Analysis of a Cu‐Doped Metal–Organic Framework, MFM‐520(Zn_1‐xCu_x), for NO₂ Adsorption

Abstract MFM‐520(Zn) confines dimers of NO₂ with a high adsorption of 4.52 mmol g⁻¹ at 1 bar at 298 K. The synthesis and the incommensurate structure of Cu‐doped MFM‐520(Zn) are reported. The introduction of paramagnetic Cu²⁺ sites allows investigation of the electronic and geometric structure of metal site by in situ electron paramagnetic resonance (EPR) spectroscopy upon adsorption of NO₂. By combining continuous wave and electron‐nuclear double resonance spectroscopy, an unusual reverse Berry distorted coordination geometry of the Cu²⁺ centers is observed. Interestingly, Cu‐doped MFM‐520(Zn_0.95Cu_0.05) shows enhanced adsorption of NO₂ of 5.02 mmol g⁻¹ at 1 bar at 298 K. Whereas MFM‐520(Zn) confines adsorbed NO₂ as N₂O₄, the presence of monomeric NO₂ at low temperature suggests that doping with Cu²⁺ centers into the framework plays an important role in tuning the dimerization of NO₂ molecules in the pore via the formation of specific host‐guest interactions.