For the first time, in-situ monitoring of uninterrupted mechanochemical synthesis of two bimetallic amidoboranes, M 2 Mg(NH 2 BH 3 ) 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 MNH 2 BH 3 · NH 3 BH 3 adducts as key intermediate phases which further reacted with MgH 2 , giving M 2 Mg(NH 2 BH 3 ) 4 as final products. The intermediates partially take a competitive pathway toward the oligomeric M(BH 3 NH 2 BH 2 NH 2 BH 3 ) phases. The crystal structure of the novel bimetallic amidoborane Li 2 Mg(NH 2 BH 3 ) 4 was solved from high-resolution powder diffraction data and showed an analogous metal coordination as in Na 2 Mg(NH 2 BH 3 ) 4 , but a significantly different crystal packing. Li 2 Mg(NH 2 BH 3 ) 4 thermally dehydrogenates releasing highly pure H 2 in the amount of 7 wt% and at a lower temperature then its sodium analogue making it significantly more viable for practical applications.
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