During nuclear waste disposal process, radioactive iodine as a fission product can be released. The widespread implementation of sustainable nuclear energy thus requires the development of efficient iodine stores that have simultaneously high capacity, stability and more importantly, storage density (and hence minimized system volume). Here, we report high I₂ adsorption in a series of robust porous metal–organic materials, MFM-300(M) (M = Al, Sc, Fe, In). MFM-300(Sc) exhibits fully reversible I₂ uptake of 1.54 g g^–1, and its structure remains completely unperturbed upon inclusion/removal of I₂. Direct observation and quantification of the adsorption, binding domains and dynamics of guest I₂ molecules within these hosts have been achieved using XPS, TGA-MS, high resolution synchrotron X-ray diffraction, pair distribution function analysis, Raman, terahertz and neutron spectroscopy, coupled with density functional theory modeling. These complementary techniques reveal a comprehensive understanding of the host–I₂ and I₂–I₂ binding interactions at a molecular level. The initial binding site of I₂ in MFM-300(Sc), I₂^I, is located near the bridging hydroxyl group of the [ScO₄(OH)₂] moiety [I₂^I···H–O = 2.263(9) Å] with an occupancy of 0.268. I₂^II is located interstitially between two phenyl rings of neighboring ligand molecules [I₂^II···phenyl ring = 3.378(9) and 4.228(5) Å]. I₂^II is 4.565(2) Å from the hydroxyl group with an occupancy of 0.208. Significantly, at high I₂ loading an unprecedented self-aggregation of I₂ molecules into triple-helical chains within the confined nanovoids has been observed at crystallographic resolution, leading to a highly efficient packing of I₂ molecules with an exceptional I₂ storage density of 3.08 g cm^–3 in MFM-300(Sc).

Selective adsorption of SO₂ is realized in a porous metal–organic framework material, and in-depth structural and spectroscopic investigations using X-rays, infrared, and neutrons define the underlying interactions that cause SO₂ to bind more strongly than CO₂ and N₂.

We present an unambiguous identification of low-frequency terahertz vibrations in the archetypal imidazole-based metal-organic framework (MOF) materials: ZIF-4, ZIF-7, and ZIF-8, all of which adopt a zeolite-like nanoporous structure. Using inelastic neutron scattering and synchrotron radiation far-infrared absorption spectroscopy, in conjunction with density functional theory (DFT), we have pinpointed all major sources of vibrational modes. Ab initio DFT calculations revealed the complex nature of the collective THz modes, which enable us to establish detailed correlations with experiments. We discover that low-energy conformational dynamics offers multiple pathways to elucidate novel physical phenomena observed in MOFs. New evidence demonstrates that THz modes are intrinsically linked, not only to anomalous elasticity underpinning gate-opening and pore-breathing mechanisms, but also to shear-induced phase transitions and the onset of structural instability.