Molecular Structure and Dynamics in the Low Temperature (Orthorhombic) Phase of NH3BH3

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• 作者：Herman Cho ; Wendy J. Shaw ; Vencislav Parvanov ; Gregory K. Schenter ; Abhijeet Karkamkar ; Nancy J. Hess ; Chris Mundy ; Shawn Kathmann ; Jesse Sears ; Andrew S. Lipton ; Paul D. Ellis ; S. Thomas Autrey
• 刊名：Journal of Physical Chemistry A
• 出版年：2008
• 出版时间：May 8, 2008
• 年：2008
• 卷：112
• 期：18
• 页码：4277 - 4283
• 全文大小：152K
• 年卷期：v.112,no.18(May 8, 2008)
• ISSN：1520-5215

文摘

Variable temperature <SUP>2H NMR experiments on the orthorhombic phase of selectively deuterated NH₃BH₃spanning the static to fast exchange limits of the borane and amine motions are reported. New values of theelectric field gradient (EFG) tensor parameters have been obtained from the static ²H spectra of V_zz = 1.652(±0.082) × 10²¹ V/m² and s/gifchars/eta.gif" BORDER=0 > = 0.00 ± 0.05 for the borane hydrogens and V_zz = 2.883 (±0.144) × 10²¹ V/m²and s/gifchars/eta.gif" BORDER=0 > = 0.00 ± 0.05 for the amine hydrogens. The molecular symmetry inferred from the observation ofequal EFG tensors for the three borane hydrogens and likewise for the three amine hydrogens is in sharpcontrast with the C_s symmetry derived from diffraction studies. The origin of the apparent discrepancy hasbeen investigated using molecular dynamics methods in combination with electronic structure calculations ofNMR parameters, bond lengths, and bond angles. The computation of parameters from a statistical ensemblerather than from a single set of atomic Cartesian coordinates gives values that are in close quantitative agreementwith the ²H NMR electric field gradient tensor measurements and are more consistent with the molecularsymmetry revealed by the NMR spectra.