Microporous Self‐Assembled Pd(II) Tetrahedral Cages for Rapid and Reversible Multi‐Phase Sequestration of Iodine and Methyl Iodide

ABSTRACT Industrial and medical iodine leaks create serious environmental and health risks, creating the need for materials capable of efficiently capturing radioactive iodine from air and water. Herein, we report a systematic study of four tetrahedral, microporous, self‐assembled palladium‐based coordination cages ( C1–C4 ) incorporating high‐affinity binding motifs, including naphthalene, tetrazine, benzothiadiazole, and benzene. Despite the absence of permanent porosity, these cages exhibit exceptional iodine uptake, reaching up to ~3.78 g g ^‒1 in the vapor phase at 75 ^ο C and ~3.52 g g ^‒1 in aqueous media, accompanied by fast kinetics surpassing state‐of‐the‐art COFs and MOFs. Dynamic flow‐through experiments further demonstrate their efficiency, with C4 achieving a record elution volume of 9.2 L g ^‒1 in a 0.5 mM I ₃ ⁻ solution. The cages enable efficient iodine removal under dynamic vapor‐phase conditions (1.92 g g ^‒1 ), reduce iodine concentrations from ppm to ppb levels in real water samples, and exhibit strong affinity toward methyl iodide vapor (up to 1.44 g g ^‒1 ). DFT calculations indicate that the observed performance originates from cooperative π–iodine interactions and nucleophilic heteroatom binding. Combined with structural robustness, recyclability, and scalable synthesis, these coordination cages establish a new benchmark and represent the first example of dynamic vapor‐phase iodine capture by coordination cages.