The complex symmetry relationships of methylammonium hexafluoroantimonates [(CH₃)ₓNH₄₋ₓ]SbF₆ (x = 1–4) with CsCl-type high-temperature structures

Abstract

The methylammonium hexafluoroantimonates [(CH₃)ₓNH₄₋ₓ]SbF₆ (x = 1-4) were synthesized from the corresponding antimonates by heating in 40 wt % aqueous HF and characterized by single-crystal diffraction. At elevated temperatures, the compounds crystallize in aristotype structures of the CsCl type with practically unrestricted rotational freedom of the ions. Upon cooling, ordered hettotype structures are formed with up to a 144-fold symmetry descent with respect to the parent structure. A detailed account of the complex structural relationships and of the twinning is given.