Quantum-Chemical Simulation of Molecular Hydrogen Abstraction from Magnesium Borohydride Triammoniate

Successive abstraction of H-2 from the Mg(BH4)(2)center dot nNH(3) (n = 2, 3, 4) and (Mg(BH4)(2) center dot 3NH(3))(2) complexes has been modeled within the framework of the cluster approach with the use of the 6-31G* basis set and hybrid density functional (B3LYP). It has been demonstrated that the successive dehydrogenation of the Mg(BH4)(2)center dot nNH(3) monomers leads to a significant increase in potential barriers already at the third step, while in the (Mg(BH4)(2)center dot 3NH(3))(2) dimer such an increase is not observed almost until the complete extraction of hydrogen. The initial dehydrogenation stage (up to about 70-75%) should be exothermic, while additional energy input is required for a higher degree of conversion.