Applications of 95Mo N.M.R. Spectroscopy. XVIII. Relaxation Times, Quadrupole Coupling Constants and Partial Field Gradients in [Mo(CO)5L] Complexes

1988 ◽  
Vol 41 (9) ◽  
pp. 1457 ◽  
Author(s):  
RTC Brownlee ◽  
BP Shehan ◽  
AG Wedd
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Quadrupole Coupling Constant ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Scalar Coupling ◽  
Spin Lattice ◽  
Field Gradients ◽  
Pyridine Complex ◽  
Quadrupole Coupling

A study of ,95Mo spin-lattice relaxation times (T1) and linewidths of [Mo(CO)5L] complexes, where L = PPh3, AsPh3, SbPh3, pyridine and Cl-, has shown that the relaxation times are due entirely to the quadrupolar mechanism, with no scalar coupling contribution to linewidth where molybdenum is bonded to a quadrupolar nucleus. Based on the literature value of the quadrupole coupling constant obtained by n.q.r . for the PPh3 complex (1.972 MHz), the quadrupole coupling constants of the arsine and stibine complexes are determined to be 3.36 and 3.75 MHz respectively. These values, and that of the pyridine complex (2.80 MHz), are found to correlate with ligand partial field gradient parameters obtained from Mossbauer spectra of FeII complexes, and are rationalized in terms of metal- ligand bonding interactions. For Et4N [Mo(CO)5Cl], the correlation is very poor; this result is attributed to the effects of ion in solution.

2 D Methods in NQR Spectroscopy

1992 ◽  
Vol 47 (1-2) ◽  
pp. 333-341
Author(s):  
J. Seliger ◽  
R. Blinc
Keyword(s):  
Double Resonance ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Electric Quadrupole ◽  
Quadrupole Coupling Constant ◽  
Spin Lattice Relaxation ◽  
Two Dimensional ◽  
Spin Lattice ◽  
Quadrupole Coupling ◽  
Field Cycling

AbstractThe application of two-dimensional spectroscopy to nuclear quadrupole resonance (NQR) is reviewed with special emphasys on spin 3/2 nuclei. A new two-dimensional level crossing double resonance NQR nutation technique based on magnetic field cycling is described. This technique allows for a determination of both the electric quadrupole coupling constant and the asymmetry parameter for spin 3/2 nuclei in powdered samples even in cases where the quadrupolar signals are too weak to be observed directly. It works if the usual double resonance conditions are met, i.e. if the spin-lattice relaxation times are not too short if the quadrupolar nuclei are dipolarly coupled to "strong" nuclei. Variations of this techique can be also used for 2 D "exchange" NQR spectroscopy and NQR imaging.

Boron-11, boron-10, and nitrogen-14 NMR relaxation rates and quadrupole coupling constants in BH3NH3

1992 ◽  
Vol 70 (9) ◽  
pp. 2420-2423 ◽  
Author(s):  
Glenn H. Penner ◽  
Stephen I. Daleman ◽  
Angela R. Custodio
Keyword(s):  
Relaxation Times ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Relaxation Rates ◽  
Orbital Theory ◽  
Spin Lattice ◽  
Quadrupolar Coupling ◽  
Field Gradients

The 11B, 10B, and 14N spin–lattice relaxation times (T1) for aqueous solutions of BH3NH3 were measured by NMR spectroscopy. The results of this investigation are consistent with the nuclear quadrupolar coupling constants reported in previous nuclear quadrupolar resonance and microwave studies. The activation energy associated with rotational reorientation of BH3NH3 in aqueous solution is 11.7 ± 0.6 kJ/mol. Electric field gradients were calculated at various levels of abinitio molecular orbital theory, in order to obtain theoretical 14N and 11B quadrupolar coupling constants. At the highest level of calculation (CI(SD)/6-31G**//MP2/6-31G**), these are in agreement with recently reported microwave results but not with previously reported NQR experiments.

Deuteron Relaxation Study of the Reorienting Methyl Groups in p-Azoxyanisole

1974 ◽  
Vol 52 (12) ◽  
pp. 2294-2295 ◽  
Author(s):  
M. Wiszniewska ◽  
Ronald Y. Dong ◽  
E. Tomchuk ◽  
E. Bock
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Quadrupole Coupling Constant ◽  
Spin Lattice Relaxation ◽  
Isotropic Phase ◽  
Coupling Constant ◽  
Spin Lattice ◽  
Quadrupole Coupling ◽  
Relaxation Study ◽  
Deuteron Spin

The deuteron spin-lattice relaxation times were measured in the nematic and isotropic phases of p-azoxyanisole(CD3)2. An apparent activation energy for the methyl group reorientation in the isotropic phase is obtained. The quadrupole coupling constant along the C—D bond is found to be 147 ± 8 kHz.

NQR Study of AlBr3 Complexes with Donor-Acceptor O-Al Bond

1990 ◽  
Vol 45 (3-4) ◽  
pp. 237-242 ◽  
Author(s):  
Hideta Ishihara ◽  
Shouko Nakashima ◽  
Koji Yamada ◽  
Tsutomu Okuda ◽  
Alarich Weiss
Keyword(s):  
Phase Transitions ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Hindered Rotation ◽  
Spin Lattice ◽  
Quadrupole Coupling ◽  
Temperature Dependences ◽  
Donor Acceptor

Abstract81Br and 27Al NQR were observed in AlBr 3 complexes with 4-XC6H4 NO,(X = H, CI, Br, I, CH3 , and C2H5), C6H5COBr, (C6H5)2CO, and (C2H5)2O. In the 4-XC6H4 NO2 complexes, the 27Al quadrupole coupling constants (QCC's) were well correlated with the Hammett er p 's of the para-substituents, i.e., electron-withdrawing groups caused reduction of the charge density of O-Al bonds which resulted in large 27Al QCC's and vice versa. The temperature dependences of the 81Br NQR frequencies and quadrupolar spin-lattice relaxation times showed that the 4-C2H5C6H4NO2 and C6H5 COBr complexes undergo phase transitions at 154 K and around 200 K, respectively, and show hindered rotation of the AlBr3 groups at higher temperatures, and that the (C2H5) 2O complex reorients above ca. 120 K.

On the Nature of the “Bleaching out” Process of the 35Cl NQR Signals in 1,2,3-Trichlorobenzene

1990 ◽  
Vol 45 (3-4) ◽  
pp. 490-502 ◽  
Author(s):  
Silvia Wigand ◽  
Norbert Weiden ◽  
Alarich Weiss
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Ring Plane ◽  
Spin Lattice ◽  
H Nmr ◽  
Principal Axes ◽  
Quadrupole Coupling ◽  
Benzene Ring Plane

AbstractThe 35Cl NQR frequencies, linewidths, and spin-lattice relaxation times T1(35Cl) of 1,2,3-trichlorotrideuterobenzene were measured at various temperatures. The deuterated compound shows the same bleaching out phenomenon as 1,2,3-trichlorobenzene. Single crystal 2H NMR measurements were carried out at 295 and 193 K. The nuclear quadrupole coupling constants at room temperature are in the range of 175.8 ≦ e2qQh-1 (2H)/kHz ≦ 179.5, and the asymmetry parameters η in the range of 0.060 ≦ η (2H) ≦ 0.073. As for the principal axes of the electric field gradient tensor, it was found that Φzz(2H) is parallel to the C - D bond, Φyy (2H) is perpendicular to the benzene ring plane and Φxx(2H) lies in the ring plane. The linewidths of the 2H NMR satellites are idependent of temperature. For the undeuterated compound, the temperature dependence of T1(1H) was also measured. The mechanism leading to the bleaching out of the 35Cl NQR signals is discussed.

17O Quadrupole Dips in Ammonium Persulphate

1994 ◽  
Vol 49 (1-2) ◽  
pp. 345-350 ◽  
Author(s):  
N. F. Peirson ◽  
J. A. S. Smith ◽  
D. Stephenson
Keyword(s):  
Relaxation Time ◽  
Lattice Relaxation ◽  
Quadrupole Coupling Constant ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Ammonium Persulphate ◽  
Spin Lattice Relaxation Time ◽  
Spin Lattice ◽  
Resonance Frequencies ◽  
Quadrupole Coupling

Abstract The magnetic field dependence of the 1H spin-lattice relaxation time in ammonium persulphate shows pronounced minima near the 1H magnetic resonance frequencies of 1,200 and 2,200 kHz. These are interpreted in terms of a model involving cross-relaxation between 1H in the NH4 ion and 17O in natural abundance in the S2O2-8 ions, the latter having a much shorter spin-lattice relaxation time. A theoretical analysis of the shape of the minima is used to derive values for the 17O quadrupole parameters. This analysis results in best estimate values for the quadrupole coupling constant of 6.75 (± 0.05) MHz and an asymmetry of 0.30 (± 0.02). Such values are indicative o f O-H hydrogen bonding and suggest the S2O2-8 ion is not undergoing rapid reorientation at temperatures below 320 K.

A study of 14N relaxation and nitrogen–proton spin coupling in Watson–Crick base pair models through Fourier transform measurements on NH proton spin–lattice relaxation in the rotating frame

1979 ◽  
Vol 57 (9) ◽  
pp. 1075-1079 ◽  
Author(s):  
Michael E. Moseley ◽  
Peter Stilbs
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Lattice Relaxation ◽  
Indirect Measurements ◽  
Spin Lattice ◽  
Proton Coupling ◽  
Nuclear Spin Lattice Relaxation

Indirect measurements of nitrogen-14 nuclear spin-lattice relaxation times and direct proton coupling constants are presented together with carbon-13 T1 data for a series of alkyl-substituted nucleic acid bases and mixtures thereof in DMSO-d6. With the exception of the guanine NH nitrogen, which possibly experiences a decrease in the electric field gradient upon complexation with cytosine, no indications of significant changes in the electronic environment around the nitrogen nuclei were found for any combination of bases. Forsen–Hoffman spin saturation transfer experiments on the NH and NH2 protons are also presented.

13C and 2H spin–lattice relaxation in neopentane-d12

1978 ◽  
Vol 56 (19) ◽  
pp. 2576-2581 ◽  
Author(s):  
Brian A. Pettitt ◽  
Roderick E. Wasylishen ◽  
Ronald Y. Donc ◽  
T. Phil Pitner
Keyword(s):  
Melting Point ◽  
Variable Temperature ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Rotation ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Single Temperature ◽  
Momentum Correlation

The results of a variable temperature study of the 2H and 13C spin–lattice relaxation times in neopentane-d12 are reported. along with those for the 13C's in neopentane at a single temperature. Orientational and angular momentum correlation times derived from these T1's exhibit the following: (i) τ2 is continuous through the melting point with an activation energy of 0.98 kcal/mol, (ii) τJ is more or less constant at 0.33 ± 0.03 ps within 40 K of either side of the melting point, and (iii) they do not conform to the theoretical relationships of extended diffusion, Fokker–Planck, or Langevin theories. The spin–rotation coupling constants are calculated to be −0.69 kHz for neopentane and −0.52 kHz for neopentane-d12

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