Influence of Water Content on Speciation and Phase Formation in Zr-Porphyrin-Based MOFs Special Issue on Hygroscopic Materials.

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 whose role in MOF synthesis is often uncontrolled or neglected completely. Water, either as contaminant in the solvent, or adsorbed from the atmosphere or reactor surface, is an example of such species. 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, we investigate the role of water in the formation of the disordered Zr-porphyrin MOF dPCN-224 under controlled reaction conditions. Through X-ray total scattering and electron microscopy measurements, we observe that dPCN-224 forms via a metal-organic intermediate that consists of Zr 6 O 4 (OH) 4 clusters linked by tetrakis(4-carboxy-phenyl)porphyrin molecules. Importantly, water is not only essential to the formation of Zr 6 O 4 (OH) 4 clusters, but it also plays a primary role in dictating the formation kinetics of phase-pure dPCN-224. Our 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 article is protected by copyright. All rights reserved.