Unprecedented Pd(II) Metal–Organic Cages for Simultaneous Adsorption of Iodine Species

Metal–organic cages (MOCs) with unconventional topologies remain rare owing to the challenges associated with controlling coordination-driven self-assembly. Herein, we report the self-assembly of two unique Pd(II)-based coordination cages–peanut-shaped cage (C1, M18L14) and hemicage (C2, M12M2L22), from semiflexible tetratopic pyridyl ligands incorporating 9,10-dihydroanthracene and benzene backbones, respectively. Single-crystal X-ray diffraction studies reveal that cage C1 adopts a rare peanut-shaped structure comprising two interconnected cavities and both inward- and outward-oriented Pd(II) nodes, generating a highly electron-rich confined environment. In contrast, C2 forms an unprecedented boat-shaped architecture assembled through the cooperative incorporation of 90° and 180° Pd(II) acceptors within a single discrete cage. Despite their amorphous and nonporous nature, these assemblies demonstrate exceptional dual-capture performance toward volatile iodine species. Notably, C1 achieves iodine uptake capacities of 2.62 g g–1 under static vapor-phase conditions and 1.21 g g–1 under dynamic flow conditions, together with efficient CH3I adsorption of up to 1.05 g g–1 at 75 °C. Spectroscopic investigations and theoretical calculations reveal that the adsorption process is driven by synergistic charge-transfer interactions, polyiodide formation, electrostatic stabilization, and cavity confinement. Furthermore, both cages display excellent retention capability and recyclability, highlighting their potential as robust materials for radioactive iodine sequestration and environmental remediation.