Analysis of a Cu-Doped Metal-Organic Framework, MFM-520(Zn(1-x) Cu(x) ), for NO(2) Adsorption.

MFM-520(Zn) confines dimers of NO(2) 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 Cu(2+) sites allows investigation of the electronic and geometric structure of metal site by in situ electron paramagnetic resonance (EPR) spectroscopy upon adsorption of NO(2) . By combining continuous wave and electron-nuclear double resonance spectroscopy, an unusual reverse Berry distorted coordination geometry of the Cu(2+) centers is observed. Interestingly, Cu-doped MFM-520(Zn(0.95) Cu(0.05) ) shows enhanced adsorption of NO(2) of 5.02 mmol g(-1) at 1 bar at 298 K. Whereas MFM-520(Zn) confines adsorbed NO(2) as N(2) O(4) , the presence of monomeric NO(2) at low temperature suggests that doping with Cu(2+) centers into the framework plays an important role in tuning the dimerization of NO(2) molecules in the pore via the formation of specific host-guest interactions.