Hydrogen Release from Ammonia Alane-Based Materials: Formation of Cyclotrialazane and Alazine

In previous papers (Nguyen et al.<i> J. Phys. Chem. C</i> <b>2008</b>, <i>112</i>, 5662–5667 and <i>J. Phys. Chem. C</i> <b>2009</b>, <i>113</i>, 18914–18926), formation of H₂ molecules from ammonia alane monomer (AAl) and dimers (AAl)₂ was shown to be facilitated by the addition of one or more alane or ammonia molecules that can play the role of efficient bifunctional catalyst. Ammonia alane emerges as a good starting compound for building up materials for chemical hydrogen storage (CHS). Further exploration of the products based on the H₂ release from ammonia alane were carried out using coupled-cluster theory computations together with the aug-cc-pVTZ basis set (based on MP2/aug-cc-pVDZ optimized geometries). Our ab initio MO calculations for the first time led to the identification of cyclotrialazane [(H₂AlNH₂)₃], alazine [(HAlNH)₃], and its oligomer [H₂Al­(HNAlH)₂NH₂] that are produced along the multistep dehydrogenation processes from the reactions of ammonia alane and AlH₃NH₂AlH₂NH₃. The formation of alazine (homologue of borazine) as the final product in our H₂ elimination reactions is an important feature because of its long-debated existence. The present reaction path analyses show that the formation of this compound is an important phenomenon for explaining the entire dehydrogenation process