Transformation networks of metal-organic cages controlled by chemical stimuli

Crystal Engineering of Cyanoborate-Bridged Cubane-Type Tetranuclear Ru Complex: Synthesis, Pseudopolymorphism, and Coordination Polymer Formation

Cyanoborate anions are versatile bridging ligands that lead to structurally diverse compounds from a crystal engineering perspective. Herein, we report the synthesis of a cubane-type tetranuclear Ru complex, [Ru4(Cp)4{B(CN)4}4] (1, Cp = C5H5), obtained by photoirradiation of [Ru(Cp)(C6H6)]B(CN)4 in solution or by the reaction of [CpRu(MeCN)3]+ with KB(CN)4. This complex served as a host for various solvents, generating different pseudopolymorphs, including 1·nCH2Cl2 (n = 1, 2, 3), 1·0.5C6H6, 1·C6H5Me, and 1·3THF upon recrystallization. Moreover, the four free cyano groups in 1 allow it to act as a bridging ligand, facilitating the formation of 1D and 2D coordination polymers through reactions with transition metal complexes.

Unraveling the Surface Chemistry of Aluminum Oxo Archimedean Cages for Efficient Serial Adsorption

Multifunctional materials that meet diverse application needs hold profound significance in resource optimization, efficiency enhancement, and environmental sustainability. However, the development of these materials faces numerous challenges, including raw material acquisition, design feasibility, and long-term stability. This study demonstrates the innovative application of the surface chemistry of aluminum oxo Archimedean cages in efficient serial adsorption. The "Four-in-One" surface chemistry enables various single-crystal-to-single-crystal (SC-SC) structural transformations, involving ligand modification, cation exchange, post-synthetic metalation, and metal elimination, successfully achieving the first reversible SC-SC transformation from cluster structures to infinite frameworks. The fundamental reason behind these dynamic structural changes lies in the exceptional balance between rigidity and flexibility provided by the intercluster tri-pyrazole sites on the Archimedean cages. This diverse structural transformation characteristic offers extensive application potential for solid-liquid and solid-gas serial adsorption. For instance, this material effectively adsorbs heavy metal ions in water treatment and can subsequently be used for the permanent fixation of gaseous radionuclides. This work not only deepens our understanding of dynamic chemistry but also provides guiding significance for environmental remediation.

Coordination-assembly of a redox-active Pd6L3 cage for aerobic C(sp3)-H bond photooxidation of aromatic cyclic ethers

A redox-active Pd6L3 cage with a large lantern-shaped cavity has been synthesized and characterised by NMR, ESI-TOF-MS and X-ray diffraction analysis, which shows exceptional catalytic activity in the selective aerobic C-H photooxidation of aromatic cyclic ethers under mild conditions.

Synergistic regulation of metal-organic cage architectures via temperature- and solvent-driven atropisomerism

Regulating multistimulus responses in artificial systems remains a challenge in smart material development. We present a versatile chemical switching system that precisely controls the self-assembly of metal-organic cages via temperature and solvent changes. The key component, cyclo[2](1,3-(4,6-dimethyl)benzene) (4-pyridine)[6](1,3-(4,6-dimethyl)benzene) (CP2), was generated as three atropisomers (1, 2, and 3) with Cs, C1, and C2v symmetries. Thermally, metastable isomers (1 and 2) convert into the stable isomer (3), which reacts with Pd2+ to form specific molecular cages. Depending on the solvent, either rectangular M2L2 cages (5' and 5) form in 1,4-dioxane or hexagonal M3L3 cages (6) in 1,1',2,2'-tetrachloroethane. The solvent dictates the cage type and enables reversible transformation between cages 5 and 6. Additionally, cage 5', formed from metastable isomer 1, can switch to other cage types (i.e., 5 or 6) depending on temperature and solvent conditions. This multipathway system offers a precise strategy for controlling self-assembly in smart materials.

Pathway Engineering in Pd-Based Supramolecular Cage Synthesis via Inner-Outer Steric Synergy

For artificial supramolecular architectures designed to mimic biological systems, achieving different pathway synthesis is challenging due to the requirement of multiple stable and interconvertible intermediates. Here, we propose a novel "inner-outer steric synergy" strategy and investigate controllable pathway engineering for the synthesis of specific structures. Firstly, three structures (Ring-Pd2LA 2, Bowl-Pd2LA 3 and Cage-Pd2LA 4) with interconversion properties were selectively formed by assembling externally modified ligand LA with Pd(II). Furthermore, Ring-Pd2LA 2 can further assemble with the ligand LB with inner steric hindrance to generate heteroleptic trans-Pd2LA 2LB 2 cage, while Bowl-Pd2LA 3, as an intermediate, can assemble with LB to form Pd2LA 3LB. It is noteworthy that Ring-Pd2LA 2, Bowl-Pd2LA 3, and Cage-Pd2LA 4 can interconvert under specific conditions, enabling the synthesis of Pd2LA 3LB and trans-Pd2LA 2LB 2 through 10 and 16 pathways, respectively. This research not only introduces a novel strategy for constructing heteroleptic cages but also demonstrates the achievement of pathway engineering.

Host-Guest Approach to Enhancing Photocatalysis via Photoinduced Energy and Electron Transfer from a Photoactive Triphenylamine-Based Metal-Organic Cage to Bound Guests

The host-guest strategy presents an ideal way to construct versatile supramolecular systems that mimic the structure and functionality of natural enzymes and, therefore, achieve efficient chemical conversions. An emissive triphenylamine-based cage-like host donor was constructed as an energy or electron donor to achieve efficient photoinduced energy or electron transfer (PEnT or PET) by encapsulating the energy or electron acceptor into the cavity of the cage. The host-guest complexes, which served as enzyme-mimicking supramolecular systems, were successfully used as photocatalysts for the selective aerobic oxidation of sulfides and the efficient photocatalytic reduction of aryl halides with high reduction potentials. This work details a promising approach for creating a host-guest system via a host-guest encapsulation strategy to enhance the efficiency of the PEnT or PET process. The resulting designed artificial supramolecular systems achieve efficient chemical conversions by mimicking the structure and functionality of natural enzymes.

Metallacage-crosslinked free-standing supramolecular networks via photo-induced copolymerization for photocatalytic water decontamination

The development of polymer materials for water decontamination makes a significant contribution to environmental protection and public health. Herein, we report the preparation of metallacage-crosslinked free-standing supramolecular networks by photo-induced copolymerization of acrylate metallacages and butyl methacrylate for water decontamination. The integration of metallacages into polymer networks endows the networks good capability for generating singlet oxygen via photosensitization, making them serve as a type of decontamination materials that can effectively eliminate diverse organic pollutants and bacterial contaminants. This study not only provides a mild and effective strategy for the preparation of metallacage-cored supramolecular networks via photo-induced copolymerization but also explores their applications for photocatalytic dye degradation and bacterial killing, which will promote the future development of metallacage-based supramolecular materials for photocatalytic applications.

Fine-Tuning of the Sequential Self-Assembly of Entangled Polyhedra by Exploiting the Side-Chain Effect

The control of the sequential self-assembly processes of highly entangled (Ag3L2)n (n=2,4,6,8) and Ag21L12 coordination polyhedra using side-chain effects was studied via the introduction of linear or branched side chains into the tripodal ligands. In addition to changes in the intermediate polyhedral species affording the multi- pathway process, disruption of the kinetic control of the sequential self-assembly was observed, thus demonstrating the utility of steric control for the construction of 3D-entangled molecular materials on the 5 nm scale with high molecular complexity.

Self-assembly, interlocking, interconversion and anion-binding catalysis in phenoxazine-based Pd2L4 and Pd4L8 coordination cages

Interpenetration is a phenomenon frequently encountered in self-assembled Pd2L4-type coordination cages, while the mechanism of the interpenetration process remains unclear. Here we show the synthesis and solvent-mediated interconversion of highly soluble phenoxazine-based monomeric cage 1 and corresponding interlocked dimer 2. We succeed in the isolation and single-crystal structure analysis of both 1 and 2 with the same guest anion by changing the solvents utilized in self-assembly. The monomeric-to-dimeric cage conversion occurs by heating in weakly coordinating solvents, while dimeric-to-monomeric cage conversion takes place through a disassembly and reassembly process in strongly coordinating solvents at low concentration or by the addition/removal of competing ligand. The interconversion may be driven by the distinct thermodynamic stabilities of 1 and 2 in different solvents. Additionally, Cl- anions template the interpenetration of 1 because of the strong chloride binding affinity of 2 which could serve as an anion-binding catalyst for the C-Cl bond cleavage.

Guest Segregation in Heteromeric Multicage Systems

Dynamically interconvertible metallo-supramolecular multicomponent assemblies, coexisting orthogonally in solution, serve as simplified mimics for complex networks found in biological systems. Building on recent advances in controlling the nonstatistical self-assembly of heteroleptic coordination cages and heteromeric completive self-sorting, i.e., the coformation of multiple low-symmetry assemblies, we herein describe the first instance of emerging functionality from a heteromeric multicage system. In particular, one heteroleptic cage coexists in equilibrium with one or two different homoleptic cages, each capable of preferentially encapsulating one out of three guests within their cavities. Guest segregation occurs under thermodynamic control and can be reached following several distinct paths. Each pathway involves different sequential transformations, eventually leading to the same outcome. We found that the most complex mixture of components (three ligands, three guests, plus palladium cations) always yields an ordered, pathway-independent final state of three coexisting host-guest species, thus representing a case of simplexity in self-sorted systems. This study forms a basis for expanding the scope of dynamic transformation processes implemented in multicage host-guest systems. Together with the incorporation of stimuli-responsive elements and other functionality, complex cage populations with bioinspired applications in controllable compound separation schemes, compartmentalized cascade reactions, and multistep (even bifurcated) molecular information processing will become accessible.

Dynamic selection in metallo-organic cube CdII 8L4 conformations induced by perfluorooctanoate encapsulation

Metallo-organic cages possess flexibility comparable to that of biological receptors and can alter their conformations to better accommodate guest species due to the dynamic reversibility of the coordination bond. Induced fit is widely accepted involving conformation change of the host, while few definitive examples are related to conformation selection. Herein, we report the generation of metallo-organic cube CdII 8L4 with two coexisting conformations, which have been fully confirmed by NMR, ESI-MS and single-crystal X-ray diffraction analysis. The specific guest perfluorooctanoate PFOA selectively binds to the active conformer C 2h-1 to form the PFOA⊂C 2h-1 complex. Furthermore, conformer D 2-2 isomerizes to conformer C 2h-1 in the presence of PFOA, for maximizing the guest binding affinity. This study provides an effective working paradigm for conformation selection, facilitating the understanding of the fundamental mechanism of molecular recognition.

Double-Bridging Increases the Stability of Zinc(II) Metal-Organic Cages

A key feature of coordination cages is the dynamic nature of their coordinative bonds, which facilitates the synthesis of complex polyhedral structures and their post-assembly modification. However, this dynamic nature can limit cage stability. Increasing cage robustness is important for real-world use cases. Here we introduce a double-bridging strategy to increase cage stability, where designed pairs of bifunctional subcomponents combine to generate rectangular tetratopic ligands within pseudo-cubic Zn8L6 cages. These cages withstand transmetalation, the addition of competing ligands, and nucleophilic imines, under conditions where their single-bridged congeners decompose. Our approach not only increases the stability and robustness of the cages while maintaining their polyhedral structure, but also enables the incorporation of additional functional units in proximity to the cavity. The double-bridging strategy also facilitates the synthesis of larger cages, which are inaccessible as single-bridged congeners.

Heterometallic-Organic Cages with Customized Cavities: Constructed by Bottom-Up Step-Wise Coordination-Driven Self-Assembly

Accurately synthesizing coordination-driven metal-organic cages with customized shape and cavity remains a great challenge for chemists. In this work, a bottom-up step-wise coordination-driven self-assembly approach was put forward. Employing this strategy, three terpyridyl heterometallic-organic truncated tetrahedral cages with different sizes and cavity were precisely synthesized. Firstly, the coordination of tripodal organic ligands with Ru2+ afforded dendritic metal-organic ligands L1-L3. Then the Ru building blocks complexed with Fe2+ and shrunk to form the desired heterometallic-organic cages (C1-C3). These discrete heterometallic-organic supramolecular cages were fully characterized and displayed the large and open cavities varied from 7205 Å3 to 9384 Å3. Notably, these cages could not be directly constructed by single-step assembly process using initial organic ligands or dimeric metal-organic ligands, indicative of the irreplaceability of a bottom-up step-wise assembly strategy for size-customized architectures. This work paves a new way for precisely constructing metal-organic cages with well-defined cavities.

Supramolecular and molecular capsules, cages and containers

Stemming from early seminal notions of molecular recognition and encapsulation, three-dimensional, cavity-containing capsular compounds and assemblies have attracted intense interest due to the ability to modulate chemical and physical properties of species encapsulated within these confined spaces compared to bulk environments. With such a diverse range of covalent motifs and non-covalent (supramolecular) interactions available to assemble building blocks, an incredibly wide-range of capsular-type architectures have been developed. Furthermore, synthetic tunability of the internal environments gives chemists the opportunity to engineer systems for uses in sensing, sequestration, catalysis and transport of molecules, just to name a few. In this tutorial review, an overview is provided into the design principles, synthesis, characterisation, structural facets and properties of coordination cages, porous organic cages, supramolecular capsules, foldamers and mechanically interlocked molecules. Using seminal and recent examples, the advantages and limitations of each system are explored, highlighting their application in various tasks and functions.

London dispersion driven compaction of coordination cages in the gas-phase - a combined ion mobility and theoretical study

Large self-assembled systems (such as metallosupramolecular rings and cages) can be difficult to structurally characterize, in particular when they show a highly dynamic behavior. In the gas-phase, Ion Mobility Spectrometry (IMS), in tandem with Electrospray Ionization Mass Spectrometry (ESI MS), can yield valuable insights into the size, shape and dynamics of such supramolecular assemblies. However, the detailed relationship between experimental IMS data and the actual gas-phase structure is still poorly understood for soft and flexible self-assemblies. In this study, we combine high resolution Trapped Ion Mobility Spectrometry (TIMS), yielding collisional cross section data (CCS), with computational modeling and theoretical CCS calculations to obtain and interpret gas-phase structural data for a series of palladium-based coordination cages. We focus on derivatives of a homoleptic lantern-shaped [Pd2L4]4+ cage and its interpenetrated dimer ([3X@Pd4L8]5+, X = Cl, Br) to study the influence of flexible side chains of different lengths, counter anions and π-stacking tendencies between the ligands in the absence of solvent. The gained insights as well as the presented CCS calculation and evaluation workflow establish a basis for the systematic gas-phase characterization of a wider range of flexible, chain-decorated and guest-modulated assemblies.

π-Diamond: A Diamondoid Superstructure Driven by π-Interactions

Modulating the arrangement of superstructures through noncovalent interactions has a significant impact on macroscopic shape and the expression of unique properties. Constructing π-interaction-driven hierarchical three-dimensional (3D) superstructures poses challenges on account of limited directional control and weak intermolecular interactions. Here we report the construction of a 3D diamondoid superstructure, named π-Diamond, employing a ditopic strained Z-shaped building block comprising a porphyrin unit as bow-limb double-strapped with two m-xylylene units as bowstrings. This superstructure, reminiscent of diamond's tetrahedral carbon composition, is composed of double-walled tetrahedron (DWT) driven solely by π-interactions. Hetero-π-stacking interactions between porphyrin and m-xylylene panels drive the assembly of four building blocks predominantly into a DWT, which undergoes extension to create an adamantane unit and eventually a diamondoid superstructure wherein each porphyrin panel is shared by two neighboring tetrahedra through hetero-π-stacking. π-Diamond exhibits a solid-state fluorescent quantum yield 44 times higher than that of tetraphenylporphyrin along with excellent photocatalytic performance. The precise 3D directionality of π-interactions, achieved through strained multipanel building blocks, revolutionizes the assembly of hierarchical 3D superstructures driven by π-interactions.

Multi-Stimuli-Responsive Network of Multicatalytic Reactions using a Single Palladium/Platinum Catalyst

Given her unrivalled proficiency in the synthesis of all molecules of life, nature has been an endless source of inspiration for developing new strategies in organic chemistry and catalysis. However, one feature that remains thus far beyond chemists' grasp is her unique ability to adapt the productivity of metabolic processes in response to triggers that indicate the temporary need for specific metabolites. To demonstrate the remarkable potential of such stimuli-responsive systems, we present a metabolism-inspired network of multicatalytic processes capable of selectively synthesising a range of products from simple starting materials. Specifically, the network is built of four classes of distinct catalytic reactions-cross-couplings, substitutions, additions, and reductions, involving three organic starting materials-terminal alkyne, aryl iodide, and hydrosilane. All starting materials are either introduced sequentially or added to the system at the same time, with no continuous influx of reagents or efflux of products. All processes in the system are catalysed by a multifunctional heteronuclear PdII/PtII complex, whose performance can be controlled by specific additives and external stimuli. The reaction network exhibits a substantial degree of orthogonality between different pathways, enabling the controllable synthesis of ten distinct products with high efficiency and selectivity through simultaneous triggering and suppression mechanisms.

Host-Guest Approach to Promoting Photocatalysis Based on Consecutive Photo-Induced Electron-Transfer Processes via Efficient Förster Resonance Energy Transfer

Supramolecular artificial light-harvesting system with highly efficient host-guest energy transfer pathway provides an ideal platform for optimizing the photochemistry process. The consecutive photo-induced electron transfer (conPET) process overcomes the energy limitation of visible-light photocatalysis, but is often compromised by mismatching between the absorption of ground state dye and its radical, weakening the efficiency of photoredox reaction. By encapsulating a conPET photocatalyst rhodamine 6G into metal-organic cage, the supramolecular approach was undertaken to tackle the intrinsic difficulty of matching the light absorption of photoexcitation between rhodamine 6G and its radical. The highly efficient Förster resonance energy transfer from the photoexcited cage to rhodamine 6G forced by host-guest encapsulation facilitates the conPET process for the single-wavelength light-driven activation of aryl halides by stabilizing and accelerating the production and accumulation of the rhodamine 6G radical intermediate. The tunable and flexible nature of the supramolecular host-guest complex renders the cage-based encapsulation strategy promising for the development of ideal photocatalysts toward the better utilization of solar energy.

A Redox-Active Phenothiazine-based Pd2L4-Type Coordination Cage and Its Isolable Crystalline Polyradical Cations

Polyradical cages are of great interest because they show very fascinating physical and chemical properties, but many challenges remain, especially for their synthesis and characterization. Herein, we present the synthesis of a polyradical cation cage 14⋅+ through post-synthetic oxidation of a redox-active phenothiazine-based Pd2L4-type coordination cage 1. It's worth noting that 1 exhibits excellent reversible electrochemical and chemical redox activity due to the introduction of a bulky 3,5-di-tert-butyl-4-methoxyphenyl substituent. The generation of 14⋅+ through reversible electrochemical oxidation is investigated by in situ UV/Vis-NIR and EPR spectroelectrochemistry. Meanwhile, chemical oxidation of 1 can also produce 14⋅+ which can be reversibly reduced back to the original cage 1, and the process is monitored by EPR and NMR spectroscopies. Eventually, we succeed in the isolation and single crystal X-ray diffraction analysis of 14⋅+, whose electronic structure and conformation are distinct to original 1. The magnetic susceptibility measurements indicate the predominantly antiferromagnetic interactions between the four phenothiazine radical cations in 14⋅+. We believe that our study including the facile synthesis methodology and in situ spectroelectrochemistry will shed some light on the synthesis and characterization of novel polyradical systems, opening more perspectives for developing functional supramolecular cages.

Multiple-stimuli fluorescent responsive metallo-organic helicated cage arising from monomer and excimer emission

Effectively regulating monomer and excimer emission in a singular supramolecular luminous platform is challenging due to high difficulty of precise control over its aggregation and dispersion behavior when subjected to external stimuli. Here, we show a metallo-cage (MTH) featuring a triple helical motif that displays a unique dual emission. It arises from both intramolecular monomer and intermolecular excimer, respectively. The distorted molecular conformation and the staggered stacking mode of MTH excimer are verified through single crystal X-ray diffraction analysis. These structural features facilitate the switch between monomer and excimer emission, which are induced by changes in concentration and temperature. Significantly, adjusting the equilibrium between these two states in MTH enables the production of vibrant white light emission in both solution and solid state. Moreover, when combined with a PMMA (polymethyl methacrylate) substrate, the resulting thin films can serve as straightforward fluorescence thermometer and thermally activated information encryption materials.

Ligand Conformation Controls Assembly of a Helicate/Mesocate, Heteroleptic [Pd2L2L'2] Cages and a Six-Jagged [Pd6L12] Ring

Molecular building blocks, capable of adopting several strongly deviating conformations, are of particular interest in the development of stimuli-responsive self-assemblies. The pronounced structural flexibility of a short acridone-based bridging ligand, equipped with two monodentate isoquinoline donors, is herein exploited to assemble a surprisingly diverse series of coordination-driven Pd(II) architectures. First, it can form a highly twisted Pd2L4 helicate, transformable into the corresponding mesocate, controlled by temperature, counter anion and choice of solvent. Second, it also allows the formation of heteroleptic cages, either from a mix of ligands with Pd(II) cations or by cage-to-cage transformation from homoleptic assemblies. Here, the acridone-based ligand tolerates counter ligands that carry their donors either in a diverging or converging arrangement, as it can rotate its own coordination sites by 90° and structurally adapt to both situations via shape complementarity. Third, by a near 180° rotation of only one of its arms, the ligand can adopt an S-shape conformation and form an unprecedented C6h-symmetric Pd6L12 saw-toothed six-membered ring.

De novo construction of amine-functionalized metal-organic cages as heterogenous catalysts for microflow catalysis

Microflow catalysis is a cutting-edge approach to advancing chemical synthesis and manufacturing, but the challenge lies in developing efficient and stable multiphase catalysts. Here we showcase incorporating amine-containing metal-organic cages into automated microfluidic reactors through covalent bonds, enabling highly continuous flow catalysis. Two Fe4L4 tetrahedral cages bearing four uncoordinated amines were designed and synthesized. Post-synthetic modifications of the amine groups with 3-isocyanatopropyltriethoxysilane, introducing silane chains immobilized on the inner walls of the microfluidic reactor. The immobilized cages prove highly efficient for the reaction of anthranilamide with aldehydes, showing superior reactivity and recyclability relative to free cages. This superiority arises from the large cavity, facilitating substrate accommodation and conversion, a high mass transfer rate and stable covalent bonds between cage and microreactor. This study exemplifies the synergy of cages with microreactor technology, highlighting the benefits of heterogenous cages and the potential for future automated synthesis processes.

CageCavityCalc (C3): A Computational Tool for Calculating and Visualizing Cavities in Molecular Cages

Organic(porous) and metal-organic cages are promising biomimetic platforms with diverse applications spanning recognition, sensing, and catalysis. The key to the emergence of these functions is the presence of well-defined inner cavities capable of binding a wide range of guest molecules and modulating their properties. However, despite the myriad cage architectures currently available, the rational design of structurally diverse and functional cages with specific host-guest properties remains challenging. Efficiently predicting such properties is critical for accelerating the discovery of novel functional cages. Herein, we introduce CageCavityCalc (C3), a Python-based tool for calculating the cavity size of molecular cages. The code is available on GitHub at https://github.com/VicenteMartiCentelles/CageCavityCalc. C3 utilizes a novel algorithm that enables the rapid calculation of cavity sizes for a wide range of molecular structures and porous systems. Moreover, C3 facilitates easy visualization of the computed cavity size alongside hydrophobic and electrostatic potentials, providing insights into host-guest interactions within the cage. Furthermore, the calculated cavity can be visualized using widely available visualization software, such as PyMol, VMD, or ChimeraX. To enhance user accessibility, a PyMol plugin has been created, allowing nonspecialists to use this tool without requiring computer programming expertise. We anticipate that the deployment of this computational tool will significantly streamline cage cavity calculations, thereby accelerating the discovery of functional cages.

Solid-State Self-Assembly: Exclusive Formation and Dynamic Interconversion of Discrete Cyclic Assemblies Based on Molecular Tweezers

In contrast to self-assembly in solution systems, the construction of well-defined assemblies in the solid state has long been identified as a challenging task. Herein, we report the formation of tweezers-shaped molecules into various assemblies through a solid-state self-assembly strategy. The relatively flexible molecular tweezers undergo exclusive and quantitative assembly into either cyclic hexamers or a porous network through classical recrystallization or the exposure of powders to solvent vapor, despite the fact that they form only dimers in solution. The cyclic hexamers have high thermal stability and exhibit moderate solid-state fluorescence. The formation of heterologous assemblies consisting of different tweezers allows for tuning these solid-state properties of the cyclic hexamer. Furthermore, (trimethylsilyl)ethynyl-substituted tweezers demonstrate solvent-vapor-induced dynamic interconversion between the cyclic hexamer and a pseudocyclic dimer in the solid state. This assembly behavior, which has been studied extensively in solution-based supramolecular chemistry, had not been accomplished in the solid state so far.

Selective encapsulation of carboxylic acid dimers within a size-regulable resorcinarene-based hemicarcerand

A cavity within a resorcinarene-based hemicarcerand was contracted and expanded through conformational changes induced by the complexation and decomplexation, allowing self-sorting of homo- and heterodimeric carboxylic acid pairs.

High-order layered self-assembled multicavity metal--organic capsules and anti-cooperative host-multi-guest chemistry

The construction and application of metal-organic cages with accessible internal cavities have witnessed rapid development, however, the precise synthesis of complex metal-organic capsules with multiple cavities and achievement of multi-guest encapsulation, and further in-depth comprehension of host-multi-guest recognition remain a great challenge. Just like building LEGO blocks, herein, we have constructed a series of high-order layered metal-organic architectures of generation n (n = 1/2/3/4 is also the number of cavities) by multi-component coordination-driven self-assembly using porphyrin-containing tetrapodal ligands (like plates), multiple parallel-podal ligands (like clamps) and metal ions (like nodes). Importantly, these high-order assembled structures possessed different numbers of rigid and separate cavities formed by overlapped porphyrin planes with specific gaps. The host-guest experiments and convincing characterization proved that these capsules G2-G4 could serve as host structures to achieve multi-guest recognition and unprecedentedly encapsulate up to four C60 molecules. More interestingly, these capsules revealed negative cooperation behavior in the process of multi-guest recognition, which provides a new platform to further study complicated host-multi-guest interaction in the field of supramolecular chemistry.

Nanogels with Metal-Organic Cages as Functional Crosslinks

A dinuclear metal-organic cage with four acrylate side chains was prepared by self-assembly. Precipitation polymerization of the cage with N-isopropylacrylamide yielded a thermoresponsive nanogel. The host properties of the cage were retained within the gel matrix, endowing the nanogel with the capability to serve as a sorbent for chloride ions in water. Moreover, a heteroleptic cage with the drug abiraterone as co-ligand was integrated into a nanogel. The addition of chloride ions induced a structural rearrangement of the metal-ligand assembly, resulting in the gradual release of abiraterone.

Cage-To-Cage Transformations in Self-Assembled Coordination Cages Using "Acid/Base" or "Guest Binding-Induced Strain" as Stimuli

Controlling supramolecular systems between different functional forms by utilizing acids/bases as stimuli is a formidable challenge, especially where labile coordination bonds are involved. A pair of acid/base responsive, interconvertible 1,5-enedione/pyrylium based Pd2L4-type cages are prepared that exhibit differential guest binding abilities towards disulfonates of varied sizes. A three-state switch has been achieved, where (i) a weakly coordinating base induced cage-to-cage transformation in the first step, (ii) a strongly coordinating base triggered cage disassembly as the second step, and (iii) the third step shows acid(strong) promoted generation of initial cage, thereby completing the cycle. To our surprise, binding of a specific disulfonate guest facilitated cage-to-cage transformations by inducing strain on the cage assembly thereby opening the labile pyrylium rings of the cage. Through a competitive guest binding study, we demonstrated the superior guest binding capability of the octacationic pyrylium-based cage over a similar-sized tetracationic cage. These results provide a reliable approach to reversibly modulate the guest binding properties of acid/base-responsive self-assembled coordination cages.

Circular Heterochiral Titanium-Based Self-Assembled Architectures

Circular trinuclear helicates have been synthesized from a bis-biphenol strand (LH4), titanium isopropoxide, and various diimine ligands. These self-assembled architectures constructed around three TiO4N2 nodes have a heterochiral structure (C1 symmetry) when 2,2'-bipyridine (A), 4,4'-dimethyl-2,2'-bipyridine (B), 4,4'-bromo-2,2'-bipyridine (C), or 4,4'-dimethyl-2,2'-bipyrimidine (D) is employed. Within these complexes, one nitrogen ligand is endo-positioned inside the metallo-macrocycle, whereas the other two diimine ligands point outside the helicate framework. This investigation highlights that the nitrogen ligand which does not participate in the helicate framework of the complex controls the overall symmetry of the helicate since the 2,2'-bipyrimidine chelate (F) ends in the formation of a homochiral aggregate (C3 symmetry). The lack of symmetry found in the solid state for the trinuclear species ([Ti3L3(B)3], [Ti3L3(C)3], and [Ti3L3(D)3]) is observed for these complexes in solution (dichloromethane or chloroform). Remarkably, the 2,2'-bipyrazine ligand (ligand E) ends in the formation of a hexameric aggregate formulated as [Ti6L6(E)6], whereas the use of 4,4'-dimethyl-2,2'-bipyrimidine (ligand D) permits to generate the dinuclear complexes ([Ti2L(D)2(OiPr)4] and [Ti2L2(D)2]) in addition to the trimeric structure [Ti3L3(D)3]. The behavior of [Ti3L3(A)3] in solution, on the other hand, is unique since an equilibrium between the homochiral and the heterochiral form is reached within 17 days after the complex has been dissolved in dichloromethane (C3-[Ti3L3(A)3]/C1-[Ti3L3(A)3] ratio = 0.3). In chloroform, the heterochiral form of [Ti3L3(A)3] is stable for the same period of time, evidencing the dependence of this stereochemical transformation toward the solvent medium. The thermodynamic and kinetic parameters linked to this stereochemical equilibrium have been obtained and point to the fact that the transformation is intramolecular and not induced by the presence of external ligands. The thermodynamic constant of the C1-[Ti3L3(A)3]/C3-[Ti3L3(A)3] equilibrium is found to be K = 0.34 ± 10%. Further evidence to rationalize this solvent-induced symmetry switch is obtained via a DFT calculation and classical molecular dynamics. In particular, this computational investigation elucidates the reason why the stereochemical transformation of a heterochiral architecture into a homochiral structure is possible only for a trinuclear assembly containing ligand A.

Non-Templated Assembly of D5h-Symmetric Pd5L10 Rings by Precise Ligand Angle Adjustment

We report a series of Pd(II)nL2n coordination rings for which nuclearity is controlled by the binding angle of the corresponding bis-monodentate bridging ligands. Judicious choice of the angle within a family of rather rigid ligands allowed for the first-time to synthesize a homoleptic five-membered Pd5L10 ring that does not require any template to form. We demonstrate that control over the ring size is maintained both in the solid-, solution-, and gas-phase. Two X-ray structures of five-membered rings from ligands with ideal angles (yielding a perfect pentagonal ring) vs. suboptimal angles (resulting in a highly distorted structure) illustrate the importance of the correct ligand geometry. A mathematical model for estimating the expected ring size based on the ligand angle was derived and DFT computations show that ring-strain is the major factor determining the assembly outcome.

Precise Post-Synthetic Modification of Heterometal-Organic Capsules for Selectively Encapsulating Tetrahedral Anions

Post-synthetic modification plays a crucial role in precisely adjusting the structure and functions of advanced materials. Herein, we report the self-assembly of a tubular heterometallic Pd3Cu6L16 capsule that incorporates Pd(II) and CuL1 metalloligands. This capsule undergoes further modification with two tridentate anionic ligands (L2) to afford a bicapped Pd3Cu6L16L22 capsule with an Edshammer polyhedral structure. By employing transition metal ions, acid, and oxidation agents, the bicapped capsule can be converted into an uncapped one. This uncapped form can then revert back to the bicapped structure on the addition of Br- ions and a base. Interestingly, introducing Ag+ ions leads to the removal of one L2 ligand from the bicapped capsule, yielding a mono-capped Pd3Cu6L16L2 structure. Furthermore, the size of the anions critically influences the precise control over the post-synthetic modifications of the capsules. It was demonstrated that these capsules selectively encapsulate tetrahedral anions, offering a novel approach for the design of intelligent molecular delivery systems.

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.

Fabrication of Self-Expanding Metal-Organic Cages Using a Ring-Openable Ligand

Metal-organic cages (MOCs), which are formed via coordination-driven assembly, are being extensively developed for various applications owing to the utility of their accessible molecular-sized cavity. While MOC structures are uniquely and precisely predetermined by the metal coordination number and ligand configuration, tailoring MOCs to further modulate the size, shape, and chemical environment of the cavities has become intensively studied for a more efficient and adaptive molecular binding. Herein, we report self-expanding MOCs that exhibit remarkable structural variations in cage size and flexibility while maintaining their topology. A cyclic ligand with an oligomeric chain tethering the two benzene rings of stilbene was designed and mixed with RhII ions to obtain the parent MOCs. These MOCs were successfully transformed into expanded MOCs via the selective cleavage of the double bond in stilbene. The expanded MOCs could effectively trap multidentate N-donor molecules in their enlarged cavity, in contrast to the original MOCs with a narrow cavity. As the direct synthesis of expanded MOCs is impractical because of the entropically disfavored structures, self-expansion using ring-openable ligands is a promising approach that allows precision engineering and the production of functional MOCs that would otherwise be inaccessible.

A dynamic covalent approach to [PtnL2n]2n+ cages

A dynamic covalent approach was exploited to generate a family of homometallic [PtnL2n]2n+ cage (predominantly [Pt2L4]4+ systems) architectures. The family of platinum(II) architectures were characterized using 1H nuclear magnetic resonance (NMR) and diffusion ordered spectroscopy (DOSY), electrospray ionization mass spectrometry (ESI-MS) and the molecular structures of two cages were determined by X-ray crystallography.

Bridging the Homogeneous and Heterogeneous Catalysis by Supramolecular Metal-Organic Cages with Varied Packing Modes

Integrating the advantages of homogeneous and heterogeneous catalysis has proved to be an optimal strategy for developing catalytic systems with high efficiency, selectivity, and recoverability. Supramolecular metal-organic cages (MOCs), assembled by the coordination of metal ions with organic linkers into discrete molecules, have performed solvent processability due to their tunable packing modes, endowing them with the potential to act as homogeneous or heterogeneous catalysts in different solvent systems. Here, the design and synthesis of a series of stable {Cu3} cluster-based tetrahedral MOCs with varied packing structures are reported. These MOCs, as homogeneous catalysts, not only show high catalytic activity and selectivity regardless of substrate size during the CO2 cycloaddition reaction, but also can be easily recovered from the reaction media through separating products and co-catalysts by one-step work-up. This is because that these MOCs have varied solubilities in different solvents due to the tunable packing of MOCs in the solid state. Moreover, the entire catalytic reaction system is very clean, and the purity of cyclic carbonates is as high as 97% without further purification. This work provides a unique strategy for developing novel supramolecular catalysts that can be used for homogeneous catalysis and recycled in a heterogeneous manner.

Heteromeric Completive Self-Sorting in Coordination Cage Systems

Heteroleptic coordination cages, nonstatistically assembled from a set of matching ligands, can be obtained by mixing individual components or via cage-to-cage transformations from homoleptic precursors. Based on the latter approach, we here describe a new level of self-sorting in coordination cage systems, namely, 'heteromeric completive self-sorting'. Here, two heteroleptic assemblies of type Pd2A2B2 and Pd2A2C2, sharing one common ligand component A but differing in the other, are shown to coexist in solution. This level of self-sorting can be reached either from a statistical mixture of assemblies based on some ligands B and C or, alternatively, following a first step of integrative self-sorting giving a distinct Pd2B2C2 intermediate. While subtle enthalpic factors dictate the outcome of the self-sorting, we found that it is controllable. From a unique set of three ligands, we demonstrate the transition from strict integrative self-sorting forming a Pd2AB2C cage to heteromeric completive self-sorting to give Pd2A2B2 and Pd2A2C2 by variation of the ligand ratio. Cage-to-cage transformations were followed by NMR and MS experiments. Single crystal X-ray structures for three new heteroleptic cages were obtained, impressively highlighting the versatility of ligand A to either form a π-stacked trans-figure-of-eight arrangement in Pd2A2B2 or occupy two cis-edges in Pd2A2C2 or only a single edge in Pd2AB2C. This study paves the way toward the control of heteroleptic cage populations in a systems chemistry context with emerging features such as chemical information processing, adaptive guest selectivity, or stimuli-responsive catalytic action.

Strain-Induced Heteromorphosis Multi-Cavity Cages: Tension-Driven Self-Expansion Strategy for Controllable Enhancement of Complexity in Supramolecular Assembly

Coordinative supramolecular cages with adjustable cavities have found extensive applications in various fields, but the cavity modification strategies for multi-functional structures are still challenging. Here, we present a tension-driven self-expansion strategy for construction of multi-cavity cages with high structural complexity. Under the regulation of strain-induced capping ligands, unprecedented heteromorphosis triple-cavity cages S2 /S4 were obtained based on a metallo-organic ligand (MOL) scaffold. The heteromorphosis cages exhibited significant higher cavity diversity than the homomorphous double-cavity cages S1 /S3 ; all of the cages were thoroughly characterized through various analytical techniques including (1D and 2D) NMR, ESI-MS, TWIM-MS, AFM, and SAXS analyses. Furthermore, the encapsulation of porphyrin in the cavities of these multi-cavity cages were investigated. This research opens up new possibilities for the architecture of heteromorphosis supramolecular cages via precisely controlled "scaffold-capping" assembly with preorganized ligands, which could have potential applications in the development of multifunctional structures with higher complexity.

Automated Structural Activity Screening of β-Diketonate Assemblies with High-Throughput Ion Mobility-Mass Spectrometry

Embracing complexity in design, metallo-supramolecular self-assembly presents an opportunity for fabricating materials of economic significance. The array of accessible supramolecules is alluring, along with favourable energy requirements. Implementation is hampered by an inability to efficiently characterise complex mixtures. The stoichiometry, size, shape, guest binding properties and reactivity of individual components and combinations thereof are inherently challenging to resolve. A large combinatorial library of four transition metals (Fe, Cu, Ni and Zn), and six β-diketonate ligands at different molar ratios and pH was robotically prepared and directly analysed over multiple timepoints with electrospray ionisation travelling wave ion mobility-mass spectrometry. The dataset was parsed for self-assembling activity without first attempting to structurally assign individual species. Self-assembling systems were readily categorised without manual data-handling, allowing efficient screening of self-assembly activity. This workflow clarifies solution phase supramolecular assembly processes without manual, bottom-up processing. The complex behaviour of the self-assembling systems was reduced to simpler qualities, which could be automatically processed.

Heterometallic cages: synthesis and applications

High symmetry metallosupramolecular architectures (MSAs) have been exploited for a range of applications including molecular recognition, catalysis and drug delivery. Recently there have been increasing efforts to enhance those applications by generating reduced symmetry MSAs. While there are several emerging methods for generating lower symmetry MSAs, this tutorial review examines the general methods used for synthesizing heterometallic MSAs with a particular focus on heterometallic cages. Additionally, the intrinsic properties of the cages and their potential emerging applications as host-guest systems and reaction catalysts are described.

Parallel Chirality Inductions in Möbius Zn(II) Hexaphyrin Transformation Networks

Networked chemical transformations are key features of biological systems, in which complex multicomponent interactions enable the emergence of sophisticated functions. Being interested in chirality induction phenomena with dynamic Möbius π-systems, we have designed a pair of Möbius [28]hexaphyrin ligands in order to investigate mixtures rather than isolated molecules. Thus, a hexaphyrin bearing a chiral amino arm was first optimized and found to bind a ZnOAc moiety, triggering an impressive quasi-quantitative chirality induction over the Möbius π-system. Second, this amino-type hexaphyrin was mixed with a second hexaphyrin bearing a chiral carboxylate arm, affording at first ill-defined coordination assemblies in the presence of zinc. In contrast, a social self-sorting behavior occurred upon the addition of two exogenous achiral effectors (AcO- and BuNH2), leading to a well-defined 1:1 mixture of two Möbius complexes featuring a sole Möbius twist configuration (parallel chirality inductions). We next successfully achieved compartmentalized switching, i.e., a single-component transformation from such a complex mixture. The BuNH2 effector was selectively protected with Boc2O, owing to a lower reactivity of the arm's NH2 function intramolecularly bound to zinc, and subsequent addition of BuNH2 restored the initial mixture, retaining parallel chirality inductions (five cycles). By changing the nature and twist configuration of only one of the two complexes, at initial state or by switching, this approach enables a "two-channel" tuning of the chiroptical properties of the ensemble. Such multiple dynamic chirality inductions, controlled by selective metal-ligand recognition and chemical reactivity, set down the basis for Möbius-type stereoselective transformation networks with new functions.

Guest-Induced Reversible Transformation between an Azulene-Based Pd2L4 Lantern-Shaped Cage and a Pd4L8 Tetrahedron

Azulene, a blue structural isomer of naphthalene, is introduced as the backbone for a new family of Pd(II)-based self-assemblies. Three organic ligands, equipped with varying donor groups, produce three [Pd2L4] cages of different cavity dimensions. Unexpectedly, the addition of organic disulfonate guests to the smallest lantern-shaped cage (featuring pyridine donors) led to a rapid and quantitative transformation to a distorted-tetrahedral [Pd4L8] species. On the contrary, [Pd2L4] cages formed from ligands with isoquinoline donors either just encapsulated the guests or showed no interaction. The tetrahedral species could be fully reverted back to its original [Pd2L4] topology by capturing the guest by another, stronger binding [Pd2L'4] coordination cage, narcissistically self-sorting from the first cage. The azulenes, serving as colored hydrocarbon backbones of minimal atom count, allow one to follow cage assembly and guest-induced transformation by the naked eye. Furthermore, we propose that their peculiar electronic structure influences the system's assembly behavior.

Controllable Topological Transformations of 818 Molecular Metalla-knots by Oxidation of Thiazole-Based Ligands

By exploiting coordination-driven self-assembly, high yields of two 818 molecular metalla-knots could be obtained using a thiazole-moiety-containing asymmetric dipyridyl ligand 2-(pyridin-4-yl)-5-(pyridin-4-ylethynyl)benzo[d]thiazole (L1 ), as confirmed using X-ray crystallographic analysis, electrospray ionization-time-of-flight/mass spectrometry (ESI-TOF/MS), and detailed liquid-state nuclear magnetic resonance (NMR) spectroscopy. To modulate the self-assembled structures, m-chloroperbenzoic acid (m-CPBA) was utilized to oxidize thiazole-based ligand L1 to N-thiazole-oxide-based ligand 2-(pyridin-4-yl)-5-(pyridin-4-ylethynyl)benzo[d]thiazole 3-oxide (L2 ), which enabled the selective construction of the corresponding tetranuclear macrocycles. Notably, two molecular metalla-knots could be topologically transformed from 818 knots to simple monocycles because the L1 alkyne bond was inert toward m-CPBA, as confirmed by liquid-state NMR spectroscopy, ESI-TOF/MS, and elemental analysis.

Rhenium-Pyrazolyl-Based Figure-Eight- and Z-Shaped Metallocycles: Self-Assembly, Solid-State Structures, Dynamic Properties in Solution, and Competitive Ligand-Induced Supramolecular Transformations into Rhenium-Pyridyl/-Benzimidazolyl/-Phosphine-Based Metallocycles/Acyclic Complexes

Rhenium(I)tricarbonyl core-based heteroleptic "figure-eight"- and Z-shaped metallocycles (1a-4a) of the general formula fac-[{(CO)3Re(μ-L)Re(CO)3}2(dppz)2] were self-assembled from Re2(CO)10, H2-L (H2-L = 5,8-dihydroxy-1,4-naphthaquinone (H2-dhnq) for 1a; 1,4-dihydroxy-9,10-anthraquinone (H2-dhaq) for 2a; 6,11-dihydroxy-5,12-naphthacenedione (H2-dhnd) for 3a; 2,2'-bisbenzimidazole (H2-bbim) for 4a), and bis(4-((pyrazolyl)methyl)phenylmethane) (dppz) via one-pot coordination-driven synthetic approach. The molecular structures of 1a and 4a were unambiguously confirmed by single-crystal X-ray diffraction (SC-XRD) methods. The metallocycles in the DMSO solution exist as an acyclic dinuclear-DMSO adduct of the general formula fac-[{(CO)3Re(μ-L)Re(CO)3}(DMSO)2] (1b, L = dhnq; 2b, L = dhaq; 3b, L = dhnd; 4b, L = bbim) and dppz, which are in dynamic equilibrium. The dynamic behavior of the rhenium-pyrazolyl bond in the solution state was effectively utilized to transform metallocycles 1a-4a into pyridyl/benzimidazolyl/phosphine donor-based heteroleptic metallocycles and acyclic dinuclear complexes (4-13). These include tetranuclear rectangles fac-[{(CO)3Re(μ-L)Re(CO)3}2(4,4'-bpy)2] (4 and 11, L = dhaq for 4 and bbim for 11), dinuclear metallocycles fac-[{(CO)3Re(μ-L)Re(CO)3}(dpbim)] (5-7 and 12; L = dhnq for 5, dhaq for 6, dhnd for 7, and bbim for 12), and dinuclear acyclic complexes fac-[{(CO)3Re(μ-L)Re(CO)3}(PTA)2] (8-10 and 13; L = dhnq for 8, dhaq for 9, dhnd for 10, and bbim for 13). These transformations were achieved through component-induced supramolecular reactions while treating with competitive ligands 4,4'-bipyridine (4,4'-bpy), bis(4-((1H-benzoimidazole-1-yl)methyl)phenyl)methane (dpbim), and 1,3,5-triaza-7-phosphaadamantane (PTA). The reaction mixture in the solution was analyzed using NMR and electrospray ionization mass spectrometry (ESI-MS) analysis. Additionally, crystal structures of 4, 6, and 13, which were obtained in the mixture of the solutions, were determined, providing unequivocal evidence for the occurrence of supramolecular transformation within the system. The results reveal that the size of the chelating ligand and the pyrazolyl donor angle of the ditopic ligand play crucial roles in determining the resulting solid-state metallacyclic architecture in these synthetic combinations. The dynamic behavior of the rhenium-pyrazolyl bond in the metallocycles can be utilized to transform into other metallocycles and acyclic complexes using suitable competing ligands via ligand-induced supramolecular transformations.

Guest Encapsulation Alters the Thermodynamic Landscape of a Coordination Host

The architecture of self-assembled host molecules can profoundly affect the properties of the encapsulated guests. For example, a rigid cage with small windows can efficiently protect its contents from the environment; in contrast, tube-shaped, flexible hosts with large openings and an easily accessible cavity are ideally suited for catalysis. Here, we report a "Janus" nature of a Pd6L4 coordination host previously reported to exist exclusively as a tube isomer (T). We show that upon encapsulating various tetrahedrally shaped guests, T can reconfigure into a cage-shaped host (C) in quantitative yield. Extracting the guest affords empty C, which is metastable and spontaneously relaxes to T, and the T⇄C interconversion can be repeated for multiple cycles. Reversible toggling between two vastly different isomers paves the way toward controlling functional properties of coordination hosts "on demand".

Anion-Regulated Hierarchical Self-Assembly and Chiral Induction of Metallo-Tetrahedra

The precise control over hierarchical self-assembly of superstructures relying on the elaboration of multiple noncovalent interactions between basic building blocks is both elusive and highly desirable. We herein report a terpyridine-based metallo-cage T with a tetrahedral motif and utilized it as an efficient building block for the controlled hierarchical self-assembly of superstructures in response to different halide ions. Initially, the hierarchical superstructure of metallo-cage T adopted a hexagonal close-packed structure. By adding Cl- /Br- or I- , drastically different hierarchical superstructures with highly-tight hexagonal packing or graphite-like packing arrangements, respectively, have been achieved. These unusual halide-ion-triggered hierarchical structural changes resulted in quite distinct intermolecular channels, which provided new insights into the mechanism of three-dimensional supramolecular aggregation and crystal growth based on macromolecular construction. In addition, the chiral induction of the metallo-cage T can be realized with the addition of chiral anions, which stereoselectively generated either PPPP- or MMMM-type enantiomers.

Characterization of an unanticipated indium-sulfur metallocycle complex

We have produced a novel indium-based metallocycle complex (In-MeSH), which we initially observed as an unanticipated side-product in metal-organic framework (MOF) syntheses. The serendipitously synthesized metallocycle forms via the acid-catalysed decomposition of dimethyl sulfoxide (DMSO) during solvothermal reactions in the presence of indium nitrate, dimethylformamide and nitric acid. A search through the Cambridge Structural Database revealed isostructural zinc, ruthenium and palladium metallocycle complexes formed by other routes. The ruthenium analogue is catalytically active and the In-MeSH structure similarly displays accessible open metal sites around the outside of the ring. Furthermore, this study also gives access to the relatively uncommon oxidation state of In(II), the targeted synthesis of which can be challenging. In(II) complexes have been reported as having potentially important applications in areas such as catalytic water splitting.

Potential of nonporous adaptive crystals for hydrocarbon separation

Hydrocarbon separation is an important process in the field of petrochemical industry, which provides a variety of raw materials for industrial production and a strong support for the development of national economy. However, traditional separation processes involve huge energy consumption. Adsorptive separation based on nonporous adaptive crystal (NAC) materials is considered as an attractive green alternative to traditional energy-intensive separation technologies due to its advantages of low energy consumption, high chemical and thermal stability, excellent selective adsorption and separation performance, and outstanding recyclability. Considering the exceptional potential of NAC materials for hydrocarbon separation, this review comprehensively summarizes recent advances in various supramolecular host-based NACs. Moreover, the current challenges and future directions are illustrated in detail. It is expected that this review will provide useful and timely references for researchers in this area. Based on a large number of state-of-the-art studies, the review will definitely advance the development of NAC materials for hydrocarbon separation and stimulate more interesting studies in related fields.

Constructing Ultrastable Metallo-Cages via In Situ Deprotonation/Oxidation of Dynamic Supramolecular Assemblies

Coordination-driven self-assembly enables the spontaneous construction of metallo-supramolecules with high precision, facilitated by dynamic and reversible metal-ligand interactions. The dynamic nature of coordination, however, results in structural lability in many metallo-supramolecular assembly systems. Consequently, it remains a formidable challenge to achieve self-assembly reversibility and structural stability simultaneously in metallo-supramolecular systems. To tackle this issue, herein, we incorporate an acid-/base-responsive tridentate ligand into multitopic building blocks to precisely construct a series of metallo-supramolecular cages through coordination-driven self-assembly. These dynamic cagelike assemblies can be transformed to their static states through mild in situ deprotonation/oxidation, leading to ultrastable skeletons that can withstand high temperatures, metal ion chelators, and strong acid/base conditions. This in situ transformation provides a reliable and powerful approach to manipulate the kinetic features and stability of metallo-supramolecules and allows for modulation of encapsulation and release behaviors of metallo-cages when utilizing nanoscale quantum dots (QDs) as guest molecules.

The sharp structural switch of covalent cages mediated by subtle variation of directing groups

It is considered a more formidable task to precisely control the self-assembled products containing purely covalent components, due to a lack of intrinsic templates such as transition metals to suppress entropy loss during self-assembly. Here, we attempt to tackle this challenge by using directing groups. That is, the self-assembly products of condensing a 1:2 mixture of a tetraformyl and a biamine can be precisely controlled by slightly changing the substituent groups in the aldehyde precursor. This is because different directing groups provide hydrogen bonds with different modes to the adjacent imine units, so that the building blocks are endowed with totally different conformations. Each conformation favors the formation of a specific product that is thus produced selectively, including chiral and achiral cages. These results of using a specific directing group to favor a target product pave the way for accomplishing atom economy in synthesizing purely covalent molecules without relying on toxic transition metal templates.

Programmed guest confinement via hierarchical cage to cage transformations

Taking inspiration from Nature, where (bio)molecular geometry variations are exploited to tune a large variety of functions, supramolecular chemistry has continuously developed novel systems in which, as a consequence of a specific stimulus, structural changes occur. Among the different architectures, supramolecular cages have been continuously investigated for their capability to act as functional hosts where guests can be released in a controlled fashion. In this paper, a novel methodology based on the use of phenanthrenequinone is applied to selectively change the binding properties of a tris(2-pyridylmethyl)amine TPMA-based cage. In particular, subcomponent substitution has been used to change structural cage features thus controlling the inclusion ratio of competing guests differing in size or chirality.