Synthesis and Thermal Decomposition Behaviors of Magnesium Borohydride Ammoniates with Controllable Composition as Hydrogen Storage Materials

An ammonia‐redistribution strategy for synthesizing metal borohydride ammoniates with controllable coordination number of NH 3 was proposed, and a series of magnesium borohydride ammoniates were easily synthesized by a mechanochemical reaction between Mg(BH 4 ) 2 and its hexaammoniate. A strong dependence of the dehydrogenation temperature and purity of the released hydrogen upon heating on the coordination number of NH 3 was elaborated for Mg(BH 4 ) 2 ⋅ x  NH 3 owing to the change in the molar ratio of H δ+ and H δ− , the charge distribution on H δ+ and H δ− , and the strength of the coordinate bond N:→Mg 2+ . The monoammoniate of magnesium borohydride (Mg(BH 4 ) 2 ⋅NH 3 ) was obtained for the first time. It can release 6.5 % pure hydrogen within 50 minutes at 180 °C.