Dihydrogen Elimination from Hydrated Magnesium Borohydride: Quantum-Chemical Modeling

The successive elimination of H 2 from Mg(BH 4 ) 2 · n H 2 O ( n = 1, 4, 6), (Mg(BH 4 ) 2 ) 2 · 8H 2 O, and (Mg(BH 4 ) 2 ) 4 · 4H 2 O complexes has been modeled in the framework of the cluster approach with the use of the 6-31G* basis set and hybrid density functional (B3LYP). It has been shown that the structures in which the proton-donating water molecule is located between two metal cations have the lowest potential barriers. The barrier to elimination of the first H 2 molecule is low, but it increases as OH groups are substituted for the H atoms in the BH 4 − anion. The elimination of H 2 occurs with a considerable energy release.