skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Isomers and Conformers of H(NH₂BH₂)(n)H Oligomers: Understanding the Geometries and Electronic Structure of Boron-Nitrogen-Hydrogen Compounds as Potential Hydrogen Storage Materials

Abstract

Boron-nitrogen-hydrogen (BNHx) materials are polar analogs of hydrocarbons with potential applications as media for hydrogen storage. As H(NH₂BH₂)nH oligomers result from dehydrogenation of NH₃BH₃ and NH₄BH₄ materials, understanding the geometries, stabilities, and electronic structure of these oligomers is essential for developing chemical methods of hydrogen release and regeneration of the BNHx-based hydrogen storage materials. In this work we have performed computational modeling on the H(NH₂BH₂)nH (n = 1 – 6) oligomers using density functional theory (DFT). We have investigated linear chain structures and the stabilizing effects of coiling, biradicalization, and branching through Car-Parrinello molecular dynamics simulations and geometry optimizations. We find that the zig-zag linear oligomers are unstable with respect to the coiled, square-wave chain, and branched structures, with the coiled structures being the most stable. Dihydrogen bonding in oligomers, where protic Hδ⁺(N) hydrogens interact with hydridic Hδ⁻(B) hydrogens, plays a crucial role in stabilizing different isomers and conformers. The results are consistent with structures of products that are seen in experimental NMR studies of dehydrogenated ammonia borane.

Authors:
; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
902670
Report Number(s):
PNNL-SA-51976
9601; KP1704020; TRN: US200717%%606
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry C, 111(8):3294-3299; Journal Volume: 111; Journal Issue: 8
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; AMMONIA; BONDING; CHAINS; DEHYDROGENATION; ELECTRONIC STRUCTURE; FUNCTIONALS; GEOMETRY; HYDROCARBONS; HYDROGEN; HYDROGEN STORAGE; ISOMERS; REGENERATION; SIMULATION; Environmental Molecular Sciences Laboratory

Citation Formats

Li, Jun, Kathmann, Shawn M., Schenter, Gregory K., and Gutowski, Maciej S.. Isomers and Conformers of H(NH₂BH₂)(n)H Oligomers: Understanding the Geometries and Electronic Structure of Boron-Nitrogen-Hydrogen Compounds as Potential Hydrogen Storage Materials. United States: N. p., 2007. Web. doi:10.1021/jp066360b.
Li, Jun, Kathmann, Shawn M., Schenter, Gregory K., & Gutowski, Maciej S.. Isomers and Conformers of H(NH₂BH₂)(n)H Oligomers: Understanding the Geometries and Electronic Structure of Boron-Nitrogen-Hydrogen Compounds as Potential Hydrogen Storage Materials. United States. doi:10.1021/jp066360b.
Li, Jun, Kathmann, Shawn M., Schenter, Gregory K., and Gutowski, Maciej S.. Wed . "Isomers and Conformers of H(NH₂BH₂)(n)H Oligomers: Understanding the Geometries and Electronic Structure of Boron-Nitrogen-Hydrogen Compounds as Potential Hydrogen Storage Materials". United States. doi:10.1021/jp066360b.
@article{osti_902670,
title = {Isomers and Conformers of H(NH₂BH₂)(n)H Oligomers: Understanding the Geometries and Electronic Structure of Boron-Nitrogen-Hydrogen Compounds as Potential Hydrogen Storage Materials},
author = {Li, Jun and Kathmann, Shawn M. and Schenter, Gregory K. and Gutowski, Maciej S.},
abstractNote = {Boron-nitrogen-hydrogen (BNHx) materials are polar analogs of hydrocarbons with potential applications as media for hydrogen storage. As H(NH₂BH₂)nH oligomers result from dehydrogenation of NH₃BH₃ and NH₄BH₄ materials, understanding the geometries, stabilities, and electronic structure of these oligomers is essential for developing chemical methods of hydrogen release and regeneration of the BNHx-based hydrogen storage materials. In this work we have performed computational modeling on the H(NH₂BH₂)nH (n = 1 – 6) oligomers using density functional theory (DFT). We have investigated linear chain structures and the stabilizing effects of coiling, biradicalization, and branching through Car-Parrinello molecular dynamics simulations and geometry optimizations. We find that the zig-zag linear oligomers are unstable with respect to the coiled, square-wave chain, and branched structures, with the coiled structures being the most stable. Dihydrogen bonding in oligomers, where protic Hδ⁺(N) hydrogens interact with hydridic Hδ⁻(B) hydrogens, plays a crucial role in stabilizing different isomers and conformers. The results are consistent with structures of products that are seen in experimental NMR studies of dehydrogenated ammonia borane.},
doi = {10.1021/jp066360b},
journal = {Journal of Physical Chemistry C, 111(8):3294-3299},
number = 8,
volume = 111,
place = {United States},
year = {Wed Feb 07 00:00:00 EST 2007},
month = {Wed Feb 07 00:00:00 EST 2007}
}
  • The heats of formation for the boron amines BH{sub 3}NH{sub 3}, BH{sub 2}NH{sub 2}, and HBNH, tetrahedral BH{sub 4}{sup -}, and the BN molecule have been calculated by using ab initio molecular orbital theory. Coupled cluster calculations with perturbative triples (CCSD(T)) were employed for the total valence electronic energies. Correlation consistent basis sets were used, up through the augmented quadruple zeta, to extrapolate to the complete basis set limit. Core/valence, scalar relativistic, and spin-orbit corrections were included in an additive fashion to predict the atomization energies. Geometries were calculated at the CCSD(T) level up through at least aug-cc-pVTZ and frequenciesmore » were calculated at the CCSD(T)/aug-cc-pVDZ level. The heats of formation at 0K in the gas phase are {Delta}H{sub f}(BH{sub 3}NH{sub 3}) = -9.1, {Delta}H{sub f}(BH{sub 2}NH{sub 2}) = -15.9, {Delta}H{sub f}(BHNH) = 13.6, {Delta}H{sub f}(BN) = 146.4, and {Delta}H{sub f}(BH{sub 4}{sup -}) = -11.6 kcal/mol. The reported experimental value for {Delta}H{sub f}(BN) is clearly in error. The heat of formation of the salt [BH{sub 4}{sup -}NH{sub 4}{sup +}] (s) has been estimated by using an empirical expression for the lattice energy and the calculated heats of formation of the two component ions. The calculations show that both BH{sub 3}NH{sub 3}(g) and [BH{sub 4}{sup -}][NH{sub 4}{sup +}](s) can serve as good hydrogen storage systems which release H{sub 2} in a slightly exothermic process. The hydride affinity of BH{sub 3} is calculated to be 72.2 kcal/mol in excellent agreement with the experimental value at 298K of 74.2 {+-} 2.8 kcal/mol.« less
  • Boraneamines tend to have close N-H{sup {delta}+}{hor{underscore}ellipsis}{sup {delta}{minus}}H-B contacts as a result of the intermolecular interaction of the NH proton with the BH bond by a novel type of hydrogen bond (the dihydrogen bond). A CSD structural search provides characteristic metric data for the interaction: the H{hor{underscore}ellipsis}H distance is in the range 1.7--2.2 {angstrom}, and the N-H{hor{underscore}ellipsis}H group tends to be linear while B-H{hor{underscore}ellipsis}H tends to be bent. The reported X-ray structure of BH{sub 3}NH{sub 3} seemed to provide a singular exception in having bent N-H{hor{underscore}ellipsis}H and linear B-H{hor{underscore}ellipsis}H. Neutron diffraction structure of BH{sub 3}NH{sub 3} now shows that themore » B and N atoms must be reversed from the assignment previously published. With the correct assignment the authors find the expected bent B-H{hor{underscore}ellipsis}H and linear N-H{hor{underscore}ellipsis}H arrangement in the closest intermolecular N-H{hor{underscore}ellipsis}H-B interaction (d{sub HH} = 2.02 {angstrom}).« less
  • Combining X-ray diffraction, Raman spectroscopy, and ab initio simulations we characterize an extremely hydrogen-rich phase with the chemical formula (NH 3BH 3)(H 2) x (x = 1.5). This phase was formed by compressing ammonia borane (AB, NH 3BH 3) in an environment with an excess of molecular hydrogen (H 2). This compound can store a total of 26.8 wt% hydrogen, both as molecular hydrogen and chemically bonded hydrogen in AB, making it one of the most hydrogen-rich solids currently known. The new compound possesses a layered AB structure where additional H 2 molecules reside in channels created through the weavingmore » of AB layers. The unconventional dihydrogen bonding network of the new compound is significantly modified from its parent AB phase and contains H•••H contacts between adjacent AB molecules and between AB and H 2 molecules. H–H can be either a proton donor or a proton acceptor that forms new types of dihydrogen bonding with the host AB molecules, which are depicted as H–H•••H–B or H–H•••H–N, respectively. Furthermore, this study not only demonstrates the strategy and the promise of using pressure for new material synthesis, but also unleashes the power of combining experiments and ab initio calculations for elucidating novel structures and unusual bonding configurations in dense low-Z materials.« less
  • High-level electronic structure calculations have been used to map out the relevant portions of the potential energy surfaces for the release of H₂ from dimers of ammonia borane, BH₃NH₃ (AB). Using the correlationconsistent aug-cc-pVTZ basis set at the second-order perturbation MP2 level, geometries of stationary points were optimized. Relative energies were computed at these points using coupled-cluster CCSD(T) theory with the correlation-consistent basis sets at least up to the aug-cc-pVTZ level and in some cases extrapolated to the complete basis set limit. The results show that there are a number of possible dimers involving different types of hydrogen-bonded interactions. Themore » most stable gaseous phase (AB)₂ dimer results from a head-totail cyclic conformation and is stabilized by 14.0 kcal/mol with respect to two AB monomers. (AB)₂ can generate one or two H₂ molecules via several direct pathways with energy barriers ranging from 44 to 50 kcal/mol. The diammoniate of diborane ion pair isomer, [BH₄ -][NH₃BH₂NH₃ +] (DADB), is 10.6 kcal/mol less stable than (AB)₂ and can be formed from two AB monomers by overcoming an energy barrier of ~26 kcal/mol. DADB can also be generated from successive additions of two NH₃ molecules to B₂H sub 6 and from condensation of AB with separated BH₃ and NH₃ molecules. The pathway for H₂ elimination from DADB is characterized by a smaller energy barrier of 20.1 kcal/mol. The alternative ion pair [NH₄ +][BH₃NH₂BH₃ -] is calculated to be 16.4 kcal/mol above (AB)₂ and undergoes H₂ release with an energy barrier of 17.7 kcal/ mol. H₂ elimination from both ion pair isomers yields the chain BH₃NH₂BH₂NH₃ as product. Our results suggest that the neutral dimer will play a minor role in the release of H₂ from ammonia borane, with a dominant role from the ion pairs as observed experimentally in ionic liquids and the solid state.« less