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 NH3 was proposed, and a series of magnesium borohydride ammoniates were easily synthesized by a mechanochemical reaction between Mg(BH4)2 and its hexaammoniate. A strong dependence of the dehydrogenation temperature and purity of the released hydrogen upon heating on the coordination number of NH3 was elaborated for Mg(BH4)2 center dot x?NH3 owing to the change in the molar ratio of Hd+ and Hd-, the charge distribution on Hd+ and Hd-, and the strength of the coordinate bond N:-> Mg2+. The monoammoniate of magnesium borohydride (Mg(BH4)2 center dot NH3) was obtained for the first time. It can release 6.5?% pure hydrogen within 50 minutes at 180 degrees C.