Nuclear quadrupolar resonance

Nuclear Quadrupolar Resonance. - A variety of dichlorophosphanes have n.q.r. 35C1 resonances whose average for each compound correlate linearly uith the total Taft constants.103 The spectra of a number of po1yf1uoroary1 hexachlorophosphazenes have been studied.104 A n.q.r. study of pentafluorophenyl-... 

Whilst diffraction techniques immediately spring to mind for solid samples, the quadrupolar nature of the heavier halogen nuclei means that a principle technique related to SS NMR spectroscopy is nuclear quadruple resonance spectroscopy.6 For systems with a quadrupole moment, an EFG generates two energy states in the absence of an applied magnetic field.3/7 It is appropriate to start by considering illustrative cases in which SS NMR spectroscopy provides information that the closely related nuclear quadrupolar resonance (NQR) technique does not. 

The nuclear quadrupolar resonances observed for transition metal halides which form molecular crystals are very similar to those observed for the transition metal complex ions, and can also be divided into the same two classes (Table 9). One class again having coupling constants of the order expected from electronegativity considerations, the other having anomalously low ones. 

In solid state. Nuclear Quadrupolar Resonance (NQR) [41] is the standard technique to measure quadrupolar coupling constants, while in gas phase Microwave (MW) spectroscopy [42] can be used for small molecules. The MW quantities, however, are obtained in the inertial frame of the molecule. In liquid state, there is no direct method to obtain QCCs. In some favorable cases, QCC can be obtained from simultaneous studies of non-deuterated compounds using NMR (Ti minima, partially oriented systems, etc). 

Since the very beginning, nuclear magnetic resonance (NMR)1 and nuclear quadrupolar resonance (NQR) belong to the family of experimental techniques, along with neutron or X-ray diffraction, thermodynamical or spectroscopic techniques, which were used as tools of primary importance in the study of phase transformations. This is because NMR probes, through the coupling of a nuclei having a nuclear spin to its close environment, by different interactions, the chemical and structural nature of the phase under... 

BCS Bardeen-Cooper-Schrieffer NQR Nuclear quadrupolar resonance... 

Werbelow L G 1996 Relaxation theory for quadrupolar nuclei Encyclopedia of Nuclear Magnetic Resonance ed D M Grant and R K Harris (Chichester Wiley) pp 4092-101... 

The usefulness of quadrupolar effects on the nuclear magnetic resonance c I 7 yi nuclei in the defect solid state arises from the fact that point defects, dislocations, etc., give rise to electric field gradients, which in cubic ciystals produce a large effect on the nuclear resonance line. In noncubic crystals defects of course produce an effect, but it may be masked by the already present quadrupole interaction. Considerable experimental data have been obtained by Reif (96,97) on the NMR of nuclei in doped, cubic, polycrystalline solids. The effect of defect-producing impurities is quite... 

In the standard mathematical expressions for the contribution of quadrupolar relaxation to the relaxation rates of the quadrupolar nucleus (in nuclear magnetic resonance), rapid isotropic motion is assumed to occur. This behavior, in most cases, will not be true in the solid or liquid crystalline state ". ... 

Another important nuclear characteristic is the nuclear quadrupole moment which, possessed by nuclei for which 7 1, has given rise to the important field of nuclear quadrupole resonance spectroscopy. A major importance of the quadrupole moment with respect to NMR absorption resides in the effects of quadrupole coupling constants on nuclear relaxation times and, therefore, on the line widths and saturation characteristics of NMR absorption (9). In addition, in favorable situations, quadrupole coupling constants can be derived from the characteristics of nuclear resonance of quadrupolar nuclei 127). Some examples of these effects will be described in Sections III, IV and VI of this chapter. 

Abstract We use Nuclear Magnetic Resonance relaxometry (i.e. the frequency variation of the NMR relaxation rates) of quadrupolar nucleus ( Na) and H Pulsed Gradient Spin Echo NMR to determine the mobility of the counterions and the water molecules within aqueous dispersions of clays. The local ordering of isotropic dilute clay dispersions is investigated by NMR relaxometry. In contrast, the NMR spectra of the quadrupolar nucleus and the anisotropy of the water self-diffusion tensor clearly exhibit the occurrence of nematic ordering in dense aqueous dispersions. Multi-scale numerical models exploiting molecular orbital quantum calculations, Grand Canonical Monte Carlo simulations, Molecular and Brownian Dynamics are used to interpret the measured water mobility and the ionic quadrupolar relaxation measurements. 

In their 31P 1H nuclear magnetic resonance (NMR) spectra, the 1,4,2-diphosphastibolide salts display an AX spin system (<5 = 278 ppm, Ox = 309 ppm,. /ax = 55 Hz) with the low field signal considerably broadened, which suggests that it originates from the phosphorus atom adjacent to the quadrupolar antimony center < 1997JOM291, 2001JOM61>. 

It is useful to emphasise from the outset that alternative techniques for investigating solid samples, other than NMR spectroscopy of the quadrupolar halogen nuclei, tend to be considered first this is likely due to the (perceived) difficulty of the technique and may be related to the issues of sensitivity and line broadening mentioned above. However, the information gained is often complementary, and hence solid state nuclear magnetic resonance (SS NMR) spectroscopy is primarily used when it can provide unique insight unavailable with other techniques. 

Nuclear magnetic resonance is potentially useful for analyzing E-M compounds. The other E atoms, however, are quadrupolar and their observation... 

Wu, G. (1998) Recent developments in solid-state nuclear magnetic resonance of quadrupolar nuclei and applications to biological systems, Biochemistry and Cell Biology, 76, 429-442. 

Nuclear Magnetic Resonance of the Less Common Quadrupolar Nuclei... 

Quadrupolar nuclei constitute most of the magnetic nuclei within the Periodic Table of the elements. However, the lack of suitable instrumentation as well as the misconception of the deleterious nature of these nuclei have impeded a more widespread utilization of their resonances. Quadrupolar relaxation resulting from the interaction of the nuclear quadrupolar moment with finite electric field gradients is the principal source of nuclear relaxation in nearly all compounds. However, albeit generally eonsidered a nuisance, the phenomenon may as well be exploited to the experimenter s advantage. In contrast to spin-j nuclei whose relaxation behaviour is principally dictated by the dynamics of the molecules in solution, structural and electronic effects play the key role in the relaxation process of quadrupolar nuclei. 

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