Halogen-bond induced unusual polyhalogen anions formation in hydrogen-bonded frameworks to secure iodine sequestration

Safe confinement of fission iodine isotopes for long-term radioactive waste disposal remains a formidable challenge, as conventional sorbents provide inherently weak iodine-host interactions. We report here a novel halogen bond (X-bond) directed strategy to sequester volatile iodine in hydrogen-bonded (H-bonded) frameworks with unprecedented stability. Charge-assisted H-bonded frameworks bearing open halide sites are developed, showing distinctive iodine encapsulation behaviors without compromising the crystallinity. Direct crystallographic evidence indicates the formation of X-bonds, i.e., I–I···Cl⁻ and I–I···Br⁻, within the confined pore channels. Unusual polyhalogen anions, i.e., [I₂Cl₂]²⁻ and [I₂Br₂]²⁻, sustained in H-bonded frameworks are identified for the first time. The X-bond reinforced host-guest interaction affords robust iodine trapping without leaking out even at elevated temperatures up to 180 °C. By integrating the halogen-bond chemistry with H-bonded frameworks, this study offers fresh concepts for developing effective host reservoirs to secure fission iodine isotopes from spent fuel reprocessing off-gases.