Slow orientational-motional correlation-time measurements for anisotropic NMR centers in polycrystalline-amorphous condensed matter

1985 ◽  
Vol 32 (7) ◽  
pp. 4734-4737 ◽  
Author(s):  
Sook Lee ◽  
Anil Shetty
Keyword(s):  
Correlation Time ◽  
Condensed Matter ◽  
Motional Correlation Time

Motional Correlation Time of Dilute 111Cd Impurities in Se-Rich Liquid Se-Te Alloys

1980 ◽  
Vol 3 ◽  
Author(s):  
D. K. Gaskill ◽  
J. A. Gardner ◽  
K. S. Krane ◽  
K. Krusch ◽  
R. L. Rasera
Keyword(s):  
Correlation Time ◽  
Average Lifetime ◽  
Host Molecule ◽  
Angular Correlations ◽  
Perturbed Angular Correlations ◽  
Time Differential ◽  
Rich Liquid ◽  
Motional Correlation Time

ABSTRACTThe motional correlation time, τc, in liquid Se and Se-rich Se-Te alloys has been investigated between 500 and 900°C using time differential perturbed angular correlations of y-rays from dilute 111Cd impurities. In all alloys we find τc ∝ exp (E0/kT) at low T where E0 = 0.36 eV. τC deviates from this relation at high T. At low T, τCis tentatively identified as the lifetime of a Cd to host molecule bond, and at high T as the average lifetime of bonds in the host molecule.

A novel 1:1 benzenesulfonamide: 18-crown-6 complex as uncovered via 13C solid phase NMR spectroscopy and X-ray crystallography

1989 ◽  
Vol 67 (7) ◽  
pp. 1212-1218 ◽  
Author(s):  
G. W. Buchanan ◽  
C. Morat ◽  
J. P. Charland ◽  
C. I. Ratcliffe ◽  
J. A. Ripmeester
Keyword(s):  
Crown Ether ◽  
Correlation Time ◽  
Molecular Motion ◽  
Solid Phase ◽  
Crystallographic Structure ◽  
Temperature Dependent ◽  
X Ray ◽  
X Ray Crystallography ◽  
Anisotropic Motion ◽  
Motional Correlation Time

A 1:1 complex of 18-crown-6 ether and benzenesulfonamide has been prepared, whose melting point is within 4° of the previously reported 1:2 complex. The X-ray crystallographic structure shows pseudo D3d symmetry in the crown ether portion of this complex, in contrast to the 1:2 complex, which exhibits Ci symmetry in the macrocycle. The temperature dependent 13C CPMAS NMR spectra of these complexes have two regions of broadening for the crown ether carbons. At higher temperatures, a dipolar "washout" mechanism is operative, leading to broadening when molecular motion has a correlation time approximately equal to the inverse of the decoupling field. At lower temperatures broadening occurs when the motional correlation time is equal to the inverse of the chemical shift difference. From application of the Arrhenius equation, the activation energy for the molecular motion in solid 18-crown-6 is found to be approximately 10kcal/mol. Evidence for independent anisotropic motion in the benzenesulfonamide moiety of the 1:1 complex is also presented. Keywords: crown ether, molecular motion, solid phase NMR.

The 18-crown-6.2 chloroacetonitrile complex. X-ray crystal structure and solid phase motions of guest and host as studied by variable temperature 13C CPMAS NMR spectroscopy

1992 ◽  
Vol 70 (4) ◽  
pp. 1033-1041 ◽  
Author(s):  
G. W. Buchanan ◽  
A. Rodrigue ◽  
C. Bensimon ◽  
C. I. Ratcliffe
Keyword(s):  
Activation Energy ◽  
Correlation Time ◽  
Molecular Motion ◽  
Solid Phase ◽  
Variable Temperature ◽  
13C Cpmas Nmr ◽  
X Ray ◽  
Guest Species ◽  
Motional Correlation Time ◽  
13C Cpmas Nmr Spectroscopy

The title complex has two distinct 18-crown-6 moieties of approximate D3d symmetry in the unit cell. The 45.3 MHz 13C CPMAS spectra have two regions of broadening for the crown ether carbons. At high temperatures a dipolar washout mechanism is operative, leading to broadening when molecular motion has a correlation time approximately equal to the inverse of the decoupling field. At lower temperatures broadening occurs when the motional correlation time is equal to the inverse of the chemical shift difference. The activation energy for 18-crown-6 reorientation in this solid is calculated to be ca. 48 kJ/mol. For the chloroacetonitrile, the CH2 carbon also shows dipolar washout, but at a temperature much lower than the 18-crown-6. The activation energy for reorientation for this "guest species" is ca. 42 kJ/mol.

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