γ-alumina $(\gamma -{\mathrm{Al}}_2{\mathrm{O}}_3)$ derived from boehmite has historically been described as having a cubic spinel structure with $\mathrm{Fd}3\mathrm{}¯m$ symmetry, despite reports of tetragonal distortion in the structure. Based on neutron diffraction, transmission electron microscopy, and magic angle spinning NMR data, we propose a tetragonal model for the structure of boehmite-derived $\gamma -{\mathrm{Al}}_2{\mathrm{O}}_3$ with ${I4\mathrm{}}_1/amd$ space group symmetry, a maximal subgroup of $\mathrm{Fd}3\mathrm{}¯m.\mathrm{}$ It is also demonstrated that an accurate average structural model cannot be achieved if the cations are restricted to spinel positions.

Hydrogen has a very diverse chemistry and reacts with most other elements to form compounds, which have fascinating structures, compositions and properties. Complex metal hydrides are a rapidly expanding class of materials, approaching multi-functionality, in particular within the energy storage field. This review illustrates that complex metal hydrides may store hydrogen in the solid state, act as novel battery materials, both as electrolytes and electrode materials, or store solar heat in a more efficient manner as compared to traditional heat storage materials. Furthermore, it is highlighted how complex metal hydrides may act in an integrated setup with a fuel cell. This review focuses on the unique properties of light element complex metal hydrides mainly based on boron, nitrogen and aluminum, e.g., metal borohydrides and metal alanates. Our hope is that this review can provide new inspiration to solve the great challenge of our time: efficient conversion and large-scale storage of renewable energy.