Nuclear magnetic resonance study of hydrogen dynamics in Y(BH4)3

In order to study the reorientational motion of BH4 groups in the low-temperature (α) phase of Y(BH4)3, we have performed 1H and 11B nuclear magnetic resonance (NMR) measurements of the spectra and spin–lattice relaxation rates in this compound over the temperature range 6–400 K. It is found that the thermally activated reorientational motion in α-Y(BH4)3 is characterized by a coexistence of at least two jump processes with strongly differing activation energies. Taking into account the nearly linear coordination of each BH4 group in α-Y(BH4)3 by two Y atoms, these jump processes can be attributed to reorientations around inequivalent axes. The slower jump process is characterized by the activation energy of 337 ± 8 meV, and the faster process can be described in terms of a broad distribution of activation energies centered on 200 ± 10 meV.

► Jump rates for BH4 reorientations in α-Y(BH4)3 have been determined from 1H and 11B NMR measurements.
► Coexistence of two jump processes with strongly differing activation energies.
► Nearly linear coordination of BH4 groups by two Y atoms can lead to this coexistence.