Raman Spectroscopy, X-ray Diffraction, and Hydrogenation Thermochemistry of N,N,N,N-Tetramethylcyclotriborazane under Pressure

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• 作者：Robert G. Potter ; Maddury Somayazulu ; George Cody ; Russell J. Hemley
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：May 15, 2014
• 年：2014
• 卷：118
• 期：19
• 页码：9871-9879
• 全文大小：435K
• 年卷期：v.118,no.19(May 15, 2014)
• ISSN：1932-7455

文摘

The novel hydrogen-rich BN materials Me₂NHBH₃ and c-N₂B₂H₄Me₄ have been studied by a combination of vibrational spectroscopy and single crystal X-ray diffraction over the pressure range 0鈥?0 GPa. Assignments of Raman-active vibrational modes were made for c-N₂B₂H₄Me₄ on the basis of a combination of gas-phase predictions and previous assignments for similar compounds. The Raman spectrum of single crystals were found to have excellent signal-to-noise for pressures over the 0鈥?0 GPa range, making it an ideal method for in situ analysis of high pressure reactions involving c-N₂B₂H₄Me₄. The enthalpy of the reaction c-N₂B₂H₄Me₄ + 2 H₂ 鈫?2 Me₂NHBH₃ was estimated to be 2.9 kcal/mol endothermic at ambient pressure. The corresponding pressure dependence of 螖G_rxn was estimated from the P鈥揤 equations of state (EOS) measured for Me₂NHBH₃, c-N₂B₂H₄Me₄, and H₂ over the 0鈥?2 GPa range. Using the EOS for fluid hydrogen, the reaction is estimated to have a favorable 螖螖G_rxn of 10 kcal/mol over the 0鈥? GPa pressure range. Above 2 GPa, a positive pressure dependence of 螖G_rxn is observed. On the basis of these experimental observations, we estimate the reaction thermochemistry to approach a thermoneutral equilibrium over the 0鈥? GPa range. Above 2 GPa, the reaction volume becomes positive, causing this hydrogenation pathway to remain unfavorable over a pressure range extending to greater than 100 GPa at 298 K.