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

Linköpings universitet

Stockholms universitet

Jakob B. Grinderslev

Aarhus Universitet

Mikael Andersson

Chalmers, Kemi och kemiteknik, Energi och material, Oorganisk miljökemi 2

Jeff Armstrong

STFC Rutherford Appleton Laboratory

Maths Karlsson

Chalmers, Kemi och kemiteknik, Energi och material, Oorganisk miljökemi 2

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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