A study of molecular motion in tetramethylphosphonium halides by proton magnetic resonance

1976 ◽  
Vol 54 (12) ◽  
pp. 1985-1990 ◽  
Author(s):  
T. T. Ang ◽  
B. A. Dunell
Keyword(s):  
Molecular Motion ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
X Ray Diffraction ◽  
Hexagonal Crystal ◽  
Methyl Group ◽  
X Ray ◽  
Spin Lattice ◽  
Second Moments

Spin–lattice relaxation times of tetramethylphosphonium chloride, bromide, and iodide were measured between 100 and 500 K and the two minima in T1 found for each compound have been assigned to methyl group reorientation and whole cation tumbling. The second moments also indicate that the cations are tumbling isotropically at nmr frequencies in the upper half of this temperature range, and suggest that librational oscillation of the whole cation occurs at frequencies at least of the order of 105 s−1 near 150 K. The energy barriers for both methyl group reorientation and isotropic tumbling decrease from chloride to bromide but increase when one goes from bromide to iodide. Powder photograph X-ray diffraction analysis indicates that the chloride and bromide have hexagonal crystal structures (a and c measured), but that the iodide has lower, undetermined symmetry.

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.

Application of Adiabatic Rapid Passage Nuclear Magnetic Resonance Techniques to the Study of Molecular Motions in Solids

1974 ◽  
Vol 52 (2) ◽  
pp. 191-197 ◽  
Author(s):  
J. A. Ripmeester ◽  
B. A. Dunell
Keyword(s):  
Molecular Motion ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Adiabatic Rapid Passage ◽  
Spin Lattice ◽  
Second Moments ◽  
New Information ◽  
Rotating Frame Relaxation ◽  
Rapid Passage

The adiabatic rapid passage (ARP) technique was applied to the study of molecular motion in solids. Second moments and spin–lattice relaxation times for solid furan and benzene were derived using ARP methods from 77 °K to the respective melting points. Unusual variations of the ARP signal height and shape with temperature were observed for these solids. These effects were interpreted as being due to the presence of short rotating frame relaxation times. New information regarding molecular motion in solid furan, as well as acetic acid-d1, was obtained. Also some quantitative statements have been made regarding the conditions required to observe an ARP signal in the solid state.

A nuclear magnetic resonance investigation of n -pentane, n -hexane and cyclo pentane

1954 ◽  
Vol 222 (1151) ◽  
pp. 526-541 ◽  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Motion ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Kcal Mole ◽  
Second Moment ◽  
Spin Lattice ◽  
Second Moments

The nuclear magnetic resonance spectra and spin-lattice relaxation times have been measured for the protons in n -pentane (C 5 H 12 ), n -hexane (C 6 H 14 ) and cyclo pentane (C 5 H 10 ) all in the solid state. The temperature range covered was from 70° K to the melting-points of 143·4° K for n -pentane, 177·8° K for n -hexane and 179·4° K for cyclo pentane. In the case of n -pentane and n -hexane the second moments of the absorption lines were found to be smaller than the computed rigid lattice values over the. whole temperature range. Possible molecular motions which might cause this reduction are discussed. It is suggested that the most probable type of motion is reorientation of the methyl groups at the ends of each molecule about the adjacent C—C bonds. An analysis of the spin-lattice relaxation times shows that this reorientation process is governed by an activation energy of 2·7 kcal/mole for n -pentane and 2·9 kcal/mole for n -hexane, values which support the mechanism postulated. At the lowest temperature the absorption lines had not reached their full widths, even though the reorientation frequencies at these temperatures were considerably less than the line-widths. The experimental second moment for cyclo pentane below about 120° K indicates that the lattice is effectively rigid in this temperature region. The uncertainties in both the experimental and theoretical second moments do not allow a distinction to be drawn between the plane and puckered molecular models. At the temperature of the first transition (122·4° K) the line-width second moment and relaxation time all show a sudden decrease. The low value of second moment at the higher temperatures indicates that considerable molecular motion is occurring, the molecules rotating with spherical symmetry. The change in crystal structure at the temperature of the second transition (138·1° K) is thought to be a direct result of this spherical symmetry. As the temperature increases, the results indicate that more molecular motion must be occurring, and it is thought that the rotating molecules are diffusing through the lattice.

Molecular Reorientation in the Plastic Crystalline Phase of Tris

1979 ◽  
Vol 32 (4) ◽  
pp. 905 ◽  
Author(s):  
RE Wasylishen ◽  
PF Barron ◽  
DM Doddrell
Keyword(s):  
Phase Transition ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Molecular Reorientation ◽  
Liquid Phase Transition ◽  
X Ray ◽  
Spin Lattice

Carbon-13 N.M.R. spectra of tris(hydroxymethyl)aminomethane (Tris) have been measured between 407 and 461 K. Proton-decoupled 13C N.M.R. spectra of solid Tris between 407 K and its melting point are relatively sharp (v� < 30 Hz) indicating rapid overall molecular reorientation in this temperature range. It was not possible to detect a 13C N.M.R, signal for Tris below 407 K. The observed 13C N.M.R. spin-lattice relaxation times appear continuous across the solid ↔ liquid phase transition. From the temperature dependence of T1, a rotational activation energy of 51.6 � 6 kJ mol-1 is calculated, which indicates that the molecules must expend considerable energy in reorienting. The N.M.R. results are discussed in relation to previous differential scanning calorimetry and X-ray diffraction data which indicate that Tris undergoes a solid ↔ solid transition at 407 K.

Proton Magnetic Resonance and Molecular Motion in Solid Methyl-Piperidines and Piperazines

1977 ◽  
Vol 32 (8) ◽  
pp. 882-885 ◽  
Author(s):  
R. Schüler ◽  
L. Brücher ◽  
W. Müller-Warmuth
Keyword(s):  
Proton Magnetic Resonance ◽  
Molecular Motion ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Methyl Group ◽  
Spin Lattice ◽  
H Nmr ◽  
Second Moments ◽  
Line Narrowing

Abstract The 1H-NMR spin-lattice relaxation time and lineshape in solid 2-, 3-, and 4-methyl-piperidine, in 2-and N-methyl-piperazine, and in NN′-diinethyl-piperazine has been measured from low temperatures to the melting point. For all cases, the experimental data can be described by classical rotation of the methyl group. Activation energies governing this motion are between 9 and 14 kJ/mole. Second moments are reduced from about 25 G2 to 17 G2. No further line-narrowing was observed.

Molecular Motions in Halogen-Bridged One-Dimensional Pt Complexes, [PtII(en)2][PtIVX2(en)2](ClO4)4 (X = Cl, Br) Studied by 2H and 1H NMR

2002 ◽  
Vol 57 (6-7) ◽  
pp. 413-418 ◽  
Author(s):  
Noriyoshi Kimura ◽  
Toru Hachisuka ◽  
Yukitaka Nakano ◽  
Ryuichi Ikeda
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Energy Difference ◽  
Spin Lattice Relaxation ◽  
X Ray Diffraction ◽  
Potential Wells ◽  
One Dimensional ◽  
X Ray ◽  
Spin Lattice ◽  
H Nmr

2H and 1H NMR measurements were performed on crystalline [Pt(en)2][PtX2(en)2](ClO4)4 (X = Cl, Br), where the protonated and partially deuterated ethylenediamines (en’s), NH2(CH2)2NH2, NH2(CD2)2NH2 and ND2(CH2)2ND2 were used as ligands. Measurements of 2H and 1H NMR spin-lattice relaxation times showed the presence of motions of en chelate rings at the temperatures near the phase transitions, whereas broad 2H NMR spectra and the reported X-ray diffraction data showed no marked motions. These results were consistently explained by introducing the en puckering motion between highly asymmetric potential wells with an energy difference of 10 - 13 kJ mol-1. This difference was shown to be much larger than 2 - 5 kJ mol-1, reported for the iodo-complex, [Pt(en)2][PtI2(en)2](ClO4)4

Molecular Motion in Solid Tetrabutylammonium Iodide

1987 ◽  
Vol 42 (3) ◽  
pp. 253-257 ◽  
Author(s):  
Barbara Szafrańska ◽  
Zdzisław Pająk
Keyword(s):  
Molecular Motion ◽  
Structural Phase ◽  
Relaxation Times ◽  
Activation Parameters ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Methyl Group ◽  
Self Diffusion ◽  
Spin Lattice ◽  
Tetrabutylammonium Iodide

The temperature dependence of the 1H second moment and the T1 and T1ϱ spin-lattice relaxation times obtained for polycrystalline tetrabutylammonium iodide are interpreted in terms of the C3 methyl group reorientation appearing together with cationic tumbling for which the activation parameters have been determined. IR spectra point to the existence of weak C - H . . . I hydrogen bonds. A structural phase transition evidenced at about 386 K is found to be related to the onset of cationic self-diffusion.

NUCLEAR MAGNETIC RESONANCE STUDY OF 205Tl IN MULTIPHASE Tl-Ba-Ca-Cu OXIDE SUPERCONDUCTORS

1988 ◽  
Vol 02 (05) ◽  
pp. 1227-1234 ◽  
Author(s):  
L. Mihály ◽  
K. Tompa ◽  
I. Bakonyi ◽  
P. Bánki ◽  
É. Zsoldos ◽  
...  
Keyword(s):  
Room Temperature ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Nuclear Magnetic Resonance Study ◽  
Spin Lattice Relaxation ◽  
Oxide Superconductors ◽  
X Ray Diffraction ◽  
Magnetic Resonance Study ◽  
X Ray ◽  
Spin Lattice

Several batches of T l- Ba - Ca - Cu oxide superconductors have been synthesized and characterized by resistivity, magnetic susceptibility and X-ray diffraction measurements. The 205 T l NMR line snifts (K), the spin-lattice and spin-spin relaxation times have been measured at room temperature. The temperature dependence of the spin-lattice relaxation rate is also reported. The resonance around K = 0.25 % has a composite line shape indicating the presence of two T l sites. The two sites are tentatively assigned to thallium atoms in the (2223) and (2212) T l- Ba - Ca - Cu phases.

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