Adsorption of Sulfur Dioxide in Cu(II)-Carboxylate Framework Materials: The Role of Ligand Functionalization and Open Metal Sites

[Image: see text] 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.