Monoammoniate of Calcium Amidoborane: Synthesis, Structure, and Hydrogen-Storage Properties

The monoammoniate of calcium amidoborane, Ca­(NH₂BH₃)₂·NH₃, was synthesized by ball milling an equimolar mixture of CaNH and AB. Its crystal structure has been determined and was found to contain a dihydrogen-bonded network. Thermal decomposition under an open-system begins with the evolution of about 1 equivalent/formula unit (equiv.) of NH₃ at temperatures <100 °C followed by the decomposition of Ca­(NH₂BH₃)₂ to release hydrogen. In a closed-system thermal decomposition process, hydrogen is liberated in two stages, at about 70 and 180 °C, with the first stage corresponding to an exothermic process. It has been found that the presence of the coordinated NH₃ has induced the dehydrogenation to occur at low temperature. At the end of the dehydrogenation, about 6 equiv. (∼ 10.2 wt %) of hydrogen can be released, giving rise to the formation of CaB₂N₃H