DFT investigation on the decomposition of dihydrogen-bonded methylamine-borane octamer

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 H-2. Significant positive charges on protonic H delta+ (N) (similar to 0.45 a.u.) leads to its higher chemical shift (similar to 5.0 ppm), and the negative charges on hydridic H delta- (B) (similar to-0.10 a.u.) expresses strong shielding effect and provides lower chemical shift (similar to 1.8 ppm). The interaction of H delta+center dot center dot center dot H delta- is characterized by their contribution to the stabilization energy (several kcal/mol) and the spin-spin coupling constants (-0.58 similar to 0.40 Hz). The dehydrogenation process is exothermic and the enthalpy increases along with the H-2 release. High temperature and low pressure favor the thermal decomposition of MAB8 and the release of generated H-2. (C) 2018 Elsevier B.V. All rights reserved.