The role of cations in the interactions between anionic N-heterocycles and SO₂

Our study shows that cation plays a more important role in the interactions between anionic N-heterocycles and SO₂ than in the NHC-CO₂ case. The adducts of NHC, SO₂ and cation often exhibit multiple stable configurations with close energies rather than the only reported "CO₂-sandwiched" planar NHC-CO₂-cation structure. The structural diversity makes the models omitting cation inappropriate for predicting the SO₂ capture products, which also leads to less clear trends of the cation effects than those observed in the CO₂ case. The detailed cation effects are discussed in the text.