Aluminum methylamidoborane complexes: mechanochemical synthesis, structure, stability, and reactive hydride composites

Abstract

Methyl-substituted Al-based amidoborane Na[Al(CH₃NHBH₃)₄] was designed and synthesized as a potential candidate for hydrogen-storage purposes. Its structure as well as that of Na[AlH(CH₃NHBH₃)₃], forming as an intermediate in mechanochemical synthesis, were determined by high-resolution powder X-ray diffraction. The synthesis of Na[Al(CH₃NHBH₃)₄] required the much cheaper CH₃NH₂BH₃ and could be performed under less harsh conditions compared to the unsubstituted analogue. Na[AlH(CH₃NHBH₃)₃] is the first example of an Al-based compound containing both hydride and amidoborane species. Despite Na[Al(CH₃NHBH₃)₄] not being suitable for hydrogen storage on its own, reactive hydride composites (RHCs) made of Na[Al(CH₃NHBH₃)₄] and 12 eq. of NaH, or 6 eq. of NaNH₂, showed the release of pure hydrogen at moderate temperatures, making this and similar systems interesting candidates for hydrogen storage.