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2004
Structure
D 2000
52- 008
Crystal Structures of Sr4Sn2Se9 and Sr4Sn2Se10 and the Oxidation State of Tin in
an Unusual Geometry. — The new ternary selenostannates of title are synthesized by
reaction of stoichiometric mixtures of the elements (1073→1173 K, argon atmosphere)
and their structures are determined by single-crystal XRD. Sr4Sn2Se9 crystallizes in a
2new structure type (space group Pbam, Z = 4) with Sn2 Se46 - , Sn Se44 , and Se2 subunits. Sr4Sn 2Se 10 (P21212, Z = 4) has a similar structure but with Se23 - triangles instead
of the Se22 - dumbbells. Strontium is 8-fold-coordinated by selenium in both cases. The
opening angles between tin and the terminal selenium atoms in the Sn2Se 6 subunits are
close to 160°, which is nearer to a typical Sn2+ coordination geometry than classical
SnSe4 tetrahedra, and suggests the tin oxidation state in the Sn2Se 6 units to be lower
than the expected Sn4+. However, self-consistent LMTO and LAPW band structure calculations expanded by Bader analysis of the charge density indicate the presence of Sn4+
in the Sn Se44 subunit. — (POCHA, R.; JOHRENDT*, D.; Inorg. Chem. 43 (2004)
21, 6830-6837; Inst. Biochem., Ludwig-Maximilians-Univ., D-81377 Muenchen,
Germany; Eng.) — Schramke
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