In-Situ and Real-time Monitoring of Mechanochemical Preparation of Li 2 Mg(NH 2 BH 3 ) 4 and Na 2 Mg(NH 2 BH 3 ) 4 and Their Thermal Dehydrogenation

For the first time, in situ monitoring of uninterrupted mechanochemical synthesis of two bimetallic amidoboranes, M Mg(NH BH ) (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 MNH BH ⋅NH BH adducts as key intermediate phases which further reacted with MgH , giving M Mg(NH BH ) as final products. The intermediates partially take a competitive pathway toward the oligomeric M(BH NH BH NH BH ) phases. The crystal structure of the novel bimetallic amidoborane Li Mg(NH BH ) was solved from high-resolution powder diffraction data and showed an analogous metal coordination to Na Mg(NH BH ) , but a significantly different crystal packing. Li Mg(NH BH ) thermally dehydrogenates releasing highly pure H in the amount of 7 wt.%, and at a lower temperature then its sodium analogue, making it significantly more viable for practical applications.