◽  
Spin Lattice Relaxation ◽  
Water Molecules ◽  
Temperature Phase ◽  
Nmr Studies ◽  
Teller Distortion ◽  
Exponential Factor

Abstract The temperature dependences of 2H and 195Pt NMR spectra and the spin-lattice relaxation time T1 were measured for [Cu(H2O)6][PtCl6]. From the simulation of 2H NMR spectra, the jump rate of 180° flips of the water molecules (k), the nuclear quadrupole interaction parameters (e2Qq/h, ƞ) and the electron-nucleon dipolar interaction parameter (vD) were obtained. By measuring 2H T1, k was estimated in the temperature range where the spectrum is insensitive to the motion of the water molecules. Above the phase transition temperature, the pre-exponential factor k0 = 8 x1011 s-1 and the activation energy Ea = 15 kJmol-1 for 180° flips of the water molecules were obtained from the spectral simulation and T1. 195Pt NMR spectra showed an axially symmetric and unsymmetric powder pattern of the chemical shift anisotropy at the high and low temperature phase, respectively. For the deuterated compound, the correlation times of the electron spin in Cu2+ were estimated from 195Pt T1 and the activation energy for jumping between the different configurations of Jahn-Teller distortion Δ = 200 K was obtained.

NQR and Phase Transitions of Tetramethylammonium Tetrahalogenomercurates (II)

1996 ◽  
Vol 51 (5-6) ◽  
pp. 755-760 ◽  
Author(s):  
Hiromitsu Terao ◽  
Tsutomu Okuda ◽  
Koji Yamada ◽  
Hideta Ishihara ◽  
Alarich Weiss
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Reorientational Motion ◽  
Spin Lattice ◽  
Increasing Temperature

NQR and DTA revealed phase transitions in [(CH3)4N] 2HgBr4 and [(CH3)4N] 2HgI4 at 272 K and 264 K, respectively. The NQR resonance lines faded out with increasing temperature. From preliminary measurements of 81Br NQR spin-lattice relaxation times and 199Hg NMR a reorientational motion of HgBr4 ions around one of their pseudo C3 axes in the room temperature phase of [(CH3)4N] 2HgBr4 is suggested.

H NMR Study of Ionic Motions in High Temperature Solid Phases of (CH3NH3)2ZnCl4

2000 ◽  
Vol 55 (3-4) ◽  
pp. 412-414 ◽  
Author(s):  
Hiroyuki Ishida
Keyword(s):  
Activation Energy ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
The Self ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Self Diffusion ◽  
Spin Lattice ◽  
H Nmr ◽  
Nmr Study

Abstract The reorientation of the tetrahedral complex anion ZnCl42- and the self-diffusion of the cation in (CH3NH3)2ZnCl4 were studied by 1H NMR spin-lattice relaxation time (1H T1) experiments. In the second highest-temperature phase, the temperature dependence of 1H T1 observed at 8.5 MHz could be explained by a magnetic dipolar-electric quadrupolar cross relaxation between 1H and chlorine nuclei, and the activation energy of the anion motion was determined to be 105 kJ mol -1 . In the highest-temperature phase, the activation energy of the self-diffusion of the cation was determined to be 58 kJ mol -1 from the temperature and frequency dependence of 1H T1

Temperature Dependences of NQR Frequencies and Nuclear Quadrupole Relaxation Times of Chlorine in 2,6-Lutidinium Hexachlorotellurate (IV) as Studied by Pulsed NQR Techniques

1990 ◽  
Vol 45 (3-4) ◽  
pp. 485-489
Author(s):  
Keizo Horiuchi ◽  
Takashige Shimizu ◽  
Hitomi Iwafune ◽  
Tetsuo Asaji ◽  
Daiyu Nakamura
Keyword(s):  
Phase Transition ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Quadrupole Relaxation ◽  
Spin Lattice ◽  
Resonance Frequencies ◽  
Temperature Dependences ◽  
Nuclear Quadrupole

Abstract The temperature dependences of the 35Cl NQR frequencies vQ and the nuclear quadrupole spin-lattice relaxation times T1Q in 2,6-lutidinium hexachlorotellurate (IV) was observed at various temperatures between 80 and 343 K. This crystal undergoes a phase transition at Tc = 229 K. A single and three pairs of 35Cl NQR frequencies were observed above and below Tc , respectively. The hysteresis of the phase transition and a discontinuity in the temperature dependence of the resonance frequencies at Tc indicate that this phase transition is of first order. Although the resonance frequencies of the pairs in the low temperature phase are very close to one another, T1Q and below Tc could be accurately determined by measuring the Fourier transform spectra of each line. Above ca. 250 K, T1Q showed an exponential decrease which is attributable to the overall reorientational motion of [TeCl6]2- with an activation energy of 82 kJ mol-1

35Cl NQR Study of Guest Dynamics in Thiourea-CCl4 Inclusion Complex

1990 ◽  
Vol 45 (3-4) ◽  
pp. 519-522 ◽  
Author(s):  
Takasuke Matsuo ◽  
Masako Sekii ◽  
Hiroshi Suga ◽  
Nobuo Nakamura ◽  
Hideaki Chihara
Keyword(s):  
Activation Energy ◽  
Inclusion Complex ◽  
Nuclear Quadrupole Resonance ◽  
Intensity Ratio ◽  
Resonance Frequencies ◽  
Quadrupole Resonance ◽  
35Cl Nqr ◽  
Nuclear Quadrupole

Abstract35Cl nuclear quadrupole resonance measurements on thiourea-CCl4 inclusion complex yielded two resonance lines with intensity ratio 1:3. This indicates that the guest CCl4 molecule occupies the three-fold symmetry site in the channel formed by the thiourea framework. The resonance frequencies closely follow Bayer's equation between 4.2 K and 27 K. At higher temperatures the resonance lines faded out. This is attributed to the onset of reorientation of the CCl4 molecule. The activation energy for this motion was estimated to be 6 kJ mol-1 .

Structural Phase Transitions and Cationic Motions in Pvridinium Dichloroiodate(I) as Studied by 1H NMR, Differential Thermal Analysis, and Powder X-Ray Diffraction

1989 ◽  
Vol 44 (11) ◽  
pp. 1111-1115 ◽  
Author(s):  
Reiko Watanabe ◽  
Tetsuo Asaji ◽  
Yoshihiro Furukawa ◽  
Daiyu Nakamura ◽  
Ryuichi Ikeda
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Phase Transitions ◽  
Room Temperature ◽  
Structural Phase ◽  
Spin Lattice Relaxation ◽  
Growth Time ◽  
Stable Phase ◽  
Temperature Phase ◽  
H Nmr

For crystals of pyridinium dichloroiodate (I), (pyH)ICl2, the temperature dependences of the 1H NMR spin-lattice relaxation time T1 and the 1H second moment M2 were determined. M2 was found to be small (~ 1 G2) above room temperature, indicating that the cations perform rapid reorientational motion about their pseudohexad axis perpendicular to the cationic plane. 1H T1 at its minimum was unusually long, indicating this motion occurring in the low symmetry local environments. Phase transitions between stable solid phases were revealed at 282 and 373 K by the 1H NMR measurements and differential thermal analysis. The highest-temperature phase was easily supercooled and transformed reversibly into another metastable phase and back on cooling and warming at almost the same temperature of 138 K. The kinetics of the phase transition from the supercooled to the stable phase at room temperature was analyzed using an Avrami type relation. The growth time of the stable phase was estimated to be about 14 h at room temperature

The Observation of Incipient Phase Transitions in K2PtCl6, K2PdCl6, and K2IrCl6

1972 ◽  
Vol 50 (17) ◽  
pp. 2048-2053 ◽  
Author(s):  
Robin L. Armstrong ◽  
Henry M. Van Driel
Keyword(s):  
Phase Transitions ◽  
Temperature Dependence ◽  
Relaxation Times ◽  
Mode Frequency ◽  
Spin Lattice Relaxation ◽  
Frequency Data ◽  
Time Data ◽  
Resonance Frequencies ◽  
Lattice Mode ◽  
Static Lattice

Measurements of the temperature dependence of the nuclear quadrupole resonance (NQR) frequencies and spin–lattice relaxation times for the 35Cl nuclei in Cs2PtCl6, Rb2PtCl6, K2PtCl6, and K2PdCl6 provide information on the temperature dependence of two averages of the rotary lattice mode frequency over the-Brillouin zone. An iterative method is introduced to analyze the NQR frequency data and simultaneously yield the static lattice resonance frequencies and the temperature dependence of one of the average rotary mode frequencies. The results show that previous analyses of the data yielded erroneous values of the static lattice resonance frequencies. What is more interesting, the analysis presented clearly indicates incipient phase transitions in both K2PtCl6 and K2PdCl6 but shows that the structures of Cs2PtCl6 and Rb2PtCl6 remain stable to 0 K. The interpretation of the relaxation time data yields the temperature dependence of the second average rotary mode frequency and substantiates the conclusions drawn from the frequency data. A comparison of data for K2PtCl6 and K2IrCl6 reveals an incipient phase transition in the latter substance as well.

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