Reorientational Motion in Alkali-Metal Borohydrides: NMR Data for RbBH4 and CsBH4 and Systematics of the Activation Energy Variations

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• 作者：Olga A. Babanova ; Alexei V. Soloninin ; Alexander V. Skripov ; Dorthe B. Ravnsb忙k ; Torben R. Jensen ; Yaroslav Filinchuk
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：May 26, 2011
• 年：2011
• 卷：115
• 期：20
• 页码：10305-10309
• 全文大小：788K
• 年卷期：v.115,no.20(May 26, 2011)
• ISSN：1932-7455

文摘

To study the reorientational motion of the BH₄ groups in RbBH₄ and CsBH₄, we have performed nuclear magnetic resonance (NMR) measurements of the ¹H and ¹¹B spin鈥搇attice relaxation rates in these compounds over wide ranges of temperature (48鈥?00 K) and resonance frequency (14鈥?0 MHz). It is found that at low temperatures the reorientational motion in CsBH₄ is the fastest among all of the borohydrides studied so far. The activation energies E_a for BH₄ reorientations obtained from our data are 138 卤 4 meV for RbBH₄ and 105 卤 7 meV for CsBH₄. Investigating the systematics of E_a variations in alkali-metal borohydrides MBH₄, we have found a correlation between E_a and the relative deviation of the actual M鈥揃 distance from the sum of the ionic radii of M and BH₄.