K₂ScSn(AsO₄)₃: an arsenate-containing langbeinite

Abstract

The title compound, dipotassium tri-mu-arsenato-scandium(III)tin(IV), is the first arsenate-containing langbeinite to be characterized by single-crystal methods and crystallizes in the aristotype P2(1)3 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.

K2MIII2(MVIO4)(PO4)2 (MIII = Fe, Sc; MVI = Mo, W), Novel Members of the Lagbeinite-Related Family: Synthesis, Structure, and Magnetic Properties

“…Despite having a different metal partner in both positions B, for a set of iron-containing compounds (K 1.84 Fe 1.42 Nb 0.58 (PO 4 ) 3 , K 2 FeSn(PO 4 ) 3 , K 2 Fe 0.5 Ti 1.5 (PO 4 ) 3 , and KFeMo) these values are alike and approach 2.25(6) and 2.21(4) Å correspondingly. The same dependence is observed for scandium-containing ones: K 2 ScSn(AsO 4 ) 3 and KScMo, KScW.…”

“…5 8 ( P O 4 ) 3 , 1 8 K 2 F e S n ( P O 4 ) 3 , 1 9 K 2 Fe 0.5 Ti 1.5 (PO 4 ) 3 , 20 and KFeMo) these values are alike and approach 2.25(6) and 2.21(4) Å correspondingly. The same dependence is observed for scandium-containing ones: K 2 ScSn-(AsO 4 ) 3 21 and KScMo, KScW. However, a newly proposed value d td changes significantly with transition from phosphate to other tetrahedral groups.…”