Analysis of a Cu‐Doped Metal–Organic Framework, MFM‐520(Zn1‐xCux), for NO2 Adsorption

Abstract

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(Zn0.95Cu0.05) 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.

Keywords

• ENDOR
• EPR spectroscopy
• incommensurate modulation
• MOFs
• NO2 adsorption