Materials for hydrogen storage: structure and dynamics of borane ammonia complex

Abstract

The activation energies for rotations in low-temperature orthorhombic ammonia borane were analyzed and characterized in terms of electronic structure theory. The perdeuterated (11)B-enriched ammonia borane, (11)BD(3)ND(3), 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 NH(3) rotation, E(a) = 12.7 kJ mol(-1), largely depends on the molecular conformational torsion in the solid-state geometry. The barrier for independent BH(3) rotation, E(a) = 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 E(a) = 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 BH(3) group involves strongly correlated rotation of the NH(3) end of the molecule. This observation suggests that the barrier from previously reported measurement of BH(3) rotation corresponds to H(3)B-NH(3) correlated rotation.

Theoretical study on the mechanism for NH3BH3reduction of ketones and imines

“…In the work of LiNH 2 BH 3 hydrogenation [7] we have validated the reliability of different DFT methods for the LiNH 2 BH 3 decompose step by comparing the results with CCSD(T) calculations, and we find that both B3LYP and M06-2x produce reliable results. Here we have compared B3LYP, BLYP, M06-2x, MP2 methods with CCSD(T) for the whole reaction pathways of stepwise and DHT mechanisms.…”

“…ABs have hydridic H(B) and protic H(N) co-existing in the molecule [7,8], and the dehydrogenation of AB can be carried out through thermal [9][10][11][12][13][14][15], acid-catalysed [16] or metal-catalysed [17][18][19][20][21][22][23][24] methods. In addition to being taken as potential hydrogen storage materials, recently it was found that AB is also a good hydrogenation reagent which is able to hydrogenate polar unsaturated bond under mild conditions [25][26][27][28].…”

Hydrogen-mediated affinity of ions found in compressed potassium amidoborane, K[NH2BH3]

“…3 The dihydrogen bonds, i.e. protonic-hydridic, are known to have strength and directionality comparable with those found in conventional hydrogen-bonded systems.…”

Hydrogen Storage Properties of the Mg(NH<SUB>3</SUB>)<SUB>6</SUB>Cl<SUB>2</SUB>-LiH Combined System

“…1) In contrast to the compressed hydrogen and the liquefaction hydrogen, hydrogen storage in the solid state is the most promising alternative. [2][3][4][5] In the past decades, the complex hydrides consisting of light elements, e.g., alanates, [6][7][8][9][10] amides, [11][12][13][14][15] borohydrides [16][17][18][19][20] and ammonia borane (AB), [21][22][23] have been attracting extensive attention as the potential hydrogen storage materials due to their high gravimetric and volumetric hydrogen storage densities. In particular, significant efforts have been made in recent years with metal amide-hydride combined systems since Chen et al reported that lithium nitride, Li 3 N could absorb/desorb reversibly 11.4 mass% of hydrogen in 2002.…”