Ammonium Aminodiboranate: A Long-Sought Isomer of Diammoniate of Diborane and Ammonia Borane Dimer.

Ammonium aminodiboranate ([NH4 ][BH3 NH2 BH3 ]) is a long-sought isomer of diammoniate of diborane ([NH3 BH2 NH3 ][BH4 ]) and ammonia borane (NH3 BH3 ) dimer. Our results show that [NH4 ][BH3 NH2 BH3 ] is stable in tetrahydrofuran at -18 °C and decomposes rapidly to NH3 BH2 NH2 BH3 and H2 at elevated temperatures. The decomposition pathway is dictated by the dihydrogen bonding between H(δ+) on NH4 (+) and H(δ-) on BH3 , as confirmed by theoretical calculations. This is in contrast to the interconversion between [NH3 BH2 NH3 ][BH4 ] and (NH3 BH3 )2 , although all three have dihydrogen bonds and the same stoichiometry.