Role of charge transfer in dehydrogenation of M(NH<inf>2</inf>BH<inf>3</inf>)<inf>2</inf> (M = Mg, Sr)

Abstract

The dehydrogenation mechanism of M(NH2BH3)2(M = Mg, Sr) was studied by a first-principles method. The results show that the gas-phase energy barrier for the first H2release is 2.15 eV via a N-H···B transition state and 1.35 eV via a Mg···H transition state for the second H2release in Mg(NH2BH3)2. The barrier is 1.21 and 2.27 eV via a N-H···B transition state for the first and second H2release in Sr(NH2BH3)2, respectively. For the dimer, both compounds release the first H2via oligomerization and the corresponding barriers are 1.01 eV for Mg(NH2BH3)2and 1.25 eV for Sr(NH2BH3)2. Further analysis of the charges of the transition states and the initial states leads to a general conclusion: for the same final state, the smaller the charge transfer, the lower the barrier. For Mg(NH2BH3)2, the reaction pathway is determined by the HOMO and LUMO orbitals of the initial state. © 2014 American Chemical Society.