Lawrence Berkeley National Laboratory

Air pollution by SO₂ and NO₂ has caused significant risks on the environment and human health. Understanding the mechanism of active sites within capture materials is of fundamental importance to the development of new clean-up technologies. Here we report the crystallographic observation of reversible coordinative binding of SO₂ and NO₂ on open Ni^II sites in a metal-organic framework (NKU-100) incorporating unprecedented {Ni₁₂ }-wheels; each wheel exhibits six open Ni^II sites on desolvation. Immobilised gas molecules are further stabilised by cooperative host-guest interactions comprised of hydrogen bonds, π⋅⋅⋅π interactions and dipole interactions. At 298 K and 1.0 bar, NKU-100 shows adsorption uptakes of 6.21 and 5.80 mmol g^-1 for SO₂ and NO₂ , respectively. Dynamic breakthrough experiments have confirmed the selective retention of SO₂ and NO₂ at low concentrations under dry conditions. This work will inspire the future design of efficient sorbents for the capture of SO₂ and NO₂ .