Influence of Water Content on Speciation and Phase Formation in Zr–Porphyrin‐Based MOFs

Controlled synthesis of phase‐pure metal–organic frameworks (MOFs) is essential for their application in technological areas such as catalysis or gas sorption. Yet, knowledge of their phase formation and growth remain rather limited, particularly with respect to species such as water whose vital role in MOF synthesis is often neglected. As a consequence, synthetic protocols often lack reproducibility when multiple MOFs can form from the same metal source and linker, and phase mixtures are obtained with little or no control over their composition. In this work, the role of water in the formation of the Zr–porphyrin MOF disordered PCN‐224 (dPCN‐224) is investigated. Through X‐ray total scattering and scanning electron microscopy, it is observed that dPCN‐224 forms via a metal–organic intermediate that consists of Zr6O4(OH)4 clusters linked by tetrakis(4‐carboxy‐phenyl)porphyrin molecules. Importantly, water is not only essential to the formation of Zr6O4(OH)4 clusters, but it also plays a primary role in dictating the formation kinetics of dPCN‐224. This multidisciplinary approach to studying the speciation of dPCN‐224 provides a blueprint for how Zr‐MOF synthesis protocols can be assessed and their reproducibility increased, and highlights the importance of understanding the role of water as a decisive component in Zr‐MOF formation. This work evaluates the complexities of synthesizing porphyrinic Zr‐based metal–organic frameworks (MOFs), specifically disordered PCN‐224 (dPCN‐224). It is shown that hydrolysis of ZrCl4 or the addition of water is crucial for the formation of the inorganic building unit, and hence, the MOF. In addition, MOF's formation pathway is characterized, revealing that dPCN‐224 forms via at least one intermediate.