Understanding disorder and linker deficiency in porphyrinic zirconium-based metal–organic frameworks by resolving the Zr8O6 cluster conundrum in PCN-221

Abstract

Porphyrin-based metal–organic frameworks (MOFs), exemplified by MOF-525, PCN-221, and PCN-224, are promising systems for catalysis, optoelectronics, and solar energy conversion. However, subtle differences between synthetic protocols for these three MOFs give rise to vast discrepancies in purported product outcomes and description of framework topologies. Here, based on a comprehensive synthetic and structural analysis spanning local and long-range length scales, we show that PCN-221 consists of Zr6O4(OH)4 clusters in four distinct orientations within the unit cell, rather than Zr8O6 clusters as originally published, and linker vacancies at levels of around 50%, which may form in a locally correlated manner. We propose disordered PCN-224 (dPCN-224) as a unified model to understand PCN-221, MOF-525, and PCN-224 by varying the degree of orientational cluster disorder, linker conformation and vacancies, and cluster–linker binding. Our work thus introduces a new perspective on network topology and disorder in Zr-MOFs and pinpoints the structural variables that direct their functional properties.

Porphyrin based metal–organic frameworks: highly sensitive materials for optical sensing of oxygen in gas phase

“…However, only PCN-224 features the superstructure reflections observed at scattering angles of 3.2 and 5.51 so that the occurrence of ordered vacancies in the crystals discussed here is prevailing. 47 experiments (Fig. S12-S14, ESI †) are in very good agreement with data from literature.…”

Exploring the Role of Cluster Formation in UiO Family Hf Metal–Organic Frameworks with in Situ X-ray Pair Distribution Function Analysis

“…The remaining 25 clusters included the classic (fcu) UiO M 6 single cluster and hcp UiO M 12 double cluster [Figure 1]. Of note, one of these original 25 clusters, the HIKSIF Zr 8 cluster, has subsequently been shown to be instead a Zr 6 cluster, 78 consistent with the stability of this particular cluster type.…”

Guest-responsive thermal expansion in the Zr-porphyrin metal-organic framework PCN-222

“…As mentioned, thermal response can sometimes be tuned by changing the guest, 32,40,41 and it remains to be seen whether this occurs in PCN-222. Finally, while the study of defects in porphyrin MOFs is relatively nascent, 42,43 this may also provide a means to tuning the elastic properties. 28 FKF) for assistance with DSC, ICP, and NMR, respectively.…”