Role of NH₃ in the Dehydrogenation of Calcium Amidoborane Ammoniate and Magnesium Amidoborane Ammoniate: A First-Principles Study

First-principles calculations show that [NH₃] molecules play crucial roles as both activator for the break-up of B–H bond and supplier of protic H for the establishment of dihydrogen bonding, which could facilitate the dehydrogenation of Ca­(NH₂BH₃)₂·2NH₃ or Mg­(NH₂BH₃)₂·NH₃ occurring at lower temperatures compared to those of Ca­(NH₂BH₃)₂ and Mg­(NH₂BH₃)₂. Moreover, the calculations of Helmholtz Free energy and [NH₃] molecule removal energy evidence that coordination between [NH₃] and Mg cation is stronger than that between [NH₃] and Ca cation; therefore, Mg­(NH₂BH₃)₂·NH₃ will undergo directly dehydrogenation rather than deammoniation at lower temperatures.