Theoretical study of the hydrogen release mechanism from a lithium derivative of ammonia borane, LiNH2BH3–NH3BH3

Ammonia borane and lithium amidoborane proved to have potential as efficient hydrogen storage materials. Although a combination of both compounds, LiNH2BH3–NH3BH3 has been shown to have even better hydrogen release characteristics, the inherent process was not clear. We determined the reaction mechanism of H2 release from LiNH2BH3–NH3BH3 using computational quantum chemistry methods (MP2 and CCSD(T) methods and aug-cc-pVnZ basis sets). The energy barrier for H2 release becomes lower than in pure LiNH2BH3 or NH3BH3 in agreement with experiment. Relevant transition structures are analyzed in detail and the initial formation of a cyclic adduct is likely responsible for the strong reduction of energy barriers.