Star PolyMOCs with Diverse Structures, Dynamics, and Functions by Three-Component Assembly

Nested non-covalent interactions expand the functions of supramolecular polymer networks

Supramolecular polymer networks contain non-covalent cross-links that enable access to broadly tunable mechanical properties and stimuli-responsive behaviors; the incorporation of multiple unique non-covalent cross-links within such materials further expands their mechanical responses and functionality. To date, however, the design of such materials has been accomplished through discrete combinations of distinct interaction types in series, limiting materials design logic. Here we introduce the concept of leveraging "nested" supramolecular crosslinks, wherein two distinct types of non-covalent interactions exist in parallel, to control bulk material functions. To demonstrate this concept, we use polymer-linked Pd2L4 metal-organic cage (polyMOC) gels that form hollow metal-organic cage junctions through metal-ligand coordination and can exhibit well-defined host-guest binding within their cavity. In these "nested" supramolecular network junctions, the thermodynamics of host-guest interactions within the junctions affect the metal-ligand interactions that form those junctions, ultimately translating to substantial guest-dependent changes in bulk material properties that could not be achieved in traditional supramolecular networks with multiple interactions in series.

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.

Supramolecular Synthesis of Star Polymers

Supramolecular polymers, in which monomers are assembled via intermolecular interactions, have been extensively studied. The fusion of supramolecular polymers with conventional polymers has attracted the attention of many researchers. In this review article, the recent progress in the construction of supramolecular star polymers, including regular star polymers and miktoarm star polymers, is discussed. The initial sections briefly provide an overview of the conventional classification and synthesis methods for star polymers. Coordination-driven self-assembly was investigated for the supramolecular synthesis of star polymers. Star polymers with multiple polymer chains radiating from metal-organic polyhedra (MOPs) have also been described. Particular focus has been placed on the synthesis of star polymers featuring supramolecular cores formed through hydrogen-bonding-directed self-assembly. After describing the synthesis of star polymers based on host-guest complexes, the construction of miktoarm star polymers based on the molecular recognition of coordination capsules is detailed.

Modulating Ligand-Exchange Dynamics on Metal-Organic Polyhedra for Reversible Sorting and Hybridization of Miktoarm Star Polymers

The precise synthesis of miktoarm star polymers (MSPs) remains one of the great challenges in synthetic chemistry due to the difficulty in locating appropriate structural templates and polymer grafting/growing strategies with high selectivity and efficiency. Herein, ≈2 nm metal-organic polyhedra (MOPs), constructed from the coordination of isophthalic acid (IPA) and Cu2+ , are applied as templates for the precise synthesis of 24-arm MSPs for their unique logarithmic ligand-exchange dynamics. Six different polymers are prepared with IPA as an end group and they further coordinated with Cu2+ to afford the corresponding 24-arm star homo-polymers. MSPs can be obtained by mixing targeted homo-arm star polymers in solutions upon thermal annealing. The compositions of MSPs can be facilely and precisely tuned by the recipe of the star polymer mixtures used. Interestingly, the obtained MSPs can be sorted into homo-arm star polymers through a typical solvent extraction procedure. The hybridization and sorting process can be reversibly conducted through the cycle of thermal annealing and solvent treatment. The complex coordination framework not only opens new avenues for the facile and precise synthesis of MSPs and MOPs with hybrid functionalities, but also provides the capability to design sustainable polymer systems.

The Coordination Nanocages-Integrated Polymer Brush Networks for Flexible Microporous Membranes with Exceptional H2 /CO2 Separation Performance

The emergence of polymers with intrinsic microporosity provides solutions for flexible gas separation membranes with both high gas permeability and selectivity. However, their applications are significantly hindered by the costly synthetic efforts, limited availability of chemical systems, and narrow window of microporosity sizes. Herein, flexible mixed matrix membranes with tunable intrinsic microporosity can be facilely fabricated from the coordination assembly of polymer brushes and coordination nanocages. Polymer brushes bearing isophthalic acid side groups can coordinate with Cu2+ to assemble into polymer networks crosslinked by 2 nm nanocages. The semi-flexible feature of the polymer brush and the high crosslinking density of the network prevent the network from collapsing during solvent removal and the obtained aerogels demonstrate hierarchical structure with dual porosity from the crosslinked polymer network and coordination nanocage, respectively. The porosity can be facilely tuned via the amount of Cu2+ by regulating the network crosslinking density and nanocage loadings, and finally, optimized gas separation that surpasses Robeson upper bound for H2 /CO2 can be achieved. The coordination-driven assembly protocol paves a new avenue for the cost-effective synthesis of polymers with intrinsic microporosity and the fabrication of flexible gas separation membranes.

The network structure in transient telechelic polymer networks: extension of the Miller-Macosko model

The combination of supramolecular chemistry and polymer science has resulted in the development of transient polymer networks with diverse properties and applications. Specifically, polymer networks based on transient linking of telechelic polymer precursors offer a high degree of control over the network structure, which can reform in response to external stimuli that change the connectivity of transient bonds. Therefore, the combination of the versatile polymer functionality and the adjustable connectivity of transient bonds may result in complex network structures that are not easy to predict or characterize. To address this gap, herein we extend the Miller-Macosko model to forecast the network connectivity of transient telechelic polymer networks made with various polymer functionalities and transient connectivities represented by metal-ligand complexes. This model predicts a universal dependence of the network structure and modulus on preparative parameters including the metal ion identity, characterized by the complexation thermodynamics, and concentration. Moreover, we demonstrate that given the thermodynamic tendency of forming network defects like loops, the model can include such imperfections, enabling rheological properties to be used indirectly for the characterization of defect content. We outline general guidelines to extend the model to more intricate structures, enhancing our understanding of the structure-property relationship in complex transient polymer networks.

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.

Polymer Networks with Cubic, Mixed Pd(II) and Pt(II) M6L12 Metal-Organic Cage Junctions: Synthesis and Stress Relaxation Behavior

Metal-organic cages/polyhedra (MOCs) are versatile building blocks for advanced polymer networks with properties that synergistically blend those of traditional polymers and crystalline frameworks. Nevertheless, constructing polyMOCs from very stable Pt(II)-based MOCs or mixtures of metal ions such as Pd(II) and Pt(II) has not, to our knowledge, been demonstrated, nor has exploration of how the dynamics of metal-ligand exchange at the MOC level may impact bulk polyMOC energy dissipation. Here, we introduce a new class of polymer metal-organic cage (polyMOC) gels featuring polyethylene glycol (PEG) strands of varied length cross-linked through bis-pyridyl-carbazole-based M6L12 cubes, where M is Pd(II), Pt(II), or mixtures thereof. We show that, while polyMOCs with varied Pd(II) content have similar network structures, their average stress-relaxation rates are tunable over 3 orders of magnitude due to differences in Pd(II)- and Pt(II)-ligand exchange rates at the M6L12 junction level. Moreover, mixed-metal polyMOCs display relaxation times indicative of intrajunction cooperative interactions, which stands in contrast to previous materials based on point metal junctions. Altogether, this work (1) introduces a novel MOC architecture for polyMOC design, (2) shows that polyMOCs can be prepared from mixtures of Pd(II)/Pt(II), and (3) demonstrates that polyMOCs display unique relaxation behavior due to their multivalent junctions, offering a strategy for controlling polyMOC properties independently of their polymer components.

Mechanoresponsive Metal-Organic Cage-Crosslinked Polymer Hydrogels

We report the formation of metal-organic cage-crosslinked polymer hydrogels. To enable crosslinking of the cages and subsequent network formation, we used homodifunctionalized poly(ethylene glycol) (PEG) chains terminally substituted with bipyridines as ligands for the Pd₆ L₄ corners. The encapsulation of guest molecules into supramolecular self-assembled metal-organic cage-crosslinked hydrogels, as well as ultrasound-induced disassembly of the cages with release of their cargo, is presented in addition to their characterization by nuclear magnetic resonance (NMR) techniques, rheology, and comprehensive small-angle X-ray scattering (SAXS) experiments. The constrained geometries simulating external force (CoGEF) method and barriers using a force-modified potential energy surface (FMPES) suggest that the cage-opening mechanism starts with the dissociation of one pyridine ligand at around 0.5 nN. We show the efficient sonochemical activation of the hydrogels HG_{3 -6} , increasing the non-covalent guest-loading of completely unmodified drugs available for release by a factor of ten in comparison to non-crosslinked, star-shaped assemblies in solution.

Non-equilibrium Nanoassemblies Constructed by Confined Coordination on a Polymer Chain

Biological systems employ non-equilibrium self-assembly to create ordered nanoarchitectures with sophisticated functions. However, it is challenging to construct artificial non-equilibrium nanoassemblies due to lack of control over assembly dynamics and kinetics. Herein, we design a series of linear polymers with different side groups for further coordination-driven self-assembly based on shape-complementarity. Such a design introduces a main-chain confinement which effectively slows down the assembly process of side groups, thus allowing us to monitor the real-time evolution of lychee-like nanostructures. The function related to the non-equilibrium nature is further explored by performing photothermal conversion study. The ability to observe and capture non-equilibrium states in this supramolecular system will enhance our understanding of the thermodynamic and kinetic features as well as functions of living systems.

Orientational self-sorting in cuboctahedral Pd cages

Cuboctahedral coordination cages of the general formula [Pd12L24]24+ (L = low-symmetry ligand) were analyzed theoretically and experimentally. With 350 696 potential isomers, the structural space of these assemblies is vast. Orientational self-sorting refers to the preferential formation of particular isomers within the pool of potential structures. Geometric and computational analyses predict the preferred formation of cages with a cis arrangement at the metal centers. This prediction was corroborated experimentally by synthesizing a [Pd12L24]24+ cage with a bridging 3-(4-(pyridin-4-yl)phenyl)pyridine ligand. A crystallographic analysis of this assembly showed exclusive cis coordination of the 3- and the 4-pyridyl donor groups at the Pd2+ ions.

Endohedrally Functionalized Metal-Organic Cage-Cross-Linked Polymer Gels as Modular Heterogeneous Catalysts

The immobilization of homogeneous catalysts onto supports to improve recyclability while maintaining catalytic efficiency is often a trial-and-error process limited by poor control of the local catalyst environment and few strategies to append catalysts to support materials. Here, we introduce a modular heterogenous catalysis platform that addresses these challenges. Our approach leverages the well-defined interiors of self-assembled Pd₁₂L₂₄ metal-organic cages/polyhedra (MOCs): simple mixing of a catalyst-ligand of choice with a polymeric ligand, spacer ligands, and a Pd salt induces self-assembly of Pd₁₂L₂₄-cross-linked polymer gels featuring endohedrally catalyst-functionalized junctions. Semi-empirical calculations show that catalyst incorporation into the MOC junctions of these materials has minimal affect on the MOC geometry, giving rise to well-defined nanoconfined catalyst domains as confirmed experimentally using several techniques. Given the unique network topology of these freestanding gels, they are mechanically robust regardless of their endohedral catalyst composition, allowing them to be physically manipulated and transferred from one reaction to another to achieve multiple rounds of catalysis. Moreover, by decoupling the catalyst environment (interior of MOC junctions) from the physical properties of the support (the polymer matrix), this strategy enables catalysis in environments where homogeneous catalyst analogues are not viable, as demonstrated for the Au(I)-catalyzed cyclization of 4-pentynoic acid in aqueous media.

Bond strength regime dictates stress relaxation behavior

Reconfigurable polymer networks are gaining interest for their potential applications as self-healing, recyclable, and stimuli-responsive smart materials. Relating the bond strength of dynamic interactions to material properties including stress relaxation time and modulus is crucial for smart material design. In this work, in situ crosslinked transition metal-terpyridine reconfigurable networks were utilized to modulate the characteristic network stress relaxation time, τ_R. The use of stress relaxation experiments rather than oscillatory frequency sweeps allowed for the measurement of network bond dynamics across a wider dynamic range than has been previously reported. The stress relaxation time was shown to be tunable by metal center, counterion, and crosslink density. Remarkably, the network crosslinked with covalent-like ruthenium chloride-terpyridine interaction, while having a longer τ_R, was qualitatively similar to the other metal-ligand networks. Furthermore, the relaxation time was independent of crosslink density in strongly bonded networks, allowing for independent tunability of modulus and τ_R. In contrast, increasing crosslink density reduced τ_R in networks crosslinked with weaker interactions.

Recent Technical Advances in Sample Preparation for Single-Particle Cryo-EM

Cryo-sample preparation is a vital step in the process of obtaining high-resolution structures of macromolecules by using the single-particle cryo–electron microscopy (cryo-EM) method; however, cryo-sample preparation is commonly hampered by high uncertainty and low reproducibility. Specifically, the existence of air-water interfaces during the sample vitrification process could cause protein denaturation and aggregation, complex disassembly, adoption of preferred orientations, and other serious problems affecting the protein particles, thereby making it challenging to pursue high-resolution 3D reconstruction. Therefore, sample preparation has emerged as a critical research topic, and several new methods for application at various preparation stages have been proposed to overcome the aforementioned hurdles. Here, we summarize the methods developed for enhancing the quality of cryo-samples at distinct stages of sample preparation, and we offer insights for developing future strategies based on diverse viewpoints. We anticipate that cryo-sample preparation will no longer be a limiting step in the single-particle cryo-EM field as increasing numbers of methods are developed in the near future, which will ultimately benefit the entire research community.

Beyond Platonic: How to Build Metal-Organic Polyhedra Capable of Binding Low-Symmetry, Information-Rich Molecular Cargoes

The field of metallosupramolecular chemistry has advanced rapidly in recent years. Much work in this area has focused on the formation of hollow self-assembled metal-organic architectures and exploration of the applications of their confined nanospaces. These discrete, soluble structures incorporate metal ions as ‘glue’ to link organic ligands together into polyhedra.Most of the architectures employed thus far have been highly symmetrical, as these have been the easiest to prepare. Such high-symmetry structures contain pseudospherical cavities, and so typically bind roughly spherical guests. Biomolecules and high-value synthetic compounds are rarely isotropic, highly-symmetrical species. To bind, sense, separate, and transform such substrates, new, lower-symmetry, metal-organic cages are needed. Herein we summarize recent approaches, which taken together form the first draft of a handbook for the design of higher-complexity, lower-symmetry, self-assembled metal-organic architectures.

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.

Star polymer networks: a toolbox for cross-linked polymers with controlled structure

The synthesis of precisely controlled polymer networks has been a long-cherished dream of polymer scientists. Traditional random cross-linking strategies often lead to uncontrolled networks with various kinds of defects. Recent...

Orientational self-sorting: formation of structurally defined Pd4L8 and Pd6L12 cages from low-symmetry dipyridyl ligands

Tetra- and hexanuclear coordination cages were obtained in reactions of [Pd(CH₃CN)₄](BF₄)₂ with low-symmetry dipyridyl ligands. In both cases, only one structurally defined complex was formed out of a vast pool of potential isomers.

Tuning the Size and Geometry of Heteroleptic Coordination Cages by Varying the Ligand Bent Angle

Spherical assemblies of the type [Pd_n L_2n ]²ⁿ⁺ can be obtained from Pd^II salts and curved N-donor ligands, L. It is well established that the bent angle, α, of the ligand is a decisive factor in the self-assembly process, with larger angles leading to complexes with a higher nuclearity, n. Herein, we report heteroleptic coordination cages of the type [Pd_n L_n L'_n ]²ⁿ⁺ , for which a similar correlation between the ligand bent angle and the nuclearity is observed. Tetranuclear cages were obtained by combining [Pd(CH₃ CN)₄ ](BF₄ )₂ with 1,3-di(pyridin-3-yl)benzene and ligands featuring a bent angle of α=120°. The use of a dipyridyl ligand with α=149° led to the formation of a hexanuclear complex with a trigonal prismatic geometry; for linear ligands, octanuclear assemblies of the type [Pd₈ L₈ L'₈ ]¹⁶⁺ were obtained. The predictable formation of heteroleptic Pd^II cages from 1,3-di(pyridin-3-yl)benzene and different dipyridyl ligands is evidence that there are entire classes of heteroleptic cage structures that are privileged from a thermodynamic point of view.

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.

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.

Identification of a Heteroleptic Pd6L6L'6 Coordination Cage by Screening of a Virtual Combinatorial Library

The design of structurally defined heteroleptic coordination cages is a challenging task, and only few examples are known to date. Here we describe a selection approach that allowed the identification of a novel hexanuclear Pd cage containing two types of dipyridyl ligands. A virtual combinatorial library of [Pd_nL_2n](BF₄)_2n complexes was prepared by mixing six different dipyridyl ligands with substoichiometric amounts of [Pd(CH₃CN)₄](BF₄)₂. Analysis of the equilibrated reaction mixture revealed the preferential formation of a heteroleptic [Pd₆L₆L'₆](BF₄)₁₂ assembly. The complex was prepared on a preparative scale by a targeted synthesis, and its structure was elucidated by single-crystal X-ray diffraction. It features an unprecedented trigonal-antiprismatic cage structure with two triangular Pd₃L₃ macrocycles bridged by six L' ligands. A related but significantly larger [Pd₆L₆L'₆](BF₄)₁₂ cage was obtained by using metalloligands instead of organic dipyridyl ligands.

Supramolecular and Physically Double-Cross-Linked Network Strategy toward Strong and Tough Elastic Fibers

The strength and toughness are two trade-off properties of a material, yet Nature can achieve strong and tough materials by introducing sacrificial bonds into a system. Here, we present a four-component multiblock copolymer (mBCP) approach toward strong and tough elastic fibers, by introducing terpyridine moieties into poly(ether ester) mBCP elastomers. After coordination with Fe(II), supramolecular cross-links are formed within the physically cross-linked thermoplastic elastomers. The toughening elastic fibers with a double-cross-linked network structure show high tensile strength (ca. 300 MPa) and toughness (ca. 100 MJ m^-3). In addition, they display excellent resilience with enhanced self-healing properties. Our strategy provides a promising way for the development of strong and tough elastomers by introducing metal-ligand sacrificial bonds into mBCPs elastomers.

Recent advances in coordination-driven polymeric gel materials: design and applications

Recently, research attention has been directed towards the coordination driven synthesis of gels, including coordination polymer gels (CPGs) and metal-organic cage based gels, which have shown applications in diverse fields, including optoelectronics, catalysis, sensing, gas-storage, and self-healing. A wide variety of CPGs and metal-organic cage based gels have been reported, to date, by choosing the right combination of metal ions and rationally designed organic linkers. In this article, we focused on recent developments in CPGs and metal-organic cage based gels and their applications.

Photoswitchable Sol-Gel Transitions and Catalysis Mediated by Polymer Networks with Coumarin-Decorated Cu24 L24 Metal-Organic Cages as Junctions

Photoresponsive materials that change in response to light have been studied for a range of applications. These materials are often metastable during irradiation, returning to their pre-irradiated state after removal of the light source. Herein, we report a polymer gel comprising poly(ethylene glycol) star polymers linked by Cu₂₄ L₂₄ metal-organic cages/polyhedra (MOCs) with coumarin ligands. In the presence of UV light, a photosensitizer, and a hydrogen donor, this "polyMOC" material can be reversibly switched between Cu^II , Cu^I , and Cu⁰ . The instability of the MOC junctions in the Cu^I and Cu⁰ states leads to network disassembly, forming Cu^I /Cu⁰ solutions, respectively, that are stable until re-oxidation to Cu^II and supramolecular gelation. This reversible disassembly of the polyMOC network can occur in the presence of a fixed covalent second network generated in situ by copper-catalyzed azide-alkyne cycloaddition (CuAAC), providing interpenetrating supramolecular and covalent networks.

Polymer Networks: From Plastics and Gels to Porous Frameworks

Polymer networks, which are materials composed of many smaller components-referred to as "junctions" and "strands"-connected together via covalent or non-covalent/supramolecular interactions, are arguably the most versatile, widely studied, broadly used, and important materials known. From the first commercial polymers through the plastics revolution of the 20^th century to today, there are almost no aspects of modern life that are not impacted by polymer networks. Nevertheless, there are still many challenges that must be addressed to enable a complete understanding of these materials and facilitate their development for emerging applications ranging from sustainability and energy harvesting/storage to tissue engineering and additive manufacturing. Here, we provide a unifying overview of the fundamentals of polymer network synthesis, structure, and properties, tying together recent trends in the field that are not always associated with classical polymer networks, such as the advent of crystalline "framework" materials. We also highlight recent advances in using molecular design and control of topology to showcase how a deep understanding of structure-property relationships can lead to advanced networks with exceptional properties.

Supramolecular metallacyclic hydrogels with tunable strength switched by host–guest interactions

A new family of supramolecular hydrogels with tunable strength was successfully constructed through a combination of coordination-driven self-assembly, post-assembly polymerization and host–guest interactions.

Photo-regulated supramolecular star with a pillar[6]arene-coated metal–organic polyhedron (MOP) core

We report a photo-regulated supramolecular star centered by a pillar[6]arene-coated metal–organic polyhedron (MOP) core.

The Microscopic Structure-Property Relationship of Metal-Organic Polyhedron Nanocomposites

Monodispersed hairy nanocomposites with typical 2 nm (isophthalic acid)₂₄ Cu₂₄ metal-organic polyhedra (MOP) as a core protected by 24 polymer chains with controlled narrow molecular weight distribution has been probed by imaging and scattering studies for the heterogeneity of polymers in the nanocomposites and the confinement effect the MOPs imposing on anchored polymers. Typical confined-extending surrounded by one entanglement area is proposed to describe the physical states of the polymer chains. This model dictates the counterintuitive thermal and rheological properties and prohibited solvent exchange properties of the nanocomposites, whilst those polymer chain states are tunable and deterministic based on their component inputs. From the relationship between the structure and behavior of the MOP nanocomposites, a MOP-composited thermoplastic elastomer was obtained, providing practical solutions to improve mechanical/rheological performances and processabilities of inorganic MOPs.

Soft Materials with Diverse Suprastructures via the Self-Assembly of Metal-Organic Complexes

Inspired by assemblies in the natural world, researchers have prepared diverse suprastructures with distinct spatial arrangements by artificial self-assembly, including micelles, vesicles, ribbons, films, fibers, and tubes. The field of assembly is undergoing a transition from single-component to multicomponent assembly and single-step to multistep processing. Control over the size, shape, and composition of these building blocks has enabled the formation of suprastructures with substantial structural diversity. More importantly, harnessing noncovalent interactions to create suprastructures in a controlled manner will lead to a better understanding of the formation of complex self-organized patterns. However, for the construction of multiscale self-assemblies with controllable shapes and functions, the selection of a suitable protocol remains challenging. Coordination-driven self-assembly provides a bottom-up approach to construct various metal-organic complexes (MOCs), which could be further used as building blocks with controllable shapes and sizes. Despite the tremendous progress made in the design of MOC-based supramolecular materials, most of these MOCs have dimensions of only several nanometers, and investigations of these structures rely on the characterization of their crystal structure. However, most of the functional suprastructures in living organisms have dimensions ranging from microns to centimeters and have the form of soft materials. Thus, obtaining MOC-based highly ordered materials of larger size remains a challenge. This Account focuses on our recent advances in the construction of soft suprastructure materials with MOCs. A series of functionalized MOCs was first constructed through coordination-driven self-assembly. Then, further self-assembly of the as-prepared MOCs gave rise to the formation of higher-order structures. By changing the functional groups in the acceptors and donors in the MOCs, different suprastructures, including nanospheres, nanodiamonds, nanorods, nanofibers, membranes, films, and gels, were prepared. These studies suggest that using MOCs as building blocks is a highly efficient strategy to achieve complex architectures and functional materials for the development of desired MOC-based soft materials with high precision and fidelity.

Palladium-Based Metal-Ligand Assemblies: The Contrasting Behavior upon Addition of Pyridine or Acid

The stability of five different [Pd _n(N-donor) _m]^{2 n+} assemblies was examined by performing disassembly experiments with pyridine and with trifluoroacetic acid. Pyridine-induced disassembly was found to be most pronounced for Pd complexes containing N-donor ligands of low basicity. At the same time, these assemblies displayed high acid resistance. The contrasting stability in the presence of acid or pyridine can be used for the pH-controlled switching between different metallosupramolecular structures.

Metallopolymers cross-linked with self-assembled Ln4L4 cages

Herein, we report a metallopolymer based on a polydivinylbenzene (PDVB) matrix cross-linked by tetranuclear Ln₄L₄ cages.

The chemistry of multi-component and hierarchical framework compounds

This review is expected to provide a library of multi-component hierarchically porous compounds, which shall guide the state-of-the-art design of future porous materials with unprecedented tunability, synergism and precision.

Recent developments in the construction of metallacycle/metallacage-cored supramolecular polymers via hierarchical self-assembly

Supramolecular polymers have received considerable attention during the last few decades due to their scientific value in polymer chemistry and profound implications for future developments of advanced materials. Discrete supramolecular coordination complexes (SCCs) with well-defined size, shape, and geometry have been widely employed to construct hierarchical systems by coordination-driven self-assembly with the spontaneous formation of metal-ligand bonds, which results in the formation of well-defined two-dimensional (2D) metallacycles or three-dimensional (3D) metallacages with high functionalities. The incorporation of discrete SCCs into supramolecular polymers by the orthogonal combination of metal-ligand coordination and other noncovalent interactions or covalent bonding could further facilitate the construction of novel supramolecular polymers with hierarchical architectures and multiple functions including controllable uptake and release of guest molecules, providing a flexible platform for the development of smart materials. In this review, the recent progress in metallacycle/metallacage-cored supramolecular polymers that were constructed by the combination of metal-ligand interactions and other orthogonal interactions (including hydrophobic or hydrophilic interactions, hydrogen bonding, van der Waals forces, π-π stacking, electrostatic interactions, host-guest interactions and covalent bonding) has been discussed. In addition, the potential applications of metallacycle/metallacage-cored supramolecular polymers in the areas of light emitting, sensing, bio-imaging, delivery and release, etc., are also presented.

Discrete and Polymeric Self-Assembled Palladium(II) Complexes as Supramolecular Gelators

Supramolecular gels prepared from low-molecular-weight gelators have been extensively explored. However, the exploitation of discrete or polymeric metal complexes as gelators is a relatively recent trend. The synthesis of self-assembled coordination complexes from palladium(II) and selected ligands is well established, but the potential of these complexes as gelators is a less explored treasure. Herein we focus on the gelation abilities of some self-assembled palladium(II) complexes and the resulting unique properties. First, discrete complexes with PdL, PdL₂ , Pd₂ L, Pd₂ L₂ , Pd₂ L₄ , and Pd₃ L₆ compositions are discussed. Second, gelation behavior promoted by coordination-polymer-like gelators formed in situ is explored. These gel samples have been employed in catalysis and the uptake of organic and dye molecules from the solution and gas phases. It is concluded that untapped unique properties can be realized by further exploration of designer palladium(II) complexes.

Modular Design of Porous Soft Materials via Self-Organization of Metal-Organic Cages

Metal-organic frameworks (MOFs) and porous coordination polymers (PCPs) have been well-recognized as emerging porous materials that afford highly tailorable and well-defined nanoporous structures with three-dimensional lattices. Because of their microporous nature, MOFs can accommodate small molecules in their lattice structure, thus discriminating them on the basis of their size and physical properties and enabling their separation even in the gas phase. Such characteristics of MOFs have attracted significant attention in recent years for diverse applications and have ignited a worldwide race toward their development in both academic and industrial fields. Most recently, new challenges in porous materials science demand processable liquid, melt, and amorphous forms of MOFs. This trend will provide a new fundamental class of microporous materials for further widespread applications in many fields. In particular, the application of flexible membranes for gas separation is expected as an efficient solution to tackle current energy-intensive issues. To date, amorphous MOFs have been prepared in a top-down approach by the introduction of disorder into the parent frameworks. However, this new paradigm is still in its infancy with respect to the rational design principles that need to be developed for any approach that may include bottom-up synthesis of porous soft materials. Herein we describe recent progress in bottom-up "modular" approaches for the synthesis of porous, processable MOF-based materials, wherein metal-organic cages (MOCs), alternatively called metal-organic polyhedra (MOPs), are used as "modular cavities" to build porous soft materials. The outer periphery of a MOP is decorated with polymeric and dendritic side chains to obtain a polymer-grafted MOP, imparting both solution and thermal processability to the MOP cages, which have an inherent nanocavity along with high tailorability analogous to MOFs. Well-ordered MOP assemblies can be designed to obtain phases ranging from crystals to liquid crystals, allowing the fabrication of flexible free-standing sheets with preservation of the long-range ordering of MOPs. Furthermore, future prospects of the modular design for porous soft materials are provided with the anticipation that the bottom-up design will combine porous materials and soft matter sciences, leading to the discovery and development of many unexplored new materials and devices such as MOF-based self-healing membranes possessing well-defined nanochannels. The macroscopic alignment of channels can be controlled by external factors, including electric and magnetic fields, external forces, and modified surfaces (templating and patterning), which are conventionally used for engineering of soft materials.

Metal Organic Polyhedra: A Click-and-Clack Approach Toward Targeted Delivery

Mixed self-assembly of ligands 1 and 2, PXDA (3), and Pd(NO₃)₂ afforded metal organic polyhedra (MOP 1 - MOP 3) which bear 24 covalently attached CB[7] and cyclooctyne moieties. Post assembly modification (PAM) of MOP 3 by covalent strain promoted alkyne azide click reaction provided MOP 4 ^R bearing covalently attached functionality (PEG, sulfonate, biotin, c-RGD, fluorescein and cyanine). Orthogonal CB[7] guest mediated non-covalent PAM of MOP 4 ^R with Ad-FITC afforded MOP 5 ^RGD Ad-FITC and MOP 5 ^biotin 0020Ad-FITC. Flow cytometry analysis of the uptake of MOP 5 ^RGD Ad-FITC toward U87 cells demonstrated improved uptake relative to control MOP lacking c-RGD ligands. These results suggest a broad applicability of orthogonally functionalizable (covalent and non-covalent) MOPs in targeted drug delivery and imaging applications.