A Stable Triphenylamine-Based Zn(II)-MOF for Photocatalytic H2 Evolution and Photooxidative Carbon-Carbon Coupling Reaction

Efficient charge transfer has always been a challenge in heterogeneous MOF-based photoredox catalysis due to the poor electrical conductivity of the MOF photocatalyst, the toilless electron-hole recombination, and the uncontrollable host-guest interactions. Herein, a propeller-like tris(3'-carboxybiphenyl)amine (H₃TCBA) ligand was synthesized to fabricate a 3D Zn₃O cluster-based Zn(II)-MOF photocatalyst, Zn₃(TCBA)₂(μ₃-H₂O)H₂O (Zn-TCBA), which was applied to efficient photoreductive H₂ evolution and photooxidative aerobic cross-dehydrogenation coupling reactions of N-aryl-tetrahydroisoquinolines and nitromethane. In Zn-TCBA, the ingenious introduction of the meta-position benzene carboxylates on the triphenylamine motif not only promotes Zn-TCBA to exhibit a broad visible-light absorption with a maximum absorption edge of 480 nm but also causes special phenyl plane twists with dihedral angles of 27.8-45.8° through the coordination to Zn nodes. The semiconductor-like Zn clusters and the twisted TCBA^3- antenna with multidimensional π interaction sites facilitate photoinduced electron transfer to render Zn-TCBA a good photocatalytic H₂ evolution efficiency of 27.104 mmol·g^-1·h^-1 in the presence of [Co(bpy)₃]Cl₂ under visible-light illumination, surpassing many non-noble-metal MOF systems. Moreover, the positive enough excited-state potential of 2.03 V and the semiconductor-like characteristics of Zn-TCBA endow Zn-TCBA with double oxygen activation ability for photocatalytic oxidation of N-aryl-tetrahydroisoquinoline substrates with a yield up to 98.7% over 6 h. The durability of Zn-TCBA and the possible catalytic mechanisms were also investigated by a series of experiments including PXRD, IR, EPR, and fluorescence analyses.

Nanoconfinement-Enhanced Electrochemiluminescence for in Situ Imaging of Single Biomolecules

Direct imaging of electrochemical reactions at the single-molecule level is of potential interest in materials, diagnostic, and catalysis applications. Electrochemiluminescence (ECL) offers the opportunity to convert redox events into photons. However, it is challenging to capture single photons emitted from a single-molecule ECL reaction at a specific location, thus limiting high-quality imaging applications. We developed the nanoreactors based on Ru(bpy)₃²⁺-doped nanoporous zeolite nanoparticles (Ru@zeolite) for direct visualization of nanoconfinement-enhanced ECL reactions. Each nanoreactor not only acts as a matrix to host Ru(bpy)₃²⁺ molecules but also provides a nanoconfined environment for the collision reactions of Ru(bpy)₃²⁺ and co-reactant radicals to realize efficient in situ ECL reactions. The nanoscale confinement resulted in enhanced ECL. Using such nanoreactors as ECL probes, a dual-signal sensing protocol for visual tracking of a single biomolecule was performed. High-resolution imaging of single membrane proteins on heterogeneous cells was effectively addressed with near-zero backgrounds. This could provide a more sensitive tool for imaging individual biomolecules and significantly advance ECL imaging in biological applications.

Construction of Benzo-Fused Polycyclic Heteroaromatic Compounds through Palladium-Catalyzed Intramolecular C-H/C-H Biaryl Coupling

Dibenzo-fused five-membered heteroaromatic compounds, including dibenzofuran, carbazole, and dibenzothiophene, are fundamental structural units in various important polycyclic heteroaromatic compounds. The intramolecular C-H/C-H biaryl coupling of diaryl (thio)ethers and amines based on palladium(II) catalysis under oxidative conditions is known to be one of the most effective, step-economic methods for their construction. Representative examples for the construction of structurally intriguing π-extended polycyclic heteroaromatics through catalytic coupling reactions are briefly summarized in this mini-review.

Ionic metal-organic frameworks (iMOFs): progress and prospects as ionic functional materials

Metal-organic frameworks (MOFs) have been a research hotspot for the last two decades, witnessing an extraordinary upsurge across various domains in materials chemistry. Ionic MOFs (both anionic and cationic MOFs) have emerged as next-generation ionic functional materials and are an important subclass of MOFs owing to their ability to generate strong electrostatic interactions between their charged framework and guest molecules. Furthermore, the presence of extra-framework counter-ions in their confined nanospaces can serve as additional functionality in these materials, which endows them a significant advantage in specific host-guest interactions and ion-exchange-based applications. In the present review, we summarize the progress and future prospects of iMOFs both in terms of fundamental developments and potential applications. Furthermore, the design principles of ionic MOFs and their state-of-the-art ion exchange performances are discussed in detail and the future perspectives of these promising ionic materials are proposed.

High Electrochemiluminescence from Ru(bpy)3 2+ Embedded Metal-Organic Frameworks to Visualize Single Molecule Movement at the Cellular Membrane

Direct imaging of single-molecule and its movement is of fundamental importance in biology, but challenging. Herein, aided by the nanoconfinement effect and resultant high reaction activity within metal-organic frameworks (MOFs), the designed Ru(bpy)₃ ²⁺ embedded MOF complex (RuMOFs) exhibits bright electrochemiluminescence (ECL) emission permitting high-quality imaging of ECL events at single molecule level. By labeling individual proteins of living cells with single RuMOFs, the distribution of membrane tyrosine-protein-kinase-like7 (PTK7) proteins at low-expressing cells is imaged via ECL. More importantly, the efficient capture of ECL photons generated inside the MOFs results in a stable ECL emission up to 1 h, allowing the in operando visualization of protein movements at the cellular membrane. As compared with the fluorescence observation, near-zero ECL background surrounding the target protein with the ECL emitter gives a better contrast for the dynamic imaging of discrete protein movement. This achievement of single molecule ECL dynamic imaging using RuMOFs will provide a more effective nanoemitter to observe the distribution and motion of individual proteins at living cells.

Ionic encapsulation of a methanol carbonylation catalyst in a microporous metal-organic framework

The anionic rhodium complex cis-[Rh(CO)₂I₂]^-, active in the Monsanto process for acetic acid production, has been heterogenised via Coulombic interactions in the pores of a UiO-66-type metal-organic framework (MOF). The MOF-supported catalyst is active for the carbonylation of methanol and is recyclable, retaining its framework crystallinity following catalysis. Intermediates in the catalytic cycle observed by IR spectroscopy confirm the same mechanism as the established homogeneous process.

Heterogenisation of a carbonylation catalyst on dispersible microporous polymer nanoparticles

A rhodium carbonylation catalyst is supported on dispersible microporous polymer nanoparticles, facilitating in situ kinetic measurements for a key step of the catalytic cycle.

Recent advances in in situ oxygen-generating and oxygen-replenishing strategies for hypoxic-enhanced photodynamic therapy

Cancer is a leading cause of death worldwide, accounting for an estimated 10 million deaths by 2020. Over the decades, various strategies for tumor therapy have been developed and evaluated. Photodynamic therapy (PDT) has attracted increasing attention due to its unique characteristics, including low systemic toxicity and minimally invasive nature. Despite the excellent clinical promise of PDT, hypoxia is still the Achilles' heel associated with its oxygen-dependent nature related to increased tumor proliferation, angiogenesis, and distant metastases. Moreover, PDT-mediated oxygen consumption further exacerbates the hypoxia condition, which will eventually lead to the poor effect of drug treatment and resistance and irreversible tumor metastasis, even limiting its effective application in the treatment of hypoxic tumors. Hypoxia, with increased oxygen consumption, may occur in acute and chronic hypoxia conditions in developing tumors. Tumor cells farther away from the capillaries have much lower oxygen levels than cells in adjacent areas. However, it is difficult to change the tumor's deep hypoxia state through different ways to reduce the tumor tissue's oxygen consumption. Therefore, it will become more difficult to cure malignant tumors completely. In recent years, numerous investigations have focused on improving PDT therapy's efficacy by providing molecular oxygen directly or indirectly to tumor tissues. In this review, different molecular oxygen supplementation methods are summarized to alleviate tumor hypoxia from the innovative perspective of using supplemental oxygen. Besides, the existing problems, future prospects and potential challenges of this strategy are also discussed.

Synthesis and crystal structure of poly[(3-amino-1,2,4-triazole)(μ3-1H-benzimidazole-5,6-di-carboxyl-ato)cobalt(II)]

The asymmetric unit of the title coordination polymer, [Co(C9H4N2O4)(C2H4N4)] n or [Co(L 1)(L 2)] n , consists of one crystallographically independent Co2+ centre, one L 1 2- ligand and one L 2 ligand (L 1 = 1H-benzimidazole-5,6-di-carb-oxy-lic acid, L 2 = 3-amino-1,2,4-triazole). The Co2+ centre is coordinated by two carboxyl-ato-O atoms from two independent L 1 2- ligands and two nitro-gen atoms from L 2 and another L 1 ligand. Thus, the metal center adopts a four-coordinate mode, forming a tetra-hedral geometry. Inter-estingly, through the combination of two L 1 2-, two L 2 ligands and two Co2+ ions, a basic repeating unit is constructed, resulting in the formation of a one-dimensional straight chain structure. These chains are further expanded to the final three-dimensional framework via N-H⋯O hydrogen-bonding inter-actions.

Metal-Organic Frameworks: Synthetic Methods and Potential Applications

Metal-organic frameworks represent a porous class of materials that are build up from metal ions or oligonuclear metallic complexes and organic ligands. They can be considered as sub-class of coordination polymers and can be extended into one-dimension, two-dimensions, and three-dimensions. Depending on the size of the pores, MOFs are divided into nanoporous, mesoporous, and macroporous items. The latter two are usually amorphous. MOFs display high porosity, a large specific surface area, and high thermal stability due to the presence of coordination bonds. The pores can incorporate neutral molecules, such as solvent molecules, anions, and cations, depending on the overall charge of the MOF, gas molecules, and biomolecules. The structural diversity of the framework and the multifunctionality of the pores render this class of materials as candidates for a plethora of environmental and biomedical applications and also as catalysts, sensors, piezo/ferroelectric, thermoelectric, and magnetic materials. In the present review, the synthetic methods reported in the literature for preparing MOFs and their derived materials, and their potential applications in environment, energy, and biomedicine are discussed.

Heterogenisation of polyoxometalates and other metal-based complexes in metal–organic frameworks: from synthesis to characterisation and applications in catalysis

This review provides a thorough overview of composites with molecular catalysts (polyoxometalates, or organometallic or coordination complexes) immobilised into MOFs via non-covalent interactions.

Regioselective Functionalization of the Mesoporous Metal-Organic Framework, NU-1000, with Photo-Active Tris-(2,2'-bipyridine)ruthenium(II)

Solvent-assisted ligand incorporation is an excellent method for the post-synthetic functionalization of Zr-based metal-organic frameworks (MOFs), as carboxylate-derivative functionalities readily coordinate to the Zr6 nodes by displacing node-based aqua and terminal hydroxo ligands. In this study, a photocatalytically active ruthenium complex RuII(bpy)2(dcbpy), that is, bis-(2,2'-bipyridine)-(4,4'-dicarboxy-2,2'-bipyridine)ruthenium, was installed in the mono-protonated (carboxylic acid) form within NU-1000 via SALI. Crystallographic information regarding the siting of the ruthenium complex within the MOF pores is obtained by difference envelope density analysis. The ruthenium-functionalized MOF, termed Ru-NU-1000, shows excellent heterogeneous photocatalytic activity for an oxidative amine coupling reaction.

Two Mixed-ligand Coordination Polymers: Crystal Structures and Protective Effect on Ischemic Stroke by Increasing glp1r Expression

In this study, two new mixed-ligand coordination polymers {[Co(bbi)(tdc)]·5H₂O}_n (1, bbi = 1,4-bis(imidazolyl)butane) and {[Cu₂(bimb)(H₂O)(μ₃-tdc)₂(DMF)₂]·H₂O}_n (2, bimb = 4-bis(1H-imidazol-1-yl-methyl)benzene) were synthesized under the solvothermal conditions via reaction of 2,5-thiophenedicarboxylic acid (H₂tdc) with the corresponding metal salts in the existence of different flexible bis-imidazole ligands (bbi for 1 and bimb for 2). The as-prepared two structures were detected via the single crystal X-ray diffraction (SXRD) and then characterized via the analysis of element, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) as well as infrared (IR) spectroscopy. Furthermore, the protective activity of the compound on the mice with ischemic stroke was evaluated. Firstly, the real time reverse transcription-polymerase chain raction (RT-PCR) was carried out to determine the effect of compounds 1 and 2 against the relative expression level of the glucagon-like peptide 1 receptors (glp1r) on the cerebrovascular endothelial cells. Next, the Morris Water Maze Experiment was also used to detect the improvement function of compounds 1 and 2 on the nice mice cognitive function.

Crystal-to-Crystal Synthesis of Photocatalytic Metal-Organic Frameworks for Visible-Light Reductive Coupling and Mechanistic Investigations

Postmodification of reticular materials with well-defined catalysts is an appealing approach to produce new catalytic functional materials with improved stability and recyclability, but also to study catalysis in confined spaces. A promising strategy to this end is the postfunctionalization of crystalline and robust metal-organic frameworks (MOFs) to exploit the potential of crystal-to-crystal transformations for further characterization of the catalysts. In this regard, two new photocatalytic materials, MOF-520-PC1 and MOF-520-PC2, are straightforwardly obtained by the postfunctionalization of MOF-520 with perylene-3-carboxylic acid (PC1) and perylene-3-butyric acid (PC2). The single crystal-to-crystal transformation yielded the X-ray diffraction structure of catalytic MOF-520-PC2. The well-defined disposition of the perylenes inside the MOF served as suitable model systems to gain insights into the photophysical properties and mechanism by combining steady-state, time-resolved, and transient absorption spectroscopy. The resulting materials are active organophotoredox catalysts in the reductive dimerization of aromatic aldehydes, benzophenones, and imines under mild reaction conditions. Moreover, MOF-520-PC2 can be applied for synthesizing gram-scale quantities of products in continuous-flow conditions under steady-state light irradiation. This work provides an alternative approach for the construction of well-defined, metal-free, MOF-based catalysts.

Metal–Organic Frameworks (MOFs) and Covalent Organic Frameworks (COFs) Applied to Photocatalytic Organic Transformations

Among the different alternatives for catalysis using metal–organic frameworks (MOFs) or covalent organic frameworks (COFs), photocatalysis has remarkably evolved during the last decade. Photocatalytic reticular materials allowed recyclability and easy separation of catalyst from the product, also reaching the activity and selectivity commonly observed for molecular systems. Recently, photocatalytic MOFs and COFs have been applied to synthetic applications in order to obtain organic molecules of different complexity. However, although a good number of works have been devoted to this issue, an updated comprehensive revision on this field is still needed. The aim of this review was to fill this gap covering the following three general aspects: (1) common strategies on the design of reticular photocatalytic materials, (2) a comprehensive discussion of the photocatalytic organic reactions achieved by the use of COFs and MOFs, and (3) some critical considerations highlighting directions that should be considered in order to make advances in the study of photocatalytic COFs and MOFs.

Metal-Organic Framework-Based Catalysts with Single Metal Sites

Metal-organic frameworks (MOFs) are a class of distinctive porous crystalline materials constructed by metal ions/clusters and organic linkers. Owing to their structural diversity, functional adjustability, and high surface area, different types of MOF-based single metal sites are well exploited, including coordinately unsaturated metal sites from metal nodes and metallolinkers, as well as active metal species immobilized to MOFs. Furthermore, controllable thermal transformation of MOFs can upgrade them to nanomaterials functionalized with active single-atom catalysts (SACs). These unique features of MOFs and their derivatives enable them to serve as a highly versatile platform for catalysis, which has actually been becoming a rapidly developing interdisciplinary research area. In this review, we overview the recent developments of catalysis at single metal sites in MOF-based materials with emphasis on their structures and applications for thermocatalysis, electrocatalysis, and photocatalysis. We also compare the results and summarize the major insights gained from the works in this review, providing the challenges and prospects in this emerging field.

Tritopic Triazatruxene Ligands for Multicomponent Metal-Organic Frameworks

Multicomponent metal-organic frameworks (MOFs) are built up from multiple ligands that are geometrically distinct. These ligands occupy specific positions in the MOF lattice. Installing different functionalities at precise locations in the framework is an important step in making MOFs for specific applications. This can be achieved by designing functionalized ligands for multicomponent MOFs. Here, we report a simple synthetic procedure for a new tritopic triazatruxene based tricarboxylic acid, H₃ tat. We show that this ligand can be symmetrically derivatized with various substituents on its nitrogen centres. We report a new isoreticular series of well-ordered quaternary MOFs based on these new triazatruxene ligands together with two linear carboxylate ligands and Zn₄ O clusters. These MOFs are isostructural to the previously reported MUF-77 series and show similar high surface areas and large pore volumes. Furthermore, H-bonding between the NH sites of the incorporated triazatruxene ligands and guest molecules is employed to modify their fluorescence behavior.

A Sensitive Electrochemiluminescence Sensor for Brilliant Blue FCF Using Ru(bpy)32+ Immobilized Zn-MOF

A novel electrochemiluminescence (ECL) sensor for detection of brilliant blue FCF (BB) has been developed using Ru@Zn-MOF/nafion modified GCE (glass carbon electrode) in this research. Different from conventional method for usage of Ru(bpy)₃²⁺ in solution-phase, Ru(bpy)₃²⁺ here was immobilized on a zinc-metal-organic-framework (Zn-MOF). After adding BB, a significant quenching phenomenon of ECL intensity was observed. The behavior of BB on the quenching effect of Ru(bpy)₃²⁺/Zn-MOF in different conditions was investigated thoroughly and the detection limit was achieved to 2.5 × 10^-8 M in an optimized condition. Furthermore, the interference of some conventional ions and amino acids to the detection of BB was also investigated. Additionally, the composite showed a good effect on the detection of BB in commercial samples. The proposed sensor provided a promising platform for food safety analysis, environmental monitoring and clinical testing.

A mesoporous NNN-pincer-based metal–organic framework scaffold for the preparation of noble-metal-free catalysts

A terpyridine-based mesoporous 3D MOF was synthesized as a general scaffold for catalyst preparation.

Incorporation of a Ru complex into an amine-functionalized metal–organic framework for enhanced activity in photocatalytic aerobic benzyl alcohol oxidation

Encapsulation of [Ru(bpy)₃]²⁺ in the cavity of a metal–organic framework was found to enhance its activity in the photocatalytic aerobic oxidation of benzyl alcohol.

Porous functionalized MOF self-evolution promoting molecule encapsulation and Hg2+ removal

Porous functionalized MOF self-evolution has successfully improved the Hg²⁺ removal performance and implemented dye molecule encapsulation.

Two metal–organic frameworks based on pyridyl–tricarboxylate ligands as size-selective catalysts for solvent-free cyanosilylation reaction

Two novel 3D metal–organic frameworks based on multifunctional pyridyl–tricarboxylate ligands as size-selective heterogeneous catalysts for the cyanosilylation of acetaldehydes.

Stable metal–organic frameworks as a host platform for catalysis and biomimetics

Recent years have witnessed the exploration and synthesis of an increasing number of metal–organic frameworks (MOFs). The utilization of stable MOFs as a platform for catalysis and biomimetics is discussed.

Flexible Zirconium MOF as the Crystalline Sponge for Coordinative Alignment of Dicarboxylates

Because of their permanent porosity and unparalleled structural diversities, flexible metal-organic frameworks (MOFs) are promising and highly desirable in host-guest chemistry. In this work, we employed a flexible Zr-MOF system, namely PCN-700 species, as the crystalline sponge for guest inclusion. A family of linear dicarboxylate ligands was adsorbed in the void space of PCN-700, which were subsequently confirmed by crystallographic observation. The stretching degree of the PCN-700 series was varied by means of dicarboxylate encapsulation through coordinative alignment.

Ruthenium(II) Complex Incorporated UiO-67 Metal-Organic Framework Nanoparticles for Enhanced Two-Photon Fluorescence Imaging and Photodynamic Cancer Therapy

Ruthenium(II) tris(bipyridyl) cationic complex (Ru(bpy)₃²⁺) incorporated UiO-67 (Universitetet i Oslo) nanoscale metal-organic frameworks (NMOFs) with an average diameter of ∼92 nm were developed as theranostic nanoplatform for in vitro two-photon fluorescence imaging and photodynamic therapy. After incorporation into porous UiO-67 nanoparticles, the quantum yield, luminescence lifetime, and two-photon fluorescence intensity of Ru(bpy)₃²⁺ guest molecules were much improved owing to the steric confinement effect of MOF pores. Benefiting from these merits, the as-synthesized nanoparticles managed to be internalized by A549 cells while providing excellent red fluorescence in cytoplasm upon excitation with 880 nm irradiation. Photodynamic therapeutic application of the Ru(bpy)₃²⁺-incorporated UiO-67 NMOFs was investigated in vitro. The Ru(bpy)₃²⁺-incorporated UiO-67 NMOFs exhibited good biocompatibility without irradiation while having good cell-killing rates upon irradiation. In view of these facts, the developed Ru(bpy)₃²⁺-incorporated NMOFs give a new potential pathway to achieve enhanced two-photon fluorescence imaging and photodynamic therapy.

Photocatalytic metal–organic frameworks for organic transformations

Metal–organic frameworks (MOFs) have attracted increasing attention for applications in heterogeneous photocatalysis.

Nanosizing a Metal-Organic Framework Enzyme Carrier for Accelerating Nerve Agent Hydrolysis

We report the synthesis and characterization of a water-stable zirconium metal-organic framework (MOF), NU-1003, featuring the largest mesoporous aperture known for a zirconium MOF. This material has been used to immobilize the nerve agent hydrolyzing enzyme, organophosphorus acid anhydrolase (OPAA). The catalytic efficiency of immobilized OPAA in nanosized NU-1003 is significantly increased compared to that of OPAA immobilized in microsized NU-1003 and even exceeds that of the free OPAA enzyme. This paper highlights a method for rapid and highly efficient hydrolysis of nerve agents using nanosized enzyme carriers.

Highly Porous Zirconium Metal-Organic Frameworks with β-UH3-like Topology Based on Elongated Tetrahedral Linkers

Two non-interpenetrated zirconium metal-organic frameworks (Zr-MOFs), NPF-200 and NPF-201, were synthesized via the assembly of elongated tetrahedral linkers with Zr6 and Zr8 clusters. They represent the first examples of MOFs to have the β-UH3-like, 4,12,12T1 topology. Upon activation, NPF-200 exhibits the largest BET surface area (5463 m(2) g(-1)) and void volume (81.6%) among all MOFs formed from tetrahedral ligands. Composed of negative-charged boron-centered tetrahedral linkers, NPF-201 is an anionic Zr-MOF which selectively uptakes photoactive [Ru(bpy)3](2+) for heterogeneous photo-oxidation of thioanisole.