Self-Driven Seeding, Acid Stalling, and Solidifying: Time-Resolved Mapping of Nonclassical Pathways in Metal-Organic...

Metal-organic gels (MOGs), an innovative subset of metal-organic frameworks (MOFs), feature hierarchically porous architecture and self-shaping monolithic morphologies, demonstrating them significantly potential for advanced applications in catalysis, gas storage, and energy conversion. Despite their functional versatility, the synthesis of MOGs remains empirical, as the actual formation mechanisms are largely unexplored. Here, a multiscale characterization strategy integrating time-resolved in-situ small-angle X-ray scattering (SAXS), Zr K-edge X-ray absorption fine structure (XAFS), and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) analyses are systematically employed to elucidate the formation mechanism of UiO-66(Zr) gel. The synthetic techniques provide a multidimensional perspective: (1) At the mesoscale, self-induced heterogeneous nucleation triggers a rapid evolution from linear prenucleation clusters to a 3D fractal network governed by autocatalytic hydrolysis of Zr precursors. (2) At the atomic level, the reorganization of Zr-oxo clusters and the substitution of coordinating H₂O molecules and chloride ions with terephthalate ligands over prolonged timescales are uncovered. Crucially, in-situ generated acid-mediated coordination suppression emerges as a pivotal factor preventing the conversion of MOGs into their crystalline MOF counterparts. These findings highlight a nonclassical evolution pathways distinct from classical MOF crystallization, thereby providing a mechanistic foundation for tailoring MOGs with programmable morphological and structural attributes.