Coordination-Controlled Synthesis of Aluminum Nanoparticles: Insights from AlH₃·(NMP)_x Complexes

The controlled chemical synthesis of aluminum nanocrystals (Al NCs) is crucial for their applications in plasmonics, photocatalysis, and optoelectronics. However, there is still a lack of correlation between the precursor of Al hydride N-methylpyrrolidine (AlH₃·(NMP)_x) and the Al NC synthesis outcomes. Here, we report the synthesis of AlH₃·(NMP)_x complexes with different coordination numbers (x from 1.0 to 2.0) and their characterization as precursors regulating the morphology of Al NCs. We isolated AlH₃·(NMP)_1.0 single crystals from AlH₃·(NMP)_x mixtures and successfully elucidated the structure of AlH₃·(NMP)_1.0 through single-crystal X-ray diffraction. Importantly, AlH₃·(NMP)_1.0 exhibited the fastest decomposition rate, yielding highly monodisperse Al NCs with well-defined shapes and the narrowest size distribution, while higher coordination numbers led to increased dispersity in size and irregular morphologies. Additionally, we observed distinct multipole plasmonic resonances in Al NCs synthesized from lower coordination number precursors, highlighting their superior optical properties. This work establishes a direct correlation between precursor coordination chemistry and Al NC synthesis outcomes, providing a foundation for optimizing nanoparticle production for advanced material applications.