Low-Temperature Rotational Tunneling of Tetrahydroborate Anions in Lithium Benzimidazolate-Borohydride Li2(bIm)BH4
| Autor: | Olga A. Babanova, Antonio Faraone, Terrence J. Udovic, Alexei V. Soloninin, Mirjana Dimitrievska, Roman V. Skoryunov, Wei Zhou, Fabrice Morelle, Alexander V. Skripov, Hui Wu, Yaroslav Filinchuk |
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| Přispěvatelé: | UCL - SST/IMCN/MOST - Molecular Chemistry, Materials and Catalysis |
| Jazyk: | angličtina |
| Rok vydání: | 2019 |
| Předmět: |
Spin polarization
Materials science chemistry.chemical_element 02 engineering and technology Neutron scattering Quasi elastic neutron scattering Hybrid compound 010402 general chemistry Borohydride 01 natural sciences Negative ions Rotational tunneling Ion Nuclear magnetic resonance chemistry.chemical_compound Dynamical properties Activation energy Physical and Theoretical Chemistry Physics::Chemical Physics Increasing temperatures Quantum tunnelling Nuclear magnetic resonance spectroscopy Reorientational motion Complementary techniques Temperature Lithium compounds 021001 nanoscience & nanotechnology 0104 chemical sciences Surfaces Coatings and Films Electronic Optical and Magnetic Materials General Energy chemistry Ab initio density functional theories (DFT) Quantum theory Neutron vibrational spectroscopy Density functional theory Physical chemistry Lithium 0210 nano-technology Calculations |
| Zdroj: | Journal of Physical Chemistry C, Vol. 123, no. 34, p. 20789-20799 (2019) |
| Popis: | To investigate the dynamical properties of the novel hybrid compound, lithium benzimidazolate-borohydride Li2(bIm)BH4 (where bIm denotes a benzimidazolate anion, C7N2H5 -), we have used a set of complementary techniques: neutron powder diffraction, ab initio density functional theory calculations, neutron vibrational spectroscopy, nuclear magnetic resonance, neutron spin echo, and quasi-elastic neutron scattering. Our measurements performed over the temperature range from 1.5 to 385 K have revealed the exceptionally fast low-temperature reorientational motion of BH4 - anions. This motion is facilitated by the unusual coordination of tetrahedral BH4 - anions in Li2(bIm)BH4: each anion has one of its H atoms anchored within a nearly square hollow formed by four coplanar Li+ cations, while the remaining -BH3 fragment extends into a relatively open space, being only loosely coordinated to other atoms. As a result, the energy barriers for reorientations of this fragment around the anchored B-H bond axis are very small, and at low temperatures, this motion can be described as rotational tunneling. The tunnel splitting derived from the neutron spin echo measurements at 3.6 K is 0.43(2) μeV. With increasing temperature, we have observed a gradual transition from the regime of low-temperature quantum dynamics to the regime of classical thermally activated jump reorientations. The jump rate of the uniaxial 3-fold reorientations reaches 5 × 1011 s-1 at 80 K. Nearer room temperature and above, both nuclear magnetic resonance and quasi-elastic neutron scattering measurements have revealed the second process of BH4 - reorientations characterized by the activation energy of 261 meV. This process is several orders of magnitude slower than the uniaxial 3-fold reorientations; the corresponding jump rate reaches ∼7 × 108 s-1 at 300 K. © 2019 American Chemical Society. |
| Databáze: | OpenAIRE |
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