Ta3SBr7—A New Structure Type in theM3QX7Family (M=Nb, Ta;Q=S, Se, Te;X=Cl, Br, I)
✍ Scribed by Mark Smith; Gordon J. Miller
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 486 KB
- Volume
- 140
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
The layered compound Ta 3 SBr 7 has been prepared by direct reaction of the elements at 550°C for 2 weeks in evacuated Pyrex ampules, and its structure determined by single-crystal X-ray diffraction. Ta 3 SBr 7 crystallizes with monoclinic symmetry in space group Cm; a ؍ 12.249(2) A s , b ؍ 7.071(2) A s , c ؍ 8.829(2) A s , ؍ 134)421(8)°, V ؍ 546.16(23) A s 3 , Z ؍ 2, R ؍ 0.027, R ؍ 0.032. The structure, related to the Cd(OH) 2 type, consists of triangular tantalum clusters located between every other layer of a closed-packed mixed S/SBr ordered anion framework. The slightly distorted, quasi-infinite 2 [Ta 3 SBr 7 ] slabs stack parallel to the crystallographic ab plane in a new variant, with each successive 2
[Ta 3 SBr 7 ] slab related by a 1/2b؉c stacking vector. This stacking mode is the sixth layered structure type observed in the M 3 QX 7 system. Ta 3 SBr 7 represents the first Ta 3 QX 7 compound discovered that is not isostructural with its niobium counterpart and is the second of the two one-slab per unit cell stacking types possible in the M 3 QX 7 system Nb 3 SBr 7 being the other. Synthesis, structural characterization, and lattice energy calculations of Ta 3 SBr 7 and related compounds are reported.