Thermolysis and solid state NMR studies of NaB3H8, NH3B3H7, and NH4B3H8

Abstract

In an effort to broaden the search for high-capacity hydrogen storage materials, three triborane compounds, NaB₃H₈, NH₃B₃H₇, and NH₄B₃H₈, were studied. In addition to hydrogen, thermal decomposition also releases volatile boranes, and the relative amounts and species depend on the cations (Na⁺, NH₄⁺) and the Lewis base (NH₃). Static-sample hydrogen NMR is used to probe molecular motion in the three solids. In each case, the line width decreases from low temperatures to room temperature in accordance with a model of isotropic or nearly isotropic reorientations. Such motions also explain a deep minimum in the relaxation time T₁. Translational diffusion never appears to be rapid on the 10⁻⁵ s time scale of NMR.