Sufficient pore size, appropriate stability, and hierarchical porosity are three prerequisites for open frameworks designed for drug delivery, enzyme immobilization, and catalysis involving large molecules. Herein, we report a powerful and general strategy, linker thermolysis, to construct ultrastable hierarchically porous metal-organic frameworks (HP-MOFs) with tunable pore size distribution. Linker instability, usually an undesirable trait of MOFs, was exploited to create mesopores by generating crystal defects throughout a microporous MOF crystal via thermolysis. The crystallinity and stability of HP-MOFs remain after thermolabile linkers are selectively removed from multivariate metal-organic frameworks (MTV-MOFs) through a decarboxylation process. A domain-based linker spatial distribution was found to be critical for creating hierarchical pores inside MTV-MOFs. Furthermore, linker thermolysis promotes the formation of ultrasmall metal oxide nanoparticles immobilized in an open framework that exhibits high catalytic activity for Lewis acid-catalyzed reactions. Most importantly, this work provides fresh insights into the connection between linker apportionment and vacancy distribution, which may shed light on probing the disordered linker apportionment in multivariate systems, a long-standing challenge in the study of MTV-MOFs.

Multivariate (MTV) hierarchical metal–organic frameworks (MOFs), which contain multiple regions arranged in ordered structures, show promise for applications such as gas separation, size-selective catalysis, and controlled drug delivery. However, the complexity of these hierarchical MOFs is limited by a lack of control during framework assembly. Herein, we report the controlled generation of hierarchical MOF-on-MOF structural formation under the guidance of two design principles, surface functionalization and retrosynthetic techniques for stability control. Accordingly, the tunability of spatial distributions, compositions, and crystal sizes has been achieved in these hierarchical systems. The resulting MOF-on-MOF hierarchical structures represent a unique crystalline porous material which contains a controllable distribution of functional groups and metal clusters that are associated together within a framework composite. This general synthetic approach not only expands the scope and tunability of the traditional MTV strategy to multicomponent materials, but also offers a facile route to introduce variants and sequences to sophisticated three-dimensional hierarchical and cooperative systems. As a proof of concept, the photothermal effects of a porphyrinic core-MOF are exploited to trigger the controlled guest release from a shell-MOF with high guest capacity, highlighting the integrated cooperative behaviors in multivariate hierarchical systems.

Hierarchically porous superstructures have been successfully assembled from nanoporous MOF crystallites. Benefiting from the dynamic coordination bond formation, hierarchical helical or multichannel tubular superstructures can be accessed through oriented assembly of MOF crystallites. This temperaturecontrolled structural evolution also enables the formation of crystalline hollow MOF tubes via self-templating and self-healing processes. Further incorporation of multiple components into these frameworks provides a fresh route for preparing stable, multivariate, and hierarchical frameworks with accessible catalytically active sites for heterogeneous catalysis.

Metal-organic frameworks (MOFs), a class of porous crystalline framework materials, are linked by strong bonds between inorganic and organic building blocks. [1-3] In the past two decades, MOFs have rapidly grown as a star material due to their exceptional performance in areas such as storage, separation and catalysis. [4] The outstanding performance of MOFs in applications benefits from their intrinsically porous structures and highly tunable pore environment. [5-7] The creation and modification of pore space with optimized size, functionality and diversity can be precisely tuned at the molecular level by rationally designing building blocks and synthetic procedures. [8,9] The diversity of MOFs can be enriched by expanding the library of organic linkers with varying lengths, geometries, and functional groups. [10] Additionally, very diverse metal cations are applied to MOF synthesis, ranging from monovalent (Ag + , Cu + , etc.), divalent (Mg 2+ , Fe 2+ , Co 2+ , Ni 2+ , etc.), trivalent (Al 3+ , Sc 3+ , V 3+ , Cr 3+ , etc.), to tetravalent (Ti 4+ , Zr 4+ , Hf 4+ , etc.) cations. [11] In this review, we mainly focus on MOFs with group 3 and 4 metals, including Y, lanthanides (Ln, from La to Lu), actinides (An, from Ac to Lr), Ti, and Zr (Figure 1). Group 3 metal cations are generally found in the oxidation state of +3 in the MOF structures, while group 4 metal cations mainly exist in the oxidation state of +4, leading to the formation of much stronger coordination bonds with carboxylates. [12] Therefore, group 4 metal-based MOFs (M IV-MOFs) generally have enhanced stability compared with MOFs constructed from metals of group 3 and other groups. This series of MOFs stands out because the involved metals can generally coordinate with carboxylates to form frameworks with strong coordination bonds, according to the Pearson's hard/soft acid/base principle, where group 3 and 4 metal cations are regarded as hard acids while carboxylate ligands are hard bases. [11] One remarkable feature of MOFs with group 3 and 4 metals is that they generally can form phases containing M 6 O 8 (M = Y, Ln, An, Zr and Hf) clusters, regardless of their atomic numbers, charges and radius. This series of M 6-based MOFs is best represented by UiO series such as UiO-66 with fcu topology. [13] Under different synthetic conditions, UiO-66(M, M = An, Zr and Hf) constructed from [M 6 (μ 3-O) 4 (μ 3-OH) 4 ] clusters and linear carboxylates can be obtained, while UiO-66(M, M = Y, Ln) is assembled from Metal-organic frameworks (MOFs) based on group 3 and 4 metals are considered as the most promising MOFs for varying practical applications including water adsorption, carbon conversion, and biomedical applications. The relatively strong coordination bonds and versatile coordination modes within these MOFs endow the framework with high chemical stability, diverse structures and topologies, and interesting properties and functions. Herein, the significant progress made on this series of MOFs since 2018 is summarized and an update on the current status an...

Artemisinin, an essential antimalarial drug, requires a synthetic pathway that has a high environmental and financial cost. Conventional homogeneous photocatalysts and acid catalysts usually suffer from recycling problems that lead to a dramatic decrease in catalytic activity, while current heterogeneous catalysts with low surface areas are limited by issues such as active-site accessibility and precise reaction tailorability. Herein, we report the successful installation of Brønsted acid sites into a series of porphyrinic metal–organic frameworks (MOFs) that feature large channels, high surface areas, and tailored pore environments for catalysis via a postsynthetic installation strategy. Accordingly, the resulting dual-function solid acid/photocatalyst can be utilized for the tandem semisynthesis of artemisinin from dihydroartemisinic acid and demonstrates efficient catalytic performance. It is worth noting that this dual-functionalized nanoreactor acts as the most efficient catalyst for artemisinin production among all known homogeneous and heterogeneous photocatalysts. The facile heterogeneous catalytic system can be efficiently recycled, showing enhanced stability in comparison to the traditional homogeneous catalysts. The result highlights the advantage of the hierarchically porous MOF catalyst with tailored functionalities and cooperative motifs as a highly accessible and recyclable heterogeneous catalyst, providing a more efficient and recyclable approach to drug production.