Accessing the Pores and Unlocking Open Metal Sites in a Rare-Earth Cluster-Based Metal–Organic Framework

While post-synthetic modification (PSM) of metal–organic frameworks (MOFs) through solvent assisted ligand incorporation (SALI) has been extensively studied, particularly in Zr6-based MOFs, this PSM approach is largely overlooked in the literature on rare-earth (RE) cluster-based MOFs. In this work, we explore SALI in Y-CU-45 (CU = Concordia University), a Y6-MOF analo-gous to Zr-MOF-808 with a 6-connected Y6-node. The structural connectivity of Y-CU-45 allows for the existence of six coordi-natively unsaturated sites per cluster. We previously demonstrated that these sites are capped by modulators used in the synthesis of Y-CU-45, which partially occlude the pores of the MOF. By performing SALI on Y-CU-45 with seven different ligands: for-mate, acetate, trifluoroacetate, pivalate, benzoate, 2,3,4,5-tetrafluorobenzoate, and 2,6-bis(trifluoromethyl)benzoate, we demon-strate trends relating the acidity of the incoming ligand to the SALI efficiency. Furthermore, we show that the pores of Y-CU-45 can be made more accessible while demonstrating the potential for open metal sites in this RE cluster-based MOF.