Exploring structure and reactivity of Cu sites in functionalized UiO-67 MOFs

The exceptional thermal stability of the Ui0-67/68-family MOFs makes them ideal candidates to explore post-synthetic functionalization routes aiming to the heterogenization of homogeneous catalysts. We previously demonstrated that a small fraction of the linkers in the UiO-67 MOF can be replaced by bipyridine-dicarboxylate (bpydc) moieties exhibiting metal-chelating ability and enabling the grafting of Pt(II) and Pt(IV) ions in the MOF framework [Chem. Mater., 27 (2015) 1042]. Herein, we investigate a novel Cu-functionalized UiO-67 MOF obtained by a simple synthesis method, consisting in contacting the bpydc-containing UiO-67-bpy MOF with a CuC12 dihydrate precursor. By combining in situ and operando XAS and FTIR spectroscopies, we assessed the successful incorporation of well-defined Cu complexes in the Ui0-67 framework and explored local coordination geometry, redox properties and reactivity of the dominant Cu species formed in different conditions relevant to potential future applications in catalysis. EXAFS fits and XANES simulations, based on DFT-optimized geometries, yielded detailed structural and electronic information on the major Cu-species formed. Data analysis revealed three-coordinated Cu(I) complexes with the bpydc linker of the Cu-UiO-67 MOFs and a Cl- ligand, formed after thermal treatment at 523 K in inert gas flow able to efficiently and reversibly form Cu(I)-mono-carbonyl adducts with CO adsorbate.