Date Published: April 01, 2012
Publisher: International Union of Crystallography
Author(s): Abdelghani Oudahmane, Malika El-Ghozzi, Daniel Avignant.
Single crystals of Ca5Zr3F22, pentacalcium trizirconium docosafluoride, were obtained unexpectedly by solid-state reaction between CaF2 and ZrF4 in the presence of AgF. The structure of the title compound is isotypic with that of Sr5Zr3F22 and can be described as being composed of layers with composition [Zr3F20]8− made up from two different [ZrF8]4− square antiprisms (one with site symmetry 2) by corner-sharing. The layers extending parallel to the (001) plane are further linked by Ca2+ cations, forming a three-dimensional network. Amongst the four crystallographically different Ca2+ ions, three are located on twofold rotation axes. The Ca2+ ions exhibit coordination numbers ranging from 8 to 12, depending on the cut off, with very distorted fluorine environments. Two of the Ca2+ ions occupy interstices between the layers whereas the other two are located in void spaces of the [Zr3F20]8− layer and alternate with the two Zr atoms along . The crystal under investigation was an inversion twin.
For the isotypic Sr analogue, see: Le Bail (1996 ▶). The crystal chemistry of fluorides has been reviewed by Babel & Tressaud (1985 ▶). For phase relationships in the CaF2–ZrF4 system, see: L’Helgoualch et al. (1971 ▶); Kotsar et al. (1973 ▶); Ratnikov et al. (1977 ▶); Laval et al. (1987 ▶). For bond-valence analysis, see: Brese & O’Keeffe (1991 ▶).