Self-Healing Hyper-Cross-Linked Metal–Organic Polyhedra (HCMOPs) Membranes with Antimicrobial Activity and Highly Selective Separation Properties

Metal Ions Trigger the Gelation of Cysteine-Containing Peptide-Appended Coordination Cages

We report a series of coordination cages that incorporate peptide chains at their vertices, prepared through subcomponent self-assembly. Three distinct heterochiral tripeptide subcomponents were incorporated, each exhibiting an L-D-L stereoconfiguration. Through this approach, we prepared and characterized three tetrahedral metal-peptide cages that incorporate thiol and methylthio groups. The gelation of these cages was probed through the binding of additional metal ions, with the metal-peptide cages acting as junctions, owing to the presence of sulfur atoms on the peripheral peptides. Gels were obtained with cages bearing cysteine at the C-terminus. Our strategy for developing functional metal-coordinated supramolecular gels with a modular design may result in the development of materials useful for chemical separations or drug delivery.

Humidity-Induced Self-Oscillating and Self-Healing Hypercrosslinked Metal-Organic Polyhedra Membranes

Designing autonomously oscillating materials is highly desirable for emerging smart material fields but challenging. Herein, a type of hypercrosslinked metal-organic polyhedra (HCMOPs) membranes formed by covalent crosslinking of boronic acid-modified Zr-based MOPs with polyvinyl alcohol (PVA) are rationally designed. In these membranes, MOPs serve as high-connectivity nodes and provide dynamic borate bonds with PVA in hypercrosslinked networks, which can be broken/formed reversibly upon the stimulus of water vapor. The humidity response characteristic of HCMOPs promotes their self-oscillating and self-healing properties. HCMOP membranes can realize a self-oscillating property above the water surface even after loading a cargo that is 1.5 times the weight of the membrane due to the fast adsorption and desorption kinetics. Finally, the HCMOP actuator can realize energy conversion from mechanical energy into electricity when coupled with a piezoelectric membrane. This work not only paves a new avenue to construct MOP-polymer hybrid materials but also expands the application scopes of MOPs for smart actuation devices.

Covalent Post-Synthetic Modification of Metal-Organic Cages: Concepts and Recent Progress

Metal-organic cages (MOCs) are supramolecular coordination complexes that have internal cavities for hosting guest molecules and exhibiting various properties. However, the functions of MOCs are limited by the choice of the building blocks. Post-synthetic modification (PSM) is a technique that can introduce new functional groups and replace existing ones on the MOCs without changing their geometry. Among many PSM methods, covalent PSM is a promising approach to modify MOCs with tailored structures and functions. Covalent PSM can be applied to either the internal cavity or the external surface of the MOCs, depending on the functionality expected to be customized. However, there are still some challenges and limitations in the field of covalent PSM of MOCs, such as the balance between the stability of MOCs and the harshness of organic reactions involved in covalent PSMs. This concept article introduces the organic reaction types involved in covalent PSM of MOCs, their new applications after modification, and summarizes and provides an outlook of this research field.

Ionic Polyimine-Based Composite Membrane with Inductive and Complexation Synergistic Effects for Sensitive and On-Site Fluorescent Detection of Volatile Iodine

Along with the development of nuclear power, concerns about radioactive emissions and the potential for nuclear leakage have been widely raised, particularly of harmful iodine isotopes. However, as a significant component of nuclear air waste, the enrichment and detection of air-dispersed gaseous iodine remain a challenge. In this work, it is focused on developing an attraction-immobilization-detection strategy-based fluorescence method for the on-site detection of volatile iodine, by employing a photoluminescent ionic polyimine network-polyvinylpyrrolidone (IPIN-PVP) composite membrane. This strategy synergizes ion-induced dipole interactions from IPIN and complexation effects from PVP, allowing effective iodine enrichment and immobilization. As a result, the optimized IPIN-PVP membrane exhibits rapid response times of 5 s and a low detection limit of 4.087 × 10-8 m for gaseous iodine. It also introduces a portable handheld detection device that utilizes the composite membrane, offering a practical solution for real-time on-site detection of volatile iodine. This innovation enhances nuclear safety measures and disaster management by providing rapid and reliable iodine detection capabilities.

Mechanically Robust, Durable, and Multifunctional Hyper-Crosslinked Elastomer Based on Metal-Organic-Cluster Crosslinker: The Role of Topological Structure

Polymer materials formed by conventional metal-ligand bonds have very low branch functionality, the crosslinker of such polymer usually consists of 2-4 polymer chains and a single metal ion. Thus, these materials are weak, soft, humidity-sensitive, and unable to withstand their shape under long-term service. In this work, a new hyperbranched metal-organic cluster (MOC) crosslinker containing up to 16 vinyl groups is prepared by a straightforward coordination reaction. Compared with the current typical synthesis of metal-organic cages (MOCs) or metal-organic-polyhedra (MOP) crosslinkers with complex operations and low yield, the preparation of the MOC is simple and gram-scale. Thus, MOC can serve as a high-connectivity crosslinker to construct hyper-crosslinked polymer networks. The as-prepared elastomer exhibits mechanical robustness, creep-resistance, and humidity-stability. Besides, the elastomer possesses self-healing and recyclability at mild condition as well as fluorescence stability. These impressive comprehensive properties are proven to originate from the hyper-crosslinked topological structure and microphase-separated morphology. The MOC-driven hyper-crosslinked elastomers provide a new solution for the construction of mechanically robust, durable, and multifunctional polymers.

Ultralight crystalline hybrid composite material for highly efficient sequestration of radioiodine

Considering the importance of sustainable nuclear energy, effective management of radioactive nuclear waste, such as sequestration of radioiodine has inflicted a significant research attention in recent years. Despite the fact that materials have been reported for the adsorption of iodine, development of effective adsorbent with significantly improved segregation properties for widespread practical applications still remain exceedingly difficult due to lack of proper design strategies. Herein, utilizing unique hybridization synthetic strategy, a composite crystalline aerogel material has been fabricated by covalent stepping of an amino-functionalized stable cationic discrete metal-organic polyhedra with dual-pore containing imine-functionalized covalent organic framework. The ultralight hybrid composite exhibits large surface area with hierarchical macro-micro porosity and multifunctional binding sites, which collectively interact with iodine. The developed nano-adsorbent demonstrate ultrahigh vapor and aqueous-phase iodine adsorption capacities of 9.98 g.g-1 and 4.74 g.g-1, respectively, in static conditions with fast adsorption kinetics, high retention efficiency, reusability and recovery.

Pore-Networked Soft Materials Based on Metal-Organic Polyhedra

ConspectusThe last two decades have witnessed a tremendous development of crystalline microporous adsorbents in a wide range of applications including molecular adsorption, storage and separation, purification, as well as catalysis. The main players as porous materials that have contributed to the developments are extended molecular frameworks (e.g., metal-organic frameworks, MOFs; covalent-organic frameworks, COFs) or discrete porous molecules (e.g., metal-organic cages, MOCs; porous organic cages, POCs) thanks to the high degrees of freedom in their structural designability and tunability. To overcome the processability issue originating from their powder forms after synthesis, one main strategy is to hybridize the microporous adsorbents as pore-containing fillers with solvents or polymers as processable matrices to produce porous soft materials, such as porous liquids, gels/aerogels, and mixed-matrix membranes, depending on the form of matrix used. Nevertheless, the fabrication of "ideal" hybrid materials relies on the homogeneous distribution of the pore-containing fillers within the matrices. It is still challenging to find a versatile way to solve the aggregation issues of fillers and their insufficient interaction with the matrices, which are concerned with inhibiting the translation of the distinctive properties of microporous adsorbents into the obtained hybrid soft materials.Herein, we describe a new bottom-up approach for the fabrication of "pore-networked soft materials" based on the concept of directly interconnecting the pore-containing fillers into a continuous pore network within the matrices. The advantages of the pore-networking strategy lie in two main aspects: (i) the elimination of the need to struggle with the aggregation issue of fillers due to their overall interconnection throughout the matrices; (ii) the generation of continuous pore networks that guarantee the efficient molecular mass transfer in the materials. In this Account, we summarize our state-of-the-art progress of pore-networked soft materials based on the use of MOCs, alternatively called metal-organic polyhedra (MOPs) herein, as pore units for the pore network construction. The good solubility of MOPs in organic solvents allows them to be feasibly processed in solution, wherein the coordination of MOPs with organic linkers leads to the formation of linked MOP gels featuring not only intrinsic MOP cavities but also tunable extrinsic porosities generated between linked MOPs through the control of MOP/linker structures and network connectivity. Furthermore, the matrix of the linked MOP network, here referred to as the continuous phase with respect to the entire porous MOP network, is not limited to the solvents. We anticipate that the implementation of air, liquids, and polymers as the matrices could result in different forms of pore-networked soft materials like aerogels, foams, gels, monoliths, and membranes. For instance, we demonstrate the fabrication of linked MOP aerogel and permanently porous gel with their potential applications on selective CO2 photoreduction and gas sorption, respectively. We believe that the pore-network strategies will advance the development of porous soft materials featuring unique advantages and properties beyond the current hybrid systems.

Antimicrobial mechanism of cuprous oxide (Cu2O) coatings

Some very effective antimicrobial coatings exploit copper or cuprous oxide (Cu2O) as the active agent. The aim of this study is to determine which species is the active antimicrobial - dissolved ions, the Cu2O solid, or reactive oxygen species. Copper ions were leached from Cu2O into various solutions and the leachate tested for both dissolved copper and the efficacy in killing Pseudomonas aeruginosa. The concentration of copper species leached from Cu2O into aqueous solution varied greatly with the composition of the aqueous solution. For a range of solution buffers, killing of P. aeruginosa was highly correlated with the concentration of copper in the leachate. Further, 10 µL bacterial suspension droplets were placed on Cu2O coatings, with or without a polymer barrier layer, and tested for bacterial kill. Killing occurred without contact between bacterium and solid, demonstrating that contact with Cu2O is not necessary. We therefore conclude that soluble copper species are the antimicrobial agent, and that the most potent species is Cu+. The solid quickly raises and sustains the concentration of soluble copper species near the bacterium. Killing via soluble copper ions rather than contact should allow copper coatings to kill bacteria even when fouled, which is an important practical consideration.

Recent advances in porous molecular cages for photocatalytic organic conversions

Photocatalytic organic conversion is considered an efficient, environmentally friendly, and energy-saving strategy for organic synthesis. In recent decades, the molecular cage has emerged as a creative functional material with broad applications in host-guest recognition, drug delivery, catalysis, intelligent materials and other fields. Based on the unique properties of porous molecular cage materials, they provide an ideal platform for leveraging pre-structuring in catalytic reactions and show great potential in various photocatalytic organic reactions. As a result, they have emerged as promising alternatives to conventional molecules or inorganic photocatalysts in redox processes. In this Review, the synthesis strategies based on coordination cages and organic cages, as well as their recent progress in photocatalytic organic conversion, are comprehensively summarized. Finally, we deliver the persistent challenges associated with porous molecular cage compounds that need to be overcome for further development in this field.

Dynamic Cages-Towards Nanostructured Smart Materials

The interest in capsular assemblies such as dynamic organic and coordination cages has blossomed over the last decade. Given their chemical and structural variability, these systems have found applications in diverse fields of research, including energy conversion and storage, catalysis, separation, molecular recognition, and live-cell imaging. In the exploration of the potential of these discrete architectures, they are increasingly being employed in the formation of more complex systems and smart materials. This Review highlights the most promising pathways to overcome common drawbacks of cage systems (stability, recovery) and discusses the most promising strategies for their hybridization with systems featuring various dimensionalities. Following the description of the most recent advances in the fabrication of zero to three-dimensional cage-based systems, this Review will provide the reader with the structure-dependent relationship between the employed cages and the properties of the materials.

Tailor-Made Pdn L2n Metal-Organic Cages through Covalent Post-Synthetic Modification

Post-synthetic modification (PSM) is an effective approach for the tailored functionalization of metal-organic architectures, but its generalizability remains challenging. Herein we report a general covalent PSM strategy to functionalize Pd_n L_2n metal-organic cages (MOCs, n=2, 12) through an efficient Diels-Alder cycloaddition between peripheral anthracene substituents and various functional motifs bearing a maleimide group. As expected, the solubility of functionalized Pd₁₂ L₂₄ in common solvents can be greatly improved. Interestingly, concentration-dependent circular dichroism and aggregation-induced emission are achieved with chiral binaphthol (BINOL)- and tetraphenylethylene-modified Pd₁₂ L₂₄ , respectively. Furthermore, Pd₁₂ L₂₄ can be introduced with two different functional groups (e.g., chiral BINOL and achiral pyrene) through a step-by-step PSM route to obtain chirality-induced circularly polarized luminescence. Moreover, similar results are readily observed with a smaller Pd₂ L₄ system.

Solvent-Responsive Reversible and Controllable Conversion between a Polyimine Membrane and an Organic Molecule Cage

Adaptive bionic self-correcting behavior offers an attractive property for chemical systems. Here, based on the dynamic feature of imine formation, we propose a solvent-responsive strategy for smart switching between an amorphous ionic polyimine membrane and a crystalline organic molecule cage without the addition of other building blocks. To adapt to solvent environmental constraints, the aldehyde and amine components undergo self-correction to form a polymer network or a molecular cage. Studies have shown that the amorphous film can be switched in acetonitrile to generate a discrete cage with bright birefringence under polarized light. Conversely, the membrane from the cage crystal conversion can be regained in ethanol. Such a membrane-cage interconversion can be cycled continuously at least 5 times by switching the two solvents. This work builds a bridge between the polymer network and crystalline molecules and offers prospects for smart dynamic materials.

Rationally Designed Ionic Covalent Organic Networks (iCONs) with Efficient Antimicrobial Activities

Two unique ionic covalent organic networks (iCONs) incorporated with guanidinium motifs were obtained and characterized by various techniques. Upon 8 h of treatment with iCON-HCCP (250 μg/mL), >97% killing of Staphylococcus aureus, Candida albicans, and Candida glabrata strains was observed. Antimicrobial efficacies against bacteria and fungi were also evident from FE-SEM studies. High antifungal efficacies also correlated well with >60% reduction of ergosterol content, high lipid peroxidation, and membrane damage leading to necrosis.

A rapid self-healing glassy polymer/metal-organic-framework hybrid membrane at room temperature

The development of repairable MOF-polymer hybrid materials will greatly extend their service life by repairing fractured parts on the spot; however, it is difficult for robust glassy polymers to self-heal below the glass transition temperature (T_g) as the polymer network is frozen. We herein report glassy polyMOF-RHP hybrid membranes by integrating lanthanide polyMOF (polyLnMOF) with randomly hyperbranched polymers (RHP) bearing a high density of hydrogen bonds. Since crystalline lanthanide MOFs act as multiconnected cross-linking agents and cross-link the interpenetrating polymer network, the obtained polyLnMOF-polymer membrane shows enhanced mechanical strength with a storage modulus of 3.09 GPa and a T_g up to 49 °C. Meanwhile, the high intersegment migration ability of the polyLnMOF-polymer network facilitates the exchange of hydrogen-bonded pairs even in the glassy state, leading to an instantaneous room-temperature self-healing ability. The polyLnMOF-polymer membranes inherit the ratiometric temperature-sensing behavior of pristine lanthanide MOFs, resulting in more processable temperature-sensing membranes. This work provides an appealing strategy for the design of mechanically robust, yet self-healing, MOF-polymer functional materials.

A 12-Connected [Y4((μ3-OH)4]8+ Cluster-Based Luminescent Metal-Organic Framework for Selective Turn-on Detection of F- in H2O

Fluoride ion (F^-) is one of the most hazardous elements in potable water. Over intake of F^- can give rise to dental fluorosis, kidney failure, or DNA damage. As a result, developing affordable, equipment-free and credible approaches for F^- detection is an important task. In this work, a new three dimensional rare earth cluster-based metal-organic framework assembled from lanthanide Y(III) ion, and a linear multifunctional ligand 3-nitro-4,4'-biphenyldicarboxylic acid, formulated as {[Y(μ₃-OH)]₄[Y(μ₃-OH)(μ₂-H₂O)_0.25(H₂O)_0.5]₄[μ₄-nba]₈}_n (1), where H₂nba = 3-nitro-4,4'-biphenyldicarboxylic acid, has been hydrothermally synthesized and characterized through infrared spectroscopy (IR), elemental and thermal analysis (EA), power X-ray diffraction (PXRD), and single-crystal X-ray diffraction (SCXRD) analyses. X-ray diffraction structural analysis revealed that 1 crystallizes in tetragonal system with P4¯2₁m space group, and features a 3D framework with 1D square 18.07(3)² Ų channels running along the [0,0,1] or c-axis direction. The structure of 1 is built up of unusual eight-membered rings formed by two types of {Y₄O₄} clusters connected to each other via 12 μ₄-nba^2- and 4 μ₃-OH^- ligands. Three crystallographic independent Y³⁺ ions display two coordinated configurations with a seven-coordinated distorted monocapped trigonal-prism (YO₇) and an eight-coordinated approximately bicapped trigonal-prism (YO₈). 1 is further stabilized through O-H⋯O, O-H⋯N, C-H⋯O, and π⋯π interactions. Topologically, MOF 1 can be simplified as a 12-connected 2-nodal Au₄Ho topology with a Schläfli symbol {4²⁰·6²⁸·8¹⁸}{4³}₄ or a 6-connected uninodal pcu topology with a Schläfli symbol {4¹²·6³}. The fluorescent sensing application of 1 was investigated to cations and anions in H₂O. 1 exhibits good luminescence probing turn-on recognition ability toward F^- and with a limit detection concentration of F^- down to 14.2 μM in aqueous solution (K_ec = 11403 M^-1, R² = 0.99289, σ = 0.0539). The findings here provide a feasible detection platform of LnMOFs for highly sensitive discrimination of F^- in aqueous media.

Defect Healing of Micro/Nanocrystals via the Coordination Competition of Rare Earth in Crystal Engineering

Defect engineering has been generally observed and utilized in crystal materials including metal oxides, metal-organic frameworks, and so on; however, how to relate the defect formation and crystallization process is needed to be revealed clearly, and how to heal the defect is a big challenge. Herein, based on the new coordination complex (HNU-53), the crystal defects were created by increasing the reaction time and crystal size. Following the crystal growth process, the crystal color centers were simultaneously generated, resulting in fluorescence quenching. To heal the defect, the crystal growth was controlled by the introduction of rare earth ions. With the coordination competition of rare earth ions, the crystal defects were reduced and recovery of fluorescence emission was achieved.

Metal Organic Polygons and Polyhedra: Instabilities and Remedies

The field of coordination chemistry has undergone rapid transformation from preparation of monometallic complexes to multimetallic complexes. So far numerous multimetallic coordination complexes have been synthesized. Multimetallic coordination complexes with well-defined architectures are often called as metal organic polygons and polyhedra (MOPs). In recent past, MOPs have received tremendous attention due to their potential applicability in various emerging fields. However, the field of coordination chemistry of MOPs often suffer set back due to the instability of coordination complexes particularly in aqueous environment-mostly by aqueous solvent and atmospheric moisture. Accordingly, the fate of the field does not rely only on the water solubilities of newly synthesized MOPs but very much dependent on their stabilities both in solution and solid state. The present review discusses several methodologies to prepare MOPs and investigates their stabilities under various circumstances. Considering the potential applicability of MOPs in sustainable way, several methodologies (remedies) to enhance the stabilities of MOPs are discussed here.

Altering the solubility of metal-organic polyhedra via pendant functionalization of Cp3Zr3O(OH)3 nodes

The chemistry of zirconium-based metal-organic polyhedra (ZrMOPs) is often limited by their poor solubilities. Despite their attractive features-including high yielding and facile syntheses, predictable topologies, high stability, and tunability-problematic solubilities have caused ZrMOPs to be under-studied and under-applied. Although these cages have been synthesized with a wide variety of carboxylate-based bridging ligands, we explored a new method for ZrMOP functionalization via node-modification, which we hypothesized could influence solubility. Herein, we report ZrMOPs with benzyl-, vinylbenzyl-, and trifluoromethylbenzyl-pendant groups decorating cyclopentadienyl moieties. The series was characterized by ¹H/¹⁹F NMR, high-resolution mass spectrometry, infrared spectroscopy, and single-crystal X-ray diffraction. The effects of node functionalities on ZrMOP solubility were quantified using inductively coupled plasma mass spectrometry. Substitution caused a decrease in water solubility, but for certain organic solvents, e.g. DMF, solubility could be enhanced by ∼20×, from 16 μM for the unfunctionalized cage to 310 μM for the vinylbenzyl- and trifluoromethylbenzyl-cages.

Self-assembly of stable and high-performance molecular cage-crosslinked graphene oxide membranes for contaminant removal

Membrane separation is regarded as efficient technology to alleviate global water crisis. Two-dimensional membranes are promising for contaminant removal from wastewaters, but their uncontrollable transport pathway and instability hinder the further development. In this study, the high-performance and stable two-dimensional framework membranes are self-assembled by graphene oxide (GO) nanosheets and amino-appended metal-organic polyhedrons (MOPs) for water purification and remediation. The MOP molecular cages are uniformly intercalated between GO nanosheets and enriched at defects/edges, and can crosslink membranes, to provide in-plane selective channels, refine vertical passageways, and fix out-of-plane interlayer spaces. The prepared GO/MOP framework membranes have improved stability and nanofiltration performance under cross-flow condition, can keep performance in water after 50 h filtration, and show high rejections over 92% for Na₂SO₄ and 99% for antibiotic and dye contaminants with molecular weights over 280 g mol^-1, and sixfold permeance as that of GO membranes. Our molecular cage-intercalated and crosslinked two-dimensional frameworks offer an alternative route to design robust membranes for efficient removal of contaminants in wastewaters.

Trap Inlaid Cationic Hybrid Composite Material for Efficient Segregation of Toxic Chemicals from Water

Metal-based oxoanions are potentially toxic pollutants that can cause serious water pollution. Therefore, the segregation of such species has recently received significant research attention. Even though several adsorbents have been employed for effective management of chemicals, their limited microporous nature along with non-monolithic applicability has thwarted their large-scale real-time application. Herein, we developed a unique anion exchangeable hybrid composite aerogel material (IPcomp-6), integrating a stable cationic metal-organic polyhedron with a hierarchically porous metal-organic gel. The composite scavenger demonstrated a highly selective and very fast segregation efficiency for various hazardous oxoanions such as, HAsO₄ ^2- , SeO₄ ^2- , ReO₄ ^- , CrO₄ ^2- , MnO₄ ^- , in water, in the presence of 100-fold excess of other coexisting anions. The material was able to selectively eliminate trace HAsO₄ ^2- even at low concentration to well below the As^V limit in drinking water defined by WHO.

Strategies for the Construction of Functional Materials Utilizing Presynthesized Metal-Organic Cages (MOCs)

Metal-organic cages (MOCs) that assemble from metal ions or metal clusters and organic ligands have attracted the interest of the scientific community because of their various functional coordination cavities. Unlike metal-organic frameworks (MOFs) with infinite frameworks, MOCs have discrete structures, making them soluble and stable in certain solvents and facilitating their application as starting reagents in the further construction of single components or composite materials. In recent years, increasing progress has been made in this field. In this review, we introduce these works from the perspective of design strategies, and focus on how presynthesized MOCs can be used to construct functional materials. Finally, we discuss the challenges and development prospects in this field.

Metal-organic cage incorporating thin-film nanocomposite membranes with antifouling properties

We report the antifouling properties of thin-film nanocomposite (TFN) membranes containing two water-stable metal-organic cages (MOCs). The MOC-containing TFN membranes possess excellent antifouling properties against positively-charged foulants and protein (BSA, up to 99.7% water permeability retention) and achieve up to 100% water permeability recovery.

Zirconium Metal-Organic Cages: Synthesis and Applications

ConspectusFor the last two decades, materials scientists have contributed to a growing library of porous crystalline materials. These synthetic materials are typically extended networks, including metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), or discrete materials like metal-organic cages (MOCs) and porous organic cages (POCs). Advanced porous materials have shown promise for various applications due to their modular nature and structural tunability. MOCs have recently garnered attention because of their molecularity that bestows them with many unique possibilities (e.g., solution-processability, structural diversity, and postsynthetic processability).MOCs are discrete molecular assemblies of organic ligands coordinated with either metal cations or metal oxide clusters of different nuclearities, resulting in architectures with inherent porosity. Notably, the molecular nature of MOCs endows them with easy solution-processability unattainable with traditional framework materials. To date, a number of stable MOCs have been reported, such as those based on Rh (Rh-O bond energy: 405 ± 42 kJ/mol), Fe (Fe-O bond energy: 407.0 ± 1.0 kJ/mol), Cr (Cr-O bond energy: 461 ± 8.7 kJ/mol), Ti (Ti-O bond energy: 666.5 ± 5.6 kJ/mol), and Zr (Zr-O bond energy: 766.1 ± 10.6 kJ/mol). Paddle-wheel MOCs have also shown great stability in aqueous environments due to their rigid backbones. The zirconium MOC (Zr-MOCs) family emerges as a class of very robust cages for which their high bond energy endows them with high hydrothermal stability.In 2013, we reported the first four zirconocene tetrahedrons assembled from trinuclear zirconium oxide clusters with ditopic or tritopic organic ligands. Since then, significant progress in the rational design of Zr-MOC has led to an assortment of structures dedicated to meaningful applications.In this Account, we highlight the recent progress in synthesizing Zr-MOCs and Zr-MOC-based higher dimensional frameworks and their applications dedicated in our laboratories and beyond. The general Zr-MOC synthetic strategy involves assembling Zr trinuclear clusters with organic ligands (rigid or flexible) containing various functional groups. This chemistry has afforded cages with structural versatility and active sites, e.g., amino groups, for postsynthetic modifications (PSMs). Since the extrinsic porosity of cage-based frameworks is relatively weak, the resulting frameworks are susceptible to structural rearrangement after solvent removal. To circumvent this limitation, increasing the hydrogen bond ratio and strength between interlinked cages and conducting in situ catalytic polymerizations have been reported to afford permanently porous structures amenable to host-guest reactions.To expand their potential applications, multifunctional Zr-MOCs are highly desired. Such multivariate MOCs can be attained by either employing the isoreticular expansion strategy to create MOCs with high surface areas or using mixed-ligand approaches to afford heterogeneous MOCs. In addition, amorphous MOCs, flexible organic ligands, new functionalities, and MOC-based extended networks are exciting new approaches to developing materials with structural versatility and enhanced characteristics. Thereby, we believe the stability and versatility of the Zr-MOC family hold great potential in expanding and addressing challenging applications.

Biofiber waste derived zwitterionic and photocatalytic dye adsorbent: Switchable selectivity, in-situ degradation and multi-tasking application

Dye wastewater and discarded biofiber have brought huge pressure to sustainable developments of ecology and economy. By utilizing dopamine chemistry and benzophenone mediated "grafting onto" atom transfer radical polymerization (ATRP), this work reported a biomass adsorbent containing discarded wool substrate, photocatalytic PDA coating and zwitterionic polymer brushes for dyes removal. The grafted zwitterionic polymer brushes impart the material with not only high adsorption capacity and rapid adsorption rate, but also switchable adsorption selectivity and pH-controlled regeneration capability. Benefiting from such outstanding adsorption performance and excellent free-standing property, the adsorbent could fulfill diversified needs of both static and dynamic adsorptions. Under daylight, the constructed photocatalytic PDA coating could in-situ degrade the captured pollutant, thus achieving consecutive adsorption-degradation-regeneration utilization. Furthermore, through simple dip-coating and cleaner UV-irradiation techniques, the preparation process could be scaled up. This work contributes to both the upcycling of discarded biofiber waste and the development of advanced biomass adsorbent.

Stimuli-Responsive Crystalline Smart Materials: From Rational Design and Fabrication to Applications

Stimuli-responsive smart materials that can undergo reversible chemical/physical changes under external stimuli such as mechanical stress, heat, light, gas, electricity, and pH, are currently attracting increasing attention in the fields of sensors, actuators, optoelectronic devices, information storage, medical applications, and so forth. The current smart materials mostly concentrate on polymers, carbon materials, crystalline liquids, and hydrogels, which have no or low structural order (i.e., the responsive groups/moieties are disorderly in the structures), inevitably introducing deficiencies such as a relatively low response speeds, energy transformation inefficiencies, and unclear structure-property relationships. Consequently, crystalline materials with well-defined and regular molecular arrays can offer a new opportunity to create novel smart materials with improved stimuli-responsive performance. Crystalline materials include framework materials (e.g., metal-organic frameworks, MOFs; covalent organic frameworks, COFs) and molecular crystals (e.g., organic molecules and molecular cages), which have obvious advantages as smart materials compared to amorphous materials. For example, responsive groups/moieties can be uniformly installed in the skeleton of the crystal materials to form ordered molecular arrays, making energy transfer between external-stimulus signals and responsive sites much faster and more efficiently. Besides that, the well-defined structures facilitate in situ characterization of their structural transformation at the molecular level by means of various techniques and high-tech equipment such as in situ spectra and single-crystal/powder X-ray diffraction, thus benefiting the investigation and understanding of the mechanism behind the stimuli-responsive behaviors and structure-property relationships. Nevertheless, some unsolved challenges remain for crystalline smart materials (CSMs), hampering the fabrication of smart material systems for practical applications. For instance, as the materials' crystallinity increases, their processability and mechanical properties usually decrease, unavoidably hindering their practical application. Moreover, crystalline smart materials mostly exist as micro/nanosized powders, which are difficult to make stimuli-responsive on the macroscale. Thus, developing strategies that can balance the materials' crystallinity and processability and establishing macroscale smart material systems are of great significance for practical applications.In this Account, we mainly summarize the recent research progress achieved by our groups, including (i) the rational design and fabrication of new stimuli-responsive crystalline smart materials, including molecular crystals and framework materials, and an in-depth investigation of their response mechanism and structure-property relationship and (ii) creating chemical/physical modification strategies to improve the processability and mechanical properties for crystalline materials and establishing macroscale smart systems for practical applications. Overall, this Account summarizes the state-of-the-art progress of stimuli-responsive crystalline smart materials and points out the existing challenges and future development directions in the field.

Post-synthetic modifications of metal–organic cages

Metal-organic cages (MOCs) are discrete, supramolecular entities that consist of metal nodes and organic linkers, which can offer solution processability and high porosity. Thereby, their predesigned structures can undergo post-synthetic modifications (PSMs) to introduce new functional groups and properties by modifying the linker, metal node, pore or surface environment. This Review explores current PSM strategies used for MOCs, including covalent, coordination and noncovalent methods. The effects of newly introduced functional groups or generated complexes upon the PSMs of MOCs are also detailed, such as improving structural stability or endowing desired functionalities. The development of the aforementioned design principles has enabled systematic approaches for the development and characterization of families of MOCs and, thereby, provides insight into structure-function relationships that will guide future developments.

Metal-Organic Polyhedra as Building Blocks for Porous Extended Networks

Metal-organic polyhedra (MOPs) are a subclass of coordination cages that can adsorb and host species in solution and are permanently porous in solid-state. These characteristics, together with the recent development of their orthogonal surface chemistry and the assembly of more stable cages, have awakened the latent potential of MOPs to be used as building blocks for the synthesis of extended porous networks. This review article focuses on exploring the key developments that make the extension of MOPs possible, highlighting the most remarkable examples of MOP-based soft materials and crystalline extended frameworks. Finally, the article ventures to offer future perspectives on the exploitation of MOPs in fields that still remain ripe toward the use of such unorthodox molecular porous platforms.

Precise fabrication of porous polymer frameworks using rigid polyisocyanides as building blocks: from structural regulation to efficient iodine capture

Porous materials have recently attracted much attention owing to their fascinating structures and broad applications. Moreover, exploring novel porous polymers affording the efficient capture of iodine is of significant interest. In contrast to the reported porous polymers fabricated with small molecular blocks, we herein report the preparation of porous polymer frameworks using rigid polyisocyanides as building blocks. First, tetrahedral four-arm star polyisocyanides with predictable molecular weight and low dispersity were synthesized; the chain-ends of the rigid polyisocyanide blocks were then crosslinked, yielding well-defined porous organic frameworks with a designed pore size and narrow distribution. Polymers of appropriate pore size were observed to efficiently capture radioactive iodine in both aqueous and vapor phases. More than 98% of iodine could be captured within 1 minute from a saturated aqueous solution (capacity of up to 3.2 g g-1), and an adsorption capacity of up to 574 wt% of iodine in vapor was measured within 4 hours. Moreover, the polymers could be recovered and recycled for iodine capture for at least six times, while maintaining high performance.

Polymer networks of imine-crosslinked metal–organic cages: tuneable viscoelasticity and iodine adsorption

The solution-state structure of MOP-15 is elucidated, enabling its direct use as a porous monomer for covalent polymer networks.

Permanent Porosity in Hydroxamate Titanium-Organic Polyhedra

Following the synthesis of hydroxamate titanium-organic frameworks, we now extend these siderophore-type linkers to the assembly of the first titanium-organic polyhedra displaying permanent porosity. Mixed-linker versions of this molecular cage (cMUV-11) are also used to demonstrate the effect of pore chemistry in accessing high surface areas of near 1200 m²·g^-1.

Morphology-Dependent Peroxidase Mimicking Enzyme Activity of Copper Metal-Organic Polyhedra Assemblies

The morphology of nanomaterials (geometric shape and dimension) play a significant role in its various physical and chemical properties. Thus, it is essential to link morphology with performance in specific applications. For this purpose, the morphology of copper metal-organic polyhedra (Cu-MOP) can be modulated through distinct assembly process, which facilitates the exploration of the relationship between morphology and catalytic performance. In this work, the assemblies of Cu-MOP with three different morphologies (nanorods, nanofibers and nanosheets) were facilely prepared by the variation of solvent mixture of N, N-dimethylformamide (DMF) and methanol, revealed the important role of the interaction between the surface group and the solvent on the morphology of these assemblies. Cu-MOP nanofibers exhibited the highest mimetic peroxidase enzyme activity over the Cu-MOP nanosheets and nanorods, which have been utilized in the detection of glucose. Cu-MOPs assemblies with tunable morphology accompanied with adjustable mimic peroxidase activity, had great potential applications in the field of bioanalytical chemistry and biomedicals.

Multiscale structural control of linked metal-organic polyhedra gel by aging-induced linkage-reorganization

Assembly of permanently porous metal-organic polyhedra/cages (MOPs) with bifunctional linkers leads to soft supramolecular networks featuring both porosity and processability. However, the amorphous nature of such soft materials complicates their characterization and thus limits rational structural control. Here we demonstrate that aging is an effective strategy to control the hierarchical network of supramolecular gels, which are assembled from organic ligands as linkers and MOPs as junctions. Normally, the initial gel formation by rapid gelation leads to a kinetically trapped structure with low controllability. Through a controlled post-synthetic aging process, we show that it is possible to tune the network of the linked MOP gel over multiple length scales. This process allows control on the molecular-scale rearrangement of interlinking MOPs, mesoscale fusion of colloidal particles and macroscale densification of the whole colloidal network. In this work we elucidate the relationships between the gel properties, such as porosity and rheology, and their hierarchical structures, which suggest that porosity measurement of the dried gels can be used as a powerful tool to characterize the microscale structural transition of their corresponding gels. This aging strategy can be applied in other supramolecular polymer systems particularly containing kinetically controlled structures and shows an opportunity to engineer the structure and the permanent porosity of amorphous materials for further applications.

Acridine-Based Covalent Organic Framework Photosensitizer with Broad-Spectrum Light Absorption for Antibacterial Photocatalytic Therapy

Antibiotic resistance is considered as one of the serious public health issues. Antibacterial photocatalytic therapy, a clinically proven antibacterial therapy, is gaining increasing attention in recent years owing to its high efficacy. Here, an acridine-based covalent organic framework (COF) photosensitizer, named TPDA, with multiple active sites is synthesized via Schiff base condensation between 2,4,6-triformylphloroglucinol (TFP) and 3,6-diaminoacridine (DAA). Owing to the increased conjugation effect of the COF skeleton and outstanding light harvesting ability of DAA, TPDA exhibits a narrow optical band gap (1.6 eV), enhancing light energy transformation and conferring a wide optical absorption spectrum (intensity arbitrary unit > 0.8) ranging from the UV to near-infrared region. Moreover, TPDA shows high antibacterial activities against both gram-negative and gram-positive bacteria within a short time (10 min) of light irradiation and is found to efficiently protect fish from skin infections. Molecular dynamics simulation data show that the introduction of DAA and TFP facilitates the interaction between TPDA and bacteria and is conducive to reactive oxygen species migration, which further improves the antimicrobial performance. These findings indicate the potential of TPDA as a novel photosensitive material for photodynamic therapy.

Coordination Polymer Glasses with Lava and Healing Ability for High-Performance Gas Sieving

Coordination polymer (CP) glasses offer a way to tackle the fabrication challenges encountered by inorganic porous membranes and show great potentials for size-exclusive gas separation. However, their processability and performance still cannot simultaneously meet the requirements for high-performance membrane separation. Herein, we have developed a series of CP glasses (M-P-dmbIm, M=Zn, Cd, Cu, and Mn), which possess low vitrification temperature as well as low viscosity (η) and lave capability above the transition temperatures. The derived glass (a_g M-P-dmbIm) membranes show outstanding performances for H₂ /CO₂ , H₂ /N₂ , and H₂ /CH₄ separation, which all far surpass the Robeson upper bound and even rival against the best of the state-of-the-art gas separation membranes. The low viscosities not only allow us to hot-cast or hot-press the CP glasses into thin membranes within 5 min without sacrificing their selectivity and permeability, but also endow the resulted glass membranes with healing ability.