X-ray Diffraction, NMR Studies, and DFT Calculations of the Room and High Temperature Structures of Rubidium Cryolite, Rb3AlF6

Aydar Rakhmatullin; František Šimko; Emmanuel Véron; Mathieu Allix; Charlotte Martineau-Corcos; Andy Fitch; Franck Fayon; Roman A Shakhovoy; Kirill Okhotnikov; Vincent Sarou-Kanian; Michal Korenko; Zuzana Netriová; Ilja B Polovov; Catherine Bessada

doi:10.1021/acs.inorgchem.0c00415

X-ray Diffraction, NMR Studies, and DFT Calculations of the Room and High Temperature Structures of Rubidium Cryolite, Rb₃AlF₆

Inorg Chem. 2020 May 4;59(9):6308-6318. doi: 10.1021/acs.inorgchem.0c00415. Epub 2020 Apr 14.

Authors

Aydar Rakhmatullin¹, František Šimko^{2

3}, Emmanuel Véron¹, Mathieu Allix¹, Charlotte Martineau-Corcos^{1

4}, Andy Fitch⁵, Franck Fayon¹, Roman A Shakhovoy¹, Kirill Okhotnikov¹, Vincent Sarou-Kanian¹, Michal Korenko^{2

3}, Zuzana Netriová², Ilja B Polovov⁶, Catherine Bessada¹

Affiliations

¹ Conditions Extrêmes ét Matériaux: Haute Température et Irradiation, CEMHTI, UPR 3079-CNRS Université Orléans, 45071, Orléans, France.
² Institute of Inorganic Chemistry, Slovak Academy of Sciences, 845 36 Bratislava, Slovakia.
³ Centre of Excellence for advanced Materials Application - CEMEA, Slovak Academy of Sciences, Dúbravská cesta 5807/9, 845 11 Bratislava, Slovakia.
⁴ Université de Versailles Saint-Quentin en Yvelines, 45 Avenue des Etats-Unis, 78035 Versailles Cedex, France.
⁵ ID22, ESRF, Grenoble, France.
⁶ Department of Rare Metals and Nanomaterials, Institute of Physics and Technology Ural Federal University, Ekaterinburg, Russia.

PMID: 32286067
DOI: 10.1021/acs.inorgchem.0c00415

Abstract

A crystallographic approach incorporating multinuclear high field solid state NMR (SSNMR), X-ray structure determinations, TEM observation, and density functional theory (DFT) was used to characterize two polymorphs of rubidium cryolite, Rb₃AlF₆. The room temperature phase was found to be ordered and crystallizes in the Fddd (no. 70) space group with a = 37.26491(1) Å, b = 12.45405(4) Å, and c = 17.68341(6) Å. Comparison of NMR measurements and computational results revealed the dynamic rotations of the AlF₆ octahedra. Using in situ variable temperature MAS NMR measurements, the chemical exchange between rubidium sites was observed. The β-phase, i.e., high temperature polymorph, adopts the ideal cubic double-perovskite structure, space group Fm3m, with a = 8.9930(2) Å at 600 °C. Additionally, a series of polymorphs of K₃AlF₆ has been further characterized by high field high temperature SSNMR and DFT computation.