Dihydrogen Elimination from Hydrated Magnesium Borohydride: Quantum-Chemical Modeling

Abstract

The successive elimination of H₂ from Mg(BH₄)₂ · nH₂O (n = 1, 4, 6), (Mg(BH₄)₂)₂ · 8H₂O, and (Mg(BH₄)₂)₄ · 4H₂O 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 H₂ molecule is low, but it increases as OH groups are substituted for the H atoms in the BH₄⁻ anion. The elimination of H₂ occurs with a considerable energy release.