Quantum-Chemical Modeling of Molecular Hydrogen Abstraction from the ZnMg(BH4)4⋅4NH3 Bicationic Complex

Successive abstraction of H₂ from the [ZnMg(BH₄)₄·4NH₃] and [Zn₂Mg₂(BH₄)₈·8NH₃] complexes has been modeled within the framework of the cluster approach using the 6-31G* basis set and the hybrid density functional (B3LYP). It has been found that to start the dehydrogenation process, it is necessary to overcome the energy barrier of ~1.25 eV, then the process proceeds with energy release until about 70% of the available H₂ is extracted; for a higher degree of conversion, additional energy input is required. The cleavage of H₂ molecules occurs through several intermediate structures with significant participation of metal cations to form chain fragments based on B–N bonds containing N–H and B–H bonds, which can be detected by IR spectroscopy, when dehydrogenation is stopped.