Homochiral metal-organic frameworks for asymmetric heterogeneous catalysis

An Imine-Linked Metal-Organic Framework as a Reactive Oxygen Species Generator

A new metal-organic framework (MOF) with both coordination linkages and covalent linkages is prepared by coordinating Cu^I with pyrazolate for an aldehyde-functionalized trinuclear complex, and subsequent imine condensation with p-phenylenediamine, a reaction typical for covalent organic framework (COF) synthesis. This MOF×COF collaboration yields FDM-71 with honeycomb layers stacked in eclipsed fashion. After dissociating the Cu^I -pyrazolate coordination in FDM-71, the obtained organic components carry the information of structural defects, and thus vacancy identity (aldehyde-based unit vacancy and amine-based unit vacancy) and concentration are definitely resolved. Further to the redox catalytic activity inherited from the complex, FDM-71 features effective photosensitizing activity. The two functions integrated in one well-defined structure is demonstrated by its high efficiency in decomposing H₂ O₂ and consequent excitation of O₂ to reactive oxygen species.

Chiral porous organic frameworks and their application in enantioseparation

Porous organic frameworks (POFs) are a kind of porous material with a network structure composed of repeated monomers, which have excellent physical and chemical properties, such as a high surface area, high porosity, uniform pore sizes and structural diversity, and which have aroused broad interest among researchers. With the rapid development of materials science, increasingly more porous materials have been developed and applied, especially metal organic frameworks (MOFs) and covalent organic frameworks (COFs), which have been widely applied in the fields of luminous materials, catalytic research, adsorption and drug transport. One of the most important applications for chiral porous materials is in chiral separation and these materials have become a research hotspot in the field of chromatographic separation and analysis in recent years. In this review, from the viewpoint of enantioseparation, the synthesis of chiral porous materials and their applications in high-performance liquid chromatography (HPLC), capillary electrochromatography (CEC), and gas chromatography (GC) are reviewed. The typical applications of MOFs in solid-phase microextraction (SPME) are also discussed.

Green facile synthesis to develop nanoscale coordination polymers as lysosome-targetable luminescent bioprobes

Three new coordination polymers (CPs), namely [{M(HL)(L)(H2O)}(ClO4)(H2O)]∞ (M = Zn for CP 1, Mn for CP 2, Cu for CP 3) were synthesized to explore their efficacy as lysosome-targetable luminescent bioprobes. The synthesized CPs were characterized by techniques including single-crystal X-ray analysis, FTIR spectroscopy and elemental analysis. Single-crystal analysis revealed the formation of iso-structural CPs displaying distorted adamantoid topology developed by bridging ligands and H-bonds connections and metals at the nodes. A green hand-grinding technique with a mortar and pestle resulted in nanoscale coordination polymers (NCPs) suitable for cell permeability and was further confirmed by SEM and DLS analyses. Two of these hand-ground nanoscale coordination polymers NCP 1 and NCP 2 showed excellent green luminescence and were explored as potential and selective long-time biotrackers towards lysosome using the human lung carcinoma cell line (A549). Strikingly, the developed bioprobe displayed excellent bio-availability, photostability and excellent selectivity towards lysosomes sustained by various in vitro cell imaging experiments. Moreover, the long-term probing ability of these NCPs turned out to be better than the commercially available lysosome tracker i.e. LysoTracker Red, indicating their potential real-life application in bio-imaging. To the best ofour knowledge, this is the first example of nonexpensive and less toxic essential transition metal-based nanoscale coordination polymers that can behave as effective lysosome-targetable luminescent bioprobes.

pH response of a hydroxyl-functionalized luminescent metal–organic framework based phosphor

The ligand sensitized Tb³⁺ centered emission of Tb-doped Y-based hydroxyl functionalized MOFs has been utilized for pH sensing in the visible range.

Diverse physical functionalities of rare-earth hexacyanidometallate frameworks and their molecular analogues

The combination of rare-earth metal complexes and hexacyanidometallates of transition metals is a fruitful pathway for achieving functional materials exhibiting a wide scope of mechanical, magnetic, optical, and electrochemical properties.

Recent advances in process engineering and upcoming applications of metal-organic frameworks

Progress in metal-organic frameworks (MOFs) has advanced from fundamental chemistry to engineering processes and applications, resulting in new industrial opportunities. The unique features of MOFs, such as their permanent porosity, high surface area, and structural flexibility, continue to draw industrial interest outside the traditional MOF field, both to solve existing challenges and to create new businesses. In this context, diverse research has been directed toward commercializing MOFs, but such studies have been performed according to a variety of individual goals. Therefore, there have been limited opportunities to share the challenges, goals, and findings with most of the MOF field. In this review, we examine the issues and demands for MOF commercialization and investigate recent advances in MOF process engineering and applications. Specifically, we discuss the criteria for MOF commercialization from the views of stability, producibility, regulations, and production cost. This review covers progress in the mass production and formation of MOFs along with future applications that are not currently well known but have high potential for new areas of MOF commercialization.

A new series of 3D lanthanide phenoxycarboxylates: synthesis, crystal structure, magnetism and photoluminescence studies

A new series of 3D Ln-carboxylates was synthesized, where the Tb one shows antiferromagnetic coupling and the Dy one shows ferromagnetic interaction, and with emission spectra combining the intra-4f emission of the Ln ions and that of the ligand.

Recent progress in lanthanide metal–organic frameworks and their derivatives in catalytic applications

Research progress in lanthanide metal–organic frameworks and their derivatives in the field of catalysis has been presented on the basis of different organic reactions.

Single molecule magnet behavior and magnetic refrigeration of carbonyl oxygen-bridged tetranuclear lanthanide complexes

Three lanthanide complexes were fabricated and characterized. 1 exhibited cryogenic magnetic refrigeration property and 3 displayed slow relaxation of the magnetization.

A different approach: highly encapsulating macrocycles being used as organic tectons in the building of CPs

For the first time, the cross-bridged cyclam unit is used as an organic tecton to build coordination polymers.

Supramolecular chirality in the crystals of mononuclear and polymeric cobalt(ii) complexes with enantiopure and racemic N-thiophosphorylated thioureas

The control of stereochemistry in Co(ii) complexes was provided by additional pyridine and pyrazine ligands. 1D and 2D supramolecular homochiral arrangements in racemic crystals of mononuclear complexes are transferred to their polymeric counterparts.

A green and sustainable approach for the synthesis of 1,5-benzodiazepines and spirooxindoles in one-pot using a MIL-101(Cr) metal–organic framework as a reusable catalyst

Green and efficient protocols for the synthesis of 1,5-benzodiazepines and spirooxindoles were developed utilizing MIL-101(Cr) in SFRC and water as solvent respectively.

The state of the field: from inception to commercialization of metal–organic frameworks

We provide a brief overview of the state of the MOF field from their inception to their synthesis, potential applications, and finally, to their commercialization.

Metal-organic frameworks containing xanthene dyes for photocatalytic applications

Metal-organic frameworks (MOFs) have recently emerged as a new type of prospective photocatalytic material due to their characteristics such as tunable structures, pore modification, crystalline nature with eliminated structural defects, unique semiconductor properties, etc. However, most of these systems also suffer from low activity, high cost, and low visible light utilization. Xanthene dyes are eco-friendly organic dyes used in photocatalysis. They possess the advantages of low cost, low toxicity, and high visible light response; so, they can be directly used as building blocks to fabricate MOF materials or as proper cocatalysts to increase the absorbance of irradiation leading to the construction of a reasonable photocatalytic system. Herein, we have summarized the recent developments in the study of MOFs containing xanthene dyes for photocatalytic applications. The paper can be divided into two sections depending on whether the xanthene dyes are coordinated in the MOF structure: (i) MOFs synergized with xanthene dyes for photocatalytic applications and (ii) MOFs with xanthene dyes incorporated within ligand backbones for photocatalytic applications. Moreover, in this paper, the present challenges and future opportunities in this field are also discussed.

Recent Advances in the Application of Metal–Organic Frameworks for Polymerization and Oligomerization Reactions

Polymers have become one of the major types of materials that are essential in our daily life. The controlled synthesis of value-added polymers with unique mechanical and chemical properties have attracted broad research interest. Metal–organic framework (MOF) is a class of porous material with immense structural diversity which offers unique advantages for catalyzing polymerization and oligomerization reactions including the uniformity of the catalytic active site, and the templating effect of the nano-sized channels. We summarized in this review the important recent progress in the field of MOF-catalyzed and MOF-templated polymerizations, to reveal the chemical principle and structural aspects of these systems and hope to inspire the future design of novel polymerization systems with improved activity and specificity.

ZIF-8 Modified Polypropylene Membrane: A Biomimetic Cell Culture Platform with a View to the Improvement of Guided Bone Regeneration

PURPOSE

Despite the significant advances in modeling of biomechanical aspects of cell microenvironment, it remains a major challenge to precisely mimic the physiological condition of the particular cell niche. Here, the metal-organic frameworks (MOFs) have been introduced as a feasible platform for multifactorial control of cell-substrate interaction, given the wide range of physical and mechanical properties of MOF materials and their structural flexibility.

RESULTS

In situ crystallization of zeolitic imidazolate framework-8 (ZIF-8) on the polydopamine (PDA)-modified membrane significantly raised surface energy, wettability, roughness, and stiffness of the substrate. This modulation led to an almost twofold increment in the primary attachment of dental pulp stem cells (DPSCs) compare to conventional plastic culture dishes. The findings indicate that polypropylene (PP) membrane modified by PDA/ZIF-8 coating effectively supports the growth and proliferation of DPSCs at a substantial rate. Further analysis also displayed the exaggerated multilineage differentiation of DPSCs with amplified level of autocrine cell fate determination signals, like BSP1, BMP2, PPARG, FABP4, ACAN, and COL2A. Notably, osteogenic markers were dramatically overexpressed (more than 100-folds rather than tissue culture plate) in response to biomechanical characteristics of the ZIF-8 layer.

CONCLUSION

Hence, surface modification of cell culture platforms with MOF nanostructures proposed as a powerful nanomedical approach for selectively guiding stem cells for tissue regeneration. In particular, PP/PDA/ZIF-8 membrane presented ideal characteristics for using as a barrier membrane for guided bone regeneration (GBR) in periodontal tissue engineering.

A critical review on recent developments in MOF adsorbents for the elimination of toxic heavy metals from aqueous solutions

Effective and substantial remediation of contaminants especially heavy metals from water is still a big challenge in terms of both environmental and biological perspectives because of their adverse effects on the human health. Many techniques including adsorption, ion exchange, co-precipitation, chemical reduction, ultrafiltration, etc. are reported for eliminating heavy metal ions from the water. However, adsorption has preferred because of its simple and easy handlings. Several types of adsorbents are observed and documented well for the purpose. Recently, highly porous metal-organic frameworks (MOFs) were developed by incorporating metals and organic ligands together and claimed as potent adsorbents for the remediation of highly toxic heavy metals from the aqueous solutions due to their unique features like greater surface area, high chemical stability, green and reuse material, etc. In this review, the authors discussed systematically some recent developments about secure MOFs to eliminate the toxic metals such as arsenic (both arsenite and arsenate), chromium(VI), cadmium (Cd), mercury (Hg) and lead (Pb). MOFs are observed as the most efficient adsorbents with greater selectivity as well as high adsorption capacity for metallic contamination. Graphical abstract.

Ambient CO2/N2 Switchable Pickering Emulsion Emulsified by TETA-Functionalized Metal-Organic Frameworks

In recent years, metal-organic frameworks (MOFs) have been explored as emulsifiers for the fabrication of Pickering emulsions and then used for hybrid material synthesis and interface catalysis. Nevertheless, stimuli-responsive Pickering emulsions stabilized by MOFs have been rarely reported so far, although they are of great importance for fundamental research studies and practical applications. Herein, for the first time, triethylenetetramine (TETA)-functionalized MOFs (ZIF-90/TETA) have been designed, synthesized, and used for fabricating CO₂-/N₂-response Pickering emulsions. It is shown that even at the ZIF-90/TETA content of 0.25 wt %, the functional MOF can still efficiently emulsify n-hexane and water to form a high internal phase Pickering emulsion. Importantly, the Pickering emulsion can be easily and reversibly switched between emulsification and demulsification by bubbling of CO₂ and N₂ alternatively at atmospheric pressure. The possible mechanism of the CO₂/N₂ switchable emulsion is investigated by zeta potential, water contact angle, interfacial tension, ¹³C NMR spectroscopy, and an optical microscope. It is found that the acid-base reaction of CO₂ with TETA anchored on the surface of ZIF-90 leads to the production of hydrophilic ammonium bicarbonate and carbamate, which results in the emulsification of the Pickering emulsion. However, when N₂ is bubbled to remove CO₂, the reverse reaction takes place to cause the demulsification of the Pickering emulsion. Moreover, the CO₂/N₂ switchable Pickering emulsion has been successfully used as a microreactor for Knoevenagel reactions to demonstrate a highly efficient integration of chemical reaction, product separation, and ZIF-90/TETA recycling for a sustainable chemical process.

CFA-18: a homochiral metal-organic framework (MOF) constructed from rigid enantiopure bistriazolate linker molecules

In this work, we introduce the first enantiopure bistriazolate-based metal-organic framework, CFA-18 (Coordination Framework Augsburg-18), built from the R-enantiomer of 7,7,7',7'-tetramethyl-6,6',7,7'-tetrahydro-3H,3'H-5,5'-spirobi[indeno[5,6-d]-[1,2,3]triazole] (H2-spirta). The enantiopurity and absolute configuration of the new linker were confirmed by several chiroselective methods. Reacting H2-spirta in hot N,N-dimethylformamide (DMF) with manganese(ii) chloride gave CFA-18 as colorless crystals. The crystal structure with the composition [Mn2Cl2(spirta)(DMF)2] was solved using synchrotron single-crystal X-ray diffraction. CFA-18 shows a framework topology that is closely related to previously reported metal-azolate framework (MAF) structures in which the octahedrally coordinated manganese(ii) ions are triazolate moieties, and the chloride anions form crosslinked one-dimensional helical chains, giving rise to hexagonal channels. In contrast to MAFs crystallizing in the centrosymmetric space group R3[combining macron], the handedness of the helices found in CFA-18 is strictly uniform, leading to a homochiral framework that crystallizes in the trigonal crystal system within the chiral space group P3121 (no. 152).

Ultrasensitive, rapid and selective sensing of hazardous fluoride ion in aqueous solution using a zirconium porphyrinic luminescent metal-organic framework

The development of a rapid and sensitive method for the detection of fluoride ion (F^-) in aqueous systems is of great significance for human health and environmental monitoring. In this study, a zirconium porphyrinic luminescent metal-organic framework (LMOF), PCN-222, was employed as a novel fluorescent probe for the ultrasensitive, rapid and selective detection of F^- in water. The PCN-222 probe was prepared by a facile solvothermal method. It exhibited good fluorescence stability and was highly stable in water. The fluorescence emission of PCN-222 could be effectively and selectively quenched by F^- due to the strong coordination affinity of F^- to the zirconium clusters in PCN-222. The proposed fluorescence method for F^- detection based on PCN-222 probe afforded a linear response range of 1-20 μmol/L and a very low detection limit (0.048-0.065 μmol/L) in reference to many reported F^- fluorescent probes. Moreover, a rapid response time (<10 s) was obtained due to the open and uniform pore structure of PCN-222 that allowed the fast diffusion of F^- to interact with the zirconium recognition sites. Finally, the PCN-222 probe was successfully applied for the fluorescence detection of F^- in real water samples. These results highlight the great application potential of LMOF in the sensing fields.

99TcO4- removal from legacy defense nuclear waste by an alkaline-stable 2D cationic metal organic framework

Removal of ⁹⁹TcO₄⁻ from legacy defense nuclear tank waste at Savannah River Site is highly desirable for the purpose of nuclear safety and environmental protection, but currently not achievable given the extreme conditions including high alkalinity, high ionic strength, and strong radiation field. Herein, we present a potential solution to this long-term issue by developing a two-dimensional cationic metal organic framework SCU-103, showing ultrahigh stability in alkaline aqueous media and great resistance to both β and γ radiation. More importantly, it is very effective for ⁹⁹TcO₄⁻ separation from aqueous media as demonstrated by fast exchange kinetics, high sorption capacity, and superior selectivity, leading to the successful removal of ⁹⁹TcO₄⁻ from actual Savannah River Site high level tank waste for the first time, to the best of our knowledge. In addition, the uptake mechanism is comprehensively elucidated by molecular dynamics simulation and density functional theory calculation, showing a unique chemical recognition of anions with low charge density.

Separation of ⁹⁹TcO₄⁻ from nuclear waste at the Savannah River Site is hampered by the extreme conditions. Here, the authors propose a solution by developing an alkaline-resistant metal organic framework material featuring unique recognition sites for selective incorporation of ⁹⁹TcO₄⁻ anions.

Solid-state NMR studies of the acidity of functionalized metal-organic framework UiO-66 materials

The acid strength of metal-organic frameworks plays a key role in their catalytic performance such as activity and selectivity during catalytic reactions. Solid-state nuclear magnetic resonance in combination with probe molecules including 2-¹³ C-acetone and pyridine-d₅ was employed to characterize the acid strength of UiO-66-X (X = -H, -2COOH, -SO₃ H). It was found that after introduction of the functional groups, the acid strength of UiO-66-2COOH and UiO-66-SO₃ H is considerably enhanced compared with that of parent UiO-66, with that of the former being similar to that of zeolite H-ZSM-5, and with that of the latter being slightly stronger than that of the former. Even though the acid density can efficiently be modified through changing the relative ratio in multivariate functionalized UiO-66-X, no significant alternation for the acid strength could be discerned in the MTV-UiO-66-X compared with acidic same-link counterpart. Theoretical calculations were employed to further confirm the acid strength of UiO-66-SO₃ H and UiO-66-2COOH.

Porphyrins Through the Looking Glass: Spectroscopic and Mechanistic Insights in Supramolecular Chirogenesis of New Self-Assembled Porphyrin Derivatives

The solvent driven aggregation of porphyrin derivatives, covalently linked to a L- or D-prolinate enantiomer, results in the stereospecific formation of species featuring remarkable supramolecular chirality, as a consequence of reading and amplification of the stereochemical information stored in the proline-appended group. Spectroscopic, kinetic, and topographic SEM studies gave important information on the aggregation processes, and on the structures of the final chiral architectures. The results obtained may be the seeds for the construction of stereoselective sensors aiming at the detection, for example, of novel emergent pollutants from agrochemical, food, and pharmaceutical industry.

Cd-Based Metal-Organic Framework Containing Uncoordinated Carbonyl Groups as Lanthanide Postsynthetic Modification Sites and Chemical Sensing of Diphenyl Phosphate as a Flame-Retardant Biomarker

With the judicious selection of an appropriate semirigid polycarboxylate, 2,5-bis(3',5'-dicarboxylphenyl)benzoic acid (H₅bdba), and an inorganic metal ion, a novel anionic framework, {[NH₂(CH₃)₂]₂·[Cd_3.5(bdba)(Hbdba)(H₂O)_1.5]}_n (Cd-MOF), has been synthesized solvothermally. Single-crystal measurement results show that the prepared Cd-MOF features a three-dimensional structure containing two types of one-dimensional channels, and as we expected, there exist accessible uncoordinated -COOH groups on Hbdba pointing toward the rhombus channels. Powder X-ray diffraction and thermogravimetric analysis measurements were performed for the thermal and chemical stability analysis of Cd-MOF. In addition, the lanthanide(III)-functionalized hybrids, Ln(III)@Cd-MOF, were initially prepared by coordinated postsynthetic modification to incorporate luminescent Ln(III) ions into the structure. The luminescence properties of the hybrids are studied, and the results show notable and specialized fluorescent sensitization of Cd-MOF to Tb(III) ions. Moreover, the Tb(III)@Cd-MOF hybrid with outstanding fluorescence properties was developed as a highly sensitive and selective luminescent probe for the biomarker diphenyl phosphate (DPP) based on multiquenching effects. Tb(III)@Cd-MOF is the first case to realize the detection of urinary DPP through lanthanide metal-organic framework fluorescence spectrometry and shows practical detection potential.

Chirality and Surface Bonding Correlation in Atomically Precise Metal Nanoclusters

Chirality is ubiquitous in nature and occurs at all length scales. The development of applications for chiral nanostructures is rising rapidly. With the recent achievements of atomically precise nanochemistry, total structures of ligand-protected Au and other metal nanoclusters (NCs) are successfully obtained, and the origins of chirality are discovered to be associated with different parts of the cluster, including the surface ligands (e.g., swirl patterns), the organic-inorganic interface (e.g., helical stripes), and the kernel. Herein, a unified picture of metal-ligand surface bonding-induced chirality for the nanoclusters is proposed. The different bonding modes of M-X (where M = metal and X = the binding atom of ligand) lead to different surface structures on nanoclusters, which in turn give rise to various characteristic features of chirality. A comparison of Au-thiolate NCs with Au-phosphine ones further reveals the important roles of surface bonding. Compared to the Au-thiolate NCs, the Ag/Cu/Cd-thiolate systems exhibit different coordination modes between the metal and the thiolate. Other than thiolate and phosphine ligands, alkynyls are also briefly discussed. Several methods of obtaining chiroptically active nanoclusters are introduced, such as enantioseparation by high-performance liquid chromatography and enantioselective synthesis. Future perspectives on chiral NCs are also proposed.

Supramolecular Chiral Nanoarchitectonics

Exploration of molecular functions and material properties based on the control of chirality would be a scientifically elegant approach. Here, the fabrication and function of chiral-featured materials from both chiral and achiral components using a supramolecular nanoarchitectonics concept are discussed. The contents are classified in to three topics: i) chiral nanoarchitectonics of rather general molecular assemblies; ii) chiral nanoarchitectonics of metal-organic frameworks (MOFs); iii) chiral nanoarchitectonics in liquid crystals. MOF structures are based on nanoscopically well-defined coordinations, while mesoscopic orientations of liquid-crystalline phases are often flexibly altered. Discussion on the effects and features in these representative materials systems with totally different natures reveals the universal importance of supramolecular chiral nanoarchitectonics. Amplification of chiral molecular information from molecules to materials-level structures and the creation of chirality from achiral components upon temporal statistic fluctuations are universal, regardless of the nature of the assemblies. These features are thus surely advantageous characteristics for a wide range of applications.