Karl W. Krämer, Ralph Schenker, Jürg Hauser, Høgni Weihe, Hans U. Güdel and Hans-Beat Bürgi
Crystal Structures of (Et₄N)₃M₂F₉ (M = V, Cr, Fe) determined by X-Ray Single-Crystal and Powder Diffraction: A New Structure Type for A₃M₂X₉ Compounds
Z. Anorg. Allg. Chem. 627, 2511-2516 (2001)                 

Abstract: The syntheses and X-ray structure determinations of single crystals and powders are reported for the compounds (Et₄N)₃M₂F₉ (M = V³⁺, Cr³⁺, Fe³⁺). The compounds are isostructural and represent a new structure type for A₃M₂X₉ compounds. They crystallize in the hexagonal space group P6₃/m with Z = 2. Their lattice parameters are (Et₄N)₃V₂F₉: a = 13.3017(3), c = 10.7714(2) Å; (Et₄N)₃Cr₂F₉: a = 13.2691(3), c = 10.7148(3) Å; and (Et₄N)₃Fe₂F₉: a = 13.3040(3), c = 10.7650(3) Å.