Synergistic effects between –NO2 groups and open metal sites lead to optimal binding of CO2 molecules within MFM-102-NO2via hydrogen bonding to C–H groups.

The development of efficient sorbent materials for sulfur dioxide (SO 2 ) is of key industrial interest. However, due to the corrosive nature of SO 2 , conventional porous materials often exhibit poor reversibility and limited uptake toward SO 2 sorption. Here, we report high adsorption of SO 2 in a series of Cu(II)-carboxylate-based metal–organic framework materials. We describe the impact of ligand functionalization and open metal sites on the uptake and reversibility of SO 2 adsorption. Specifically, MFM-101 and MFM-190(F) show fully reversible SO 2 adsorption with remarkable capacities of 18.7 and 18.3 mmol g –1 , respectively, at 298 K and 1 bar; the former represents the highest reversible uptake of SO 2 under ambient conditions among all porous solids reported to date. In situ neutron powder diffraction and synchrotron infrared microspectroscopy enable the direct visualization of binding domains of adsorbed SO 2 molecules as well as host–guest binding dynamics. We have found that the combination of open Cu(II) sites and ligand functionalization, together with the size and geometry of metal–ligand cages, plays an integral role in the enhancement of SO 2 binding.

We report the first example of crystallographic observation of acetylene binding to −NO2 groups in a metal–organic framework (MOF). Functionalization of MFM-102 with −NO2 groups on phenyl groups leads to a 15% reduction in BET surface area in MFM-102-NO2. However, this is coupled to a 28% increase in acetylene adsorption to 192 cm3 g–1 at 298 K and 1 bar, comparable to other leading porous materials. Neutron diffraction and inelastic scattering experiments reveal the role of −NO2 groups, in cooperation with open metal sites, in the binding of acetylene in MFM-102-NO2.

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