Soloninin, A.V.
[Ural Division of the Russian Academy (Russia)]
Babanova, O.A.
[Ural Division of the Russian Academy (Russia)]
Skripov, A.V.
[Ural Division of the Russian Academy (Russia)]
Hagemann, H.
[University of Geneva (Switzerland)]
Richter, B.
[Aarhus University (Denmark)]
Jensen, T.R.
[Aarhus University (Denmark)]
Filinchuk, Yaroslav
[UCL]
et al. [show all ]
To study the reorientational motion of BH 4 groups in β and γ phases of Mg(BH 4) 2 and in α and β phases of Ca(BH 4) 2, we have performed nuclear magnetic resonance (NMR) measurements of the 1H and 11B spin-lattice relaxation rates in these compounds over wide ranges of temperature and resonance frequency. It is found that at low temperatures the reorientational motion in β phases of Mg(BH 4) 2 and Ca(BH 4) 2 is considerably faster than in other studied phases of these alkaline-earth borohydrides. The behavior of the measured spin-lattice relaxation rates in both β phases can be satisfactorily described in terms of a Gaussian distribution of activation energies E a with the average E a values of 138 meV for β-Mg(BH 4) 2 and 116 meV for β-Ca(BH 4) 2. The α phase of Ca(BH 4) 2 is characterized by the activation energy of 286 ± 7 meV. For the novel porous γ phase of Mg(BH 4) 2, the main reorientational process responsible for the observed spin-lattice relaxation rate maximum can be described by the activation energy of 276 ± 5 meV. The barriers for reorientational motion in different phases of alkaline-earth borohydrides are discussed on the basis of changes in the local environment of BH 4 groups. © 2012 American Chemical Society.
Bibliographic reference
Soloninin, A.V. ; Babanova, O.A. ; Skripov, A.V. ; Hagemann, H. ; Richter, B. ; et. al. NMR study of reorientational motion in alkaline-earth borohydrides: β and γ phases of Mg(BH 4) 2 and α and β Phases of Ca(BH 4) 2. In: The Journal of Physical Chemistry Part C: Nanomaterials and Interfaces , Vol. 116, no. 7, p. 4913-4920 (2012)
Permanent URL
http://hdl.handle.net/2078.1/126358