Fundamental Insights into the Reactivity and Utilization of Open Metal Sites in Cu(I)-MFU‑4l

Metal–organic frameworks (MOFs) having open metal sites have the potential to approach the activity of homogeneous organometallic complexes, thus combining the advantages of homogeneous and heterogeneous catalysis. We present a fundamental study of the effectiveness of incorporating open metal sites into MOFs. We have modeled the binding of a series of adsorbates in a Cu­(I)-substituted MOF, Cu­(I)-MFU-4l, using density functional theory and compared the activity of the Cu­(I) sites in Cu­(I)-MFU-4l with that of two different Cu­(I) scorpionate complexes. The computational results confirm the single-site nature of the Cu­(I) active site. This is further supported by complementary experiments to measure the chemisorption uptake inside our synthesized samples in order to estimate the amount of active Cu sites present. We observed a level of chemisorption that is roughly half the theoretical maximum, which implies that only half of the Cu atoms incorporated into MFU-4l via metal ion exchange are able to act as binding sites. We speculate that the inactive Cu atoms are coordinately saturated Cu­(II) sites. Our work suggests that the performance of Cu­(I)-MFU-4l could be significantly increased by optimizing the metal exchange and activation processes.