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Biswal, M., Body, M., Legein, C., Sadoc, A. & Boucher, F. (2013) NbF5 and TaF5: Assignment of F-19 NMR resonances and chemical bond analysis from GIPAW calculations. J. Solid State Chem. 207 208–217.
Added by: Laurent Cournède (2016-03-10 21:23:29) |
| Type de référence: Article DOI: 10.1016/j.jssc.2013.09.001 Numéro d'identification (ISBN etc.): 0022-4596 Clé BibTeX: Biswal2013 Voir tous les détails bibliographiques  |
Catégories: ST2E Mots-clés: ab-initio calculations, aluminosilicate glasses, augmented-wave method, coordination-compounds, crystal-structures, DFT calculations, F-19 solid state NMR, Inorganic fluorides, metal fluoride glasses, niobium pentafluoride, nuclear-magnetic-resonance, solid-state NMR, x-ray-diffraction Créateurs: Biswal, Body, Boucher, Legein, Sadoc Collection: J. Solid State Chem. |
Consultations : 1/465
Indice de consultation : 2% Indice de popularité : 0.5% |
| Résumé |
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The F-19 isotropic chemical shifts (delta(iso)) of two isomorphic compounds, NbF5 and TaF5, which involve six nonequivalent fluorine sites, have been experimentally determined from the reconstruction of 1D F-19 MAS NMR spectra. In parallel, the corresponding F-19 chemical shielding tensors have been calculated using the GIPAW method for both experimental and DFT-optimized structures. Furthermore, the [M4F20] units of NbF5 and TaF5 being held together by van der Waals interactions, the relevance of Grimme corrections to the DFT optimization processes has been evaluated. However, the semi-empirical dispersion correction term introduced by such a method does not show any significant improvement. Nonetheless, a complete and convincing assignment of the F-19 NMR lines of NbF5 and TaF5 is obtained, ensured by the linearity between experimental F-19 oiso values and calculated 19F isotropic chemical shielding O-iso values. The effects of the geometry optimizations have been carefully analyzed, confirming among other matters, the inaccuracy of the experimental structure of NbF5. The relationships between the fluorine chemical shifts, the nature of the fluorine atoms (bridging or terminal), the position of the terminal ones (opposite or perpendicular to the bridging ones), the fluorine charges, the ionicity and the length of the M-F bonds have been established. Additionally, for three of the 19F NMR lines of NbF5, distorted multiplets, arising from IJ-coupling and residual dipolar coupling between the F-19 and Nb-93 nuclei, were simulated yielding to values of Nb-93-F-19 (1)J-coupling for the corresponding fluorine sites. (C) 2013 Elsevier Inc. All rights reserved.
Added by: Laurent Cournède |