Decoding Flat-Al 13 Structural Evolution in the Sol–Gel Process toward Aluminum Hydroxide Formation

Understanding the molecular mechanisms underlying the sol–gel transition of aluminum-based systems remains a long-standing challenge due to complex species transformations and aggregation dynamics. In this study, we uncover the critical role of the flat-Al 13 cluster, which is formed via pH-driven isomerization of ε-Al 13, in directing the structural evolution over the sol–gel transition and in guiding low-temperature crystallization. Comprehensive spectral characterizations reveal a two-stage transformation, that is, the conversion of the ε-Al 13 cluster to the flat-Al 13 cluster, followed by their oriented aggregation, ultimately forming a gel system characterized by global disorder coexisting with local ordering. Notably, gels enriched with flat-Al 13 exhibit significantly enhanced crystallinity and transform into layered aluminum hydroxide at temperatures lower than those of conventional systems. This energy-efficient pathway stems from the structural templating effect of flat-Al 13, which enables topological condensation to bypass the high-energy barrier of classical nucleation. These findings elucidate the structure-directing role of flat-Al 13 in bridging molecular-scale transformations to macroscopic material properties, establishing a mechanistic framework for the design of hierarchically structured aluminum-based materials through controlled sol–gel dynamics.