BH<sub>3</sub> under Pressure: Leaving the Molecular Diborane Motif

Yao, Yansun; Hoffmann, Roald

doi:10.1021/ja2092568

Cited by 35 publications

(55 citation statements)

References 64 publications

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“…The purpose of the annealing step is to ensure that the crystalline structure indeed reaches an energy minimum as, occasionally, new structures were found after annealing. 27 Geometry optimization, enthalpies, and phonon band structures were calculated using first-principles electronic structure methods based on the density-functional theory (DFT). Electronic and MD calculations were performed with the Vienna ab initio simulation program (VASP).…”

Section: ■ Methodsmentioning

confidence: 99%

Dihydrogen Bonding in Compressed Ammonia Borane and Its Roles in Structural Stability

et al. 2014

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Theoretical structure prediction calculations have revealed that the conformation of ammonia borane (NH 3 BH 3 ) in the crystalline state can be modified by pressure, changing from the staggered configuration at low pressure to an eclipsed geometry at high pressure. At low pressure, the crystalline structure is stabilized by the charge transfer N H δ+ ··· δ− HB dihydrogen interactions. In the high pressure polymorphs, the NH 3 BH 3 is predicted to form a layered structure. The NH δ+ ··· δ− HB bonding is still predominant within the layer. The stacking of the layers, however, is determined by the occurrence of additional homopolar B H δ− ··· δ− HB interaction unprecedented in NH 3 BH 3 and facilitated by the eclipsed conformation. This bonding is shown to be the result of secondary interactions between BH 3 groups from molecules of adjacent layers. Topological analysis of the charge density and perturbation calculations on the molecule fragments show unambiguously that the BH δ− ··· δ− HB interaction is covalent in nature with the bond strength comparable to a conventional hydrogen bond. ■ INTRODUCTIONHydrogen, the most abundant element in the universe, is a promising candidate to eventually replace petroleum as the fuel of choice. In the context of hydrogen storage research, ammonia borane (NH 3 BH 3 ) has received continuous attention for decades due to its high storage capacity and moderate dehydrogenation temperature. Molecular NH 3 BH 3 is a prototypical electron donor−acceptor complex formed between NH 3 and BH 3 molecules (1) and arranged in a staggered conformation similar to the geometry of the isoelectronic ethane (C 2 H 6 ). In solid state, however, NH 3 BH 3 and C 2 H 6 have very different physical properties. For example, the melting temperature of NH 3 BH 3 is higher than that of C 2 H 6 by 285 K. This suggests a strong intermolecular interaction, often referred to as "dihydrogen bonding" (2), 1−3 to present in NH 3 BH 3 . The dihydrogen bonding originates from the N H δ+ ··· δ− HB charge-transfer interaction which usually occurs when the intermolecular distance d H···H is shorter than the sum of the van der Waals (vdW) radii. A survey of the Cambridge Structural Database (CSD) carried out by Richardson et al. 2 shows that dihydrogen bonding has a preference for a bent B H···HN angle θ and a nearly linear NH···HB angle ψ, arranged such that the NH vector points toward the middle of the BH vector. This geometry suggests that the electron donor of the dihydrogen bond is the BH σ bond, rather than an individual atom. This is an extraordinary illustration of the versatility of the hydrogen bonding; in the past, we have seen π electrons of a multiple bond or aromatic ring, or a transition metal center, act as electron donors. 4,5 Clearly, dihydrogen bonding, to a great extent, determines the crystal structures of NH 3 BH 3 . At ambient conditions, NH 3 BH 3 adopts a dynamical disordered structure (I4mm), which exhibits halos of hydrogen atom occupancy surrounding the N and B atoms. 6,7 Be...

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Section: ■ Methodsmentioning

confidence: 99%

Dihydrogen Bonding in Compressed Ammonia Borane and Its Roles in Structural Stability

et al. 2014

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“…10(d) was estimated as being 125 K. Figure 10: (a) The β-diborane phase that forms above 90 K at atmospheric pressures. Predicted high pressure phases of BH 3 including: (b) one that contains B 3 H 9 trimers, 217 (c) one that consists of linear (BH 3 ) n polymeric chains, 217 and (d) a P bcn phase whose T c was estimated as being 125 K at 360 GPa. 218 Finally, CSP techniques have been employed to predict the most stable structures with the BH and BH 3 stoichiometries up to 300 GPa, 219 220 In Ref.…”

Section: Group 13: Icosagen Hydrides Boronmentioning

confidence: 99%

The Search for Superconductivity in High Pressure Hydrides

Zarifi

Terpstra

et al. 2019

Reference Module in Chemistry, Molecular Sciences and Chemical Engineering

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The computational and experimental exploration of the phase diagrams of binary hydrides under high pressure has uncovered phases with novel stoichiometries and structures, some which are superconducting at quite high temperatures. Herein we review the plethora of studies that have been undertaken in the last decade on the main group and transition metal hydrides, as well as a few of the rare earth hydrides at pressures attainable in diamond anvil cells. The aggregate of data shows that the propensity for superconductivity is dependent upon the species used to "dope" hydrogen, with some of the highest values obtained for elements that belong to the alkaline and rare earth, or the pnictogen and chalcogen families.

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“…GPa, and a polymeric crystal containing one-dimensional chains becomes more stable above 36 GPa [10]. However, another detailed DFT investigation [11] shows that B 2 H 6 becomes unstable in the pressure range of 40-350 GPa and decomposes into B and H 2 .…”

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confidence: 99%