CsTl: A New Example of Tetragonally Compressed Tl66- Octahedra. Electronic Effects and Packing Requirements in the Diverse Structures of ATl (A = Li, Na, K, Cs)
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- 作者：Zhen-Chao Dong and John D. Corbett
- 刊名：Inorganic Chemistry
- 出版年：1996
- 出版时间：April 10, 1996
- 年：1996
- 卷：35
- 期：8
- 页码：2301 - 2306
- 全文大小：235K
- 年卷期：v.35,no.8(April 10, 1996)
- ISSN：1520-510X
文摘
The cesium-richest phase in the Cs-Tl system, CsTl, can beisolated as a pure crystalline phase through slowcooling of cesium-richer compositions in Ta followed by vacuumsublimation of the excess Cs at ~100 
ages/entities/deg.gif">C. Thecompound melts incongruently in the neighborhood of 150 ages/entities/deg.gif">C. Thestructure was established by single crystalX-ray diffraction at room temperature (orthorhombic Fddd,Z = 48, a = 32.140(3) Å, b= 15.136(1) Å, and c =9.2400(7) Å. The isolatedTl66- ions in the structure,tetragonally compressed octahedra, exhibit D2symmetrywith ages/entities/le.gif">0.063(4) Å differences in edge lengths fromD4h. ExtendedHückel calculations confirm the classicalnature of the distortion in lowering the cluster electron count andcharge. The diamagnetic CsTl differs fromKTl, which contains more distortedTl66- ions(C2h), in a doubleda axis and an additional interpenetratingclusteranion sublattice. The smaller distortion of the clusters in CsTloriginates with the lower field of the same numberof cation neighbors in a more symmetric arrangement. Thestructural trend from LiTl (CsCl type) through theclassic NaTl (stuffed diamond) to the related KTl and CsTl withcompressed octahedra (and the absence of anysuch Rb phase) relates to the efficient packing of A+ and(Tl-)n over a widely varying rangeof A+ sizes, withonly Na+ fitting well within a
journals/inocaj/35/i08/eqn/ic951265ve10001.gif">lattice. Similarly 4-bonded thallium in KTl and CsTl withsomewhatshorter Tl-Tl distances is a necessary alternative when the infinitelattice cannot tolerate larger cations.