Abstract
Abstract As potential hydrogen storage materials, ammonia-borane and its derivatives have attracted much attention. The thermal decomposition of dihydrogen-bonded methylamine-borane octamer (MAB8) was explored employing the hybrid B3LYP functional. The decomposition process is composed by physidesorption and chemidesorption. Six-membered ring, composed by B and N alternately, is generated with the stepwise dehydrogenation of six equivalent of H2. Significant positive charges on protonic Hδ+ (N) (∼0.45 a.u.) leads to its higher chemical shift (∼5.0 ppm), and the negative charges on hydridic Hδ− (B) (∼−0.10 a.u.) expresses strong shielding effect and provides lower chemical shift (∼1.8 ppm). The interaction of Hδ+…Hδ− is characterized by their contribution to the stabilization energy (several kcal/mol) and the spin-spin coupling constants (−0.58 ∼ 0.40 Hz). The dehydrogenation process is exothermic and the enthalpy increases along with the H2 release. High temperature and low pressure favor the thermal decomposition of MAB8 and the release of generated H2.
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