Framework Flexibility and Chemical Stability of a 2D Cu(I)-Based Metal–Organic Framework for Catalytic CO Oxidation

Abstract

Cu(I)-based metal–organic frameworks (MOFs) are attractive for small-molecule binding and catalysis, but their practical use is often limited by oxidation state instability and framework degradation. Here, we report an all-N-coordinated Cu(I)-MOF, [Cu(imtpy)]·MeOH (2,4,5-tris(4-pyridyl)-1H-imidazole; Himtpy), containing both near-linear and tetrahedral Cu(I) environments within a two-dimensional sql framework. Thermal activation converts [Cu(imtpy)]·MeOH to the guest-free phase, [Cu(imtpy)], through a single-crystal-to-single-crystal transformation, allowing direct observation of the accompanying framework contraction and bending of the near-linear Cu(I) site. The guest-free framework exhibits reversible guest-responsive flexibility, high thermal stability under N2 and air, and chemical stability across a wide range of conditions, including liquid water, water vapor, and pH 3–13 aqueous media. X-ray photoelectron spectroscopy (XPS) and Cu LMM Auger spectra indicate retention of the Cu(I) oxidation state throughout these treatments. Finally, [Cu(imtpy)] shows measurable activity toward catalytic CO oxidation between 120 and 200 °C while preserving crystallinity, microporosity, and the Cu(I) oxidation state post reaction. These results highlight [Cu(imtpy)] as a stable Cu(I)-MOF that integrates framework flexibility, chemical robustness, and oxidative gas-phase catalytic function.