3349-42-6Relevant academic research and scientific papers
Quasielastic neutron scattering of -NH3 and -BH3 rotational dynamics in orthorhombic ammonia borane
Hess, Nancy J.,Hartman, Michael R.,Brown, Craig M.,Mamontov, Eugene,Karkamkar, Abhijeet,Heldebrant, David J.,Daemen, Luc L.,Autrey, Tom
, p. 85 - 88 (2008)
Energy barriers for rotation of -NH3 and -BH3 in the orthorhombic phase of ammonia borane, NH3BH3, were determined using quasielastic neutron scattering (QENS). QENS confirms the 3-site jump model of rotational
Structure and vibrational dynamics of isotopically labeled lithium borohydride using neutron diffraction and spectroscopy
Hartman, Michael R.,Rush, John J.,Udovic, Terrence J.,Bowman Jr., Robert C.,Hwang, Son-Jong
, p. 1298 - 1305 (2007)
The crystalline structure of a 7Li and 11B labeled lithium borohydride has been investigated using neutron powder diffraction at 3.5, 360, and 400 K. The B-H bond lengths and H-B-H angles for the [BH4]- tetrahedra indicated that the tetrahedra maintained a nearly ideal configuration throughout the temperature range investigated. The atomic displacement parameters at 360 K suggest that the [BH4]- tetrahedra become increasingly disordered as a result of large amplitude librational and reorientational motions as the orthorhombic to hexagonal phase transition (T=384 K) is approached. In the high-temperature hexagonal phase, the [BH4]- tetrahedra displayed extreme disorder about the trigonal axis along which they are aligned. Neutron vibrational spectroscopy data were collected at 5 K over an energy range of 10-170 meV, and were found to be in good agreement with prior Raman and low-resolution neutron spectroscopy studies.
Materials for hydrogen storage: Structure and dynamics of borane ammonia complex
Parvanov, Vencislav M.,Schenter, Gregory K.,Hess, Nancy J.,Daemen, Luke L.,Hartl, Monika,Stowe, Ashley C.,Camaioni, Donald M.,Autrey, Tom
, p. 4514 - 4522 (2008)
The activation energies for rotations in low-temperature orthorhombic ammonia borane were analyzed and characterized in terms of electronic structure theory. The perdeuterated 11B-enriched ammonia borane, 11BD3ND3, sample was synthesized, and the structure was refined from neutron powder diffraction data at 175 K. This temperature has been chosen as median of the range of previously reported nuclear magnetic resonance spectroscopy measurements of these rotations. A representative molecular cluster model was assembled from the refined geometry, and the activation energies were calculated and characterized by analysis of the environmental factors that control the rotational dynamics. The barrier for independent NH3 rotation, Ea = 12.7 kJ mol-1, largely depends on the molecular conformational torsion in the solid-state geometry. The barrier for independent BH3 rotation, Ea = 38.3 kJ mol-1, results from the summation of the effect of molecular torsion and large repulsive intermolecular hydrogen-hydrogen interactions. However, a barrier of Ea = 31.1 kJ mol-1 was calculated for internally correlated rotation with preserved molecular conformation. Analysis of the barrier heights and the corresponding rotational pathways shows that rotation of the BH3 group involves strongly correlated rotation of the NH3 end of the molecule. This observation suggests that the barrier from previously reported measurement of BH3 rotation corresponds to H3B-NH3 correlated rotation.
