RESUMEN
Magnesium amidoborane monoammoniate (Mg(NH(2)BH(3))(2) x NH(3)) which crystallizes in a monoclinic structure (space group P2(1)/a) has been synthesized by reacting MgNH with NH(3)BH(3). Dihydrogen bonds are established between coordinated NH(3) and BH(3) of [NH(2)BH(3)](-) in the structure, promoting stoichiometric conversion of NH(3) to H(2).
RESUMEN
High pressure Raman spectroscopy of NH(3)BH(3)-H(2) mixtures up to 60 GPa reveals unusual pressure-induced complexation and intermolecular interactions. Stretching modes of H(2) in the complex arise at 6.7 and 10 GPa, increasing in frequency with pressure of up to 60 GPa with different pressure coefficients, and at approximately 40 GPa, the lower frequency mode approaches vibron frequency of bulk H(2). Pressure-induced transformations in pure NH(3)BH(3) studied up to 60 GPa reveal a disorder-order transition at 1 GPa (phase II) and further transitions at 5 (phase III) and 10 GPa (phase IV). The spectra of both pure NH(3)BH(3) and the NH(3)BH(3)-H(2) complex provide evidence for strengthened of the N-H(delta+)...H(delta-)-B dihydrogen bonding linkages up to 50 GPa, beyond which they weaken. The dihydrogen bonding breaks down due to interactions with H(2) between 15 and 20 GPa in the NH(3)BH(3)-H(2) complex. The behavior of the nu(NH(3)) modes in the NH(3)BH(3)-H(2) complex indicates a dominant role of the NH(3) functional group in the observed interactions.
RESUMEN
We present the results of a detailed operando XAFS and density functional theory (DFT)-based ab initio molecular dynamics (AIMD) investigation of a proposed mechanism of the dehydrogenation of dimethylaminoborane (DMAB) by a homogeneous Rh(4) cluster catalyst. Our AIMD simulations reveal that previously proposed Rh structures, based on XAFS measurements, are highly fluxional, exhibiting both metal cluster and ligand isomerizations and dissociation that can only be accounted for by examining a finite temperature ensemble. It is found that a fluxional species Rh(4)(H(2)BNMe(2))(8)(2+) is fully compatible with operando XAFS measurements, suggesting that this species may be the observed catalyst resting state. On the basis of this assignment, we propose a mechanism for catalytic DMAB dehydrogenation that exhibits an energy barrier of approximately 28 kcal/mol.
RESUMEN
The two-step reaction between LiH and NH(3)BH(3) in THF leads to the production of more than 14 wt% of hydrogen at 40 degrees C.
RESUMEN
The safe and efficient storage of hydrogen is widely recognized as one of the key technological challenges in the transition towards a hydrogen-based energy economy. Whereas hydrogen for transportation applications is currently stored using cryogenics or high pressure, there is substantial research and development activity in the use of novel condensed-phase hydride materials. However, the multiple-target criteria accepted as necessary for the successful implementation of such stores have not yet been met by any single material. Ammonia borane, NH3BH3, is one of a number of condensed-phase compounds that have received significant attention because of its reported release of approximately 12 wt% hydrogen at moderate temperatures (approximately 150 degrees C). However, the hydrogen purity suffers from the release of trace quantities of borazine. Here, we report that the related alkali-metal amidoboranes, LiNH2BH3 and NaNH2BH3, release approximately 10.9 wt% and approximately 7.5 wt% hydrogen, respectively, at significantly lower temperatures (approximately 90 degrees C) with no borazine emission. The low-temperature release of a large amount of hydrogen is significant and provides the potential to fulfil many of the principal criteria required for an on-board hydrogen store.
