Understanding from First-Principles Why LiNH₂BH₃·NH₃BH₃ Shows Improved Dehydrogenation over LiNH₂BH₃ and NH₃BH₃

Lithium amidoborane−ammonia borane (LiNH 2 BH 3 ·NH 3 BH 3, LiAB·AB for short) was synthesized recently. Compared with lithium amidoborane (LiNH 2 BH 3, LiAB for short) and ammonia borane (NH 3 BH 3, AB for short), this new ammonia borane derivative has better dehydrogenation kinetics and releases 14.8 wt % hydrogen with peak temperatures at ca. 80 and 140 °C, respectively. In this report, first-principles calculations were employed to reveal the differences in dehydrogenation properties of AB, LiAB, and LiAB·AB. Furthermore, we attempted to correlate the crystal structure and electronic properties with dehydrogenation performance. The results show that Li + cations play similar roles in LiAB·AB as in LiAB in destabilizing the B−H and N−H bonds, and the mechanism of the first-step dehydrogenation of LiAB·AB is likely via the dissociation and combination of hydridic H δ− (B) from LiAB molecule and protonic H δ+ (N) from the adjacent AB molecule, rather than from the [LiAB] or [AB] layer alone, resulting in the desorption of H 2 at lower temperatures.