Nuclear Magnetic Resonance in Uranium Hydride and Deuteride

Grunzweig-Genossar, J.; Kuznietz, Moshe; Meerovici, Balfour

doi:10.1103/physrevb.1.1958

Cited by 50 publications

(7 citation statements)

References 59 publications

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“…The response of a representative uranium(IV) bis(ketimide) complex, 11, is shown in Figure 6. This compound shows typical magnetic behavior for a U IV 5f 2 ion with a nominal 3 H 4 ground-state term and attains a χT product of 0.97 emu K mol -1 (2.78 µ B ) at 350 K, consistent with reported values for U IV complexes 27,[29][30][31][32][33] and only coincidentally close to the expected value of 1.0 emu K mol -1 for a simple S ) 1, g ) 2 Curie paramagnet. Compared to a J ) 4 Curie paramagnet, complex 11 exhibits a small but measurable temperature dependence.…”

Section: Uranium(iv) Fluoroketimidessupporting

confidence: 87%

“…This results in an admixture, making the quantum number J an ineffective reckoning for the accounting of states. The reality of the situation for many U IV complexes is that the admixture turns out to be small enough (<10% 6d 1 5f 1 contribution to the ground-state 6d 0 5f 2 configuration) that Russell-Saunders coupling can be used successfully, 29 especially in the context of a series of complexes such as those under investigation here.…”

Section: Uranium(iv) Fluoroketimidesmentioning

confidence: 99%

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Systematic Studies of Early Actinide Complexes: Uranium(IV) Fluoroketimides

et al. 2007

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The reaction of (C5Me5)2U(CH3)2 with 2 equiv of N[triple bond]C-ArF gives the fluorinated uranium(IV) bis(ketimide) complexes (C5Me5)2U[-N=C(CH3)(ArF)]2 [where ArF=2-F-C6H4 (4), 3-F-C6H4 (5), 4-F-C6H4 (6), 2,6-F2-C6H3 (7), 3,5-F2-C6H3 (8), 2,4,6-F3-C6H2 (9), 3,4,5-F3-C6H2 (10), and C6F5 (11)]. These have been characterized by single-crystal X-ray diffraction, 1H and 19F NMR, cyclic voltammetry, UV-visible-near-IR absorption spectroscopy, and variable-temperature magnetic susceptibility. Density functional theory (DFT) results are reported for complexes 6 and 11 for comparison with experimental data. The most significant structural perturbation imparted by the F substitution in these complexes is a rotation of the fluorinated aryl (ArF) group out of the plane defined by the N=C(CMe)(Cipso) fragment in complexes 7, 9, and 11 when the ArF group possesses two o-fluorine atoms. Excellent agreement is obtained between the DFT-calculated and experimental crystal structures for 11, which displays the distortion, as well as for 6, which does not. In 7, 9, and 11, the out-of-plane rotation results in large angles (phi=53.7-89.4 degrees) between the planes formed by ketimide atoms N=C(CMe)(Cipso) and the ketimide aryl groups. Complexes 6 and 10 do not contain o-fluorine atoms and display interplanar angles in the range of phi=7-26.8 degrees. Complex 4 with a single o-fluorine substituent has intermediate values of phi=20.4 and 49.5 degrees. The distortions in 7, 9, and 11 result from an unfavorable steric interaction between one of the two o-fluorine atoms and the methyl group [-N=C(CH3)] on the ketimide ligand. All complexes exhibit UV/UIV and UIV/UIII redox couples, although the distortion in 7, 9, and 11 appears to be a factor in rendering the UIV/UIII couple irreversible. The potential separation between these couples remains constant at 2.15+/-0.03 V. The electronic spectra are dominated by unusually intense f-f transitions in the near-IR that retain nearly identical band energies but vary in intensity as a function of the fluorinated ketimide ligand, and visible and near-UV bands assigned to metal (5f)-to-ligand (pi*) charge-transfer and interconfiguration (5f2-->5f16d1) transitions, respectively. Variable-temperature magnetic susceptibility data for these complexes indicate a temperature-independent paramagnetism (TIP) below approximately 50 K that results from admixing of low-lying crystal-field excited states derived from the symmetry-split 3H4 5f2 manifold into the ground state. The magnitude of the TIP is smaller for the complexes possessing two o-fluorine atoms (7, 9, and 11), indicating that the energy separation between ground and TIP-admixed excited states is larger as a consequence of the greater basicity of these ligands.

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Section: Uranium(iv) Fluoroketimidessupporting

confidence: 87%

Section: Uranium(iv) Fluoroketimidesmentioning

confidence: 99%

Systematic Studies of Early Actinide Complexes: Uranium(IV) Fluoroketimides

et al. 2007

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“…It has been discussed either in terms of localized moments (incompatible with the itinerant nature of the 5f electrons) or itinerant magnetism. Whereas nuclear magnetic resonance (NMR) measurements seem to suggest localized 5f states for ␤-UH 3 and thus localized magnetism, 3 the magnetoelastic properties and pressure dependence of the magnetic moment point to the itinerant nature of magnetism. 4 Band structure calculations (nonrelativistic, non-self-consistent) came to the conclusion that there are both itinerant and localized f states.…”

Section: Introductionmentioning

confidence: 99%

“…This is primarily due to the very high reactivity of UH 3 , which is pyrophoric in powder form, and the absence of a protective overlayer preventing oxidation. Moreover, UH 3 is not stable and easily decomposes under vacuum: its dissociation pressure at 375 K is 0.27 Pa. 6 So any surface cleaning by heating or ion bombardment can itself result in the decomposition of the sample. Also, breaking under vacuum or scraping 7 may lead to dirty surfaces, because the breaking plane often contains impurities.…”

Section: Introductionmentioning

confidence: 99%

Electronic structure ofUH3thin films prepared by sputter deposition

et al. 2004

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UH 3 thin films have been prepared by dc sputtering of uranium in presence of hydrogen, and studied in situ by valence band and core level spectroscopy. X-ray diffraction measurements showed formation of ␤-UH 3 , and magnetization experiments demonstrate that the films are ferromagnetic with T C = 178 K. Valence band spectra showed that the films are metallic. The 5f states are positioned at the Fermi level, proving their itinerant character. Broadening of the 5f peak is attributed to correlation effects, or possibly the appearance of final-state multiplets. U 4f core level spectra showed a main peak at slightly higher binding energy (BE) than U metal, accompanied by a broad correlation satellite at 6 eV high BE.

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“…The second moments of 'H and 'H in B-UH3 contain a constant term and a term proportional to the square of the magnetization in the paramagnetic state, Grunzweig-Genossar, Kuznietz, and Meerovici [41]. At temperatures above 370"K, line narrowing was observed from which it was found E, = 0.36 f 0.4eV/atom for 'H and E, = 0.39 f 0.4eV/atom for 'H.…”

Section: Experimental A) Steady State Nmr Linewidths and Spectramentioning

confidence: 99%

Hydrogen diffusion studies using nuclear magnetic resonance

Cotts

1972

Ber Bunsenges Phys Chem

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Nuclear magnetic resonance (NMR) techniques have been applied in a considerable number of experimental studies of molecular and atomic motion in solids. In most experiments designed to measure diffusion parameters, the power spectrum of the random variation of local magnetic dipolar fields is determined directly from the data. Data usually consists of measurements of the nuclear spin system longitudinal spin‐lattice relaxation time T1 or the transverse spin‐spin relaxation time T2, or both. From these measurements the frequency of atomic jumps can be calculated. The analysis also yields the value of the activation energy of self‐diffusion for the diffusing atom.Two relatively new NMR techniques, the measurement of the spin lattice relaxation time in the rotating frame, T1ρ, and the direct measurement of the diffusion coefficient by observation of the spin echo decay in the presence of an applied magnetic field gradient, are beginning to be utilized in solid state diffusion experiments, but have not yet been applied to metal hydrides.The theory of the effect of atomic motion on nuclear magnetic dipolar interactions is reviewed as the mechanism responsible for spin relaxation.The relationships between T1, T2, and T1ρ and the time between atomic jumps, τc is discussed. The pulsed‐gradient spin echo technique is outlined for direct measurement of the translational diffusion coefficient.NMR experiments utilizing steady‐state and pulsed techniques for studying diffusion in metal hydrides are described for several transition metals including Sc, Ti, V, Y, Zr, Nb, and Ta. Experiments in La, Th, and U‐hydrogen systems are also reported. Diffusion parameters. including Ea, and A in the Arrhenius relation, τ1 = (A−1) exp (Ea/RT), are reported.

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Nuclear Magnetic Resonance in Uranium Hydride and Deuteride

Cited by 50 publications

References 59 publications

Systematic Studies of Early Actinide Complexes: Uranium(IV) Fluoroketimides

Systematic Studies of Early Actinide Complexes: Uranium(IV) Fluoroketimides

Electronic structure ofUH3thin films prepared by sputter deposition

Hydrogen diffusion studies using nuclear magnetic resonance

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