Single-Electron Transfer Stabilizes Metastable Alane in a Bipyridine-Functionalized MOF Nanopore

Nanoconfinement of metastable hydrides such as alane (AlH₃) in functionalized porous frameworks represents a promising yet largely untapped strategy for high-capacity energy storage. Despite its potential, the underlying mechanisms responsible for the thermodynamic stabilization of metastable hydrides are poorly understood. Here, concepts from solution Lewis acid-base chemistry were applied to a crystalline metal-organic framework (MOF) to stabilize AlH₃. The long-range order and synthetically versatile pore chemistry enabled us to reveal the intimate details of the hydride-host interactions. Powder X-ray diffraction (PXRD) of AlH₃-infiltrated UiO-67bpy (Zr₆O₄(OH)₄(bpydc)₆; bpydc^2- = 2,2'-bipyridine-5,5'-dicarboxylate) confirms that the framework maintains its crystallinity up to 250 °C and is stable under 70 MPa H₂ pressure. We find that thermodynamic stabilization arises from coupled single-electron and hydrogen-atom transfer from AlH₃ to bipyridine-containing linkers. Electron paramagnetic resonance detects a bipyridyl radical with an anisotropic <i>g</i>-tensor (<i>g</i> values of 2.00132, 2.00215, and 2.00275), consistent with Bader charge analysis predicting 0.82 e^- transferred from the hydride to the MOF. These findings establish critical structure-property relationships underpinning AlH₃ stabilization and suggest general strategies for tuning the thermodynamics and kinetics of metastable materials.