Ammonia Triborane: Theoretical Study of the Mechanism of Hydrogen Release.
High-level electronic structure calculations have been used to predict the thermodynamic stability of ammonia triborane B₃H₇NH₃ and the molecular mechanism of H₂ elimination from various isomeric forms in the gas phase. Geometries of stationary points were optimized at the second-order perturbation theory MP2 level, and total energies were computed at the coupled-cluster CCSD(T) theory with the aug-cc-pVnZ (n=D, T, Q) basis sets and extrapolated to the complete basis set limit. Heats of formation for the structures considered in the gas phase were evaluated at both 0 and 298 K. The lowest-energy process for H₂ release from the most stable isomer of B₃H₇NH₃ is a 1,3-elimination characterized by an energy barrier of 28.9 kcal/mol. Although the barrier height for H₂ release from B₃H₇NH₃ is slightly smaller than the B-N bond cleavage energy of 30.7 kcal/mol yielding B₃H₇ + NH₃, the calculated rate coefficients predict that bond cleavage is faster than H₂ release by 3 orders of magnitude at 298 K and 1 atm. We predict the heat of formation for the most stable isomer of B₃H₇ to be ΔH sub f (0 K) = 37.1 plus or minus 0.8 kcal/mol and ΔH sub f (298 K) = 32.5 plus or minus 0.8 kcal/mol, and for the most stable isomer of B₃H₇NH₃ to be ΔH sub f (0 K) = 0.4 plus or minus 1.0 kcal/mol and ΔH sub f (298 K) = -7.1 plus or minus 1.0 kcal/mol.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 921394
- Journal Information:
- Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 26 Vol. 111; ISSN 1932-7447
- Publisher:
- American Chemical Society
- Country of Publication:
- United States
- Language:
- English
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