Permanently Microporous Metal–Organic Polyhedra

Perylene- and Perylene Diimide-based Framework Materials Constructed through Metal Coordination

Metal-organic frameworks (MOFs) are a class of materials composed of coordinative interactions between metal ions and organic linkers, encompassing two-dimensional (2D), and three-dimensional (3D) architectures. Metal-organic cages (MOCs), a special case of these species, are discrete molecular "capsules" with zero-dimensional (0D) structures. Over the last two decades, MOFs and MOCs composed of organic perylene (P) and perylene diimide (PDI) linkers have gained much attention due to their versatile properties, which can be further enhanced after incorporation into frameworks. This minireview highlights recent progress in the construction and application of P/PDI-based coordination framework materials. The text offers an overview of the synthesis of P/PDI organic linkers, proceeds to their integration into coordination frameworks of different dimensionalities - 2D and 3D MOFs, and 0D MOCs, and then explores potential applications. These include sensing, photocatalysis, electrochemical devices and photothermal conversion and focus on the apparent structure-property relationships. Finally, the challenges and future prospects of P/PDI-derived coordination frameworks will be addressed.

Hypercrosslinked Metal-Organic Polyhedra Electrolyte with High Transference Number and Fast Conduction of Li Ions

Solid-state electrolytes (SSEs) with high Li-ion transference numbers and fast ionic conductivity are urgently needed for technological innovations in lithium-metal batteries. To promote the dissociation of ion pairs and overcome the mechanical brittleness and interface defects caused by traditional fillers in polymeric electrolytes, we designed and fabricated a cationic hypercrosslinking metal-organic polyhedra (HCMOPs) polymer as SSE. Benefiting a three-component synergistic effect: cationic MOPs, branched polyethyleneimine macromonomer and polyelectrolyte units, the Li-HCMOP electrolyte possesses a high Li-ion conductivity, a high Li-ion transference number and a low activation energy. The LiFePO4/Li battery exhibits high capacity with superior rate performance and cycling stability. Moreover, soluble MOPs serve as high crosslinking nodes to provide excellent mechanical strength for electrolytes and good compatibility with polymers. This work highlights an effective idea of high-performance MOP-based solid-state electrolytes applied in LMBs.

Packing Engineering of Zirconium Metal-Organic Cages in Mixed Matrix Membranes for CO2/CH4 Separation

Metal-organic cages (MOCs) have been considered as emerging zero-dimensional (0D) porous fillers to generate molecularly homogeneous MOC-based membrane materials. However, the discontinuous pore connectivity and low filler concentrations limit the improvement of membrane separation performance. Herein, we propose the dimension augmentation of MOCs in membranes using three-dimensional (3D) supramolecular MOC networks as filler materials in mixed matrix membranes (MMMs). We further explore the packing engineering of MOC networks to produce distinct polymorphs (α and β phases) for tailoring membrane performance. Synchrotron X-ray absorption and positron annihilation lifetime spectroscopy were employed to differentiate distinct MOC polymorphous networks within membranes. Gas permeation tests revealed that the corresponding MMMs showed superior CO2/CH4 separation performance, exceeding the Robeson upper bound. Our proposed approach is expected to enrich the repertoire of reticular chemistry pertaining to molecular-based networks.

Post-synthetic modification of amine-functionalized permanently porous coordination cages

This manuscript explores the post-synthetic modification (PSM) of amine-functionalized porous coordination cages, specifically focusing on the formation of imine bonds through reactions with aldehydes. Targeting various cage topologies, including zirconium-, magnesium-, and molybdenum-based structures, we demonstrate the tunability of cage solubility and porosity through selective functionalization where the proximity of amine groups on the parent cage impacts the extent of modification. The work highlights the reversible nature of imine formation, offering potential applications in solubility switching and mixed-metal solid synthesis.

Tunable synthesis of heteroleptic zirconium-based porous coordination cages

Zirconium-based porous coordination cages have been widely studied and have shown to be potentially useful for many applications as a result of their tunability and stability, likely as a result of their status as a molecular equivalent to the small 8 Å tetrahedral pores of UiO-66 (Zr6(μ3-O)4(μ2-OH)4(C8O4H4)6). Functional groups attached to these molecular materials endow them with a range of tunable properties. While so-called multivariate MOFs containing multiple types of functional groups on different bridging ligands within a structure are common, incorporating multiple functional moieties in permanently microporous molecular materials has proved challenging. By applying a mixed-ligand, or heteroleptic, synthesis strategy to cage formation, we have designed a straight-forward, one-pot synthesis of 10 Å zirconium-based molecular cages in a basket-shaped, or Zr12L6, geometry containing 3 : 3 ratios of combinations of two types of functional moieties from 11 different ligand options. Additionally, using more sterically hindered ligands, such as 5-benzyloxybenzene dicarboxylate, we show that ligand size governs the resulting cage geometry. This method allows for multiple functional groups to be incorporated in molecular cages and the ratio of moieties incorporated can be easily controlled. With this strategy in hand, we show that ligands for which zirconium cage syntheses have been elusive, such as 2,5-dihydroxybenzene dicarboxylate, have now been successfully incorporated into porous structures.

A Combined Experimental and Computational Exploration of Heteroleptic cis-Pd2L2L'2 Coordination Cages through Geometric Complementarity

Heteroleptic (mixed-ligand) coordination cages are of interest as host systems with more structurally and functionally complex cavities than homoleptic architectures. The design of heteroleptic cages, however, is far from trivial. In this work, we experimentally probed the self-assembly of Pd(II) ions with binary ligand combinations in a combinatorial fashion to search for new cis-Pd2L2L'2 heteroleptic cages. A hierarchy of computational analyses was then applied to these systems with the aim of elucidating key factors for rationalising self-assembly outcomes. Simple and inexpensive geometric analyses were shown to be effective in identifying complementary ligand pairs. Preliminary results demonstrated the viability of relatively rapid semi-empirical calculations for predicting the topology of thermodynamically favoured assemblies with rigid ligands, whilst more flexible systems proved challenging. Stemming from this, key challenges were identified for future work developing effective computational forecasting tools for self-assembled metallo-supramolecular systems.

From Elementary to Advanced Design of Functional Metal-Organic Frameworks: A User Guide to Deciphering the Reticular Chemistry Toolbox

Here, the fundamental requirements are described for understanding and using topology tools in the design of porous materials, emphasizing the relationships between nets, metal-organic framework (MOF) structures, nodes, and building blocks. Common design approaches are discussed, highlighting prerequisites for the rational design of MOFs, such as those with simple pcu topology through the molecular building block approach, or axial-to-axial pillaring. The importance of highly connected nets and building units is emphasized for achieving structural predictability. The geometrical requirements are detailed for designing highly connected MOFs using more elaborate strategies: MOFs with rht topology through the supermolecular building block approach, tbo topology through the supermolecular building layer approach, and sph topology through a merged net approach The potential for innovation through deviations from default nets, such as introducing a geometry mismatch is addressed, which can lead to novel materials with unique zeolitic structures. Examples include MOFs with sodalite (sod) topology, developed through cantellation or mixed-ligand approaches inspired by ancestral architectural methods, utilizing centring structure-directing agents. Key insights for researchers are provided to facilitate the application and expansion of design strategies to new chemical systems. The only limit is imagination, along with some chemical, physical, and thermodynamical principles, of course.

Intricate Low-Symmetry Ag64 Capsules Formed by Anion-Templated Self-Assembly of the Stereoisomers of an Unsymmetric Ligand

Metal-organic cages and capsules exhibit space-specific functions based on their discrete hollow structures. To acquire enzyme-like asymmetric or intricate structures, they have been modified by desymmetrization with two or more different ligands. There is a need to establish new strategies that can desymmetrize structures in a simple way using only one type of ligand, which is different from the mixed-ligand approach. In this study, a strategy was developed to form interconvertible stereoisomers using the unsymmetric macrocyclic ligand benzimidazole[3]arene. Single-crystal X-ray diffraction analysis revealed that the isomers assembled with silver tetrafluoroborate afforded a conformationally heteroleptic Ag6L4 capsule with an intricate structure. The six Ag ions in the capsule were desymmetrized, resulting in significantly different coordination geometries. Remarkably, the capsule encapsulates a single tetrafluoroborate anion via multipoint C-H···F-B hydrogen bonds in both the solid and solution states, suggesting that anions of appropriate size and shape can act as a template for the capsule formation. These results demonstrate that the use of isomerizable and unsymmetric ligands is the effectiveness of constructing highly dissymmetric supramolecular structures from a single ligand.

Vacancy Effect on the Luminescent and Water Responsive Properties of Vacancy-Ordered Double Perovskite Derivatives

Vacancy-ordered perovskites and derivatives represent an important subclass of hybrid metal halides with promise in applications including light emitting devices and photovoltaics. Understanding the vacancy-property relationship is crucial for designing related task-specific materials, yet research in this field remains sporadic. For the first time, we use the Connolly surface to quantitatively calculate the volume of vacancy (V□, □=vacancy) in vacancy-ordered double perovskite derivatives (VDPDs). A relationship between void fraction and the structure, photoluminescent properties and humidity stability was established based on zero-dimensional (0-D) [N(alkyl)4]2Sb□Cl5□'-type VDPDs. Compared with the more commonly studied A2M(IV)X6□-type double perovskite (A=cation, M=metal ion, X=halide), [N(alkyl)4]2Sb□Cl5□' features double vacancy sites. Our results demonstrate an inverse relationship between the photoluminescent quantum yield and V□ in 0-D VDPDs. Additionally, structural transformation from A2SbCl5 to A3Sb2Cl9 was first reported, during which the novel 'gate-opening' gas adsorption phenomenon was observed in VDPDs for the first time, as evidenced by 'S'-shaped sorption isotherms for water vapor, indicating a cation-controlled water-vapor response behavior. A mixed-cation strategy was developed to modulate the humidity stability of VDPDs. Characterized by controllable water-responsive behavior and unique 'on-off-on' luminescent switching, A2M(III)□X5□'-type materials show great promise for multi-level information anti-counterfeiting applications.

Selective Gas Adsorption in Permanently Microporous Coordination Cages with Exposed Metal Sites

Porous coordination cages (PCCs), molecular analogs of metal-organic frameworks, offer modular platforms for studying the adsorption properties of small molecules, with coordinatively unsaturated metal centers playing a pivotal role in tuning these behaviors. In this work, we present the synthesis, activation, and detailed gas adsorption studies of second-row transition metal-based M24L24 cuboctahedral cages, specifically Mo24(bdc)24, Rh24(bdc)24, and [Ru24(bdc)24]Cl12. These materials represent rare examples of Mo-, Rh-, and Ru-based hybrid porous solids. The synthesis and activation of these cages were optimized to maximize porosity, yielding BET surface areas of up to 832 m2/g. Gas adsorption studies with CO2 and CO reveal distinctive uptake behaviors linked to the metal cations, with Mo24(bdc)24 demonstrating the highest gravimetric CO2 uptake (2.12 mmol/g at 298 K) and [Ru24(bdc)24]Cl12 exhibiting the strongest CO binding (-75 kJ/mol). Additionally, we explore the selective adsorption of unsaturated hydrocarbons, such as ethylene and propylene, revealing strong binding interactions at low pressures as a result of strong metal-hydrocarbon interactions based on pi-backbonding interactions.

Solvatomorphic diversity dictates the stability and solubility of metal-organic polyhedra

The reaction between molybdenum(ii) acetate and 5-aminoisophthalic acid (H2Iso-NH2) afforded [Mo12O12(μ2-O)12(Iso-NH2)12]12-, a novel molybdenum(v) metal-organic polyhedron (MOP) with a triangular antiprismatic shape stabilized by intramolecular N-H⋯O hydrogen bonds. The synthesis conditions, particularly the choice of solvent and reaction time, led to the precipitation of the Mo(v)-MOP in five distinct crystalline forms. These forms vary in their packing arrangements, co-crystallized solvent molecules, and counter-cations, with three phases containing dimethylammonium (dma+) and the other two containing diethylammonium (dea+). Each solvatomorph exhibits unique physical properties, including differences in porosity, and stability. These properties were discerned through empirical observations and supported by density functional theory calculations. Remarkably, the solubility of these MOP solvatomorphs in water was determined for the first time, with values of 4.30(2) g L-1 for a (dma)12[Mo(v)-MOP] phase, and 10.25(7) g L-1 and 14.41(10) g L-1 for two (dea)12[Mo(v)-MOP] phases. Additionally, aqueous solutions of the Mo(v)-MOP were found to conduct electricity as weak electrolytes, showcasing their potential for applications in fields requiring partially ionized species.

Face-controlled chirality induction in octahedral thiacalixarene-based porous coordination cages

Nanosized chiral octahedral M32 coordination cages were prepared via self-assembly of sulfonylcalix[4]arene tetranuclear M(II) clusters (M = Co or Ni) with enantiomerically enriched linkers based on tris(dipyrrinato)cobalt(III) complexes, appended with peripheral carboxylic groups. Two pairs of enantiomers of cages were obtained and unambiguously characterized from a structural point of view, using single crystal X-ray diffraction. Chiral-HPLC was used to evidence the enantiomers. In the solid state, the compounds present intrinsic and extrinsic porosity: the intrinsic porosity is linked with the size of the cages, which present an inner diameter of ca. 19 Å. The obtained solid-state supramolecular architectures demonstrated good performances as adsorbents for water and 2-butanol guest molecules.

Nitrogen-Rich Conjugated Macrocycles: Synthesis, Conductivity, and Application in Electrochemical CO2 Capture

Here we report a series of nitrogen-rich conjugated macrocycles that mimic the structure and function of semiconducting 2D metal-organic and covalent organic frameworks while providing greater solution processability and surface tunability. Using a new tetraaminotriphenylene building block that is compatible with both coordination chemistry and dynamic covalent chemistry reactions, we have synthesized two distinct macrocyclic cores containing Ni-N and phenazine-based linkages, respectively. The fully conjugated macrocycle cores support strong interlayer stacking and accessible nanochannels. For the metal-organic macrocycles, good out-of-plane charge transport is preserved, with pressed pellet conductivities of 10-3 S/cm for the nickel variants. Finally, using electrochemically mediated CO2 capture as an example, we illustrate how colloidal phenazine-based organic macrocycles improve electrical contact and active site electrochemical accessibility relative to bulk covalent organic framework powders. Together, these results highlight how simple macrocycles can enable new synthetic directions as well as new applications by combining the properties of crystalline porous frameworks, the processability of nanomaterials, and the precision of molecular synthesis.

Molecular-Squeeze Triggers Guest Desorption from Sponge-Like Macrocycle Crystals

Desorption in conventional porous sorbents often employ external forces including inert gas blowing, heating, vacuum treatment to trigger guest release. We here report an unprecedented molecular-squeeze triggered guest release behavior from sponge-like macrocycle crystals. The crystals function as typical sponge to include guest molecules within their microscopic voids that are adaptively formed, thus acting as adsorbents for toluene/pyridine separations. Intriguingly, vaporized ethyl acetate (EA) molecules trigger the guest release from the crystals without entering the pores or voids of the crystals to replace the guests. Instead, they work as external forces applied directly onto the crystals themselves, ''squeezing" the materials to close the voids through supramolecular interactions between EA and macrocycles on the crystal surface and release the guest molecules. Various experimental techniques as well as molecular dynamics simulations reveal the mechanism of the molecular-squeeze induced guest release procedure. The EA-regenerated crystals can be recycled multiple times without the loss of separation performance. Compared with conventional guest release procedure, this method is manipulated in a mild condition, showing the potential in saving cost and energy.

Assembling a new generation of radiopharmaceuticals with supramolecular theranostics

Supramolecular chemistry has been used to tackle some of the major challenges in modern science, including cancer therapy and diagnosis. Supramolecular platforms provide synthetic flexibility, rapid generation through self-assembly, facile labelling, unique topologies, tunable reversibility of the enabling noncovalent interactions, and opportunities for host-guest chemistry and mechanical bonding. In this Review, we summarize recent advances in the design and radiopharmaceutical application of discrete self-assembled coordination complexes and mechanically interlocked molecules - namely, metallacages and rotaxanes, respectively - as well as in situ-forming supramolecular aggregates, specifically pinpointing their potential as next-generation radiotheranostic agents. The outlook of such supramolecular constructs for potential applications in the clinic is discussed.

Interplay of Stereochemistry and Charge Governs Guest Binding in Flexible ZnII4L4 Cages

Here, we report the synthesis of a family of chiral ZnII4L4 tetrahedral cages by subcomponent self-assembly. These cages contain a flexible trialdehyde subcomponent that allows them to adopt stereochemically distinct configurations. The incorporation of enantiopure 1-phenylethylamine produced Δ4 and Λ4 enantiopure cages, in contrast to the racemates that resulted from the incorporation of achiral 4-methoxyaniline. The stereochemistry of these ZnII4L4 tetrahedra was characterized by X-ray crystallography and chiroptical spectroscopy. Upon binding the enantiopure natural product podocarpic acid, the ZnII stereocenters of the enantiopure Δ4-ZnII4L4 cage retained their Δ handedness. In contrast, the metal stereocenters of the enantiomeric Λ4-ZnII4L4 cage underwent inversion to a Δ configuration upon encapsulation of the same guest. Insights gained about the stereochemical communication between host and guest enabled the design of a process for acid/base-responsive guest uptake and release, which could be followed by chiroptical spectroscopy.

Counterions Determine if Metal-Organic Cages Convert SO2 to Sulfate or Reversibly Adsorb It

The continuous emission of harmful gases into the atmosphere damages the environment, air quality, and public health worldwide. To mitigate their impact, materials that capture and chemically inactivate gases are required; however, integrating and precisely controlling both abilities within a single material remains challenging. Herein, we demonstrate for the first time that switching between SO2-physisorption and chemisorption is possible for porous materials by using different counterions, as illustrated with a series of Pd6L8 Metal-Organic Cages (MOCs). Pd-MOCs bearing BF4 -, PF6 -, or SO4 2- expressed reversible adsorption (up to 3.6 mmol g-1), cyclability, and SO2/CO2 selectivity. NO3 - promoted conversion of SO2 to sulfate, as corroborated with M6L8 cages built on Co(II), Cu(II), and Zn(II) ions. Noteworthy, the nitrate derivative of Pd6L8 captures 6.0 mmol g-1 of SO2, cleanly transforms it to SO4 2- within its cavity in 94 % yield at room temperature, it is quantitatively regenerated, and tolerates humid SO2; such qualities are unprecedented for SO2 adsorbents. The deliberate use of counterions for modulating adsorption could be applied to charged MOFs, COFs, or POCs, potentially leading to the development of new reactivity or catalysis pathways for advanced applications against contaminant gases.

Nano-Springe Enriched Hierarchical Porous MOP/COF Hybrid Aerogel: Efficient Recovery of Gold from Electronic Waste

Extraction of gold from secondary resources such as electronic waste (e-waste) has become crucial in recent times to compensate for the gradual scarcity of the noble metal in natural mines. However, designing and synthesizing a suitable material for highly efficient gold recovery is still a great challenge. Herein, we have strategically designed rapid fabrication of an ionic crystalline hybrid aerogel by covalent threading of an amino-functionalized metal-organic polyhedra with an imine-linked chemically stable covalent organic framework at ambient condition. The hierarchically porous ultra-light aerogel featuring imine-rich backbone, high surface area, and cationic sites have shown fast removal, high uptake capacity (2349 mg/g), and excellent selectivity towards gold sequestration. Besides, the aerogel can extract ultra-trace gold-ions from different terrestrial water bodies, aiming towards safe drinking water. This study demonstrates the great potential of the composite materials based on a novel approach to designing a hybrid porous material for efficient gold recovery from complex water matrices.

Topological control in paddlewheel metal-organic cages via ligand length variation

Varying the length of phenanthrene-derived ligands switches the selective assembly of MIInLn metal-organic cages (MOCs, n = 6 or 8) between tetrahedral, square, or triangular architectures. The limit of this approach is explored for both Cu2 and Rh2 paddlewheel MOCs, and supported by solution, solid-state and computational analysis.

UoC-10: Exploring the Packings of Chiral Copper(II) Paddle-Wheel Based Metal-Organic Cages (MOCs)

The fluorination of the central ring of 1,3,5-benzene-tris-(meta-benzoate) (referred to as BTMB) leads to a twisted tritopic linker which reacts with copper(II) ions to assemble into octahedral (pseudospherical) metal-organic cages (MOCs) with paddle-wheel units at their vertices. In this work, the different sphere packings of these MOCs are explored in detail together with their material properties, which closely resemble those of copper-based metal-organic frameworks (MOFs). Theoretical investigations of the linkers are carried out to analyze the energetic barrier imposed by the fluorine substituents to form the observed atropisomers.

Synthesis of highly soluble zirconium organic cages by iodine substitution toward a CO2/N2 separation membrane

Metal organic cages (MOCs) show promise as fillers in mixed-matrix membranes (MMMs) for gas separation; highly soluble MOCs are desirable for fabrication of high-compatibility membranes. Herein, we report an iodine substitution strategy to substantially increase the MOC solubility. The synthesized MOC of ZrT-NH2-I possesses over 10-fold higher solubility than the parent ZrT-NH2 in organic solvents whilst retaining the original molecular structure and permanent porosity. Such enhanced solubility allows for the effective integration of ZrT-NH2-I with an amidoxime polymer of intrinsic microporosity (PIM-PAO), resulting in a compatible MMM with a uniform distribution of MOC. The ZrT-NH2-I@PIM-PAO MMM demonstrates a CO2 permeability of 1377 barrer and a CO2/N2 gas selectivity of 45 which is 45 times that of the membrane made from ZrT-NH2. The permeability-selectivity performance not only surpasses the 2008 upper bound, but also exceeds those of currently available MMMs.

Installation of Copper(I) and Silver(I) Sites into TREN-Based Porous Organic Cages via Postsynthetic Metalation

Porous organic cages (POCs) and metal-organic polyhedra (MOPs) function as zero-dimensional porous materials, able to mimic many functions of insoluble framework materials while offering processability advantages. A popular approach to access tailored metal-based motifs in extended network materials is postsynthetic metalation, which allows metal installation to be decoupled from framework assembly. Surprisingly, this approach has only sparingly been reported for molecular porous materials. In this report, we demonstrate postsynthetic metalation of tetrahedral [4 + 4] POCs assembled from tris(2-aminoethyl)amine (TREN) and 1,3,5-tris(4-formylphenyl)benzene. The trigonally symmetric TREN motif is a common chelator in coordination chemistry and, in the POCs explored herein, readily binds copper(I) and silver(I) to form cationic cages bearing discrete mononuclear coordination fragments. Metalation retains cage porosity, allowing us to compare the sorption properties of the parent organic and metalated cages. Interestingly, introduction of copper(I) facilitates activated oxygen chemisorption, demonstrating how targeted metalation can be exploited to tune the sorption characteristics of porous molecular materials.

Emergent Research Trends on the Structural Relaxation Dynamics of Molecular Clusters: From Structure-Property Relationship to New Function Prediction

ConspectusMolecular clusters (MCs) are monodispersed, precisely defined ensembles of atom collections featured with shape-persistent architectures that can deliver certain functions independently. Their molecular compositions and surface functionalities can be tailored feasibly in a predefined manner, and they can be applied as basic structural units to be engineered into materials with desirable hierarchical structures and enriched functions. The chemical systems also offer great opportunities for the design and fabrication of soft structural materials without the chain topologies of polymers. The bulks of MC assemblies demonstrate viscoelasticity that is used to be considered as the unique feature of polymers, while the MC systems are distinct from polymers since their elasticities are resilient even at temperatures 100 K above their glass transition temperatures. The understanding of their anomalous viscoelasticity and the extended studies of general structure-property relationships are desired for the development of new chemical systems for emergent functions and the possibilities to resolve the intrinsic trade-offs of traditional materials.Meanwhile, general macroscopic functions or properties of materials are related to the transportation of mass, momentum, and/or energy, and they are basically realized or directed by the motions of structural units at different length scales. Structural relaxation dynamics research is critical in quantifying motions ranging from fast bond deformation, bond break/formation, and diffusion of ions and particles to the cooperative motions of structure units. Due to the advancement of measurement technology for relaxation dynamics (e.g., quasi-elastic scattering and broadband dielectric spectroscopy), the structural relaxation dynamics of MC materials have been probed for the first time, and their multiple relaxation modes across several temporal scales were systematically studied to bridge the correlation between molecular structures and macroscopic functions. The fingerprint information from dynamics studies, e.g., the temperature dependence of relaxation time and certain property, e.g., ion conductivity, was proposed to quantify the structure-property relationship, and the microscopic mechanism on the mechanical properties, ion conduction, and gas absorption and separation of MC materials can be fully understood.In this Account, to elucidate the uniqueness of MC materials, especially in comparison with polymers, four topics are mainly summarized: structural features, relaxation dynamics characterization techniques, relaxation dynamics characteristics, and quantified understanding of the structure-property relationship. The capability for new function prediction from relaxation dynamics studies is also introduced, and the typical example in impact resistant materials is provided. The Account aims to prove the significance of relaxation dynamics characterization for material innovation, while it also confirms the potential of MCs for functional material fabrications.

Enhancing Performances of Enzyme/Metal-Organic Polyhedra Composites by Mixed-Protein Co-Immobilization

Protein immobilization using water-soluble ionic metal-organic polyhedra (MOPs) acting as porous spacers has recently been demonstrated as a potent strategy for the preparation of biocatalysts. In this article, we describe a mixed-protein approach to achieve biocomposites with adjustable enzyme contents and excellent immobilization efficiencies, in a systematic and well-controlled manner. Self-assembly of either cationic or anionic MOPs with bovine serum albumin or egg white lysozyme combined with enzymes (alkaline phosphatase, laccase or cytochrome c) led to solid-state catalysts with a high retention of enzyme activity. Furthermore, for all these systems, the dilution of enzymes within the solid-state composite led to noticeably improved catalytic performances, with both higher specific activity and affinity for substrate.

A nanotrap infused ultrathin hybrid composite material for rapid and highly selective entrapment of 99TcO4. Chem Sci 2024:d4sc04010d. [PMID: 39430929 PMCID: PMC11485004 DOI: 10.1039/d4sc04010d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

99Tc is one of the potentially toxic radioactive substances owing to its long half-life and a high degree of environmental mobility. Hence, the sequestration of 99Tc from radioactive waste has become enormously important and a contemporary research priority. However, selective extraction of this species in its stable oxoanionic form (99TcO4 -) is very challenging on account of bottlenecks such as low charge density, less hydrophilic nature, etc. Herein, an ultrathin hybrid composite material has been strategically designed and fabricated by covalent anchoring of a chemically stable amino functionalized nanosized cationic metal-organic polyhedron with a positively charged robust ionic covalent organic framework. The resulting thin-layer-based hybrid composite presented multiple exfoliated exposed interactive sites, including a Zr(iv)-secondary building unit, amine and triaminoguanidine functional groups, which can selectively interact with TcO4 - oxoanions through a synergistic combination of electrostatic, H-bonding and various other supramolecular interactions. Thus synthesized function-tailored composite, by virtue of its multiple unique characteristics, manifested an ultrafast and very selective, high distribution coefficient (∼106 mL g-1), as well as recyclable entrapment of TcO4 - oxoanions from the complex mixture of superfluous (∼5000-fold) other interfering anions in both high and ultra-trace concentrations along with simulated nuclear waste and from different water systems. Dynamic flow-through experiments were conducted with the membrane of the hybrid material in simulated wastewater, which reduced the concentration of ReO4 - (surrogate of radioactive TcO4 -) to below the WHO permissible level with rapid sequestration kinetics and excellent selectivity over excessive competing anions.

Synthesis of Metal-Organic Cages via Orthogonal Bond Cleavage in 3D Metal-Organic Frameworks

Herein we address the question of whether a supramolecular finite metal-organic structure such as a cage or metal-organic polyhedron (MOP) can be synthesized via controlled cleavage of a three-dimensional (3D) metal-organic structure. To demonstrate this, we report the synthesis of a Cu(II)-based cuboctahedral MOP through orthogonal olefinic bond cleavage of the cavities of a 3D, Cu(II)-based, metal-organic framework (MOF). Additionally, we demonstrate that controlling the ozonolysis conditions used for the cleavage enables Clip-off Chemistry synthesis of two cuboctahedral MOPs that differ by their external functionalization: one in which all 24 external groups represent a mixture of aldehydes, carboxylic acids, acetals and esters, and one in which all are aldehydes.

Supramolecular Complexation Reinforced Polymer Frustrated Packing: Controllable Dual Porosity for Improved Permselectivity of Coordination Nanocage Mixed Matrix Membranes

The developments of mixed matrix membranes (MMMs) are severely hindered by the complex inter-phase interaction and the resulting poor utilization of inorganics' microporosity. Herein, a dual porosity framework is constructed in MMMs to enhance the accessibility of inorganics' microporosity to external gas molecules for the effective application of microporosity for gas separation. Nanocomposite organogels are first prepared from the supramolecular complexation of rigid polymers and 2 nm microporous coordination nanocages (CNCs). The network structures can be maintained with microporous features after solvent removal originated from the rigid nature of polymers, and the strong coordination and hydrogen bond between the two components. Moreover, the strong supramolecular attraction reinforces the frustrated packing of the rigid polymers on CNC surface, leading to polymer networks' extrinsic pores and the interconnection of CNCs' micro-cavities for the fast gas transportation. The gas permeabilities of the MMMs are 869 times for H2 and 1099 times for CO2 higher than those of pure polymers. The open metal sites from nanocage also contribute to the enhanced gas selectivity and the overall performance surpasses 2008 H2/CO2 Robeson upper bound. The supramolecular complexation reinforced packing frustration strategy offers a simple and practical solution to achieve improved gas permselectivity in MMMs.

Recent Advances in Carborane-Based Crystalline Porous Materials

The field of carborane research has witnessed continuous development, leading to the construction and development of a diverse range of crystalline porous materials for various applications. Moreover, innovative synthetic approaches are expanding in this field. Since the first report of carborane-based crystalline porous materials (CCPMs) in 2007, the synthesis of carborane ligands, particularly through innovative methods, has consistently posed a significant challenge in discovering new structures of CCPMs. This paper provides a comprehensive summary of recent advances in various synthetic approaches for CCPMs, along with their applications in different domains. The primary challenges and future opportunities are expected to stimulate further multidisciplinary development in the field of CCPMs.

Copper Atom Pairs Stabilize *OCCO Dipole Toward Highly Selective CO2 Electroreduction to C2H4

Deeply electrolytic reduction of carbon dioxide (CO2) to high-value ethylene (C2H4) is very attractive. However, the sluggish kinetics of C-C coupling seriously results in the low selectivity of CO2 electroreduction to C2H4. Herein, we report a copper-based polyhedron (Cu2) that features uniformly distributed and atomically precise bi-Cu units, which can stabilize *OCCO dipole to facilitate the C-C coupling for high selective C2H4 production. The C2H4 faradaic efficiency (FE) reaches 51 % with a current density of 469.4 mA cm-2, much superior to the Cu single site catalyst (Cu SAC) (~0 %). Moreover, the Cu2 catalyst has a higher turnover frequency (TOF, ~520 h-1) compared to Cu nanoparticles (~9.42 h-1) and Cu SAC (~0.87 h-1). In situ characterizations and theoretical calculations revealed that the unique Cu2 structural configuration could optimize the dipole moments and stabilize the *OCCO adsorbate to promote the generation of C2H4.

Supramolecular Assembly Frameworks (SAFs): Shaping the Future of Functional Materials

Supramolecular assembly frameworks (SAFs) represent a new category of porous materials, utilizing non-covalent interactions, setting them apart from metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). This category includes but is not restricted to hydrogen-bonded organic frameworks and supramolecular organic frameworks. SAFs stand out for their outstanding porosity, crystallinity, and stability, alongside unique dissolution-recrystallization dynamics that enable significant structural and functional modifications. Crucially, their non-covalent assembly strategies allow for a balanced manipulation of porosity, symmetry, crystallinity, and dimensions, facilitating the creation of advanced crystalline porous materials unattainable through conventional covalent or coordination bond synthesis. Despite their considerable promise in overcoming several limitations inherent to MOFs and COFs, particularly in terms of solution-processability, SAFs have received relatively little attention in recent literature. This Minireview aims to shed light on standout SAFs, exploring their design principles, synthesis strategies, and characterization methods. It emphasizes their distinctive features and the broad spectrum of potential applications across various domains, aiming to catalyze further development and practical application within the scientific community.

Room-Temperature Synthesis of Covalently Bridged MOP@TpPa-CH3 Composite Photocatalysts for Artificial Photosynthesis

The conversion of CO2 into useful chemicals via photocatalysts is a promising strategy for resolving the environmental problems caused by the addition of CO2. Herein, a series of composite photocatalysts MOP@TpPa-CH3 based on MOP-NH2 and TpPa-CH3 through covalent bridging have been prepared via a facile room-temperature evaporation method and employed for photocatalytic CO2 reduction. The photocatalytic performances of MOP@TpPa-CH3 are greater than those of TpPa-CH3 and MOP-NH2, where the CO generation rate of MOP@TpPa-CH3 under 10% CO2 still reaches 119.25 μmol g-1 h-1, which is 2.18 times higher than that under pure CO2 (54.74 μmol g-1 h-1). To investigate the structural factors affecting the photocatalytic activity, MOP@TBPa-CH3 without C═O groups is synthesized, and the photoreduction performance is also evaluated. The controlling experimental results demonstrate that the excellent photoreduction CO2 performance of MOP@TpPa-CH3 in a 10% CO2 atmosphere is due to the presence of C═O groups in TpPa-CH3. This work offers a new design and construction strategy for novel MOP@COF composites.

Proton-Induced Reversible Spin-State Switching in Octanuclear FeIII Spin-Crossover Metal-Organic Cages

Responsive spin-crossover (SCO) metal-organic cages (MOCs) are emerging dynamic platforms with potential for advanced applications in magnetic sensing and molecular switching. Among these, FeIII-based MOCs are particularly noteworthy for their air stability, yet they remain largely unexplored. Herein, we report the synthesis of two novel FeIII MOCs using a bis-bidentate ligand approach, which exhibit SCO activity above room temperature. These represent the first SCO-active FeIII cages and feature an atypical {FeN6}-type coordination sphere, uncommon for FeIII SCO compounds. Our study reveals that these MOCs are sensitive to acid/base variations, enabling reversible magnetic switching in solution. The presence of multiple active proton sites within these SCO-MOCs facilitates multisite, multilevel proton-induced spin-state modulation. This behavior is observed at room temperature through 1H NMR spectroscopy, capturing the subtle proton-induced spin-state transitions triggered by pH changes. Further insights from extended X-ray absorption fine structure (EXAFS) and theoretical analyses indicate that these magnetic alterations primarily result from the protonation and deprotonation processes at the NH active sites on the ligands. These processes induce changes in the secondary coordination sphere, thereby modulating the magnetic properties of the cages. The capability of these FeIII MOCs to integrate magnetic responses with environmental stimuli underscores their potential as finely tunable magnetic sensors and highlights their versatility as molecular switches. This work paves the way for the development of SCO-active materials with tailored properties for applications in sensing and molecular switching.

Enantiopure trigonal bipyramidal coordination cages templated by in situ self-organized D2h-symmetric anions

The control of a molecule's geometry, chirality, and physical properties has long been a challenging pursuit. Our study introduces a dependable method for assembling D3-symmetric trigonal bipyramidal coordination cages. Specifically, D2h-symmetric anions, like oxalate and chloranilic anions, self-organize around a metal ion to form chiral-at-metal anionic complexes, which template the formation of D3-symmetric trigonal bipyramidal coordination cages. The chirality of the trigonal bipyramid is determined by the point chirality of chiral amines used in forming the ligands. Additionally, these cages exhibit chiral selectivity for the included chiral-at-metal anionic template. Our method is broadly applicable to various ligand systems, enabling the construction of larger cages when larger D2h-symmetric anions, like chloranilic anions, are employed. Furthermore, we successfully produce enantiopure trigonal bipyramidal cages with anthracene-containing backbones using this approach, which would be otherwise infeasible. These cages exhibit circularly polarized luminescence, which is modulable through the reversible photo-oxygenation of the anthracenes.

Solvent-free mechanochemistry for the preparation of mixed-ligand cuboctahedral porous coordination cages

This study investigates post-synthetic ligand exchange in a series of copper(II) and chromium(II) cuboctahedral cages of the formula M24(R-bdc)24 through solvent-free mechanochemistry for the preparation of mixed-ligand cages. While solvent-based ligand exchange does not proceed when the cages are insoluble or when they are dissolved in non-coordinating solvents, solvent-free mechanochemistry can be used to prepare a number of mixed-ligand cages featuring a variety of functional groups regardless of cage solubility. We further extend this strategy to intercage ligand exchange reactions where the solid-state reaction of cages proceeds in just ten minutes while corresponding solvent-based reactions require more than one week of reaction time. The results highlight mechanochemically-facilitated ligand exchange as an exceptionally facile and efficient method for the production of mixed-ligand cuboctahedral cages.

Designing External Pores of Aluminum Oxo Polyhedrons for Efficient Iodine Capture

Although metal-organic polyhedra (MOPs) expansion has been studied to date, it is still a rare occurrence for their porous intermolecular assembly for iodine capture. The major limitation is the lack of programmable and controllable methods for effectively constructing and utilizing the exterior cavities. Herein, the goal of programmable porous intermolecular assembly is realized in the first family of aluminum oxo polyhedrons (AlOPs) using ligands with directional H-bonding donor/acceptor pairs and auxiliary alcohols as structural regulation sites. The approach has the advantage of avoiding the use of expensive edge-directed ditopic and face-directed tritopic ligands in the general synthesis strategy of MOPs. Combining theoretical calculations and experiments, the intrinsic relationship is revealed between alcohol ligands and the growth mechanism of AlOPs. The maximum I2 uptake based on the mass gain during sorption corresponds to 2.35 g g-1, representing the highest reported I2 sorption by an MOP. In addition, it can be easily regenerated and maintained the iodine sorption capacity, revealing its further potential application. This method of constructing stable and programmable porous materials will provide a new way to solve problems such as radionuclide capture.

Self-Assembly of Chiral Porous Metal-Organic Polyhedra from Trianglsalen Macrocycles

Metal-organic polyhedra (MOPs) can exhibit tunable porosity and functionality, suggesting potential for applications such as molecular separations. MOPs are typically constructed by the bottom-up multicomponent self-assembly of organic ligands and metal ions, and the final functionality can be hard to program. Here, we used trianglsalen macrocycles as preorganized building blocks to assemble octahedral-shaped MOPs. The resultant MOPs inherit most of the preorganized properties of the macrocyclic ligands, including their well-defined cavities and chirality. As a result, the porosity in the MOPs could be tuned by modifying the structure of the macrocycle building blocks. Using this strategy, we could systematically enlarge the size of the MOPs from 26.3 to 32.1 Å by increasing the macrocycle size. The family of MOPs shows experimental surface areas of up to 820 m2/g, and they are stable in water. One of these MOPs can efficiently separate the rare gases Xe from Kr because the prefabricated macrocyclic windows of MOPs can be modified to sit at the Xe/Kr size cutoff range.

Coalescence of Porous Coordination Cages into Crystalline and Amorphous Bulk Solids

Discrete porous coordination cages are attractive as a solution processable material whose porosity is not predicated on a network structure. Here, we leverage the peripheral functionalization of these cage structures to obtain 12 novel, solution processable, porous coordination cages that afford crystalline and amorphous single-phase millimeter-scale monolithic bulk structures (six of each) upon solidification. These structures are based upon prototypal metal-organic polyhedra [Cu24(5-x-isophthalate)24] (where x = NH2, OH), wherein meta-substitution of linker ligands with acyl chloride or isocyanate moieties afforded amide and urethane functional groups, respectively. These porous cage structures were obtainable via direct synthesis between a metal salt and a ligand as well as postsynthetic modification of the cage and formed monoliths following centrifugation and drying of the product. We rationalize their self-assembly as colloidal packing of nanoscale cuboctahedral cages through weak interactions between their hydrophobic alkyl/aromatic surfaces. In general, amorphous solids were obtained via rapid precipitation from the mother liquor upon methanol addition, while crystalline solids could be obtained only following further chloroform and pyridine additions. The structure of the materials is confirmed via gas sorption and spectroscopic methods, while powder X-ray diffraction and transmission electron microscopy are used to determine the nature of these bulk solids.

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.

Unlocking High Porosity: Post-Synthetic Solvothermal Treatment of Cu-Paddlewheel Based Metal-Organic Cages

Metal-organic cages (MOCs) have garnered significant attention due to their unique discrete structures, intrinsic porosity, designability, and tailorability. However, weak inter-cage interactions, such as van der Waals forces and hydrogen bonding can cause solid-state MOCs to lose structural integrity during desolvation, leading to the loss of porosity. In this work, a novel strategy to retain the permanent porosity of Cu-paddlewheel-based MOCs, enabling their use as heterogeneous catalysts is presented. Post-synthetic solvothermal treatments in non-coordinating solvents, mesitylene, and p-xylene, effectively preserve the packing structures of solvent-evacuated MOCs while preventing cage agglomeration. The resulting MOCs exhibit an exceptional N2 sorption capacity, with a high surface area (SBET = 1934 m2 g-1 for MOP-23), which is among the highest reported for porous MOCs. Intriguingly, while the solvothermal treatment reduced Cu(II) to Cu(I) in the Cu-paddlewheel clusters, the MOCs with mixed-valenced Cu(I)/Cu(II) maintained their crystallinity and permanent porosity. The catalytic activities of these MOCs are successfully examined in copper(I)-catalyzed hydrative amide synthesis, highlighting the prospect of MOCs as versatile reaction platforms.

Giant oligomeric porous cage-based molecules

Most reported porous materials are either extended networks or monomeric discrete cavities; indeed, porous structures of intermediate size have scarcely been explored. Herein, we present the stepwise linkage of discrete porous metal-organic cages or polyhedra (MOPs) into oligomeric structures with a finite number of MOP units. The synthesis of these new oligomeric porous molecules entails the preparation of 1-connected (1-c) MOPs with only one available azide reactive site on their surface. The azide-terminated 1-c MOP is linked through copper(i)-catalysed azide-alkyne cycloaddition click chemistry with additional alkyne-terminated 1-c MOPs, 4-c clusters, or 24-c MOPs to yield three classes of giant oligomeric molecules: dimeric, tetrameric, or satellite-like, respectively. Importantly, all the giant molecules that we synthesised are soluble in water and permanently porous in the solid state.

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.

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

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

Gas-Triggered Gate-Opening in a Flexible Three-Dimensional Covalent Organic Framework

The development of novel soft porous crystals (SPCs) that can be transformed from nonporous to porous crystals is significant because of their promising applications in gas storage and separation. Herein, we systematically investigated for the first time the gas-triggered gate-opening behavior of three-dimensional covalent organic frameworks (3D COFs) with flexible building blocks. FCOF-5, a 3D COF containing C-O single bonds in the backbone, exhibits a unique "S-shaped" isotherm for various gases, such as CO2, C2, and C3 hydrocarbons. According to in situ characterization, FCOF-5 undergoes a pressure-induced closed-to-open structural transition due to the rotation of flexible C-O single bonds in the framework. Furthermore, the gated hysteretic sorption property of FCOF-5 can enable its use as an absorbent for the efficient removal of C3H4 from C3H4/C3H6 mixtures. Therefore, 3D COFs synthesized from flexible building blocks represent a new type of SPC with gate-opening characteristics. This study will strongly inspire us to design other 3D COF-based SPCs for interesting applications in the future.

Redox-Active Ruthenium-Organic Polyhedra with Tunable Surface Functionality and Porosities

Dinuclear ruthenium paddlewheel complexes exhibit high structural stability in redox reactions. The use of these chemical motifs for the construction of Ru-based metal-organic polyhedra (RuMOPs) provides a route for redox-active porous materials. However, there are few studies on the synthesis and characterization of RuMOPs due to the difficulty in controlling the assembly process via the ligand-exchange reaction of equatorial acetates of the diruthenium tetraacetate precursors with dicarboxylic acid ligands. In this study, we synthesized three novel cuboctahedral RuMOPs based on the Ru2(II/III)-paddlewheel units with different alkyl functionalizations on the benzene-1,3-dicarboxylate moieties. We evaluated the effect of external functionalization on the molecular packing and the porous and redox properties. The electrochemical measurements revealed the multielectron transferred redox process where the electron-donating/-withdrawing nature of the functional groups allows the control of the redox behavior.

Increasing the stability of calixarene-capped porous cages through coordination sphere tuning

Chemically and thermally stable permanently porous coordination cages are appealing candidates for separations, catalysis, and as the porous component of new porous liquids. However, many of these applications have not turned to microporous cages as a result of their poor solubility and thermal or hydrolytic stability. Here we describe the design and modular synthesis of iron and cobalt cages where the carboxylate groups of the bridging ligands of well-known calixarene capped coordination cages have been replaced with more basic triazole units. The resultingly higher M-L bond strengths afford highly stable cages that are amenable to modular synthetic approaches and potential functionalization or modification. Owing to the robust nature of these cages, they are highly processable and are isolable in various physical states with tunable porosity depending on the solvation methods used. As the structural integrity of the cages is maintained upon high activation temperatures, apparent losses in porosity can be mediated by resolvation and crystallization or precipitation.

Improving the gas sorption capacity in lantern-type metal-organic polyhedra by a scrambled cage method

The synthesis of multivariate metal-organic frameworks (MOFs) is a well-known method for increasing the complexity of porous frameworks. In these materials, the structural differences of the ligands used in the synthesis are sufficiently subtle that they can each occupy the same site in the framework. However, multivariate or ligand scrambling approaches are rarely used in the synthesis of porous metal-organic polyhedra (MOPs) - the molecular equivalent of MOFs - despite the potential to retain a unique intrinsic pore from the individual cage while varying the extrinsic porosity of the material. Herein we directly synthesise scrambled cages across two families of lantern-type MOPs and find contrasting effects on their gas sorption properties. In one family, the scrambling approach sees a gradual increase in the BET surface area with the maximum and minimum uptakes associated with the two pure homoleptic cages. In the other, the scrambled materials display improved surface areas with respect to both of the original, homoleptic cages. Through analysis of the gas sorption isotherms, we attribute this effect to the balance of micro- and mesoporosity within the materials, which varies as a result of the scrambling approach. The gas uptake of the materials presented here underscores the tunability of cages that springs from their combination of intrinsic, extrinsic, micro- and meso-porosities.

A two-dimensional metal-organic framework assembled from scandium-based cages for the selective capture of sulfur hexafluoride

Herein, we report the synthesis of a two-dimensional metal-organic framework (MOF), assembled from octahedral metal-organic cages featuring phenanthroline-based carboxylate linkers and μ3-oxo-centered trinuclear Sc(III) inorganic building blocks. We study the performance of this MOF towards the capture of sulfur hexafluoride (SF6). On account of its structural features and porous nature, this MOF displays an SF6 uptake capacity of 0.92 mmol g-1 at 0.1 bar and an isosteric heat of adsorption of about 30.7 kJ mol-1 for SF6, illustrating its potential application for the selective capture of SF6 from N2. In addition, we study the adsorptive binding mechanism of SF6 and N2 inside this MOF via molecular simulations.

Ultralight crystalline hybrid composite material for highly efficient sequestration of radioiodine

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

Investigating the Cell Entry Mechanism, Disassembly, and Toxicity of the Nanocage PCC-1: Insights into Its Potential as a Drug Delivery Vehicle

The porous coordination cage PCC-1 represents a new platform potentially useful for the cellular delivery of drugs with poor cell permeability and solubility. PCC-1 is a metal-organic polyhedron constructed from zinc metal ions and organic ligands through coordination bonds. PCC-1 possesses an internal cavity that is suitable for drug encapsulation. To better understand the biocompatibility of PCC-1 with human cells, the cell entry mechanism, disassembly, and toxicity of the nanocage were investigated. PCC-1 localizes in the nuclei and cytoplasm within minutes upon incubation with cells, independent of endocytosis and cargo, suggesting direct plasma membrane translocation of the nanocage carrying its guest in its internal cavity. Furthermore, the rates of cell entry correlate to extracellular concentrations, indicating that PCC-1 is likely diffusing passively through the membrane despite its relatively large size. Once inside cells, PCC-1 disintegrates into zinc metal ions and ligands over a period of several hours, each component being cleared from cells within 1 day. PCC-1 is relatively safe for cells at low micromolar concentrations but becomes inhibitory to cell proliferation and toxic above a concentration or incubation time threshold. However, cells surviving these conditions can return to homeostasis 3-5 days after exposure. Overall, these findings demonstrate that PCC-1 enters live cells by crossing biological membranes spontaneously. This should prove useful to deliver drugs that lack this capacity on their own, provided that the dosage and exposure time are controlled to avoid toxicity.

Biasing the Formation of Solution-Unstable Intermediates in Coordination Self-Assembly by Mechanochemistry

Due to the reversible nature of coordination bonds and solvation effect, coordination self-assembly pathways are often difficult to elucidate experimentally in solution, as intermediates and products are in constant equilibration. The present study shows that some of these transient and high-energy self-assembly intermediates can be accessed by means of ball-milling approaches. Among them, highly aqueous-unstable Pd3 L11 and Pd6 L14 open-cage intermediates of the framed Fujita Pd6 L14 cage and Pd2 L22 , Pd3 L21 and Pd4 L22 intermediates of Mukherjee Pd6 L24 capsule are successfully trapped in solid-state, where Pd=tmedaPd2+ , L1=2,4,6-tris(4-pyridyl)-1,3,5-triazine and L2=1,3,5-tris(1-imidazolyl)benzene). Their structures are assigned by a combination of solution-based characterization tools such as standard NMR spectroscopy, DOSY NMR, ESI-MS and X-ray diffraction. Collectively, these results highlight the opportunity of using mechanochemistry to access unique chemical space with vastly different reactivity compared to conventional solution-based supramolecular self-assembly reactions.