Structural Investigation of 伪- and 尾-Sodium Hexafluoroarsenate, NaAsF6, by Variable Temperature X-ray Powder Diffraction and Multinuclear Solid-State NMR, and DFT Calculations

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• 作者：Mamata Biswal ; Monique Body ; Christophe Legein ; Gwena毛l Corbel ; Aymeric Sadoc ; Florent Boucher
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：May 31, 2012
• 年：2012
• 卷：116
• 期：21
• 页码：11682-11693
• 全文大小：528K
• 年卷期：v.116,no.21(May 31, 2012)
• ISSN：1932-7455

文摘

We report the phase transition between the 伪- and 尾-phases of NaAsF₆ monitored by DTA, variable temperature ¹⁹F solid-state NMR and temperature controlled X-ray powder diffraction (XRPD) as well as their crystalline structures determined from XRPD data. The structural type of 尾-NaAsF₆ has been determined thanks to ¹⁹F and ⁷⁵As solid-state NMR experiments. ¹⁹F, ²³Na, and ⁷⁵As NMR parameters, including ¹⁹F鈥?sup>75As ¹J coupling, have been measured for both phases. The ¹⁹F, ²³Na, and ⁷⁵As solid-state NMR investigations are in full agreement with both crystalline structures from a qualitative point of view. Chemical shielding tensors have been calculated from the gauge including projector augmented wave approach. The electric field gradient tensors of ²³Na and ⁷⁵As have been calculated in 伪-NaAsF₆ from the all-electrons method and the projector augmented-wave approach. Two difficulties were encountered: the libration of the rigid and regular AsF₆^{鈥?/sup> anions in the 尾-phase, highlighted by the atomic anisotropic displacement parameters for F, which leads to erroneous shortened As鈥揊 bond length, and the overestimation of the As鈥揊 bond length with the PBE functional used in the density functional theory calculations. We show that both difficulties can be overcome by full optimization and rescaling of the cell parameters of the crystalline structures. Additionally, a linear correlation is observed between experimental 23Na 未_iso values and calculated 23Na 蟽_iso values from previously reported data and from our own measurements and calculations.}