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

Smart Adsorbents for Aquatic Environmental Remediation

A noticeable interest and steady rise in research studies reporting the design and assessment of smart adsorbents for sequestering aqueous metal ions and xenobiotics has occurred in the last decade. This motivates compiling and reviewing the characteristics, potentials, and performances of this new adsorbent generation's metal ion and xenobiotics sequestration. Herein, stimuli-responsive adsorbents that respond to its media (as internal triggers; e.g., pH and temperature) or external triggers (e.g., magnetic field and light) are highlighted. Readers are then introduced to selective adsorbents that selectively capture materials of interest. This is followed by a discussion of self-healing and self-cleaning adsorbents. Finally, the review ends with research gaps in material designs.

Heterogeneous postassembly modification of zirconium metal-organic cages in supramolecular frameworks

We report a heterogeneous postassembly modification (PAM) to synthesize a zirconium metal-organic cage decorated with acrylate functional groups, ZrT-1-AA, which cannot be synthesized by direct coordination-driven self-assembly owing to the reactivity and instability of the ligand. The PAM process is carried out in a single-crystal-to-single-crystal transformation under mild reaction conditions with high efficiency, which is confirmed by ESI-TOF-MS and 1H NMR. In addition, ZrT-1-AA is crosslinked into shaped materials to demonstrate its potential applications. The proposed PAM strategy sheds light on the development of Zr-MOCs decorated with reactive functional groups, whose introduction is challenging or impossible via direct self-assembly.

Robust Synthetic Route toward Anisotropic Metal-Organic Cages with Tunable Surface Chemistry

Metal-organic cages with well-defined interior cavities and tunable surface chemistry serve as attractive building blocks for new types of soft nanoporous materials. While a compositionally diverse repertoire of metal-organic cages exists, the vast majority feature highly symmetric cores. Here, we report a robust, generalizable synthetic route toward anisotropic copper paddlewheel-based cages with tunable pendant amide groups. An isostructural family with increasingly hydrophobic surface properties has been synthesized and characterized by single-crystal X-ray diffraction, gas sorption analysis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and ¹H NMR digestion experiments. The metal-organic cages reported here may enable a deeper study of how anisotropy influences the long-range structure and emergent function of soft nanoporous materials.

When polymerization meets coordination-driven self-assembly: metallo-supramolecular polymers based on supramolecular coordination complexes

Polymers have greatly changed and are still changing the way we live ever since, and the construction of novel polymers as functional materials remains an attractive topic in polymer science and related areas. During the past few years, the marriage of discrete supramolecular coordination complexes (SCCs), including two-dimensional (2D) metallacycles and three-dimensional (3D) metallacages, and polymers gave rise to two novel types of metallo-supramolecular polymers, i.e., metallacycle/metallacage-cored star polymers (MSPs) and metallacycle/metallacage-crosslinked polymer networks (MPNs), which has attracted increasing attention and emerged as an exciting new research direction in polymer chemistry. Attributed to their well-defined and diverse topological architectures as well as the unique dynamic features of metallacycles/metallacages as cores or crosslinks, these novel polymers have shown extensive applications. In this review, aiming at providing a practical guide to this emerging area, the introduction of synthetic strategies towards MSPs and MPNs will be presented. In addition, their wide applications in areas such as functional materials, molecular sieving, drug delivery, bacterial killing and bioimaging are also discussed.

Supramolecular Coordination Cages Based on N-Heterocyclic Carbene-Gold(I) Ligands and Their Precursors: Self-Assembly, Structural Transformation and Guest-Binding Properties

The incorporation of functional groups into the cavity of discrete supramolecular coordination cages (SCCs) will bring unique functions and applications. Here, three dicarboxylate ligands (H₂ L1Cl, H₂ L2Cl and H₂ L3Cl) containing N-heterocyclic carbene (NHC) precursors as linkers were introduced to construct SCCs by combining with two C₃ -symmertic (CpZr)₃ (μ₃ -O)(μ₂ -OH)₃ clusters as three-connect vertices, resulted in a series of rugby-like V₂ E₃ (V=vertex, E=edge) type homoleptic cages (SCC-1, SCC-2 and SCC-3). However, V₄ E₆ -type tetrahedral cages (SCC-4 and SCC-5), incorporating six Au-NHC moieties, were obtained when the corresponding NHC-gold(I) functionalized ligands (H₂ L1^Au , H₂ L2^Au ) were applied. For the first time, we present a trackable CpZr-involved cage to cage conversion to generate a heteroleptic V₂ E₃ cage (SCC-6) from two homoleptic cages (SCC-2 and SCC-5) with different geometries of V₂ E₃ and V₄ E₆ . The heteroleptic assembly SCC-6 can also be formed upon a subcomponent displacement strategy. The structural transformation and reassembly processes were detected and monitored by ¹ H NMR spectroscopy and electrospray-ionization mass spectrometry. The formation of heteroleptic assembly was further supported by single crystal X-ray diffraction analysis. Moreover, homoleptic cage SCC-2 possesses a trigonal bipyramidal cationic cavity allowing the encapsulation of a series of sulfonate anionic guests.

Functional Material Systems Based on Soft Cages

Discrete molecular soft cages integrate multiple functionalities in one molecule. They express their functions from the confined space in their cavity, functional groups in the cavity interior wall and exterior wall, and the chelating nodes in many chelating cages. Such functional integrity render cage molecules special applications in material engineering. Increasing applications of cage molecules in material design have been reported in recent years. Compared with other cavity-rich molecular structures such as metal-organic framework (MOF) or covalent organic frameworks (COF), discrete soft cages present the unique advantage of material design flexibility, that they can easily composite with nanoparticles or polymers and exist in materials of various forms. We document the development of cage-based materials in recent years and expect to further inspire materials engineering to integrate contribution from the functionality specificity of cage molecules and ultimately promote the development of functional materials and thus human life qualities.

Light-induced assembly and disassembly of polymers with Pd n L2n -type network junctions

Polymers containing Pd n L2n complexes as network junctions were obtained by reaction of poly(ethylene glycol)-linked N-donor ligands with Pd2+. The addition of a metastable state photoacid renders the networks light sensitive, and gel-sol transitions can be achieved by irradiation with light. The inverse process, a light-induced sol-gel transition, was realized by using a molecularly defined Pd complex as an acid-sensitive reservoir for Pd2+. Upon irradiation, Pd2+ ions are released, allowing the formation of an acid-resistant polymer network. Both the gel-sol and the sol-gel transitions are reversed in the dark.

A thiol-functionalized zirconium metal-organic cage for the effective removal of Hg2+ from aqueous solution

The mercury ions in waste water have threatened public health and environmental protection. In this sense, novel materials with outstanding performances for removal of Hg²⁺ are imperative. Herein, we demonstrate a thiol-functionalized zirconium metal-organic cage (MOC-(SH)₂) with excellent dispersion displays ideal properties for Hg²⁺ capture. MOC-(SH)₂ exhibits the ability of removing Hg²⁺ in aqueous solutions with a capacity of 335.9 mg_Hg2+/g_MOC-(SH)2, which surpasses that of classical Zr-based metal-organic framework Uio-66-(SH)₂ by 1.89 folds. The higher loading capacity of MOC-(SH)₂ is probably owing to the excellent dispersion of the discrete cage, which makes the accessibility of binding sites (thiol) easier. Additionally, 99.6% of Hg²⁺ can be effectively captured by MOC-(SH)₂ with the concentration decreased from 5 to 0.02 ppm reaching the permissible limit for Hg²⁺, outperforming the performance of Uio-66-(SH)₂. The excellent absorption property of MOC-(SH)₂ is also achieved in terms of superior selectivity under the presence of competitive metal ions. Meanwhile, the regenerated MOC-(SH)₂ can be reused without apparent loss of Hg²⁺ loading capacity. UV-vis absorption spectra, IR spectra and emission spectra further verified the strong chemical affinity between Hg²⁺ and the thiol of MOC-(SH)₂. The study lays the groundwork for using Zr-MOCs in the removal of toxic metal ions and environmental sustainability.

Metal–organic cages for molecular separations

Separation technology is central to industries as diverse as petroleum, pharmaceuticals, mining and life sciences. Metal-organic cages, a class of molecular containers formed via coordination-driven self-assembly, show great promise as separation agents. Precise control of the shape, size and functionalization of cage cavities enables them to selectively bind and distinguish a wide scope of physicochemically similar substances in solution. Extensive research has, thus, been performed involving separations of high-value targets using coordination cages, ranging from gases and liquids to compounds dissolved in solution. Enantiopure capsules also show great potential for the separation of chiral molecules. The use of crystalline cages as absorbents, or the incorporation of cages into polymer membranes, could increase the selectivity and efficiency of separation processes. This Review covers recent progress in using metal-organic cages to achieve separations, with discussion of the many methods of using them in this context. Challenges and potential future developments are also discussed.

Coordination-Assembled Molecular Cages with Metal Cluster Nodes

Molecular cages have attracted great attention because of their fascinating topological structures and well-defined functional cavities. These discrete cages were usually fabricated by coordination assembly approach, a process employing directional metal-ligand coordination bonds due to the nature of the divinable coordination geometry and the required lability to encode dynamic equilibrium/error-correction. Compared to these coordination molecular cages with mononulcear metal-nodes, an increasing number of molecular cages featuring dinuclear and then polynuclear metal-cluster nodes have been synthesized. These metal-cluster-based coordination cages (MCCCs) combine the merits of both metal clusters and the cage structure, and exhibit excellent performances in catalysis, separation, host-guest chemistry and so on. In this review, we highlight the syntheses of MCCCs and their potential functions that is donated by the metal-cluster nodes.

Simultaneous shaping and confinement of metal-organic polyhedra in alginate-SiO2 spheres

The simultaneous shaping and confinement of Cu-based MOP in alginate-SiO2 spheres significantly enhance the mechanical strength and leaching resistance of Cu-MOP. The resulting MOP-alginate-SiO2 is shown through chemical fixation of CO2 to exhibit improved product yield over the parent Cu-MOP and Cu-alginate-SiO2.

Microporous framework membranes for precise molecule/ion separations

Microporous framework membranes such as metal-organic framework (MOF) membranes and covalent organic framework (COF) membranes are constructed by the controlled growth of small building blocks with large porosity and permanent well-defined micropore structures, which can overcome the ubiquitous tradeoff between membrane permeability and selectivity; they hold great promise for the enormous challenging separations in energy and environment fields. Therefore, microporous framework membranes are endowed with great expectations as next-generation membranes, and have evolved into a booming research field. Numerous novel membrane materials, versatile manipulation strategies of membrane structures, and fascinating applications have erupted in the last five years. First, this review summarizes and categorizes the microporous framework membranes with pore sizes lower than 2 nm based on their chemistry: inorganic microporous framework membranes, organic-inorganic microporous framework membranes, and organic microporous framework membranes, where the chemistry, fabrications, and differences among these membranes have been highlighted. Special attention is paid to the membrane structures and their corresponding modifications, including pore architecture, intercrystalline grain boundary, as well as their diverse control strategies. Then, the separation mechanisms of membranes are covered, such as diffusion-selectivity separation, adsorption-selectivity separation, and synergetic adsorption-diffusion-selectivity separation. Meanwhile, intricate membrane design to realize synergistic separation and some emerging mechanisms are highlighted. Finally, the applications of microporous framework membranes for precise gas separation, liquid molecule separation, and ion sieving are summarized. The remaining challenges and future perspectives in this field are discussed. This timely review may provide genuine guidance on the manipulation of membrane structures and inspire creative designs of novel membranes, promoting the sustainable development and steadily increasing prosperity of this field.

The rise of metal-organic polyhedra

Metal-organic polyhedra are a member of metal-organic materials, and are together with metal-organic frameworks utilized as emerging porous platforms for numerous applications in energy- and bio-related sciences. However, metal-organic polyhedra have been significantly underexplored, unlike their metal-organic framework counterparts. In this review, we will cover the topologies and the classification of metal-organic polyhedra and share several suggestions, which might be useful to synthetic chemists regarding the future directions in this rapid-growing field.

Sulfur-Decorated Hyper-Cross-Linked Coal Tar: A Microporous Organic Polymer for Efficient and Expeditious Mercury Removal

Hyper-cross-linked microporous organic polymers are a class of porous materials that have captured widespread attention owing to their high surface areas and wide range of monomeric sources. Balancing economy with performance is the initial hurdle when designing effective hyper-cross-linked microporous organic polymers. Herein, we demonstrated an inexpensive sulfurated solvent-knitted hyper-cross-linked microporous polymer scaffold, named sulfur-decorated hyper-cross-linked coal tar (CTHP-SES), utilizing coal tar as an aromatic monomer with numerous positions for potential chelation of toxic metals, particularly mercury, from water. The resulting material illustrated selective adsorption of mercury from both water (1037 mg g^-1) and the gas phase (416 mg g^-1) with rapid kinetics (183.67 mg min^-1 g^-1), good recyclability (4 runs), and excellent stability under both strong basic and acidic conditions. CTHP-SES was able to reduce the concentration of the Hg(II) solution from 1 mg L^-1 to 32 μg L^-1 after 10 min due in part to the promising distribution coefficient (K_d = 2.371 × 10⁶ mL g^-1). These results show that CTHP-SES offers a promising and practical platform to cope with a variety of environmental contaminations.

A covalent deprotection strategy for assembling supramolecular coordination polymers from metal-organic cages

A Cu₄L₄ metal-organic cage (MOC) composed of amine-protected ligands forms supramolecular coordination polymers (SCPs) upon covalent post-assembly deprotection. The amorphous SCPs form by virtue of aniline-copper coordination and possess a tunable porosity based on the rate of deprotection.

Emissive Metallacycle-Crosslinked Supramolecular Networks with Tunable Crosslinking Densities for Bacterial Imaging and Killing

The chemical structures and topologies of the crosslinks in supramolecular networks play a crucial role in their properties and functions. Herein, the preparation of a type of poly(N-isopropylacrylamide) (PNIPAAM)-based supramolecular networks crosslinked by emissive hexagonal metallacycles is presented. The topological connections in these networks greatly affect their properties, as evidenced by their differences in absorption, emission, lower critical solution temperature, and modulus along with the variation of crosslinking densities. The integration of PNIPAAM and metallacycles in the networks benefits them improved bioavailability, making them serve as reagents for bacterial imaging and killing. This study provides a strategy to prepare cavity-crosslinked polymer networks for antibacterial applications.

Metal–organic polyhedra crosslinked supramolecular polymeric elastomers

Supramolecular polymeric elastomers crosslinked by metal–organic polyhedra were developed, featuring not only tunable mechanical properties but also dynamic actuation behaviors.

Fabrication of silver chalcogenolate cluster hybrid membranes with enhanced structural stability and luminescence efficiency

The present study reports the fabrication of a silver chalcogenolate cluster hybrid membrane (SCC membrane) through self-assembly of SCCs, and then covalent cross-linking of the modified SCC assembled materials. This strategy provides access to silver clusters with superior chemical stability and enhanced luminescence efficiency for practical applications.

Molecularly Mixed Composite Membranes: Challenges and Opportunities

The fabrication of porous molecules, such as metal-organic polyhedra (MOPs), porous organic cages (POCs) and others, has given rise to the potential for creating "solid solutions" of molecular fillers and polymers. Such solid solutions circumvent longstanding interface issues associated with mixed matrix membranes (MMMs), and are referred to as molecularly mixed composite membranes (MMCMs) to distinguish them from traditional two-phase MMMs. Early investigations of MMCMs highlight the advantages of solid solutions over MMMs, including dispersion of the filler, anti-plasticization of the polymer network, and removal of deleterious interfacial issues. However, the exact microscopic structure as well as the transport modality in this new class of membrane are not well understood. Moreover, there are clear engineering challenges that need to be addressed for MMCMs to transition into the field. In this Minireview, the authors outline several scientific and technological challenges associated with the aforementioned questions and their suggestions to tackle them.