Potassium Zinc Borohydrides Containing Triangular [Zn(BH4)3]鈭?/sup> and Tetrahedral [Zn(BH4)xCl4鈥?i>x]2鈥?/sup> Anions

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• 作者：Radovan 膶ern媒 ; Dorthe B. Ravnsb忙k ; Pascal Schouwink ; Yaroslav Filinchuk ; Nicolas Penin ; Jeremie Teyssier ; L'ubom铆r Smr膷ok ; Torben R. Jensen
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：January 12, 2012
• 年：2012
• 卷：116
• 期：1
• 页码：1563-1571
• 全文大小：1068K
• 年卷期：v.116,no.1(January 12, 2012)
• ISSN：1932-7455

文摘

Three novel potassium鈥搝inc borohydrides/chlorides are described. KZn(BH₄)₃ and K₂Zn(BH₄)_xCl_4鈥?i>x form in ball-milled KBH₄:ZnCl₂ mixtures with molar ratios ranging from 1.5:1 up to 3:1. On the other hand, K₃Zn(BH₄)_xCl_5鈥?i>x forms only in the 2:1 mixture after longer milling times. The new compounds have been studied by a combination of in situ synchrotron powder diffraction, thermal analysis, Raman spectroscopy, and the solid state DFT calculations. Rhombohedral KZn(BH₄)₃ contains an anionic complex [Zn(BH₄)₃]^{鈭?/sup> with D₃ (32) symmetry, located inside a rhombohedron K₈. KZn(BH₄)₃ contains 8.1 wt % of hydrogen and decomposes at 385 K with a release of hydrogen and diborane similar to other Zn-based bimetallic borohydrides like MZn₂(BH₄)₅ (M = Li, Na) and NaZn(BH₄)₃. The decomposition temperature is much lower than for KBH₄. Monoclinic K₂Zn(BH₄)_xCl_4鈥?i>x contains a tetrahedral complex anion [Zn(BH₄)_xCl_4鈥?i>x]2鈥?/sup> located inside an Edshammar polyhedron (pentacapped trigonal prism) K₁₁. The compound is a monoclinically distorted variant of the paraelectric orthorhombic ht-phase of K₂ZnCl₄ (structure type K₂SO₄). K₂Zn(BH₄)_xCl_4鈥?i>x releases BH₄ starting from 395 K, forming Zn and KBH₄. As the reaction proceeds and x decreases, the monoclinic distortion of K₂Zn(BH₄)_xCl_4鈥?i>x diminishes and the structure transforms at 445 K into the orthorhombic ht-phase of K₂ZnCl₄. Tetragonal K₃Zn(BH₄)_xCl_5鈥?i>x is a substitutional and deformation variant of the tetragonal (I4/mcm) Cs₃CoCl₅ structure type possibly with the space group P4₂/ncm. K₃Zn(BH₄)_xCl_5鈥?i>x decomposes nearly at the same temperature as KZn(BH₄)₃, i.e., at 400 K, with the formation of K₂Zn(BH₄)_xCl_4鈥?i>x and KBH₄, indicating that the compound is an adduct of the two latter compounds.}