Neutron Powder Diffraction and Molecular Simulation Study of the Structural Evolution of Ammonia Borane from 15 to 340 K

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• 作者：Nancy J. Hess ; Gregory K. Schenter ; Michael R. Hartman ; Luc L. Daemen ; Thomas Proffen ; Shawn M. Kathmann ; Christopher J. Mundy ; Monika Hartl ; David J. Heldebrant ; Ashley C. Stowe ; Tom Autrey
• 刊名：Journal of Physical Chemistry A
• 出版年：2009
• 出版时间：May 14, 2009
• 年：2009
• 卷：113
• 期：19
• 页码：5723-5735
• 全文大小：444K
• 年卷期：v.113,no.19(May 14, 2009)
• ISSN：1520-5215

文摘

The structural behavior of ¹¹B-, ²H-enriched ammonia borane, ND₃¹¹BD₃, over the temperature range from 15 to 340 K was investigated using a combination of neutron powder diffraction and ab initio molecular dynamics simulations. In the low temperature orthorhombic phase, the progressive displacement of the borane group under the amine group was observed leading to the alignment of the B−N bond near parallel to the c-axis. The orthorhombic to tetragonal structural phase transition at 225 K is marked by dramatic change in the dynamics of both the amine and borane group. The resulting hydrogen disorder is problematic to extract from the metrics provided by Rietveld refinement but is readily apparent in molecular dynamics simulation and in difference Fourier transform maps. At the phase transition, Rietveld refinement does indicate a disruption of one of two dihydrogen bonds that link adjacent ammonia borane molecules. Metrics determined by Rietveld refinement are in excellent agreement with those determined from molecular simulation. This study highlights the valuable insights added by coupled experimental and computational studies.