Bimetallic Borohydrides in the System M(BH4)2鈥揔BH4 (M = Mg, Mn): On the Structural Diversity

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• 作者：Pascal Schouwink ; Vincenza D鈥橝nna ; Morten Brix Ley ; Lat茅vi Max Lawson Daku ; Bo Richter ; Torben R. Jensen ; Hans Hagemann ; Radovan 膶ern媒
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：May 24, 2012
• 年：2012
• 卷：116
• 期：20
• 页码：10829-10840
• 全文大小：432K
• 年卷期：v.116,no.20(May 24, 2012)
• ISSN：1932-7455

文摘

Four novel bimetallic borohydrides have been discovered, K₂M(BH₄)₄ (M = Mg or Mn), K₃Mg(BH₄)₅, and KMn(BH₄)₃, and are carefully investigated structurally as well as regarding their decomposition reaction mechanism by means of in situ synchrotron radiation powder X-ray diffraction (SR-PXD), vibrational spectroscopies (Raman and IR), thermal analysis (TGA and DTA), and ab initio density functional theory (DFT) calculations. Mechano-chemical synthesis (ball-milling) using the reactants KBH₄, 伪-Mg(BH₄)₂, and 伪-Mn(BH₄)₂ ensures chlorine-free reaction products. A detailed structural analysis reveals significant similarities as well as surprising differences among the two isomorphs K₂M(BH₄)₄, most importantly concerning the extent to which the complex anion [M(BH₄)₄]^{2鈥?/sup> is isolated in the structure. Anisotropic thermal expansion and an increase in symmetry at high temperatures in K₃Mg(BH₄)₅ is ascribed to the motion of BH₄ groups inducing hydrogen repulsive effects, and the dynamics of K₃Mg(BH₄)₅ are investigated. Decomposition in the manganese system proceeds via the formation of KMn(BH₄)₃, the first perovkite type borohydride reported to date.}