Fluorine-19 NMR

Brey, Wallace S.; Brey, Mary Louise

doi:10.1002/9780470034590.emrstm0170

Cited by 5 publications

(5 citation statements)

References 43 publications

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“…The 19 F chemical shifts were calibrated in ppm relative to CCl 3 F adopting the 19 F chemical shift for neat C 6 F 6 (-163 ppm [12]) as an external reference.…”

Section: Methodsmentioning

confidence: 99%

Terminal and bridging fluorine ligands in TiF4 as studied by 19F NMR in solids

Murakami

Noda

Takegoshi

2019

Solid State Nuclear Magnetic Resonance

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To examine bonding nature of fluorine ligands in a metal coordinated system, 19 F high-resolution solid-state NMR has been applied to TiF 4 , which bears both bridging and terminal fluorines. Observed 12 isotropic signals are assigned to 12 crystallographically different fluorines (6 terminal and 6 bridging fluorines) in TiF 4 by referring to the calculated isotropic shifts using density functional theory (DFT). The isotropic chemical shift ( iso ) for terminal F (F T ) appears at high frequency (420~480 ppm from (CCl 3 F) = 0 ppm) with large shielding anisotropy  ~ 850 ppm. Whereas the  iso and  values for bridging F (F B ) are moderate;  iso ~ 0~25 ppm and  ~ 250 ppm. The origin of the observed high-frequency shift for F T is ascribed to the second-order paramagnetic shift with increased covalency, shorter Ti-F bonds, and smaller energy difference between the occupied and vacant orbitals. Examination of the orientation of the shielding tensor relative to the molecular structure shows that the most deshielded component of the shielding tensor is oriented along the Ti-F bond. The characteristic orientation is consistent with a Ti-F  bond formed by d YZ of Ti and p z of F. Further, we show that the selectively observed spinning sideband patterns and the theoretical patterns with the calculated  and  (shielding asymmetry) values are not consistent with each other for F B , indicating deficiency of the present DFT calculation in evaluating .

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“…The 19 F chemical shifts were calibrated in ppm relative to CCl 3 F adopting the 19 F chemical shift for neat C 6 F 6 (-163 ppm [12]) as an external reference.…”

Section: Methodsmentioning

confidence: 99%

Terminal and bridging fluorine ligands in TiF4 as studied by 19F NMR in solids

Murakami

Noda

Takegoshi

2019

Solid State Nuclear Magnetic Resonance

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“…This progression was observed to be toward a smaller (less negative) chemical shift in the 19 F spectrum which suggests the transition of HFB from a dipolar environment (D 2 O) to a quadrupolar one (micelle). The change in chemical shift toward more positive values indicates deshielding of fluorine nuclei, in opposition of the expected increase in shielding as hydrophobic hydrocarbon molecules partition into the more nonpolar environments of micelles. , The anisotropic magnetic fields generated by delocalized π electrons of DBSBA and DBSBB benzyls should deshield the 19 F nuclei of HFB due to the preferential parallel displaced configuration observed between benzene and HFB. Examination of Figure also suggests that DBSBA and DBSBB have different affinities for HFB and that HFB experiences a slightly more nonpolar environment in DBSBA than DBSBB.…”

Section: Resultsmentioning

confidence: 96%

Solubilization of Hexafluorobenzene by the Micellar Aromatic Core Formed from Aggregation of Amphiphilic (2,3-O-Dibenzyl-6-O-sulfobutyl) Cyclodextrins

McKee

Green

2016

J. Phys. Chem. B

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Aggregation colloids that possess an aromatic pseudophase in an aqueous system could provide new avenues of research including micellar catalysis, aqueous remediation, and emulsion polymerization studies. The apparent aggregation of two macrocyclic surfactants, hexakis (2,3-O-dibenzyl-6-O-sulfobutyl) cyclomaltohexaose (DBSBA) and heptakis (2,3-O-dibenzyl-6-O-sulfobutyl) cyclomaltoheptaose (DBSBB), was investigated using diffusion ordered nuclear magnetic resonance (NMR) spectroscopy (DOSY), conductivity, and pyrene fluorescence techniques. These amphiphiles were found to possess near spherical symmetry at critical micelle concentrations of approximately 0.1 mM in all techniques used to study the phenomenon. Aggregation of both surfactants was found to be entropically driven at low temperatures but enthalpically driven at higher temperatures. The calculated compensation temperatures of DBSBA and DBSBB were determined to be 317 and 307 K, respectively. These surfactants contain a high percentage of aromatic moieties in their structures, which affects the thermodynamics of aggregation and their interior micellar environment. The proposed aromatic micellar core was tested using hexafluorobenzene (HFB) as a molecular probe in (19)F NMR experiments. (19)F NMR relaxation and chemical shift studies found the HFB quantitatively partitioned into the micellar interiors. Global regression analysis found that HFB interaction with DBSBA micelles possessed at least two association constants, differing by an order of magnitude, the largest being in excess of 8300 M(-1). DBSBB micellar interactions with HFB were found to be weaker, although in excess of 1100 M(-1), with a subsequent association constant of similar magnitude. Benzyl substituents of DBSBB are required for solubilization of HFB. Heteronuclear Overhauser effect spectroscopy (HOESY, (19)F-(1)H) of the DBSBB:HFB complex revealed strong interaction of HFB with benzyl substituents but not the cyclodextrin cavity.

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“…The pulse repetition time was 50 ms. The 19 F chemical shifts were calibrated in ppm relative to CCl 3 F adopting the19 F chemical shift for neat C 6 F 6 (−163 ppm28 ) as an external reference. The temperature calibration experiment was done using 207 Pb NMR of Pb(NO 3 ) 2 29.…”

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confidence: 99%

Ionic Conduction in Sr-Doped CeF₃ as Studied by ¹⁹F NMR and AC Impedance Measurement

2022

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Among the three inequivalent fluorides in tysonite CeF3 (F1, F2, and F3 in the ratio of 12:4:2 per unit cell), we show by 19F solid-state NMR that F1 is solely responsible for the ion conductivity in Ce1–x Sr x F3–x (x = 0.001) at 0 °C. It is further shown that the observed conductivity can be explained quantitatively by using the Nernst–Einstein relation with the F1–F1 exchange rate (ca. 6 × 105 s–1) estimated from lineshape analysis with the carrier–F1 concentration. As for an alternative method to obtain the hopping rate of a carrier, we adopt the AC impedance method, for which the identity of the “carrier” is rather elusive. The observed AC impedance gives the carrier hopping rate of 3.5 × 107 s–1, which is ca. 60 times of the F1–F1 exchange rate determined by NMR. The slower F1–F1 hopping rate is ascribed to the result of the long-time average of the faster carrier hopping rate. For the AC impedance analysis, the concentration of the carrier to realize the observed conductivity is much larger than that of the fluoride ion vacancy introduced by Sr doping. For explanation, we postulate that what influences AC impedance includes not only the vacancy but also fast-exchanging fluoride ions around the vacancy.

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Fluorine-19 NMR

Cited by 5 publications

References 43 publications

Terminal and bridging fluorine ligands in TiF4 as studied by 19F NMR in solids

Terminal and bridging fluorine ligands in TiF4 as studied by 19F NMR in solids

Solubilization of Hexafluorobenzene by the Micellar Aromatic Core Formed from Aggregation of Amphiphilic (2,3-O-Dibenzyl-6-O-sulfobutyl) Cyclodextrins

Ionic Conduction in Sr-Doped CeF₃ as Studied by ¹⁹F NMR and AC Impedance Measurement

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Fluorine-19 NMR

Cited by 5 publications

References 43 publications

Terminal and bridging fluorine ligands in TiF4 as studied by 19F NMR in solids

Terminal and bridging fluorine ligands in TiF4 as studied by 19F NMR in solids

Solubilization of Hexafluorobenzene by the Micellar Aromatic Core Formed from Aggregation of Amphiphilic (2,3-O-Dibenzyl-6-O-sulfobutyl) Cyclodextrins

Ionic Conduction in Sr-Doped CeF3 as Studied by 19F NMR and AC Impedance Measurement

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Ionic Conduction in Sr-Doped CeF₃ as Studied by ¹⁹F NMR and AC Impedance Measurement