A New Ammine Dual‐Cation (Li, Mg) Borohydride: Synthesis, Structure, and Dehydrogenation Enhancement

A new ammine dual‐cation borohydride, LiMg(BH 4 ) 3 (NH 3 ) 2 , has been successfully synthesized simply by ball‐milling of Mg(BH 4 ) 2 and LiBH 4 ⋅ NH 3 . Structure analysis of the synthesized LiMg(BH 4 ) 3 (NH 3 ) 2 revealed that it crystallized in the space group P 6 3 (no. 173) with lattice parameters of a = b =8.0002(1) Å, c =8.4276(1) Å, α = β =90°, and γ =120° at 50 °C. A three‐dimensional architecture is built up through corner‐connecting BH 4 units. Strong NH⋅⋅⋅HB dihydrogen bonds exist between the NH 3 and BH 4 units, enabling LiMg(BH 4 ) 3 (NH 3 ) 2 to undergo dehydrogenation at a much lower temperature. Dehydrogenation studies have revealed that the LiMg(BH 4 ) 3 (NH 3 ) 2 /LiBH 4 composite is able to release over 8 wt % hydrogen below 200 °C, which is comparable to that released by Mg(BH 4 ) 3 (NH 3 ) 2 . More importantly, it was found that release of the byproduct NH 3 in this system can be completely suppressed by adjusting the ratio of Mg(BH 4 ) 2 and LiBH 4 ⋅ NH 3 . This chemical control route highlights a potential method for modifying the dehydrogenation properties of other ammine borohydride systems.