NMR Study of Molecular Dynamics in Complex Metal Borohydride LiZn2(BH4)5

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• 作者：Anton Gradi拧ek ; Dorthe B. Ravnsb忙k ; Stanislav Vrtnik ; Andra啪 Kocjan ; Janez Lu啪nik ; Toma啪 Apih ; Torben R. Jensen ; Alexander V. Skripov ; Janez Dolin拧ek
• 刊名：Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：October 17, 2013
• 年：2013
• 卷：117
• 期：41
• 页码：21139-21147
• 全文大小：390K
• 年卷期：v.117,no.41(October 17, 2013)
• ISSN：1932-7455

文摘

In searching for hydrogen storage materials with an improved storage capacity and low hydrogen decomposition temperature, a lithium zinc borohydride LiZn₂(BH₄)₅ (LZBH) was investigated. LZBH shows the structure of two identical interpenetrated three-dimensional frameworks with no bonds between them, not observed before in metal hydrides. The structural peculiarity and uniqueness among metal hydrides prompts the investigation of molecular dynamics responsible for the thermodynamic and kinetic properties of LZBH. Molecular dynamics was investigated experimentally by ¹H and ⁷Li NMR spectrum and spin鈥搇attice relaxation techniques. Different thermally activated reorientational processes of BH₄ tetrahedra about their 2-fold and 3-fold symmetry axes were identified from the temperature-dependent proton and lithium spin鈥搇attice relaxation rates and were quantified by their activation energies, in relation to the LiZn₂(BH₄)₅ structural details. The five BH₄ tetrahedra of a given [Zn₂(BH₄)₅]^{鈭?/sup> complex anion were classified into two groups with different dynamic properties, the first group containing terminal tetrahedra with crystallographically inequivalent B1, B2, and B4 boron atoms and the second group containing the bridging tetrahedron with the B3 boron atom. Our study presents physical insight into the dynamic properties of LZBH on a microscopic level of atomic groups, providing link between the microscopic and the bulk properties of this phase.}