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Title: Nuclear Magnetic Resonance Study of Anion and Cation Reorientational Dynamics in (NH 4) 2B 12H 12

Abstract

Here, diammonium dodecahydro-closo-dodecaborate (NH 4) 2B 12H 12 is the ionic compound combining NH 4 + cations and [B 12H 12] 2– anions, both of which can exhibit high reorientational mobility. To study the dynamical properties of this material, we measured the proton NMR spectra and spin–lattice relaxation rates in (NH 4) 2B 12H 12 over the temperature range of 6–475 K. Two reorientational processes occurring at different frequency scales have been revealed. In the temperature range of 200–475 K, the proton spin–lattice relaxation data are governed by thermally activated reorientations of the icosahedral [B 12H 12] 2– anions. This motional process is characterized by the activation energy of 486(8) meV, and the corresponding reorientational jump rate reaches ~10 8 s –1 near 410 K. Below 100 K, the relaxation data are governed by the extremely fast process of NH 4 + reorientations which are not “frozen out” at the NMR frequency scale down to 6 K. The experimental results in this range are described in terms of a gradual transition from the regime of low-temperature quantum dynamics (rotational tunneling of NH 4 groups) to the regime of classical jump reorientations of NH 4 groups with an activation energy ofmore » 26.5 meV. Our study offers physical insights into the rich dynamical behavior of (NH 4) 2B 12H 12 on an atomic level, providing a link between the microscopic and thermodynamic properties of this compound.« less

Authors:
ORCiD logo [1];  [1];  [1];  [1];  [2];  [3]
  1. Ural Division of the Russian Academy of Sciences, Ekaterinburg (Russia)
  2. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  3. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-CA), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1485459
Alternate Identifier(s):
OSTI ID: 1570262; OSTI ID: 1570263
Report Number(s):
SAND-2018-12085J; SAND2019-11024J; SAND2019-11023J
Journal ID: ISSN 1932-7447; 668981
Grant/Contract Number:  
AC04-94AL85000; NA0003525; NA-0003525
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 122; Journal Issue: 6; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Complex hydride; Reorientation; Rotational tunneling; Nuclear spin relaxation

Citation Formats

Skripov, Alexander V., Skoryunov, Roman V., Soloninin, Alexei V., Babanova, Olga A., Stavila, Vitalie, and Udovic, Terrence J. Nuclear Magnetic Resonance Study of Anion and Cation Reorientational Dynamics in (NH4)2B12H12. United States: N. p., 2018. Web. doi:10.1021/acs.jpcc.7b12046.
Skripov, Alexander V., Skoryunov, Roman V., Soloninin, Alexei V., Babanova, Olga A., Stavila, Vitalie, & Udovic, Terrence J. Nuclear Magnetic Resonance Study of Anion and Cation Reorientational Dynamics in (NH4)2B12H12. United States. doi:10.1021/acs.jpcc.7b12046.
Skripov, Alexander V., Skoryunov, Roman V., Soloninin, Alexei V., Babanova, Olga A., Stavila, Vitalie, and Udovic, Terrence J. Mon . "Nuclear Magnetic Resonance Study of Anion and Cation Reorientational Dynamics in (NH4)2B12H12". United States. doi:10.1021/acs.jpcc.7b12046. https://www.osti.gov/servlets/purl/1485459.
@article{osti_1485459,
title = {Nuclear Magnetic Resonance Study of Anion and Cation Reorientational Dynamics in (NH4)2B12H12},
author = {Skripov, Alexander V. and Skoryunov, Roman V. and Soloninin, Alexei V. and Babanova, Olga A. and Stavila, Vitalie and Udovic, Terrence J.},
abstractNote = {Here, diammonium dodecahydro-closo-dodecaborate (NH4)2B12H12 is the ionic compound combining NH4+ cations and [B12H12]2– anions, both of which can exhibit high reorientational mobility. To study the dynamical properties of this material, we measured the proton NMR spectra and spin–lattice relaxation rates in (NH4)2B12H12 over the temperature range of 6–475 K. Two reorientational processes occurring at different frequency scales have been revealed. In the temperature range of 200–475 K, the proton spin–lattice relaxation data are governed by thermally activated reorientations of the icosahedral [B12H12]2– anions. This motional process is characterized by the activation energy of 486(8) meV, and the corresponding reorientational jump rate reaches ~108 s–1 near 410 K. Below 100 K, the relaxation data are governed by the extremely fast process of NH4+ reorientations which are not “frozen out” at the NMR frequency scale down to 6 K. The experimental results in this range are described in terms of a gradual transition from the regime of low-temperature quantum dynamics (rotational tunneling of NH4 groups) to the regime of classical jump reorientations of NH4 groups with an activation energy of 26.5 meV. Our study offers physical insights into the rich dynamical behavior of (NH4)2B12H12 on an atomic level, providing a link between the microscopic and thermodynamic properties of this compound.},
doi = {10.1021/acs.jpcc.7b12046},
journal = {Journal of Physical Chemistry. C},
number = 6,
volume = 122,
place = {United States},
year = {2018},
month = {1}
}

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