K2ScSn(AsO4)3: an arsenate‐containing langbeinite

The title compound, dipotassium tri‐μ‐arsenato‐scandium(III)tin(IV), is the first arsenate‐containing langbeinite to be characterized by single‐crystal methods and crystallizes in the aristotype P2₁3 cubic symmetry for this structure type in which the K⁺ ions and the octahedral scandium and tin cations lie on crystallographic threefold axes. The Sc^III and Sn^IV ions show a slight segregation over the two octahedral sites, with Sc/Sn populations of 0.582 (5):0.418 (5) on one site and 0.418 (5):0.582 (5) on the other. Bond‐valence‐sum calculations indicate that the K⁺ ions are significantly underbonded in this structure and the O atoms show large anisotropic displacement parameters, as also seen in other langbeinites. The crystal studied was found to be a merohedral twin with a 0.690 (16):0.310 (16) domain ratio.