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Acta Cryst. (2014). E70, i6  [ doi:10.1107/S1600536813033850 ]

The aluminoarsenate Na1.67K1.33Al3(AsO4)4

M. A. Bouhassine and H. Boughzala

Abstract: The title compound, sodium potassium trialuminium tetra­kis­(orthoarsenate), was prepared by solid-state reactions. The anionic framework consists of corrugated layers parallel to (010) and is made up of corner-sharing AlO6 octa­hedra (site symmetries .2. and 2/m..) that are connected to isolated AsO4 tetra­hedra (site symmetries .2. and m..) through edge- and corner-sharing. The alkali cations are occupationally disordered. The two K+ cations [site symmetries .2. and m..; occupancies 0.314 (7) and 0.035 (12)] are situated in the inter­layer space, whereas the smaller Na+ cations [both with site symmetry m..; occupancies = 0.725 (14) and 0.112 (14)] are located in the cavities of the anionic framework. The K+ cations are surrounded by six and seven O atoms, the Na+ cations by seven and nine O atoms. The resulting coordination polyhedra of the two types of cations are highly distorted.

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