Non-Covalent Interactions in Hydrogen Storage Materials LiN(CH3)2BH3 and KN(CH3)2BH3

In the present work, an in-depth, qualitative and quantitative description of non-covalent interactions in the hydrogen storage materials LiN(CH3)2BH3 and KN(CH3)2BH3 was performed by means of the charge and energy decomposition method (ETS-NOCV) as well as the Interacting Quantum Atoms (IQA) approach. It was determined that both crystals are stabilized by electrostatically dominated intra- and intermolecular M∙∙∙H–B interactions (M = Li, K). For LiN(CH3)2BH3 the intramolecular charge transfer appeared (B–H→Li) to be more pronounced compared with the corresponding intermolecular contribution. We clarified for the first time, based on the ETS-NOCV and IQA methods, that homopolar BH∙∙∙HB interactions in LiN(CH3)2BH3 can be considered as destabilizing (due to the dominance of repulsion caused by negatively charged borane units), despite the fact that some charge delocalization within BH∙∙∙HB contacts is enforced (which explains H∙∙∙H bond critical points found from the QTAIM method). Interestingly, quite similar (to BH∙∙∙HB) intermolecular homopolar dihydrogen bonds CH∙∙∙HC appared to significantly stabilize both crystals—the ETS-NOCV scheme allowed us to conclude that CH∙∙∙HC interactions are dispersion dominated, however, the electrostatic and σ/σ*(C–H) charge transfer contributions are also important. These interactions appeared to be more pronounced in KN(CH3)2BH3 compared with LiN(CH3)2BH3