(197m) The Nature and Gas Sorption Performance of Cu(I) Species in Cu(I)-Mfu-4l Metal-Organic Frameworks

Over the past decades, metal-organic frameworks have been developed as a promising novel class of highly porous materials with great prospects for various applications, including sorption, filtration, sensing, and catalysis. Binding of gas molecules at active metal sites is a critical step in heterogeneous catalysis and hence the development of MOFs with accessible redox active metals has increased tremendously in the recent years. Among the open metal sites-based MOFs, Cu(I)-MFU-4l has shown great promise due to its robustness and high affinity towards several gases. However, the study of the nature of Cu(I) species in this framework as well as their interaction with different gases remains underexplored.

In the current work, we synthesized Cu(I)-MFU-4l and investigated its binding energies with different gases (including N₂, CO₂, C₂H₄, CO) using gas sorption and temperature-programmed-desorption experiments. Moreover, we probed the Cu oxidation states by X-ray photoelectron spectroscopy (XPS) which revealed the gradual oxidation of Cu(I)-MFU-4l to Cu(II)-MFU-4l in air, while these Cu(II) species can be completely reduced to Cu(I) after activation in vacuum or inert gas at 180 ^°C, suggesting this MOF features reversible and facile redox transformations between Cu(I) and Cu(II) without compromising the stability or crystallinity of the framework as verified via X-ray diffraction (XRD).