SO₂ Capture and Oxidation in a Pd Metal-Organic Cage

The facile and green preparation of novel materials that capture sulfur dioxide (SO₂) with significant uptake at room temperature remains challenging, but it is crucial for public health and the environment. Herein, we explored for the first time the SO₂ adsorption within microporous metal-organic cages using the palladium(II)-based [Pd(NO) tetragonal prism 1, assembled in water under mild conditions. Notably and despite the low BET surface area of 1 (111 m² g^-1), sulfur dioxide was found to be irreversibly and strongly adsorbed within the activated cage at 298 K (up to 6.07 mmol g^-1). The measured values for the molar enthalpy of adsorption (ΔH_ads) coupled to the FTIR analyses imply a chemisorption process that involves the direct interaction of SO₂ with Pd(II) sites and the subsequent oxidation of this toxic chemical by the action of the nitrate anions in 1. To the best of our knowledge, this is the first reported metal-organic cage that proves useful for SO₂ adsorption. Metallosupramolecular adsorbents such as 1 could enable new detection applications and suggest that the integration of soft metal ions and self-assembly of molecular cages are a potential means for the easy tuning of SO₂ adsorption capabilities and behavior.