Reorientational Dynamics in Y(BH)·NH ( = 0, 3, and 7): The Impact of NH on BH Dynamics.

The reorientational dynamics of Y(BH)·NH ( = 0, 3, and 7) was studied using quasielastic neutron scattering (QENS) and neutron spin echo (NSE). The results showed that changing the number of NH ligands drastically alters the reorientational mobility of the BH anion. From the QENS experiments, it was determined that the BH anion performs 2-fold reorientations around the C axis in Y(BH), 3-fold reorientations around the C axis in Y(BH)·3NH, and either 2-fold reorientations around the C axis or 3-fold reorientations around the C axis in Y(BH)·7NH. The relaxation time of the BH anion at 300 K decreases from 2 × 10 s for = 0 to 1 × 10 s for = 3 and to 7 × 10 s for = 7. In addition to the reorientational dynamics of the BH anion, it was shown that the NH ligands exhibit 3-fold reorientations around the C axis in Y(BH)·3NH and Y(BH)·7NH as well as 3-fold quantum mechanical rotational tunneling around the same axis at 5 K. The new insights constitute a significant step toward understanding the relationship between the addition of ligands and the enhanced ionic conductivity observed in systems such as LiBH·NH and Mg(BH)·CHNH.