A general numerical analysis of time-domain NQR experiments

Harel, Elad; Cho, Herman M.

doi:10.1016/j.jmr.2006.06.033

Cited by 8 publications

(5 citation statements)

References 22 publications

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“…The zero-field NQR spectrum of an I = 3 / 2 nuclide consists of one line corresponding to the doubly degenerate transition. The 35 Cl line found by time domain methods at 6.350 MHz, is presented in Figure ; the corresponding 37 Cl NQR transition frequency is predicted to be 5.047 MHz, which lies outside the operational bandwidth of the spectrometer.…”

Section: Resultsmentioning

confidence: 92%

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Equatorial Electronic Structure in the Uranyl Ion: Cs₂UO₂Cl₄ and Cs₂UO₂Br₄

et al. 2021

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Electric field gradient (EFG) tensors in the equatorial plane of the linear UO 2 2+ ion have been measured by nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments and computed by relativistic Kohn−Sham methods with and without environment embedding for Cs 2 UO 2 Cl 4 and Cs 2 UO 2 Br 4 . This approach expands the possibilities for probing the electronic structure in uranyl complexes beyond the strongly covalent U−O bonds. The combined analyses find that one of the two largest principal EFG tensor components at the halogen sites points along the U−X bond (X = Cl, Br), and the second is parallel to the UO 2 2+ ion; in Cs 2 UO 2 Cl 4 , the components are nearly equal in magnitude, whereas in Cs 2 UO 2 Br 4 , due to short-range bromide−cesium interactions, the equatorial component is dominant for one pair of Br sites and the axial component is larger for the second pair. The directions and relative magnitudes of the field gradient principal axes are found to be sensitive to the σ and π electron donation by the ligands and the model of the environment. Chlorine-35 NQR spectra of 235 U-depleted and 235 U-enriched Cs 2 UO 2 Cl 4 exhibited no uranium-isotope-dependent shift, but the resonance of the depleted sample displayed a 58% broader line width.

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Section: Resultsmentioning

confidence: 92%

“…NQR. Time domain NQR experiments 44 were performed at room temperature with a Tecmag Discovery 3 spectrometer and home-built probes. Signals were acquired with a two-pulse Hahn echo 45 with a 16 step phase cycle 46 and dephasing times ranging between 50 and 100 μs.…”

Section: +mentioning

confidence: 99%

Equatorial Electronic Structure in the Uranyl Ion: Cs₂UO₂Cl₄ and Cs₂UO₂Br₄

et al. 2021

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“…If it is known a priori that Z Q a 0, one could venture into overtone NQR measurements to arrive at unambiguous EFG tensor parameters for each site, but such experiments are exceedingly insensitive or otherwise time consuming. 90,[130][131][132][133] Although the solution space is not extensive, to rapidly establish the set of 185/187 Re EFG tensor parameters for Ca(ReO 4 ) 2 Á2H 2 O, we undertook the intuitive, although novel, approach for a system with multiple sites, 134 which simultaneously fits all the SSNMR/NQR data. In essence, the NQR data were used to begin the process with several 'test' solutions as to what the expected 185/187 Re SSNMR spectrum would look like under the assumption that the NQR data had been assigned correctly.…”

Section: Resultsmentioning

confidence: 99%

Solid-state^185/187Re NMR and GIPAW DFT study of perrhenates and Re₂(CO)₁₀: chemical shift anisotropy, NMR crystallography, and a metal–metal bond

Widdifield

Perras

Bryce

2015

Phys. Chem. Chem. Phys.

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Advances in solid-state nuclear magnetic resonance (SSNMR) methods, such as dynamic nuclear polarization (DNP), intricate pulse sequences, and increased applied magnetic fields, allow for the study of systems which even very recently would be impractical. However, SSNMR methods using certain quadrupolar probe nuclei (i.e., I > 1/2), such as (185/187)Re remain far from fully developed due to the exceedingly strong interaction between the quadrupole moment of these nuclei and local electric field gradients (EFGs). We present a detailed high-field (B0 = 21.1 T) experimental SSNMR study on several perrhenates (KReO4, AgReO4, Ca(ReO4)2·2H2O), as well as ReO3 and Re2(CO)10. We propose solid ReO3 as a new rhenium SSNMR chemical shift standard due to its reproducible and sharp (185/187)Re NMR resonances. We show that for KReO4, previously poorly understood high-order quadrupole-induced effects (HOQIE) on the satellite transitions can be used to measure the EFG tensor asymmetry (i.e., ηQ) to nearly an order-of-magnitude greater precision than competing SSNMR and nuclear quadrupole resonance (NQR) approaches. Samples of AgReO4 and Ca(ReO4)2·2H2O enable us to comment on the effects of counter-ions and hydration upon Re(vii) chemical shifts. Calcium-43 and (185/187)Re NMR tensor parameters allow us to conclude that two proposed crystal structures for Ca(ReO4)2·2H2O, which would be considered as distinct, are in fact the same structure. Study of Re2(CO)10 provides insights into the effects of Re-Re bonding on the rhenium NMR tensor parameters and rhenium oxidation state on the Re chemical shift value. As overtone NQR experiments allowed us to precisely measure the (185/187)Re EFG tensor of Re2(CO)10, we were able to measure rhenium chemical shift anisotropy (CSA) for the first time in a powdered sample. Experimental observations are supported by gauge-including projector augmented-wave (GIPAW) density functional theory (DFT) calculations, with NMR tensor calculations also provided for NH4ReO4, NaReO4 and RbReO4. These calculations are able to reproduce many of the experimental trends in rhenium δiso values and EFG tensor magnitudes. Using KReO4 as a prototypical perrhenate-containing system, we establish a correlation between the tetrahedral shear strain parameter (|ψ|) and the nuclear electric quadrupolar coupling constant (CQ), which enables the refinement of the structure of ND4ReO4. Shortcomings in traditional DFT approaches, even when including relativistic effects via the zeroth-order regular approximation (ZORA), for calculating rhenium NMR tensor parameters are identified for Re2(CO)10.

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“…The NQR signal was detected in the time domain by spin echo methods. , The broad-band radio frequency amplifier output was adjusted at each temperature to avoid voltages that would cause arcing in the probe circuit. Pulse times were calibrated for the maximum echo response.…”

Section: Methodsmentioning

confidence: 99%

Temperature Dependence of Nuclear Quadrupole Resonance and the Observation of Metal–Ligand Covalency in Actinide Complexes: ³⁵Cl in Cs₂UO₂Cl₄

Park,

Walter,

Soderquist

et al. 2023

J. Phys. Chem. A

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We report a study of the temperature dependence of 35 Cl nuclear quadrupole resonance (NQR) transition energies and spin−lattice relaxation times (T 1 ) for 235 U-depleted dicesium uranyl tetrachloride (Cs 2 UO 2 Cl 4 ) aimed at elucidating electronic interactions between the uranium center and atoms in the equatorial plane of the UO 2 2+ ion. The transition frequency decreases slowly with temperature below 75 K and with a more rapid linear dependence above this temperature. The spin−lattice relaxation time becomes shorter with temperature, and as temperatures increase, the T 1 decrease becomes nearly quadratic. The observed trends are reproduced by a model that assumes phonon-induced fluctuations of the electric field gradient tensor and partial electron delocalization from Cl to U. The fit of the theoretical model to experimental data allows a Debye temperature of 96 K to be estimated. The generalization of this approach to investigations of covalency in actinide−ligand bonding is examined.

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A general numerical analysis of time-domain NQR experiments

Cited by 8 publications

References 22 publications

Equatorial Electronic Structure in the Uranyl Ion: Cs₂UO₂Cl₄ and Cs₂UO₂Br₄

Equatorial Electronic Structure in the Uranyl Ion: Cs₂UO₂Cl₄ and Cs₂UO₂Br₄

Solid-state^185/187Re NMR and GIPAW DFT study of perrhenates and Re₂(CO)₁₀: chemical shift anisotropy, NMR crystallography, and a metal–metal bond

Temperature Dependence of Nuclear Quadrupole Resonance and the Observation of Metal–Ligand Covalency in Actinide Complexes: ³⁵Cl in Cs₂UO₂Cl₄

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A general numerical analysis of time-domain NQR experiments

Cited by 8 publications

References 22 publications

Equatorial Electronic Structure in the Uranyl Ion: Cs2UO2Cl4 and Cs2UO2Br4

Equatorial Electronic Structure in the Uranyl Ion: Cs2UO2Cl4 and Cs2UO2Br4

Solid-state185/187Re NMR and GIPAW DFT study of perrhenates and Re2(CO)10: chemical shift anisotropy, NMR crystallography, and a metal–metal bond

Temperature Dependence of Nuclear Quadrupole Resonance and the Observation of Metal–Ligand Covalency in Actinide Complexes: 35Cl in Cs2UO2Cl4

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Equatorial Electronic Structure in the Uranyl Ion: Cs₂UO₂Cl₄ and Cs₂UO₂Br₄

Equatorial Electronic Structure in the Uranyl Ion: Cs₂UO₂Cl₄ and Cs₂UO₂Br₄

Solid-state^185/187Re NMR and GIPAW DFT study of perrhenates and Re₂(CO)₁₀: chemical shift anisotropy, NMR crystallography, and a metal–metal bond

Temperature Dependence of Nuclear Quadrupole Resonance and the Observation of Metal–Ligand Covalency in Actinide Complexes: ³⁵Cl in Cs₂UO₂Cl₄