A mixed-cation mixed-anion borohydride NaY(BHb>4b>)b>2b>Clb>2b>

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• 作者：Dorthe B. Ravnsbæ ; k^a ; Morten B. Ley^a ; Young-Su Lee^b ; Hans Hagemann^c ; Vincenza D&rsquo ; Anna^c ; Young Whan Cho^b ; Yaroslav Filinchuk^a ; ^d ; ¹ ; Torben R. Jensen^a ; ^{trj@chem.au.dk}
• 关键词：Hydrides ; X-ray diffraction ; Solid state structure ; Solid phase synthesis ; Transition metal
• 刊名：International Journal of Hydrogen Energy
• 出版年：2012
• 期刊代码：42_03603199
• 类别：ch
• 出版时间：May, 2012
• 卷：37
• 期：10
• 页码：8428-8438
• 文件大小：1068 K

摘要

A new sodium-yttrium borohydride-chloride, NaY(BHb>4b>)b>2b>Clb>2b>, is obtained by a combination of mechanochemical synthesis and annealing of NaBHb>4b>-YClb>3b> mixtures and is characterized by in-situ synchrotron radiation X-ray powder diffraction, density functional theory, thermal analysis and vibrational spectroscopy. Several simultaneous and coupled reactions occur during the synthesis, also yielding Nab>3b>YClb>6b> and Na(BHb>4b>)b>1鈭?em>xb>Clb>xb> besides the title compound. The polymeric pseudo-orthorhombic crystal structure of NaY(BHb>4b>)b>2b>Clb>2b> (space group P2/c) is built of edge- and corner-sharing octahedral coordination polyhedra of yttrium (4Cl聽+聽2BHb>4b>) and sodium (2Cl聽+聽4BHb>4b>). The structure is isomorphous to the high temperature polymorph of NaYClb>4b>. The BHb>4b> units in NaY(BHb>4b>)b>2b>Clb>2b> are located only on the larger of the two independent anion sites in NaYClb>4b>. Density functional theory optimization of the experimental structure suggests that the BHb>4b> units act as 畏³-ligands (face-sharing) towards yttrium and 畏¹-ligands (corner-sharing) towards sodium. Raman spectroscopy confirms this BHb>4b> configuration. NaY(BHb>4b>)b>2b>Clb>2b> decomposes at 鈭?00聽掳C under formation of Nab>3b>YClb>6b>, while the latter compound at higher temperatures reacts with Na(BHb>4b>)b>1鈭?em>xb>Clb>xb> to form NaCl and possibly amorphous products. The reactions are associated with mass losses of 2.62 and 3.78聽wt%for the NaBHb>4b>-YClb>3b> (3:1) and (4:1) samples, respectively.