Quantification of Linker Defects in UiO-Type Metal–Organic Frameworks

Metal–organic frameworks (MOFs) are nanoporous materials composed of organic linkers and inorganic nodes. The large variety of linkers and nodes and the multiple ways to combine them make MOFs highly tunable materials, which are thoroughly studied for their use in, e.g., catalysis, gas capture, and separation. The chemistry of MOFs is further enriched by defects, e.g., missing linker defects, which provide active sites for catalysis or anchoring sites for introducing new functionalities. A commonly reported method to quantify linker defects assumes the presence of one type of linker and the complete removal of capping agents, solvents, and other impurities upon activation at high temperature, e.g., 400 °C (M-400). However, attempts to use this method for MOFs containing different types of linkers, also called multivariate MOFs (MTV-MOFs), or capping agents that are not completely removed at 400 °C, give inaccurate results and hamper comparing results from different publications. In this work, we have developed a new procedure to compute missing linker defects in Zr-based MOFs using standard analytical techniques to quantify the capping agents that remain in the MOF upon activation at 200 °C (M-200). This method, which has been tested in UiO-66/67 based MOFs, should be applicable to any MOF that (1) has known decomposition products, (2) has no missing cluster defects, (3) has empty pores or contain species that can be quantified after activation, and (4) has a known node composition at 200 °C.