Homopolar Dihydrogen Bonding in Alkali-Metal Amidoboranes and Its Implications for Hydrogen Storage

The solid-state structures of LiNH2BH3 and NaNH2BH3 have been shown recently to exhibit intricate Mδ+···δ−H–B and N–Hδ+···δ−H–B interactions. However, closer inspection of these structures reveals additional homopolar H···H interactions, viz., B–Hδ−···δ−H–B and N–Hδ+···δ+H–N, which contribute to the relative stability of the extended structures of these crystalline materials. In addition, an NMR study of the isotopomer LiND2BH3 shows that a significant quantity of H2 is desorbed thermally along with HD, which can only arise from hydride–hydride interactions, either directly from B–Hδ−···δ−H–B moieties or indirectly through the participation of Li–H intermediates.