We report a record-high SO2 adsorption capacity of 12.3 mmol g–1 in a robust porous material, MFM-601, at 298 K and 1.0 bar. SO2 adsorption in MFM-601 is fully reversible and highly selective over CO2 and N2. The binding domains for adsorbed SO2 and CO2 molecules in MFM-601 have been determined by in situ synchrotron X-ray diffraction experiments, giving insights at the molecular level to the basis of the observed high selectivity.

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), I2I, is located near the bridging hydroxyl group of the [ScO4(OH)2] moiety [I2I···H–O = 2.263(9) Å] with an occupancy of 0.268. I2II is located interstitially between two phenyl rings of neighboring ligand molecules [I2II···phenyl ring = 3.378(9) and 4.228(5) Å]. I2II 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).

Nitrogen dioxide (NO) is a major air pollutant causing significant environmental and health problems. We report reversible adsorption of NO in a robust metal-organic framework. Under ambient conditions, MFM-300(Al) exhibits a reversible NO isotherm uptake of 14.1 mmol g, and, more importantly, exceptional selective removal of low-concentration NO (5,000 to <1 ppm) from gas mixtures. Complementary experiments reveal five types of supramolecular interaction that cooperatively bind both NO and NO molecules within MFM-300(Al). We find that the in situ equilibrium 2NO ↔ NO within the pores is pressure-independent, whereas ex situ this equilibrium is an exemplary pressure-dependent first-order process. The coexistence of helical monomer-dimer chains of NO in MFM-300(Al) could provide a foundation for the fundamental understanding of the chemical properties of guest molecules within porous hosts. This work may pave the way for the development of future capture and conversion technologies.

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MFM-300(Al) shows reversible uptake of NH (15.7 mmol g at 273 K and 1.0 bar) over 50 cycles with an exceptional packing density of 0.62 g cm at 293 K. In situ neutron powder diffraction and synchrotron FTIR micro-spectroscopy on ND @MFM-300(Al) confirms reversible H/D site exchange between the adsorbent and adsorbate, representing a new type of adsorption interaction.

Understanding the mechanism of gas-sorbent interactions is of fundamental importance for the design of improved gas storage materials. Here we report the binding domains of carbon dioxide and acetylene in a tetra-amide functionalized metal-organic framework, MFM-188, at crystallographic resolution. Although exhibiting moderate porosity, desolvated MFM-188a exhibits exceptionally high carbon dioxide and acetylene adsorption uptakes with the latter (232 cm3 g−1 at 295 K and 1 bar) being the highest value observed for porous solids under these conditions to the best of our knowledge. Neutron diffraction and inelastic neutron scattering studies enable the direct observation of the role of amide groups in substrate binding, representing an example of probing gas-amide binding interactions by such experiments. This study reveals that the combination of polyamide groups, open metal sites, appropriate pore geometry and cooperative binding between guest molecules is responsible for the high uptakes of acetylene and carbon dioxide in MFM-188a.

NH3 (ammonia) is a promising energy resource owing to its high hydrogen density. However, its widespread application is restricted by the lack of efficient and corrosion-resistant storage materials. Here, we report high NH3 adsorption in a series of robust metal-organic framework (MOF) materials, MFM-300(M) (M = Fe, V, Cr, In). MFM-300(M) (M = Fe, V III , Cr) show fully reversible capacity for >20 cycles, reaching capacities of 16.1, 15.6 and 14.0 mmol g -1 , respectively, at 273 K and 1 bar. Under the same condition, MFM-300(V IV ) exhibits the highest uptake among this series of MOFs of 17.3 mmol g -1 . In situ neutron powder diffraction, single crystal X-ray diffraction and electron paramagnetic resonance spectroscopy confirm that the redox-active V centre enables host-guest charge-transfer, with V IV being reduced to V III and NH3 oxidised to hydrazine, N2H4. A combination of in situ inelastic neutron scattering and DFT modelling has revealed the binding dynamics of adsorbed NH3 within these MOFs to afford a comprehensive insight into the application of MOF materials to the adsorption and conversion of NH3.

Hydrogen bonds dominate many chemical and biological processes, and chemical modification enables control and modulation of host–guest systems. Here we report a targeted modification of hydrogen bonding and its effect on guest binding in redox-active materials. MFM-300(VIII) {[VIII2(OH)2(L)], LH4=biphenyl-3,3′,5,5′-tetracarboxylic acid} can be oxidized to isostructural MFM-300(VIV), [VIV2O2(L)], in which deprotonation of the bridging hydroxyl groups occurs. MFM-300(VIII) shows the second highest CO2 uptake capacity in metal-organic framework materials at 298 K and 1 bar (6.0 mmol g−1) and involves hydrogen bonding between the OH group of the host and the O-donor of CO2, which binds in an end-on manner, =1.863(1) Å. In contrast, CO2-loaded MFM-300(VIV) shows CO2 bound side-on to the oxy group and sandwiched between two phenyl groups involving a unique ···c.g.phenyl interaction [3.069(2), 3.146(3) Å]. The macroscopic packing of CO2 in the pores is directly influenced by these primary binding sites.