Al−N−H compounds derived from ammonia alane: Solid-state NMR study of dehydrogenation-induced polymeric phases

Ammonia alane-derived Al−N−H materials remain largely unexplored due to challenges in their synthesis and characterization. Highly reactive precursors and the low thermal stability of the resulting compounds hinder their investigation prior to dehydrogenation. Here, advanced multinuclear solid-state nuclear magnetic resonance spectroscopy is employed to provide a site-resolved description of the structure and thermal evolution of polymeric Al−N−H materials. The as-prepared material consists of heterogeneous, hydrogen-rich and distorted Al−N−H environments rather than a well-defined single phase. Between −20 and 80 °C, a major structural transformation occurs, marked by the disappearance of the most hydrogen-rich aluminum sites and the formation of increasingly condensed and disordered network motifs, indicating the onset of dehydrogenation and polymerization. Further heating leads to progressively more dehydrogenated structures, with a minor fraction converting into amorphous AlN at 600 °C. These results establish a coherent site-resolved dehydrogenation pathway.