In‐Situ and Real‐time Monitoring of Mechanochemical Preparation of Li2Mg(NH2BH3)4 and Na2Mg(NH2BH3)4 and Their Thermal Dehydrogenation

For the first time, in situ monitoring of uninterrupted mechanochemical synthesis of two bimetallic amidoboranes, M2Mg(NH2BH3)4 (M=Li, Na), by means of Raman spectroscopy, has been applied. This approach allowed real‐time observation of key intermediate phases, and a straightforward follow‐up of the reaction course. Detailed analysis of time‐dependent spectra revealed a two‐step mechanism through MNH2BH3⋅NH3BH3 adducts as key intermediate phases which further reacted with MgH2, giving M2Mg(NH2BH3)4 as final products. The intermediates partially take a competitive pathway toward the oligomeric M(BH3NH2BH2NH2BH3) phases. The crystal structure of the novel bimetallic amidoborane Li2Mg(NH2BH3)4 was solved from high‐resolution powder diffraction data and showed an analogous metal coordination to Na2Mg(NH2BH3)4, but a significantly different crystal packing. Li2Mg(NH2BH3)4 thermally dehydrogenates releasing highly pure H2 in the amount of 7 wt.%, and at a lower temperature then its sodium analogue, making it significantly more viable for practical applications.