A computational investigation of J couplings involving 27Al, 17O, and 31P

Bryce, David L.

doi:10.1002/mrc.2630

Cited by 8 publications

(3 citation statements)

References 45 publications

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“…S2 of the ESIw for polycrystalline lithium diborate with 25% 11 B isotopic abundance, no zero crossing is detectable. In the context of this observation, calculations of NMR parameters provide valuable insight in combination with experiment, e.g., for J couplings [99][100][101][102] as well as 11 B chemical shift and electric field gradient tensors. 103,104 This section presents first-principles calculations of the 2 J BB couplings in lithium diborate.…”

Section: First-principles Nmr Calculations Of J Couplingsmentioning

confidence: 99%

Towards homonuclear J solid-state NMR correlation experiments for half-integer quadrupolar nuclei: experimental and simulated 11B MAS spin-echo dephasing and calculated 2JBB coupling constants for lithium diborate

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Yates

Feller

et al. 2011

Phys. Chem. Chem. Phys.

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is observed: the B3 (larger C Q ) site dephases more slowly than the B4 site at all investigated MAS frequencies (5 to 20 kHz) at 14.1 T. Increasing the MAS frequency leads to markedly slower dephasing for the B3 site, while there is a much less evident effect for the B4 site. Considering samples at 5, 25, 80 (natural abundance) and 100 % 11 B isotopic 15 abundance, dephasing becomes faster for both sites as the 11 B isotopic abundance increases. The experimental behaviour is rationalised using density matrix simulations for two and three dipolarcoupled 11 B nuclei. The experimentally observed slower dephasing for the larger C Q (B3) site is reproduced in all simulations and is explained by the reintroduction of the dipolar coupling by the so-called "spontaneous quadrupolar-driven recoupling mechanism" having a different dependence 20 on the MAS frequency for different quadrupolar frequencies. Specifically, isolated spin-pair simulations show that the spontaneous quadrupolar-driven recoupling mechanism is most efficient when the quadrupolar frequency is equal to twice the MAS frequency. While for isolated spin-pair simulations, increasing the MAS frequency leads to faster dephasing, agreement with experiment is observed for three-spin simulations which additionally include the homogeneous nature of the 25 homonuclear dipolar coupling network. First-principles calculations, using the GIPAW approach, of the 2 J 11B-11B couplings in lithium diborate, metaborate and triborate are presented: a clear trend is revealed whereby the 2 J 11B-11B couplings increase with increasing B-O-B bond angle and B-B distance. However, the calculated 2 J 11B-11B couplings are small (0.95, 1.20 and 2.65 Hz in lithium diborate), thus explaining why no zero crossing due to J modulation is observed experimentally, 30 even for the sample at 25 % 11 B where significant spin-echo intensity remains out to durations of 200 ms.

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Section: First-principles Nmr Calculations Of J Couplingsmentioning

confidence: 99%

Towards homonuclear J solid-state NMR correlation experiments for half-integer quadrupolar nuclei: experimental and simulated 11B MAS spin-echo dephasing and calculated 2JBB coupling constants for lithium diborate

Barrow

Yates

Feller

et al. 2011

Phys. Chem. Chem. Phys.

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“…Indeed, the 27 Al ( I = 5/2) quadrupolar coupling has been demonstrated to be highly sensitive to local geometry in a range of materials . Furthermore, for AlPOs, solid-state NMR experiments have been successfully combined with first-principles density functional theory (DFT) calculations in order to validate structural models, and to aid spectral assignment and interpretation . Here, we demonstrate how this work can be extended in a detailed structural study of GaPO-34, using a combination of powder X-ray diffraction, multinuclear solid-state NMR, and DFT calculations.…”

Section: Introductionmentioning

confidence: 96%

A Multinuclear Solid-State NMR Study of Templated and Calcined Chabazite-Type GaPO-34

et al. 2012

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The open-framework gallophosphate GaPO-34 is prepared with either 1-methylimidazole or pyridine as the structure-directing agent. 13 C and 1 H NMR spectra for these two variants of the as-made GaPO-34 are fully assigned, confirming the presence of the protonated amine and water within the pores of both materials. 31 P MAS NMR confirms the presence of three crystallographic P sites, while 71 Ga MAS and MQMAS NMR spectra reveal three crystallographic Ga sites: two tetrahedral and one six-coordinate. Simulations of 69 Ga MAS NMR spectra from these results are in good agreement with spectra acquired at B 0 = 20.0 T, and assignments are supported by first-principles calculations. 19 F MAS NMR proves the presence of Ga-bridging fluoride within the as-made materials, leading to the six-coordinate gallium. Calcination removes the organic species and fluoride, yielding a microporous chabazite-type GaPO 4 , containing one tetrahedral Ga site. Exposure to moist air yields calcined, rehydrated GaPO-34 containing four-, five-, and six-coordinate gallium. Upon heating this material, loss of crystallinity is observed by powder X-ray diffraction and NMR, with the latter revealing a range of P and Ga environments. The thermal instability of calcined, rehydrated GaPO-34 contrasts with the isomorphous aluminophosphate, showing that apparently analogous materials may have important differences in reactivity.

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“…More recently, this approach has been extended to enable the calculation of spin−spin scalar couplings . The calculation of J couplings from first principles offers not only a predictive tool to aid the implementation of experiments which utilize these couplings, but also new possibilities for the interpretation of NMR spectra obtained by such methods …”

Section: Introductionmentioning

confidence: 99%

High-Resolution ¹⁹F MAS NMR Spectroscopy: Structural Disorder and Unusual J Couplings in a Fluorinated Hydroxy-Silicate

et al. 2010

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High-resolution (19)F magic angle spinning (MAS) NMR spectroscopy is used to study disorder and bonding in a crystalline solid. (19)F MAS NMR reveals four distinct F sites in a 50% fluorine-substituted deuterated hydrous magnesium silicate (clinohumite, 4Mg(2)SiO(4)·Mg(OD(1-x)F(x))(2) with x = 0.5), indicating extensive structural disorder. The four (19)F peaks can be assigned using density functional theory (DFT) calculations of NMR parameters for a number of structural models with a range of possible local F environments generated by F(-)/OH(-) substitution. These assignments are supported by two-dimensional (19)F double-quantum MAS NMR experiments that correlate F sites based on either spatial proximity (via dipolar couplings) or through-bond connectivity (via scalar, or J, couplings). The observation of (19)F-(19)F J couplings is unexpected as the fluorines coordinate Mg atoms and the Mg-F interaction is normally considered to be ionic in character (i.e., there is no formal F-Mg-F covalent bonding arrangement). However, DFT calculations predict significant (19)F-(19)F J couplings, and these are in good agreement with the splittings observed in a (19)F J-resolved MAS NMR experiment. The existence of these J couplings is discussed in relation to both the nature of bonding in the solid state and the occurrence of so-called "through-space" (19)F-(19)F J couplings in solution. Finally, we note that we have found similar structural disorder and spin-spin interactions in both synthetic and naturally occurring clinohumite samples.

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A computational investigation of J couplings involving 27Al, 17O, and 31P

Cited by 8 publications

References 45 publications

Towards homonuclear J solid-state NMR correlation experiments for half-integer quadrupolar nuclei: experimental and simulated 11B MAS spin-echo dephasing and calculated 2JBB coupling constants for lithium diborate

Towards homonuclear J solid-state NMR correlation experiments for half-integer quadrupolar nuclei: experimental and simulated 11B MAS spin-echo dephasing and calculated 2JBB coupling constants for lithium diborate

A Multinuclear Solid-State NMR Study of Templated and Calcined Chabazite-Type GaPO-34

High-Resolution ¹⁹F MAS NMR Spectroscopy: Structural Disorder and Unusual J Couplings in a Fluorinated Hydroxy-Silicate

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A computational investigation of J couplings involving 27Al, 17O, and 31P

Cited by 8 publications

References 45 publications

Towards homonuclear J solid-state NMR correlation experiments for half-integer quadrupolar nuclei: experimental and simulated 11B MAS spin-echo dephasing and calculated 2JBB coupling constants for lithium diborate

Towards homonuclear J solid-state NMR correlation experiments for half-integer quadrupolar nuclei: experimental and simulated 11B MAS spin-echo dephasing and calculated 2JBB coupling constants for lithium diborate

A Multinuclear Solid-State NMR Study of Templated and Calcined Chabazite-Type GaPO-34

High-Resolution 19F MAS NMR Spectroscopy: Structural Disorder and Unusual J Couplings in a Fluorinated Hydroxy-Silicate

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High-Resolution ¹⁹F MAS NMR Spectroscopy: Structural Disorder and Unusual J Couplings in a Fluorinated Hydroxy-Silicate