Topic
Nuclear quadrupole resonance
About: Nuclear quadrupole resonance is a research topic. Over the lifetime, 3531 publications have been published within this topic receiving 38801 citations. The topic is also known as: Nuclear quadrupole resonance spectroscopy & NQR.
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TL;DR: The quantum-mechanical origin of the spin transitions leading to the QRE effects has been explained, including single and double-quantum coherences for the participating nuclei (1H and 209Bi).
Abstract: Motivated by the possibility of exploiting species containing high spin quantum number nuclei (referred to as quadrupole nuclei) as novel contrast agents for Magnetic Resonance Imaging, based on Quadrupole Relaxation Enhancement (QRE) effects, 1H spin-lattice relaxation has been investigated for tris(2-methoxyphenyl)bismuthane and tris(2,6-dimethoxyphenyl)bismuthane in powder. The relaxation experiment has been performed in the magnetic field range of 0.5 T to 3 T (the upper limit corresponds to the field used in many medical scanners). A very rich QRE pattern (several frequency specific 1H spin-lattice relaxation rate maxima) has been observed for both compounds. Complementary Nuclear Quadrupole Resonance experiments have been performed in order to determine the quadrupole parameters (quadrupole coupling constant and asymmetry parameters) for 209Bi. Knowing the parameters, the QRE pattern has been explained on the basis of a quantum-mechanical picture of the system including single and double-quantum coherences for the participating nuclei (1H and 209Bi). In this way the quantum-mechanical origin of the spin transitions leading to the QRE effects has been explained.
23 citations
TL;DR: In this article, the analogies and connexions between optical spectroscopy and radiofrequency spectrograms are discussed, and it is shown that irradiation with light will modify the intensity of radiofrequency resonance signals.
Abstract: Guided by the analogies and connexions between optical spectroscopy and radiofrequency spectroscopy, the author suggests some experiments on radiofrequency resonance phenomena. In a first part, he shows that in certain cases irradiation with light will modify the intensity of radiofrequency resonance signals, and that such an effect is particularly to be expected at low temperature and with circularly polarized light. In a second part, connexions between ultrasonic waves and magnetic resonance are examined and attention is drawn to the fact that magnetic resonance in crystals at very low temperature acts as a generator of ultrasonic waves of high frequency, those waves being detectable by study of the angular distribution of light scattered by the crystal. Finally it is emphasized that investigation of nuclear quadrupole resonance in monocrystals must reveal striking anisotropy and coherence effects and that the study of destruction of coherence by small magnetic fields provides a new method for measuring spin-spin relaxation time.
23 citations
TL;DR: This work provides insights into the changes in the antimony quadrupolar coupling constant upon pnictogen bonding: strikingly, the decreases noted here parallel those known for hydrogen bonds, but contrast with the increases reported for halogen bonds.
Abstract: Pnictogen (or pnicogen) bonding is an attractive interaction between the electrophilic region of group 15 elements (N, P, As, Sb, Bi) and a nucleophile. This interaction for which unique applications in catalysis have recently been uncovered continues to gain popularity. Here, we investigate a series of pnictogen-bonded cocrystals based on SbF3 and SbCl3, prepared via mechanochemical ball milling, with 121/123Sb (I = 5/2 and 7/2, respectively) nuclear quadrupole resonance (NQR) spectroscopy. Observed NQR frequency shifts upon cocrystallization are on the order of 0.1 to 10 MHz and are clearly diagnostic of the formation of pnictogen bonds to antimony. Further evidence for pnictogen bonding is obtained by complementary 13C cross-polarization magic-angle spinning solid-state NMR experiments. DFT calculations of NMR parameters as well as natural localized molecular orbital analyses support the experimental findings and elucidate the electronic origins of the experimental NQR frequency shifts. This work provi...
23 citations
TL;DR: A series of hydrogen bonded complexes of pentachlorophenol with various N bases, covering a wide range of ΔpKa values, was investigated using 35Cl n.q.r..
Abstract: A series of hydrogen bonded complexes of pentachlorophenol with various N bases, covering a wide range of ΔpKa values, was investigated using 35Cl n.q.r. The average frequencies of 35Cl n.q.r. of these complexes were compared with those of pentachlorophenol, tetrabutylammonium pentachlorophenolate and tetrabutylammonium bis-pentachlorophenolate. The changes of average frequencies as a function of ΔpKa are very similar to the dipole moment changes with hydrogen bond formation as a function of ΔpKa, but in solids the range of inversion is shifted to lower ΔpKa values. The region in which the dielectric and spectroscopic anomalies are observed may be formally attributed to the existence of the proton transfer equilibrium.
23 citations
23 citations