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.

Molecular Motion in Solid Tetraethyl -and Tetrapropylammonium Tetrafluoroborates

1995 ◽  
Vol 50 (6) ◽  
pp. 584-588 ◽  
Author(s):  
Barbara Szafrańska ◽  
Zdzisław Pająk
Keyword(s):  
Molecular Motion ◽  
Solid Phase ◽  
Complex Cation ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Fluorine Nmr ◽  
Spin Lattice ◽  
Second Moments ◽  
Wide Range

Abstract Proton and fluorine NMR second moments and spin-lattice relaxation times for polycrystalline tetraethyl-and tetrapropylammonium tetrafluoroborates have been measured over a wide range of temperatures. Solid-solid phase transitions were found for both compounds and confirmed by DSC. Methyl group C3 reorientation followed by more complex cation motions was evidenced in the low temperature phases. Overall cation reorientation characterises the high temperature phases of both compounds. Isotropic anion reorientation was found in both salts in both phases.

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.

scholarly journals 1H NMR and Differential Scanning Calorimetry Studies of Molecular Motion and Phase Transition in Butylammonium Iodide

1985 ◽  
Vol 40 (4) ◽  
pp. 347-354
Author(s):  
Shin-ichi Fukada ◽  
Ryuichi Ikeda ◽  
Daiyu Nakamura
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Solid Phase ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
H Nmr ◽  
Wide Range

The temperature variations of 1H NMR spin-lattice relaxation times and 1H NMR second moments in n-C4H9NH3I and its N-deuterated analog were studied in a wide range of temperatures above 77 K. DTA experiments revealed a solid-solid phase transition between room and low temperature phases taking place at 268 K for the former salt and at 267 K for the latter. For rapidly cooled ( ≳ 2 Kmin-1 ) samples, another phase transition possibly between substable low temperature phases was found at ca. 210 K for the former and ca. 205 K for the latter. The transition entropy observed at 268 K was 33 J K-1 mol-1. This is much larger than the melting entropy (16 J K-1 mol-1), suggesting that butylammonium ions obtain their motional freedom mostly at the phase transition. In the low temperature phase of n-C4H9NH3I, the CH3 and NH3+ groups perform C3 reorientation about their respective symmetry axes with the activation energies 10.4 and 26.8kJmol-1, respectively. The rapidly cooled sample showed two T1 components attributable to the stable and substable low temperature phases indicating the coexistence of both phases. In the room temperature phase, the cations rotate rapidly about their long axes and partly conformational disorder of the alkyl chains takes place. The mechanism of the phase transitions is discussed.

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 .

A Highly Disordered New Solid Phase Containing Isotropically Reorienting Cations in (CH3NH3 )2CdBr4 Studied by 1H NMR and Thermal Measurements

1990 ◽  
Vol 45 (9-10) ◽  
pp. 1190-1192 ◽  
Author(s):  
Hiroyuki Ishida ◽  
Kentaro Takagi ◽  
Mifune Terashima ◽  
Daiyu Nakamura
Keyword(s):  
Room Temperature ◽  
Solid Phase ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Spin Lattice ◽  
H Nmr ◽  
Thermal Measurements

Abstract The 1H spin-lattice relaxation time, linewidth, second moment of 1H NMR absorption, differen-tial thermal analysis, and differential scanning calorimetry of methylammonium tetrabromocado-mate(II) crystals were studied. A new solid phase was found between 482 K and the melting point (493 K). The 1H NMR measurements revealed the presence of overall reorientation of methyl-ammonium cations in this phase. In the room temperature phase, 120° reorientational jumps of the CH3 and NH3+ groups were detected.

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.

Bonded Hydrogen and Trapped H2 in a-Si1−xGex:H Alloys

1989 ◽  
Vol 149 ◽  
Author(s):  
E. J. Vanderheiden ◽  
G. A. Williams ◽  
P. C. Taylor ◽  
F. Finger ◽  
W. Fuhs
Keyword(s):  
Temperature Dependence ◽  
Molecular Hydrogen ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
H Nmr ◽  
Local Environments

ABSTRACT1H NMR has been employed to study the local environments of bonded hydrogen and trapped molecular hydrogen (H2) in a series of a-Si1−xGex:H alloys. There is a monotonic decrease of bonded hydrogen with increasing x from ≈ 10 at. % at x = 0 (a-Si:H) to ≈ 1 at. % at x = 1 (a-Ge:H). The amplitude of the broad 1H NMR line, which is attributed to clustered bonded hydrogen, decreases continuously across the system. The amplitude of the narrow 1H NMR line, which is attributed to bonded hydrogen essentially randomly distributed in the films, decreases as x increases from 0 to ≈ 0.2. From x = 0.2 to x ≈ 0.6 the amplitude of the narrow 1H NMR line is essentially constant, and for x ≥ 0.6 the amplitude decreases once again. The existence of trapped H2 molecules is inferred indirectly by their influence on the temperature dependence of the spin-lattice relaxation times, T1. Through T1, measurements it is determined that the trapped H2 concentration drops precipitously between x = 0.1 and x = 0.2, but is fairly constant for 0.2 ≤ x ≤ 0.6. For a-Si:H (x = 0) the H2 concentration is ≈ 0.1 at. %, while for x ≥ 0.2 the concentration of H2 is ≤ 0.02 at. %.

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