Analysis of Dihydrogen Bonding in Ammonium Borohydride
Artikel i vetenskaplig tidskrift, 2019

The structural and vibrational properties of ammonium borohydride, NH4BH4, have been examined by first-principles density functional theory (DFT) calculations and inelastic neutron scattering (INS). The H disordered crystal structure of NH4BH4 is composed of the tetrahedral complex ions NH4+ and BH4-, which are arranged as in the fcc NaCl structure and linked by intermolecular dihydrogen bonding. Upon cooling, the INS spectra revealed a structural transition between 45 and 40 K. The reversible transition occurs upon heating between 46 and 49 K. In the low-temperature form reorientational dynamics are frozen. The libration modes for BH4- and NH4+ are near 300 and 200 cm(-1), respectively. Upon entering the fcc high-temperature form, NH4+ ions attain fast reorientational dynamics, as indicated in the disappearance of the NH4+ libration band, whereas BH4- ions become significantly mobile only at temperatures above 100 K. The vibrational behavior of BH4- ions in NH4BH4 compares well to the heavier alkali metal borohydrides, NaBH4-CsBH4. DFT calculations revealed a nondirectional nature of the dihydrogen bonding in NH4BH4 with only weak tendency for long-range order. Different rotational configurations of complex ions appear quasi-degenerate, which is reminiscent of glasses.


Stanislav Filippov

Stockholms universitet

Linköpings universitet

Jakob B. Grinderslev

Aarhus Universitet

Mikael Andersson

Chalmers, Kemi och kemiteknik, Energi och material

Jeff Armstrong

STFC Rutherford Appleton Laboratory

Maths Karlsson

Chalmers, Kemi och kemiteknik, Energi och material

Torben R. Jensen

Aarhus Universitet

Johan Klarbring

Linköpings universitet

Sergei I. Simak

Linköpings universitet

Ulrich Haussermann

Stockholms universitet

Journal of Physical Chemistry C

1932-7447 (ISSN) 1932-7455 (eISSN)

Vol. 123 47 28631-28639


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