Optimization of active sites and stability under irradiation are important targets for sorbent materials that might be used for iodine (I) storage. Herein, we report the direct observation of I binding in a series of Cu(II)-based isostructural metal-organic frameworks, MFM-170, MFM-172, MFM-174, NJU-Bai20, and NJU-Bai21, incorporating various functional groups (-H, -CH, - NH, -C≡C-, and -CONH-, respectively). MFM-170 shows a reversible uptake of 3.37 g g and a high packing density of 4.41 g cm for physiosorbed I. The incorporation of -NH and -C≡C- moieties in MFM-174 and NJU-Bai20, respectively, enhances the binding of I, affording uptakes of up to 3.91 g g. In addition, an exceptional I packing density of 4.83 g cm is achieved in MFM-174, comparable to that of solid iodine (4.93 g cm). crystallographic studies show the formation of a range of supramolecular and chemical interactions [I···N, I···HN] and [I···C≡C, I-C═C-I] between -NH, -C≡C- sites, respectively, and adsorbed I molecules. These observations have been confirmed via a combination of solid-state nuclear magnetic resonance, X-ray photoelectron, and Raman spectroscopies. Importantly, γ-irradiation confirmed the ultraresistance of MFM-170, MFM-174, and NJU-Bai20 suggesting their potential as efficient sorbents for cleanup of radioactive waste.