Molecular motion, phase transitions, and disorder in the pyridinium halides

1976 ◽  
Vol 54 (21) ◽  
pp. 3453-3457 ◽  
Author(s):  
John A. Ripmeester
Keyword(s):  
Phase Transitions ◽  
Molecular Motion ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Pyridinium Chloride ◽  
Scanning Calorimetry ◽  
Spin Lattice

The solid pyridinium chloride, bromide, and iodide salts were studied using 1H nuclear magnetic resonance and differential scanning calorimetry. Phase transitions were observed at 345 K for the chloride, 269 K for the bromide, and 247 K for the iodide. Well below each transition, the pyridinium ions are held rigidly in the crystal lattice, whereas above each transition the ions reorientate rapidly about an axis at right angles to the ring planes. From the temperature dependence of the spin–lattice relaxation times the high temperature phase reorientational activation energies were determined to be 1.55, 2.30, and 4.20 kcal/mol for the chloride, bromide, and iodide, respectively.

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.

Self-Diffusion and Reorientation of Methylammonium Ions in (CH3NH3)2ZnCl4 Crystals as Studied by 1H-NMR

1989 ◽  
Vol 44 (8) ◽  
pp. 741-746 ◽  
Author(s):  
Hiroyuki Ishida ◽  
Tadashi Iwachido ◽  
Naomi Hayama ◽  
Ryuichi Ikeda ◽  
Mifune Terashima ◽  
...  
Keyword(s):  
Solid Phase ◽  
Relaxation Times ◽  
Three Dimensional ◽  
Lattice Relaxation ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Self Diffusion ◽  
H Nmr

Abstract Differential thermal analysis, differential scanning calorimetry, and measurements of the 1H spin-lattice relaxation times and second moments of 1H-NMR absorptions were performed on methylammonium tetrachlorozincate (II) crystals over a wide temperature range. A solid-solid phase transition was located at 477 K. From the 1H-NMR experiments it was found that the cations undergo overall reorientation as well as three dimensional translational self-diffusion in the high-temperature phase. In the low-temperature phase, a 120° reorientational motion of the CH3 and NH3+ groups of the cation about its C-N bond axis was detected. The parameters for the motional modes of the cations in the crystal were evaluated from the analysis of the 1H-NMR experimental results.

Motions of Methylammonium Ions in (CH3NH3)2ZnBr4 Crystals Studied by 1H NMR and Thermal Measurements

1990 ◽  
Vol 45 (7) ◽  
pp. 923-927
Author(s):  
Hiroyuki Ishida ◽  
Kentaro Takagi ◽  
Tadashi Iwachido
Keyword(s):  
Solid Phase ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Self Diffusion ◽  
Spin Lattice ◽  
H Nmr

AbstractMeasurements of the 1H spin-lattice relaxation time T1, the linewidth parameter T*2the second moment of 1H NMR absorption, differential thermal analysis, and differential scanning calorimetry were performed on methylammonium tetrabromozincate(II) crystals from 58 to above 500 K. A solid-solid phase transition was located at 456 K. In the room temperature phase, 120° reorientational jumps of CH3 and NH3+ groups in the cation about its C -N bond axis were detected. In the high-temperature phase, the cations undergo overall reorientation as well as translational self-diffusion. The activation energy for the cationic self-diffusion was evaluated to be 18 kJ mol-1 .

scholarly journals 35Cl NQR Relaxation of the Molecular Ferroelectric 5,6-Dichloro-2-Methylbenzimidazole with Hydrogen-Bonded Molecular Chain

Crystals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 56
Author(s):  
Tetsuo Asaji
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Spin Lattice ◽  
First Order Phase Transition ◽  
Significant Difference ◽  
First Order Phase

The 35Cl nuclear quadruple resonance (NQR) frequencies and spin-lattice relaxation times were measured in the temperature range of 4.2–420 K, of the above-room-temperature ferroelectric 5,6-dichloro-2-methylbenzimidazole, the ferroelectricity of which is thought to arise from the positional ordering of protons along chain of N-H...N hydrogen bonds. The first-order phase transition was clearly detected at around 400 K, as a discontinuity in the temperature dependence of NQR frequencies. The two NQR lines observed showed a much more significant difference in frequency in the high-temperature phase. This is consistent with the recently reported symmetry-lowering of crystal structure on warming. The relaxation mechanism in the low-temperature phase is discussed.

Nuclear magnetic resonance studies of molecular motion in guanidinium chloride, bromide, and iodide

1985 ◽  
Vol 63 (6) ◽  
pp. 1239-1244 ◽  
Author(s):  
Christopher I. Ratcliffe
Keyword(s):  
High Temperature ◽  
Molecular Motion ◽  
Lattice Relaxation ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Fold Axis ◽  
Guanidinium Chloride ◽  
Spin Lattice ◽  
H Nmr

Guanidinium [Formula: see text] chloride, bromide, and iodide salts have been studied by 1H and 2H nmr as a function of temperature. The 2H powder lineshapes show conclusively that reorientation of the guanidinium ion occurs about the principal three-fold axis in the chloride, bromide, and high temperature phase of the iodide. Activation energies for this process have been obtained from 1H spin-lattice relaxation results. The question of whether or not there are concurrent two-fold flips of the —NH2 units is discussed, but must presently remain unresolved. It was found that the high temperature phase of the iodide can be supercooled.

Cation and Anion Reorientation at Phase Transition in Pyridinium Tetrafluoroborate

1990 ◽  
Vol 45 (1) ◽  
pp. 33-36 ◽  
Author(s):  
J. Wąsicki ◽  
Z. Pająk ◽  
A. Kozak
Keyword(s):  
Phase Transition ◽  
Relaxation Times ◽  
Activation Parameters ◽  
Lattice Relaxation ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Spin Lattice ◽  
Relaxation Effects ◽  
Temperature Dependences

AbstractTemperature dependences of 1H and 19F second moment and spin-lattice relaxation times for polycrystalline pyridinium tetrafluoroborate were measured. A phase transition was discovered at 202 K. A model of cation reorientation between inequivalent (low-temperature phase) and equivalent (high-temperature phase) equilibrium positions is proposed. Whether the anion reorients isotropically or about a symmetry axis cannot be decided. An analysis of cross-relaxation effects yielded activation parameters for cation and anion reorientation. The rotational correlation times for both ions converge just at the phase transition reaching the value of 10-10s.

Molecular motion in crown ethers. Application of 13C and 2H NMR to the study of 4-carboxybenzo-24-crown-8 ether and its KNCS complex in solution and in the solid phase

1996 ◽  
Vol 74 (8) ◽  
pp. 1437-1446 ◽  
Author(s):  
G.W. Buchanan ◽  
A. Moghimi ◽  
C.I. Ratcliffe
Keyword(s):  
Molecular Motion ◽  
Solid Phase ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Scanning Calorimetry ◽  
Phase Dynamics ◽  
Spin Lattice ◽  
H Nmr ◽  
Macrocyclic Ethers

Large-amplitude solid phase molecular motion has been detected in the macrocyclic ring of the title crown either via 13C CPMAS NMR. To study the details of the dynamic processes, two selectively deuterated d4 derivatives have been prepared and examined via 2H NMR as a function of temperature. A phase change occurring around 277 K has been verified by differential scanning calorimetry (DSC) and a model for the motional processes has been developed involving equivalent two-site flips of the CD2 groups. The amplitude of the CD2 motions apparently decreases the closer the group is to the aromatic ring. The influence of KNCS complexation on the 13C CPMAS spectrum and on 13C spin lattice relaxation times in solution has been explored. Key words: macrocyclic ethers, solid phase dynamics.

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