Docking of Cu^I and Ag^I in Metal–Organic Frameworks for Adsorption and Separation of Xenon

Abstract

We present a metal docking strategy utilizing the precise spatial arrangement of organic struts as metal chelating sites in a MOF. Pairs of uncoordinated N atoms on adjacent pyrazole dicarboxylate linkers distributed along the rod-shaped Al-O secondary building units in MOF-303 [Al(OH)(C₅ H₂ O₄ N₂ )] were used to chelate Cu^I and Ag^I with atomic precision and yield the metalated Cu- and Ag-MOF-303 compounds [(CuCl)_0.50 Al(OH)(C₅ H₂ O₄ N₂ ) and (AgNO₃ )_0.49 Al(OH)(C₅ H₂ O₄ N₂ )]. The coordination geometries of Cu^I and Ag^I were examined using 3D electron diffraction and extended X-ray absorption fine structure spectroscopy techniques. The resulting metalated MOFs showed pore sizes matching the size of Xe, thus allowing for binding of Xe from Xe/Kr mixtures with high capacity and selectivity. In particular, Ag-MOF-303 exhibited Xe uptake of 59 cm³ cm^-3 at 298 K and 0.2 bar with a selectivity of 10.4, placing it among the highest performing MOFs.