Comprehensive NMR Study of Magnesium Borohydride

1 H and 11 B NMR measurements were performed to study BH 4 reorientations and diffusion in four samples of Mg(BH 4 ) 2 . These include the low (α) and high (β) temperature bulk solid phases, α-phase material with TiF 3 and ScCl 3 additives, and α-phase material incorporated into a carbon aerogel. All four samples show 1 H T 1 minima within our temperature range from reorientational motion of the BH 4 tetrahedra. The β-phase 1 H T 1 minimum occurs at a lower temperature than that for the α-phase, indicating a lower activation energy for reorientations. The α-phase 1 H spectra display the onset of broadening at low temperatures because of the slowing of reorientations but show no indication of line narrowing at high temperatures from translational diffusion. The β-phase 1 H spectra are similar, but here T 1D measurements were performed to determine the BH 4 hopping rate. Above 150 °C, a significant narrow component does appear in the 1 H spectra of the aerogel sample, indicating substantially increased diffusive motions in this component.