Bifunctional Metal-Organic Nanoballs Featuring Lewis Acidic and Basic Sites as a New Platform for One-Pot Tandem Catalysis.

The design and synthesis of polyhedra using coordination-driven self-assembly has been an intriguing research area for synthetic chemists. Metal-organic polyhedra are a class of intricate molecular architectures that have garnered significant attention in the literature due to their diverse structures and potential applications. Hereby, we report Cu-MOP, a bifunctional metal-organic cuboctahedra built using 2,6-dimethylpyridine-3,5-dicarboxylic acid and copper acetate at room temperature. The presence of both Lewis basic pyridine groups and Lewis acidic copper sites imparts catalytic activity to Cu-MOP for the tandem one-pot deacetalization-Knoevenagel/Henry reactions. The effect of solvent system and time duration on the yields of the reactions was studied, and the results illustrate the promising potential of these metal-organic cuboctahedra, also known as nanoballs for applications in catalysis.

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.

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

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

Retrosynthetic Analysis Applied to Clip-off Chemistry: Synthesis of Four Rh(II)-Based Complexes as Proof-of-Concept.

Clip-off Chemistry is a synthetic strategy that our group previously developed to obtain new molecules and materials through selective cleavage of bonds. Herein, we report recent work to expand Clip-off Chemistry by introducing into it a retrosynthetic analysis step that, based on virtual extension of the products through cleavable bonds, enables one to define the required precursor materials. As proof-of-concept, we have validated our new approach by synthesising and characterising four aldehyde-functionalised Rh(II)-based complexes: a homoleptic cluster; a cis-disubstituted paddlewheel cluster; a macrocycle; and a crown.

(Bio)Functionalisation of Metal-Organic Polyhedra by Using Click Chemistry.

The surface chemistry of Metal-Organic Polyhedra (MOPs) is crucial to their physicochemical properties because it governs how they interact with external substances such as solvents, synthetic organic molecules, metal ions, and even biomolecules. Consequently, the advancement of synthetic methods that facilitate the incorporation of diverse functional groups onto MOP surfaces will significantly broaden the range of properties and potential applications for MOPs. This study describes the use of copper(I)-catalysed, azide-alkyne cycloaddition (CuAAC) click reactions to post-synthetically modify the surface of alkyne-functionalised cuboctahedral MOPs. To this end, a novel Rh(II)-based MOP with 24 available surface alkyne groups was synthesised. Each of the 24 alkyne groups on the surface of the "clickable" Rh-MOP can react with azide-containing molecules at room temperature, without compromising the integrity of the MOP. The wide substrate catalogue and orthogonal nature of CuAAC click chemistry was exploited to densely functionalise MOPs with diverse functional groups, including polymers, carboxylic and phosphonic acids, and even biotin moieties, which retained their recognition capabilities once anchored onto the surface of the MOP.

Transformation of Type III to Type II Porous Liquids by Tuning Surface Rigidity of Rhodium(II)-Based Metal-Organic Polyhedra for CO2 Cycloaddition.

Porous liquids (PLs), a summation of porous hosts and bulky solvents bestowing permanent cavities, are the prominent emerging materials. Despite great efforts, exploration of porous hosts and bulky solvents is still needed to develop new PL systems. Metal-organic polyhedra (MOPs) with discrete molecular architectures can be considered as porous hosts; however, many of them are insoluble entities. Here we report the transformation of type III PL to type II PLs by tuning the surface rigidity of insoluble MOP, Rh24 L24 , in a bulky ionic liquid (IL). Functionalization of N-donor molecules on Rh-Rh axial sites ensue their solubilization in bulky IL which confer type II PLs. Experimental and theoretical studies reveal the bulkiness of IL as per the cage apertures, and the cause of their dissolution as well. The obtained PLs, capturing more CO2 than neat solvent, have depicted higher catalytic activity for CO2 cycloaddition compared to individual MOPs and IL.

Porous Salts as Platforms for Heterogeneous Catalysis.

The preparation of a new class of reactive porous solids, prepared via straightforward salt metathesis reactions, is described here. Reaction of the dimethylammonium salt of a magnesium-based porous coordination cage with the chloride salt of [CrII Cl(Me4 cyclam)]+ affords a porous solid with concomitant removal of dimethylammonium chloride. The salt consists of the ions combined in the expected ratio based on their charge as confirmed by UV-vis and X-ray photoelectron spectroscopies, ion chromatography (IC), and inductively coupled plasma mass spectrometry (ICP-MS). The porous salt boasts a Brunauer-Emmett-Teller (BET) surface area of 213 m2  g-1 . Single crystal X-ray diffraction reveals the chromium(II) cations in the structure reside in the interstitial space between porous cages. Importantly, the chromium(II) centers, previously shown to react with O2 to afford reactive chromium(III)-superoxide adducts, are still accessible in the solid state as confirmed by UV-vis spectroscopy. The site-isolated reactive centers have competence toward hydrogen atom abstraction chemistry and display significantly increased stability and reactivity as compared to dissolved ions.

Endowing Covalent Organic Frameworks with Photoresponsive Active Sites for Controllable Propylene Adsorption.

Photoresponsive covalent organic frameworks (PCOFs) have emerged as attractive candidates for adsorption, but it is challenging to construct PCOF adsorbents due to structural order loss of covalent organic frameworks (COFs) after introducing photoresponsive motifs and/or tedious steps of postmodification. Here, a facile strategy is developed, by dispersing photoresponsive metal-organic polyhedra (PMOP) into COFs, to endow COFs with photoresponsive adsorption sites. As a proof-of-concept study, a COF with pore size of 4.5 nm and PMOP with suitable molecular size (4.0 and 3.1 nm for trans and cis configuration, respectively) are selected to meet the requirements of proper accommodation space, good guest dispersion, and free isomerization. The structure of COF is well preserved after introducing PMOPs. Interestingly, the obtained photoresponsive host-guest composite (PHGC) adsorbents exhibit photomodulated adsorption capacity on propylene (C3 H6 ) and the change in adsorption capacity can reach up to 43.3% and is stable during multiple cycles. Density functional theory calculations reveal that visible-light irradiation drives the azobenzene motifs in PHGCs to the trans configuration and the adsorption sites are fully open and interact with C3 H6 . UV-light irradiation makes the azobenzene motifs transform to the cis configuration, leading to the shield of the adsorption sites and the consequent release of C3 H6 .

Cathodes Coating Layer with Li-Ion Diffusion Selectivity Employing Interactive Network of Metal-Organic Polyhedras for Li-Ion Batteries.

Surface modification of cathodes using Ni-rich coating layers prevents bulk and surface degradation for the stable operation of Li-ion batteries at high voltages. However, insulating and dense inorganic coating layers often impede charge transfer and ion diffusion kinetics. In this study, the fabrication of dual functional coating materials using metal-organic polyhedra (MOP) with 3D networks within microporous units of Li-ion batteries for surface stabilization and facile ion diffusion is proposed. Zr-based MOP is modified by introducing acyl groups as a chemical linkage (MOPAC), and MOPAC layers are homogenously coated by simple spray coating on the cathode. The coating allow the smooth transport of electrons and ions. MOPAC effectively suppress side reactions between the cathode and electrolyte and protect active materials against aggressive fluoride ions by forming a Li-ion selective passivation film. The MOPAC-coated Ni-rich layered cathode exhibited better cycle retention and enhanced kinetic properties than pristine and MOP-coated cathodes. Reduction of undesirable gas evolution on the cathode by MOPAC is also verified. Microporous MOPAC coating can simultaneously stabilize both the bulk and surface of the Ni-rich layered cathode and maintain good electrochemical reaction kinetics for high-performance Li-ion batteries.

Porous Liquids Responsive to Light.

A porous liquid is a unique liquid medium that combines the cavity of porous solids with the fluidity of liquids. This special characteristic offers potential in various applications. Here we report a type II photoresponsive porous ionic liquid (PPIL) from dissolving a photoresponsive metal-organic polyhedron (PMOP, constructed from dicopper and azobenzene-containing carboxylate) in a polyethylene-glycol-functionalized bulky ionic liquid (IL). Owing to favorable ion interactions, bulky IL molecules encircle outside PMOP, and the inter cavities are maintained. The azobenzene moieties can be isomerized freely in the PPILs to expose and shelter active sites upon visible and UV light irradiation. Hence, the adsorption capacity of PPILs is controllable by light irradiation, and the change in CO2 uptake is up to 30 % compared to neat IL. This study may inspire the development of new adsorption process regulated by light instead of pressure and temperature swing adsorption.

Self-Healing and Shape Memory Hypercrosslinked Metal-Organic Polyhedra Polymers via Coordination Post-Assembly.

Coordination-driven crosslinking networks with reversible and dynamic characteristics are gaining increasing interest in diverse application fields. Herein, we use a coordination crosslinking approach using metal-organic polyhedra (MOPs) as high-connectivity building blocks to post-assemble a class of coordination hypercrosslinked MOP (CHMOP) polymers. The introduction of 12-connected MOP nodes to the polymeric networks is critical to producing membranes that overcome the trade-off between mechanical properties and dynamic healing, and meanwhile possess multifunctionalities including shape memory, solution processability, and 3D printing. The CHMOPs can also be used for anticorrosion coating and achieve function couplings, e.g., shape memory-assisted self-healing (SMASH), which have not been achieved in the MOP-based hybrid materials yet. This work not only offers a feasible strategy to construct new multifunctional materials but also greatly expands the application scopes of MOPs.

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

Metal-based oxoanions are potentially toxic pollutants that can cause serious water pollution. Therefore, the segregation of such species has recently received significant research attention. Even though several adsorbents have been employed for effective management of chemicals, their limited microporous nature along with non-monolithic applicability has thwarted their large-scale real-time application. Herein, we developed a unique anion exchangeable hybrid composite aerogel material (IPcomp-6), integrating a stable cationic metal-organic polyhedron with a hierarchically porous metal-organic gel. The composite scavenger demonstrated a highly selective and very fast segregation efficiency for various hazardous oxoanions such as, HAsO42- , SeO42- , ReO4- , CrO42- , MnO4- , in water, in the presence of 100-fold excess of other coexisting anions. The material was able to selectively eliminate trace HAsO42- even at low concentration to well below the AsV limit in drinking water defined by WHO.

pH-Triggered Removal of Nitrogenous Organic Micropollutants from Water by Using Metal-Organic Polyhedra.

Water pollution threatens human and environmental health worldwide. Thus, there is a pressing need for new approaches to water purification. Herein, we report a novel supramolecular strategy based on the use of a metal-organic polyhedron (MOP) as a capture agent to remove nitrogenous organic micropollutants from water, even at very low concentrations (ppm), based exclusively on coordination chemistry at the external surface of the MOP. Specifically, we exploit the exohedral coordination positions of RhII -MOP to coordinatively sequester pollutants bearing N-donor atoms in aqueous solution, and then harness their exposed surface carboxyl groups to control their aqueous solubility through acid/base reactions. We validated this approach for removal of benzotriazole, benzothiazole, isoquinoline, and 1-napthylamine from water.

Metal-Organic Polyhedra as Building Blocks for Porous Extended Networks.

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

Metal-Organic Cages with {SiW9 Ni4 } Polyoxotungstate Nodes.

A tritopic, Ni-substituted Keggin cluster, {SiW9 Ni4 }, assembles with rigid dicarboxylate linkers to give rise to a set of discrete, POM2n L3n -type structures (POM={SiW9 Ni4 }) with defined interior voids. The outcome of coordination-driven self-assemblies of these polyhedral cages-from fused dimers to trigonal prisms-was found to be sensitive to bend angles of the ditopic ligands, which vary from 122° to 180°. These polyoxotungstate-based metal-organic polyhedra, when coupled with [Ru(bpy)3 ]Cl2 as a photosensitizer and triethanolamine as the electron donor, serve as highly effective catalysts for CO2 reduction, with turnover numbers up to 328 and CO selectivity as high as 96.2 %. The inner cavities of such cage structures, if functionalized or of sufficient size to encapsulate targeted guest molecules, could present a new strategy towards functional materials for potential applications.

Enzyme-Mimetic Molecular Selective Catalysis via Single Zr Atom Catalysis in Chelated Cage Embedded in a Flexible Piezoelectrical Matrix.

The molecularly selective catalysis in enzyme is central to life. However, their functioning mechanism remains elusive. We propose here that the synergistic effects from (i) effective orbital hybridizing and energy gap decreasing via chelating on single Zr atom as the catalytic center, (ii) selective supramolecular encapsulation in the cage, and (iii) piezoelectrical field motivation are able to achieve the enzyme-mimetic molecular selective high performance catalysis. Metal-organic polyhedra (MOPs) are added into a piezoelectrical polymer matrix to achieve the composite structure where ultrasonic treatment motivates redox reactions in the MOP-guest complex. Encapsulated and chelated guest such as Rhodamine B (RhB) is effectively converted with ratios higher than 90 % after 100 min. In comparison, molecules inefficient in either cage encapsulation or chelating with the Zr center can not be converted. This study first proposes a synergistic plot for enzyme-mimetic catalyst realization and is expected to inspire new mentality in efficient catalyst designing.

An efficient glucose sensor thermally calcined from copper-organic coordination cages.

Due to the harmfulness of diabetes, a fast and efficient glucose detector is particularly important. Metal-organic polyhedron (MOP) provides a porous framework and a special matrix, which makes it an excellent precursor for electrochemical detection. Herein, we report a novel MOP as a precursor for the preparation of an electrocatalytic detector for glucose. The new metal-organic polyhedron of Cu4(TPDC)4 can be solvothermally obtained and characterized by X-ray crystallography, which can be thermally converted into nanosized copper oxides embedded into graphitic carbon layers (MOP-CO). The as-prepared MOP-CO electrode is further applied to glucose detection, which shows a fast response time (<1 s) in a wide linear range of 0-4000 µM and high sensitivity of 2720 µA mM-1 cm-2, as well as low detection limit (26 nM (S/N = 3)), good anti-interference, repeatability and stability (>3600 s).

Clip-off Chemistry: Synthesis by Programmed Disassembly of Reticular Materials.

Bond breaking is an essential process in chemical transformations and the ability of researchers to strategically dictate which bonds in a given system will be broken translates to greater synthetic control. Here, we report extending the concept of selective bond breaking to reticular materials in a new synthetic approach that we call Clip-off Chemistry. We show that bond-breaking in these structures can be controlled at the molecular level; is periodic, quantitative, and selective; is effective in reactions performed in either solid or liquid phases; and can occur in a single-crystal-to-single-crystal fashion involving the entire bulk precursor sample. We validate Clip-off Chemistry by synthesizing two topologically distinct 3D metal-organic frameworks (MOFs) from two reported 3D MOFs, and a metal-organic macrocycle from metal-organic polyhedra (MOP). Clip-off Chemistry opens the door to the programmed disassembly of reticular materials and thus to the design and synthesis of new molecules and materials.

Self Assembled Cages with Mechanically Interlocked Cucurbiturils.

We report preparation of (bis)aniline ligand 4 which contains a central viologen binding domain and its subcomponent self-assembly with aldehyde 5 and Fe(OTf)2 in CH3CN to yield tetrahedral assembly 6. Complexation of ligand 4 with CB[7] in the form of CB[7]•4•2PF6 allows the preparation of assembly 7 which contains an average of 1.95 (range 1-3) mechanically interlocked CB[7] units. Assemblies 6 and 7 are hydrolytically unstable in water due to their imine linkages. Redesign of our system with water stable 2,2'-bipyridine end groups was realized in the form of ligands 11 and 16 which also contain a central viologen binding domain. Self-assembly of 11 with Fe(NTf2)2 gave tetrahedral MOP 12 as evidenced by 1H NMR, DOSY, and mass spectrometric analysis. In contrast, isomeric ligand 16 underwent self-assembly with Fe(OTf)2 to give cubic assembly 17. Precomplexation of ligands 11 and 16 with CB[7] gave the acetonitrile soluble CB[7]•11•2PF6 and CB[7]•16•2PF6 complexes. Self-assembly of CB[7]•11•2PF6 with Fe(OTf)2 gave tetrahedron 13 which contains on average 1.8 mechanically interlocked CB[7] units as determined by 1H NMR, DOSY, and ESI-MS analysis. Self-assembly of CB[7]•16•2PF6 with Fe(OTf)2 gave cube 13 which contains 6.59 mechanically interlocked CB[7] units as determined by 1H NMR and DOSY measurements.

Steric Hindrance in Metal Coordination Drives the Separation of Pyridine Regioisomers Using Rhodium(II)-Based Metal-Organic Polyhedra.

The physicochemical similarity of isomers makes their chemical separation through conventional techniques energy intensive. Herein, we report that, instead of using traditional encapsulation-driven processes, steric hindrance in metal coordination on the outer surface of RhII -based metal-organic polyhedra (Rh-MOPs) can be used to separate pyridine-based regioisomers via liquid-liquid extraction. Through molecular dynamics simulations and wet experiments, we discovered that the capacity of pyridines to coordinatively bind to Rh-MOPs is determined by the positions of the pyridine substituents relative to the pyridine nitrogen and is influenced by steric hindrance. Thus, we exploited the differential solubility of bound and non-bound pyridine regioisomers to engineer liquid-liquid self-sorting systems. As a proof of concept, we separated four different equimolecular mixtures of regioisomers, including a mixture of the industrially relevant compounds 2-chloropyridine and 3-chloropyridine, isolating highly pure compounds in all cases.