Raman Monitoring of Pressure-Induced Configurational Transition of Iodine Confined within Metal–Organic Frameworks

Abstract

Metal–organic frameworks (MOFs) with porous architectures serve as critical hosts for iodine storage, demonstrating significant potential in diverse application fields. The confinement effects of the MOF pore geometries profoundly influence the structural dynamics and physicochemical properties of encapsulated iodine species. This study systematically examines the influence of the MOF pore geometries on the structural dynamics of confined iodine molecules. Extended polyiodide chains (I₅^– or (I₂)_n) stabilize in MOF-177’s one-dimensional uniform channels, while discrete I₃^– anions localize within MIL-101(Cr)’s cage-like mesoporous cavities. In situ high-pressure Raman spectroscopy reveals pressure-induced structural evolution mechanisms of iodine polymers. Hydrostatic pressure deforms the uniform one-dimensional channels of MOF-177, leading to fragmentation of the confined polyiodide chains, which reconfigure upon pressure release as the framework recovers. In contrast, MIL-101(Cr)’s reversible structural transitions under pressure induce I₃^– anions into asymmetric configurations, even forming bulk iodine clusters. This work highlights the critical role of MOF pore structures in dictating confined iodine configurations and elucidates synergistic host–guest interactions under pressure. This study reveals the crucial role of MOF pore structure in determining confined iodine configurations and elucidates the mechanism of host–guest synergistic interactions under pressure, providing key theoretical guidance for optimizing MOF-based iodine capture materials.