Ammonium aminodiboranate: A long-sought isomer of diammoniate of diborane and ammonia borane dimer

Ammonium aminodiboranate ([NH4][BH3NH2BH3]) is a long-sought isomer of diammoniate of diborane ([NH3BH2NH3][BH4]) and ammonia borane (NH3BH3) dimer. Our results show that [NH4][BH3NH2BH3] is stable in tetrahydrofuran at -18°C and decomposes rapidly to NH3BH2NH2BH3 and H2 at elevated temperatures. The decomposition pathway is dictated by the dihydrogen bonding between Hδ+ on NH4 + and Hδ- on BH3, as confirmed by theoretical calculations. This is in contrast to the interconversion between [NH3BH2NH3][BH4] and (NH3BH3)2, although all three have dihydrogen bonds and the same stoichiometry.