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 M delta+center dot center dot center dot H delta--B and N-H delta+center dot center dot center dot H delta--B interactions. However, closer inspection of these structures reveals additional homopolar H center dot center dot center dot H interactions, viz., B-H delta-center dot center dot center dot H delta--B and N-H delta+center dot center dot center dot H delta--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 H-2 is desorbed thermally along with HD, which can only arise from hydride hydride interactions, either directly from B-H delta-center dot center dot center dot H delta--B moieties or indirectly through the participation of Li-H intermediates.