Received 26 January 2009
The title compound, neodymium sesquiselenide, is isotypic with the other known rare-earth metal(III) selenides M2Se3 (M = La-Pr and Sm-Lu) with the cubic C-type structure. It adopts a cation-defective Th3P4-type arrangement with close to 8/9 of the unique neodymium-cation site occupied, leading to the composition Nd2.667Se4 (Z = 4) or Nd2Se3 (Z = 5.333), respectively. The Nd3+ cations are thus surrounded by eight selenide anions, forming trigonal [NdSe8]13- dodecahedra, whereas the Se2- anions exhibit a sixfold coordination, but due to the under-occupation of neodymium, each one is statistically surrounded by only 5.333 cations. The crystal studied was a merohedral twin with a 0.31 (6):0.69 (6) domain ratio.
For the structural family with the cation-defective Th3P4-type arrangement, see: Pardo et al. (1963); Flahaut et al. (1965); Lashkarev & Paderno (1965). For the rare-earth sesquiselenides M2Se3 with M = La-Pr and Sm-Lu, see: Grundmeier & Urland (1995); Folchnandt (1997); Folchnandt & Schleid (2001); Folchnandt et al. (2004).
Data collection: DIF4 (Stoe & Cie, 1992); cell refinement: DIF4; data reduction: REDU4 (Stoe & Cie, 1992); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: SHELXL97.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: MG2064 ).
Financial support by the state of Baden-Württemberg (Stuttgart) and the Deutsche Forschungsgemeinschaft (DFG; Frankfurt/Main) is gratefully acknowledged. Furthermore we thank Dr Falk Lissner for the data collection.
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