Precisely Embedding Active Sites into a Mesoporous Zr-Framework through Linker Installation for High-Efficiency Photocatalysis.

The pore engineering of microporous metal-organic frameworks (MOFs) has been extensively investigated in the past two decades, and an expansive library of functional groups has been introduced into various frameworks. However, the reliable procurement of MOFs possessing both a targeted pore size and preferred functionality together is less common. This is especially important since the applicability of many elaborately designed materials is often restricted by the small pore sizes of microporous frameworks. Herein, we designed and synthesized a mesoporous MOF based on Zr6 clusters and tetratopic carboxylate ligands, termed PCN-808. The accessible coordinatively unsaturated metal sites as well as the intrinsic flexibility of the framework make PCN-808 a prime scaffold for postsynthetic modification via linker installation. A linear ruthenium-based metalloligand was successfully and precisely installed into the walls of open channels in PCN-808 while maintaining the mesoporosity of the framework. The photocatalytic activity of the obtained material, PCN-808-BDBR, was examined in the aza-Henry reaction and demonstrated high conversion yields after six catalytic cycles. Furthermore, thanks to the mesoporous nature of the framework, PCN-808-BDBR also exhibits exceptional yields for the photocatalytic oxidation of dihydroartemisinic acid to artemisinin.

Functionalization of Zirconium-Based Metal-Organic Layers with Tailored Pore Environments for Heterogeneous Catalysis.

Intriguing properties and functions are expected to implant into metal-organic layers (MOLs) to achieve tailored pore environments and multiple functionalities owing to the synergies among multiple components. Herein, we demonstrate a facile one-pot synthetic strategy to incorporate multiple functionalities into stable zirconium MOLs via secondary ligand pillaring. Through the combination of Zr6 -BTB (BTB=benzene-1,3,5-tribenzoate) layers and diverse secondary ligands (including ditopic and tetratopic linkers), 31 MOFs with multi-functionalities were systematically prepared. Notably, a metal-phthalocyanine fragment was successfully incorporated into this Zr-MOL system, giving rise to an ideal platform for the selective oxidation of anthracene. The organic functionalization of two-dimensional MOLs can generate tunable porous structures and environments, which may facilitate the excellent catalytic performance of as-synthesized materials.

Switching in Metal-Organic Frameworks.

In recent years, metal-organic frameworks (MOFs) have become an area of intense research interest because of their adjustable pores and nearly limitless structural diversity deriving from the design of different organic linkers and metal structural building units (SBUs). Among the recent great challenges for scientists include switchable MOFs and their corresponding applications. Switchable MOFs are a type of smart material that undergo distinct, reversible, chemical changes in their structure upon exposure to external stimuli, yielding interesting technological applicability. Although the process of switching shares similarities with flexibility, very limited studies have been devoted specifically to switching, while a fairly large amount of research and a number of Reviews have covered flexibility in MOFs. This Review focuses on the properties and general design of switchable MOFs. The switching activity has been delineated based on the cause of the switching: light, spin crossover (SCO), redox, temperature, and wettability.

Tuning the Ionicity of Stable Metal-Organic Frameworks through Ionic Linker Installation.

The predictable topologies and designable structures of metal-organic frameworks (MOFs) are the most important advantages for this emerging crystalline material compared to traditional porous materials. However, pore-environment engineering in MOF materials is still a huge challenge when it comes to the growing requirements of expanded applications. A useful method for the regulation of pore-environments, linker installation, has been developed and applied to a series of microporous MOFs. Herein, employing PCN-700 and PCN-608 as platforms, ionic linker installation was successfully implemented in both microporous and mesoporous Zr-based MOFs to afford a series of ionic frameworks. Selective ionic dye capture results support the ionic nature of these MOFs. The mesopores in PCN-608 are able to survive after installation of the ionic linkers, which is useful for ion exchange and further catalysis. To illustrate this, Ru(bpy)32+, a commonly used photoactive cation, was encapsulated into the anionic mesoporous PCN-608-SBDC via ion exchange. Photocatalytic activity of Ru(bpy)3@PCN-608-SBDC was examined by aza-Henry reactions, which show good catalytic performance over three catalytic cycles.

Enhancing Pore-Environment Complexity Using a Trapezoidal Linker: Toward Stepwise Assembly of Multivariate Quinary Metal-Organic Frameworks.

Multicomponent metal-organic frameworks (MOFs) promise the precise placement of synergistic functional groups with atomic-level precision, capable of promoting fascinating developments in basic sciences and applications. However, the complexity of multicomponent systems poses a challenge to their structural design and synthesis. Herein, we show that linkers of low symmetry can bring new opportunities to the construction of multicomponent MOFs. A carbazole-tetracarboxylate linker of  C s point group symmetry was designed and combined with an 8-connected Zr6 cluster to generate a low-symmetry MOF, PCN-609. PCN-609 contains coordinatively unsaturated Zr sites arranged within a lattice with three crystallographically distinct pockets, which can accommodate linear linkers of different lengths. Sequential linker installation was carried out to postsynthetically insert three linear linkers into PCN-609, giving rise to a quinary MOF. Functionalization of each linker from the quinary MOF system creates multivariate pore environments with unprecedented complexity.

Stable Metal-Organic Frameworks with Group 4 Metals: Current Status and Trends.

Group 4 metal-based metal-organic frameworks (MIV-MOFs), including Ti-, Zr-, and Hf-based MOFs, are one of the most attractive classes of MOF materials owing to their superior chemical stability and structural tunability. Despite being a relatively new field, MIV-MOFs have attracted significant research attention in the past few years, leading to exciting advances in syntheses and applications. In this outlook, we start with a brief overview of the history and current status of MIV-MOFs, emphasizing the challenges encountered in their syntheses. The unique properties of MIV-MOFs are discussed, including their high chemical stability and strong tolerance toward defects. Particular emphasis is placed on defect engineering in Zr-MOFs which offers additional routes to tailor their functions. Photocatalysis of MIV-MOF is introduced as a representative example of their emerging applications. Finally, we conclude with the perspective of new opportunities in synthesis and defect engineering.

¹9F magnetic resonance probes for live-cell detection of peroxynitrite using an oxidative decarbonylation reaction.

We report a newly discovered oxidative decarbonylation reaction of isatins that is selectively mediated by peroxynitrite (ONOO(-)) to provide anthranilic acid derivatives. We have harnessed this rapid and selective transformation to develop two reaction-based probes, 5-fluoroisatin and 6-fluoroisatin, for the low-background readout of ONOO(-) using (19)F magnetic resonance spectroscopy. 5-fluoroisatin was used to non-invasively detect ONOO(-) formation in living lung epithelial cells stimulated with interferon-γ (IFN-γ).

Ylide mediated carbonyl homologations for the preparation of isatin derivatives.

An exceptionally mild method for the preparation of isatin derivatives has been developed using a sulfur ylide mediated carbonyl homologation sequence starting from anthranilic acid precursors. This method proceeds at ambient temperature via a sulfur ylide intermediate without the need for protection of the amine or chromatographic isolation of the intermediate ylide. Gentle oxidation of the sulfur ylides provides isatin derivatives with N-H, N-alkyl, N-aryl substitution, electron-rich and electron-poor aromatic rings, and heterocyclic aromatic systems. We anticipate that this method will greatly expand the accessibility of complex isatin derivatives.