Ca 5Zr 3F 22

Abstract

Single crystals of Ca 5Zr 3F 22, penta-calcium trizirconium docosafluoride, were obtained unexpectedly by solid-state reaction between CaF 2 and ZrF 4 in the presence of AgF. The structure of the title compound is isotypic with that of Sr 5Zr 3F 22 and can be described as being composed of layers with composition [Zr 3F 20] 8- made up from two different [ZrF 8] 4- square anti-prisms (one with site symmetry 2) by corner-sharing. The layers extending parallel to the (001) plane are further linked by Ca 2+ cations, forming a three-dimensional network. Amongst the four crystallographically different Ca 2+ ions, three are located on twofold rotation axes. The Ca 2+ ions exhibit coordination numbers ranging from 8 to 12, depending on the cut off, with very distorted fluorine environments. Two of the Ca 2+ ions occupy inter-stices between the layers whereas the other two are located in void spaces of the [Zr 3F 20] 8- layer and alternate with the two Zr atoms along [010]. The crystal under investigation was an inversion twin.