Counterions Determine if Metal‐Organic Cages Convert SO₂ to Sulfate or Reversibly Adsorb It

Abstract The continuous emission of harmful gases into the atmosphere damages the environment, air quality, and public health worldwide. To mitigate their impact, materials that capture and chemically inactivate gases are required; however, integrating and precisely controlling both abilities within a single material remains challenging. Herein, we demonstrate for the first time that switching between SO 2 ‐physisorption and chemisorption is possible for porous materials by using different counterions, as illustrated with a series of Pd 6 L 8 Metal‐Organic Cages (MOCs). Pd‐MOCs bearing BF 4 − , PF 6 − , or SO 4 2− expressed reversible adsorption (up to 3.6 mmol g −1 ), cyclability, and SO 2 /CO 2 selectivity. NO 3 − promoted conversion of SO 2 to sulfate, as corroborated with M 6 L 8 cages built on Co(II), Cu(II), and Zn(II) ions. Noteworthy, the nitrate derivative of Pd 6 L 8 captures 6.0 mmol g −1 of SO 2 , cleanly transforms it to SO 4 2− within its cavity in 94 % yield at room temperature, it is quantitatively regenerated, and tolerates humid SO 2 ; such qualities are unprecedented for SO 2 adsorbents. The deliberate use of counterions for modulating adsorption could be applied to charged MOFs, COFs, or POCs, potentially leading to the development of new reactivity or catalysis pathways for advanced applications against contaminant gases.