Macrocycle-based metal-organic frameworks

Chiral Liquid Crystalline Metal-Organic Framework Thin Films for Highly Circularly Polarized Luminescence

Combining metal-organic frameworks (MOFs) with liquid crystals to construct liquid crystalline MOFs (LCMOF) offers the advantage of endowing and enhancing their functionality, yet it remains a challenging task. Herein, we report chiral liquid crystalline MOF (CLCMOF) thin films by cross-linking the chiral liquid crystals (CLC) with MOF thin films to realize highly circular polarization luminescence (CPL) performance with photo and thermal switching. By layer by layer cross-linking stilbene-containing CLC with stilbene-based MOF (CLC/MOF) thin film, the CLCMOF thin films were successfully obtained after UV irradiation due to the abundant [2 + 2] photocycloaddition. The resulted CLCMOF thin films have strong chirality, obvious photochromic fluorescent, and strong CPL performance (the asymmetry factor reaches to 0.4). Furthermore, due to the photochromic fluorescent MOF and thermotropic CLC, the CPL can be reversed and red-shifted after heating and UV irradiation treatment, showing photo- and thermal CPL switching. Such MOF-based CPL thin films with photo/thermal CPL switching were prepared to patterns and codes for the demonstration of potential application in advanced information anticounterfeit and encryption. This study not only opens a strategy for developing chiral thin films combining MOFs and liquid crystals but also offers a new route to achieve CPL switching in optical applications.

Pillararene incorporated metal-organic frameworks for supramolecular recognition and selective separation

Crystalline frameworks containing incorporated flexible macrocycle units can afford new opportunities in molecular recognition and selective separation. However, such functionalized frameworks are difficult to prepare and challenging to characterize due to the flexible nature of macrocycles, which limits the development of macrocycle-based crystalline frameworks. Herein, we report the design and synthesis of a set of metal-organic frameworks (MOFs) containing pillar[5]arene units. The pillar[5]arene units were uniformly embedded in the periodic frameworks. Single crystal X-ray diffraction analysis revealed an interpenetrated network that appears to hinder the rotation of the pillar[5]arene repeating units in the frameworks, and it therefore resulted in the successful determination of the precise pillar[5]arene host structure in a MOF crystal. These MOFs can recognize paraquat and 1,2,4,5-tetracyanobenzene in solution and selectively remove trace pyridine from toluene with relative ease. The work presented here represents a critical step towards the synthesis of macrocycle-incorporated crystalline frameworks with well-defined structures and functional utility.

Bismacrocycle: Structures and Applications

In the past half-century, macrocycles with different structures and functions, have played a critical role in supramolecular chemistry. Two macrocyclic moieties can be linked to form bismacrocycle molecules. Compared with monomacrocycle, the unique structures of bismacrocycles led to their specific recognition and assembly properties, also a wide range of applications, including molecular recognition, supramolecular self-assembly, advanced optical material construction, etc. In this review, we focus on the structure of bismacrocycle and their applications. Our goal is to summarize and outline the possible future development directions of bismacrocycle research.

Recent Breakthroughs in Supercapacitors Boosted by Macrocycles

Supercapacitors are essential for electrochemical energy storage because of their high-power density, good cycle stability, fast charging and discharging rates, and low maintenance cost. Macrocycles, including cucurbiturils, calixarene, and cyclodextrins, are cage-like organic compounds (with a nanocavity that contains O and N heteroatoms) with unique potential in supercapacitors. Here, we review the applications of macrocycles in supercapacitor systems, and we illustrate the merits of organic macrocycles in electrodes and electrolytes for improving the electrochemical double-layer capacitors and pseudocapacitance via supramolecular strategies. Then, the observed relationships between electrochemical performance and macrocyclic structures are introduced. This comprehensive review describes recent progress on macrocycle-block supercapacitors for researchers.

Removal of dyes (BG, MG, and SA) from aqueous solution using a novel adsorbent macrocyclic compound

The use of macrocyclic compounds to remove organic dyes is fascinating because they have a wide surface area range and can be used for different things. new (14E, 34E)-7-Hydroxy-7, 8, 22, 23, 24, 25, 26, 27-Octahydro-6H, 16H, 33H Tetrabenzo[f,k,u,z][1,5,13,20]Tetraoxacycloheptacosine-16,33-Dione (HOTTD) was obtained by a simple high-dilution method, and characterized by FTIR, 1H-NMR, FESEM, EDX, and XRD. It worked well in removing organic dyes from aqueous solutions. Contact time, pH, dosage, initial concentration and temperature were studied. The optimum conditions were achieved by using 20 mg/L dye concentration, 50 mg dose of adsorbent and pH 9.0 at room temperature. The adsorption process was remarkably fast and reached equilibrium within 10 min for both Brilliant Green and Malachite Green while 70 min for Safranin. The batch adsorption experiments followed a pseudo 2nd order and Langmuir model with maximum adsorption capacity 19.26 mg/g, 18.28 mg/g, and 14.35 mg/g for Brilliant Green, Malachite green and Safranin respectively. The process was endothermic and spontaneous in nature. Adsorbent regeneration test provides an excellent value 5 times.

Organo-macrocycle-containing hierarchical metal-organic frameworks and cages: design, structures, and applications

Developing hierarchical ordered systems is challenging. Using organo-macrocycles to construct metal-organic frameworks (MOFs) and porous coordination cages (PCCs) provides an efficient way to obtain hierarchical assemblies. Macrocycles, such as crown ethers, cyclodextrins, calixarenes, cucurbiturils, and pillararenes, can be incorporated within MOFs/PCCs and they also endow the resultant composites with enhanced properties and functionalities. This review summarizes recent developments of organo-macrocycle-containing hierarchical MOFs/PCCs, emphasizing applications and structure-property relationships of these hierarchically porous materials. This review provides insights for future research on hierarchical self-assembly using macrocycles as building blocks and functional ligands to extend the applications of the composites.

Three layered cucurbit[6]uril-based metal-organic rotaxane networks functionalized by sulfonic groups for proton conduction

Three new cucurbit[6]uril (CB[6])-based metal-organic rotaxane networks (MORNs) (named CUST-711, CUST-712, and CUST-713) functionalized by a sulfonic group (-SO₃H) have been designed and synthesized via a hydrothermal method. All three compounds exhibited similar two-dimensional (2D) wave layer structures. Their stability under different temperature and relative humidity conditions has been investigated and all the compounds showed excellent stability. Furthermore, their proton conduction properties were also discussed in detail. Due to different structures and sulfonic group sites, the three compounds exhibited different proton conduction abilities of which CUST-712 exhibited an intrinsic relatively high proton conductivity (1.75 × 10^-4 S cm^-1 at 85 °C and 97% relative humidity). These results provide ideas for the design and synthesis of functional CB[6]-based metal-organic rotaxane frameworks (MORFs) as proton conducting materials.

Cyclodextrin metal-organic frameworks and derivatives: recent developments and applications

While there is a tremendous amount of scientific research on metal organic frameworks (MOFs) for gas storage/separation, catalysis and energy storage, the development and application of biocompatible MOFs still poses major challenges. In general, they can be synthesised from various biocompatible linkers and metal ions but particularly cyclodextrins (CDs) as cyclic oligosaccharides are an astute choice for the former. Although the field of CD-MOF materials is still in the early stages and their design and fabrication comes with many hurdles, the benefits coming from CDs built in a porous framework are exciting. Versatile host-guest complexation abilities, high encapsulation capacity and hydrophilicity are among the valuable properties inherent to CDs and offer extended and novel applications to MOFs. In this review, we provide an overview of the state-of-the-art synthesis, design, properties and applications of these materials. Initially, a rationale for the preparation of CD-based MOFs is provided, based on the chemical and structural properties of CDs and including their advantages and disadvantages. Further on, the review exhaustively surveys CD-MOF based materials by categorising them into three sub-classes, namely (i) CD-MOFs, (ii) CD-MOF hybrids, obtained via combination with external materials, and (iii) CD-MOF-derived materials prepared under pyrolytic conditions. Subsequently, CD-based MOFs in practical applications, such as drug delivery and cancer therapy, sensors, gas storage, (enantiomer) separations, electrical devices, food industry, and agriculture, are discussed. We conclude by summarizing the state of the art in the field and highlighting some promising future developments of CD-MOFs.

Supramolecular systems prepared using terpyridine-containing pillararene

Recent progresses about the preparation of terpyridine-containing pillararene, as well as the utilization of those building blocks for making external stimulud-responsive supramolecular systems were summarized in this review.

Halogen-bonded architectures of multivalent calix[4]arenes

A 2D halogen bonded network of calixarene macrocycles was obtained by co-crystallization of a 1,3-alternate calix[4]arene as a tetravalent XB donor with a bidentate XB acceptor.

Giant N-heterocyclic carbene-containing macrocycles for cobalt-catalysed hydroboration of alkynes

Giant N-heterocyclic carbene-containing organic macrocycles larger than “Texas-sized” molecular boxes have been synthesized and structurally characterized. The new macrocyles were employed for the Co-NHC promoted syn-selective hydroboration of alkynes with...

Bioapplication of cyclodextrin-containing montmorillonite

Recent progresses in the integration of CDs and montmorillonite, as well as applications of CD-containing montmorillonite hybrid host systems are summarized in this review. Several efficient synthesis strategies, such as ion exchange, metal coordination, supramolecular strategies, polymerizations and organic synthesis methods, have been discussed during the preparation of CDs/montmorillonite hybrid composites. In particular, diverse instrumental techniques were highly recommended for characterizing the as-obtained hybrid systems, including their chemical composition and structures, crystallinity, surface/self-assembled morphologies, as well as other particular physiochemical properties, providing a direct guide for promoting the desired structures and exploring various applications. It should be noted that the introduction of functional groups, as well as the integration of CDs and montmorillonite granted the thus obtained CD-containing montmorillonite hybrid host systems a lot of unique features, providing great opportunities for expanding the practical applications to a series of biological and environmental areas, such as biosensors, sorption and decontamination of bio/environmental hazardous materials, biostudies about aqueous dispersity, stability and biocompatibility, drug loading and target delivery, controlled and sustained drug release, as well as antibacterial.

Stimuli-Responsive Zinc (II) Coordination Polymers: A Novel Platform for Supramolecular Chromic Smart Tools

The unique role of the zinc (II) cation prompted us to cut a cross-section of the large and complex topic of the stimuli-responsive coordination polymers (CPs). Due to its flexible coordination environment and geometries, easiness of coordination-decoordination equilibria, "optically innocent" ability to "clip" the ligands in emissive architectures, non-toxicity and sustainability, the zinc (II) cation is a good candidate for building supramolecular smart tools. The review summarizes the recent achievements of zinc-based CPs as stimuli-responsive materials able to provide a chromic response. An overview of the past five years has been organised, encompassing 1, 2 and 3D responsive zinc-based CPs; specifically zinc-based metallorganic frameworks and zinc-based nanosized polymeric probes. The most relevant examples were collected following a consequential and progressive approach, referring to the structure-responsiveness relationship, the sensing mechanisms, the analytes and/or parameters detected. Finally, applications of highly bioengineered Zn-CPs for advanced imaging technique have been discussed.

Cucurbituril-Encapsulating Metal-Organic Framework via Mechanochemistry: Adsorbents with Enhanced Performance

The first examples of monolithic crystalline host-guest hybrid materials are described. The reaction of 1,3,5-benzenetricarboxylic acid (H3 BTC) and Fe(NO3 )3 ⋅9 H2 O in the presence of decamethylcucurbit[5]uril ammonium chloride (MC5⋅2 NH4 Cl⋅4 H2 O) directly affords MC5@MIL-100(Fe) hybrid monoliths featuring hierarchical micro-, meso- and macropores. Particularly, this "bottle-around-ship" synthesis and one-pot shaping are facilitated by a newly discovered Fe-MC5 flowing gel formed by mechanochemistry. The designed MC5@MIL-100(Fe) hybrid material with MC5 as active domains shows enhanced CH4 and lead(II) uptake performance, and selective capture of lead(II) cations at low concentrations. This shows that host-guest hybrid materials can exhibit synergic properties that out-perform materials based on individual components.

Cyclotetrabenzoin Acetate: A Macrocyclic Porous Molecular Crystal for CO2 Separations by Pressure Swing Adsorption*

A porous molecular crystal (PMC) assembled by macrocyclic cyclotetrabenzoin acetate is an efficient adsorbent for CO₂ separations. The 7.1×7.1 Å square pore of PMC and its ester C=O groups play important roles in improving its affinity for CO₂ molecules. The benzene walls of macrocycle engage in an apparent [π⋅⋅⋅π] interaction with the molecule of CO₂ at low pressure. In addition, the polar carbonyl groups pointing inward the square channels reduce the size of aperture to a 5.0×5.0 Å square, which offers kinetic selectivity for CO₂ capture. The PMC features water tolerance and high structural stability under vacuum and various gas adsorption conditions, which are rare among intrinsically porous organic molecules. Most importantly, the moderate adsorbate-adsorbent interaction allows the PMC to be readily regenerated, and therefore applied to pressure swing adsorption processes. The eluted N₂ and CH₄ are obtained with over 99.9 % and 99.8 % purity, respectively, and the separation performance is stable for 30 cycles. Coupled with its easy synthesis, cyclotetrabenzoin acetate is a promising adsorbent for CO₂ separations from flue and natural gases.

Selective Photodimerization in a Cyclodextrin Metal-Organic Framework

For the most part, enzymes contain one active site wherein they catalyze in a serial manner chemical reactions between substrates both efficiently and rapidly. Imagine if a situation could be created within a chiral porous crystal containing trillions of active sites where substrates can reside in vast numbers before being converted in parallel into products. Here, we report how it is possible to incorporate 1-anthracenecarboxylate (1-AC^-) as a substrate into a γ-cyclodextrin-containing metal-organic framework (CD-MOF-1), where the metals are K⁺ cations, prior to carrying out [4+4] photodimerizations between pairs of substrate molecules, affording selectively one of four possible regioisomers. One of the high-yielding regioisomers exhibits optical activity as a result of the presence of an 8:1 ratio of the two enantiomers following separation by high-performance liquid chromatography. The solid-state superstructure of 1-anthracenecarboxylate potassium salt (1-ACK), which is co-crystallized with γ-cyclodextrin, reveals that pairs of substrate molecules are not only packed inside tunnels between spherical cavities present in CD-MOF-1, but also stabilized-in addition to hydrogen-bonding to the C-2 and C-3 hydroxyl groups on the d-glucopyranosyl residues present in the γ-cyclodextrin tori-by combinations of hydrophobic and electrostatic interactions between the carboxyl groups in 1-AC^- and four K⁺ cations on the waistline between the two γ-cyclodextrin tori in the tunnels. These non-covalent bonding interactions result in preferred co-conformations that account for the highly regio- and enantioselective [4+4] cycloaddition during photoirradiation. Theoretical calculations, in conjunction with crystallography, support the regio- and stereochemical outcome of the photodimerization.

Effective Encapsulation of C60 by Metal-Organic Frameworks with Polyamide Macrocyclic Linkers

A flexible benzylic amide macrocycle, functionalized with two carboxylic acid groups, was employed as the organic ligand for the preparation of robust copper(II)- and zinc(II)-based metal-organic frameworks. These polymers crystallized in the C2/m space group of the monoclinic crystal system, creating non-interpenetrated channels in one direction with an extraordinary solvent-accessible volume of 46 %. Unlike metal-organic rotaxane frameworks having benzylic amide macrocycles as linkers, the absence of the thread in these novel reticular materials causes a decrease of dimensionality and an improvement of pore size and dynamic guest adaptability. We studied the incorporation of fullerene C₆₀ inside the adjustable pocket generated between two macrocycles connected to the same dinuclear clusters, occupying a remarkable 98 % of the cavities inside the network. The use of these materials as hosts for the selective recognition of different fullerenes was evaluated, mainly encapsulating the smaller size fullerene derivative in several mixtures of C₆₀ and C₇₀ .

Coordination polymers with embedded recognition sites: lessons from cyclotriveratrylene-type ligands

Coordination polymers with molecular recognition sites are assembled using cyclotriveratrylene ligands. Many show differential guest-spaces with host and lattice sites available, however common host–guest and self-inclusion motifs can block sites.

Assemblies of cucurbit[6]uril-based coordination complexes with disulfonate ligands: from discrete complexes to one- and two-dimensional polymers

Nine assemblies of Q[6]-based coordination complexes incorporating disulfonate ligands were obtained and two of them were found to have the ability to sense Fe³⁺via a fluorescence quenching effect.

Pillararene-based conjugated porous polymers

The synthesis and application of promising polymeric materials–pillararene-based conjugated porous polymers–are discussed and summarized in this review.

Progress and challenges of metal-organic frameworks-based materials for SR-AOPs applications in water treatment

As environmental problems become more and more severe, sulfate radical (SO₄^-) based advanced oxidation processes (SR-AOPs) are widely recognized for their high removal efficiency of recalcitrant organic pollutants in water. Metal-organic frameworks (MOFs) have attracted wide attention in SR-AOPs due to their outstanding properties (e.g. large surface area, ultra-high porosity, and diversity of material design, etc). Herein, we present an overview of the development and challenges in the synthesis of different types of MOFs, combination of MOFs with other materials (metal centers, conductors, cellulose, etc.) and the construction of catalysts with special structures (core-shell structures and hollow structures) as well as their applications in SR-AOPs for the degradation of organic pollutants. Several review papers have already mentioned the application of a branch of MOFs or simple composites of MOFs in SR-AOP, whereas the latest progresses on the application of MOFs-based materials to SR-AOPs was described rarely. Besides, the degradation mechanism of MOFs as catalysts has not been systematically discussed. To this end, the mechanisms of MOFs and MOF-based materials as catalysts to activate PMS/PS in different systems are analyzed, including radicals and non-radicals pathways. Meanwhile, considering that the research in this field is still in its infancy, a lot of improvements are still needed to effectively promote and implement this technology.

Protonation-induced self-assembly of bis-phenanthroline macrocycles into nanofibers arrayed with tetrachloroaurate, hexachloroplatinate or phosphomolybdate ions

One-dimensional self-assembly of macrocycles is one of the important strategies for constructing fibrous nanomaterials with anisotropic functions such as one-dimensional transport and accumulation of molecules and ions. Herein we report on the synthesis and properties of self-assembled nanofibers using macrocycles to develop a multipurpose template for one-dimensional array of noble metal ions. The nanofibers were prepared by protonation-induced self-assembly of bis-phenanthroline macrocycles, which have enabled the accumulation of some metal-containing anions, such as tetrachloroaurate, hexachloroplatinate and phosphomolybdate. Microscopic observations have demonstrated that the supramolecular nanofibers were reproducibly formed in a similar way, regardless of the structures and charge numbers of the anions. Moreover, the resulting nanofibers, arrayed with several metal ions, were chemically reduced, producing dispersible gold nanoparticles and mixed-valence nanofibers.

Supramolecular-Macrocycle-Based Crystalline Organic Materials

Supramolecular macrocycles are well known as guest receptors in supramolecular chemistry, especially host-guest chemistry. In addition to their wide applications in host-guest chemistry and related areas, macrocycles have also been employed to construct crystalline organic materials (COMs) owing to their particular structures that combine both rigidity and adaptivity. There are two main types of supramolecular-macrocycle-based COMs: those constructed from macrocycles themselves and those prepared from macrocycles with other organic linkers. This review summarizes recent developments in supramolecular-macrocycle-based COMs, which are categorized by various types of macrocycles, including cyclodextrins, calixarenes, resorcinarenes, pyrogalloarenes, cucurbiturils, pillararenes, and others. Effort is made to focus on the structures of supramolecular-macrocycle-based COMs and their structure-function relationships. In addition, the application of supramolecular-macrocycle-based COMs in gas storage or separation, molecular separation, solid-state electrolytes, proton conduction, iodine capture, water or environmental treatment, etc., are also presented. Finally, perspectives and future challenges in the field of supramolecular-macrocycle-based COMs are discussed.

Pillararenes Trimer for Self-Assembly

Pillararenes trimer with particularly designed structural geometry and excellent capacity of recognizing guest molecules is a very efficient and attractive building block for the fabrication of advanced self-assembled materials. Pillararenes trimers could be prepared via both covalent and noncovalent bonds. The classic organic synthesis reactions such as click reaction, palladium-catalyzed coupling reaction, amidation, esterification, and aminolysis are employed to build covalent bonds and integrate three pieces of pillararenes subunits together into the “star-shaped” trimers and linear foldamers. Alternatively, pillararenes trimers could also be assembled in the form of host-guest inclusions and mechanically interlocked molecules via noncovalent interactions, and during those procedures, pillararenes units contribute the cavity for recognizing guest molecules and act as a “wheel” subunit, respectively. By fully utilizing the driving forces such as host-guest interactions, charge transfer, hydrophobic, hydrogen bonding, and C–H^…π and π–π stacking interactions, pillararenes trimers-based supramolecular self-assemblies provide a possibility in the construction of multi-dimensional materials such as vesicular and tubular aggregates, layered networks, as well as frameworks. Interestingly, those assembled materials exhibit interesting external stimuli responsiveness to e.g., variable concentrations, changed pH values, different temperature, as well as the addition/removal of competition guests and ions. Thus, they could further be used for diverse applications such as detection, sorption, and separation of significant multi-analytes including metal cations, anions, and amino acids.

Novel Porous Crystals with Macrocycle-Based Well-Defined Molecular Recognition Sites

Molecular recognition is one of the fundamental events in biological systems, as typified by enzymes that enable highly efficient and selective catalytic reactions through precise recognition of substrate(s) and cofactor(s) in the binding pockets. Chemists therefore have long been inspired by such excellent molecular systems to develop various synthetic receptors with well-defined binding sites. Their effort is currently being devoted to the construction of not only molecular receptors but also self-assembled host compounds possessing connected cavities (pores) in the crystalline frameworks to rationally design functional porous materials capable of efficiently adsorbing molecules or ions at binding sites on the pore walls. However, it is still challenging to design multiple distinct binding sites that are precisely arranged in an identical framework, which is currently one of the most important targets in this field to realize elaborate molecular systems beyond natural enzymes.In this Account, we provide an overview of porous crystals with well-defined molecular recognition sites. We first show several strategies for arranging macrocyclic binding sites in crystalline frameworks such as metal-organic frameworks, porous molecular crystals, and covalent organic frameworks. Porous metal-macrocycle frameworks (MMFs) that we have recently developed are then described as a new type of porous crystals with well-defined multiple distinct binding sites. The MMF-1 crystal, which was developed first and is composed of four stereoisomers of helical Pd^II₃-macrocycle complexes, has one-dimensional channels with dimensions of 1.4 nm × 1.9 nm equipped with enantiomeric pairs of five distinct binding sites. This structural feature of MMF-1 therefore allows for site-selective and asymmetric arrangement of not only single but also multiple guest molecules in the crystalline channels based on molecular recognition between the guests and the multiple binding sites. This characteristic was also exploited to develop a heterogeneous catalyst by non-covalently immobilizing an organic acid on the pore surface of MMF-1 to conduct size-specific catalytic reactions. In addition, adsorption of a photoreactive substrate in MMF was found to switch the photoreaction pathway to cause another reaction with the aid of photoactivated Pd^II centers arranged on the pore walls. Furthermore, the dynamic, transient process of molecular arrangement incorporated in MMF-1 has been successfully visualized by single-crystal X-ray diffraction analysis. The formation of homochiral MMF-2 composed of only (P)- or (M)-helical Pd^II₃-macrocycle complexes is also described. Thus, macrocycle-based porous crystals with a complex structure such as MMFs are expected to serve as novel porous materials that have great potential to mimic or surpass enzymes by utilizing well-defined multiple binding sites capable of spatially arranging a catalyst, substrate, and effector for highly selective and allosterically tunable catalytic reactions, which can be also visualized by crystallographic analysis because of their crystalline nature.

Cyclodextrins Modified/Coated Metal-Organic Frameworks

Recent progress about a novel organic–inorganic hybrid materials, namely cyclodextrins (CDs) modified/coated metal–organic frameworks (MOFs) is summarized by using a special categorization method focusing on the interactions between CDs and MOFs moieties, such as ligand–metal cations interactions, supramolecular interactions including host–guest interactions and hydrogen bonding, as well as covalent bonds. This review mainly focuses on the interactions between CDs and MOFs and the strategy of combining them together, diverse external stimuli responsiveness of CDs-modified/coated MOFs, as well as applications of these hybrid materials to drug delivery and release system, catalysis and detection materials. Additionally, due to the importance of investigating advanced chemical architectures and physiochemical properties of CDs-modified/coated MOFs, a separate section is involved in diverse characterization methods and instruments. Furthermore, this minireview also foresees future research directions in this rapidly developing field.

Syntheses of cucurbit[6]uril-based metal-organic rotaxane networks by the anion regulation strategy and their proton conduction properties

Two new cucurbit[6]uril (CB[6])-based metal-organic rotaxane networks (MORNs) were successfully obtained by tuning the coordination sphere of metal copper clusters. Compounds 1 and 2 exhibited relatively high proton conductivity at 85 °C and 97% relative humidity (RH), providing great promise for fuel cell electrolyte materials.

Syntheses and magnetic properties of high-dimensional cucurbit[6]uril-based metal-organic rotaxane frameworks

Three new high-dimensional cucurbit[6]-based metal-organic rotaxane frameworks [Co₂(PR43)(BDC)₂Cl₂]·4H₂O (1), [Co₂(PR43)(BTC)₂]·6H₂O (2) and [Co₂(PR43)(BPT)₂]·20H₂O (3) were obtained via the hydrothermal synthesis method. Compound 1 comprised a two-dimensional layered structure, while compounds 2 and 3 exhibited three-dimensional pillared structures. All the compounds showed good thermal stabilities. Furthermore, the magnetic properties of compounds 1-3 were also investigated in detail.

Cation-based Structural Tuning of Pyridine Dipyrrolate Cages and Morphological Control over Their Self-assembly

Different pyridine dipyrrolate cages including cage-based dimers and polymers may be fabricated in a controlled manner from the same two starting materials, namely, an angular ligand 1 and Zn(acac)₂, by changing the counter cation source. With tetrabutylammonium (TBA⁺) and dimethyl viologen (DMV²⁺), Cage-3 and Cage-5 are produced. In these cages, two ligands act as bridges and serve to connect together two cage subunits to produce higher order ensembles. In Cage-3 and Cage-5, the TBA⁺ and DMV²⁺ counter cations lie outside the cavities of the respective cages. This stands in contrast to what is seen with a previously reported system, Cage-1, wherein dimethylammonium (DMA⁺) counter cations reside within the cage cavity. When the counter cations are tetraethylammonium (TEA⁺) and bis(cyclopentadienyl) cobalt(III) (Cp₂Co⁺), polymeric cage materials, PC-1 and PC-2, are formed, respectively. The counter cations thus serve not only to balance charge but also to tune the structural features as a whole. The organic cations used in the present study also act to modulate the further assembly of individual cages. The present cation-based tuning emerges as a new method for a fine-tuning of the multidimensional morphology of self-assembled inorganic materials.

A fluorescent pillarene coordination polymer

A fluorescent pillarene-based coordination polymer was constructed from dicarboxylic acid-functionalized copillar[5]arene and Cr³⁺, for sensing of Fe³⁺, acetone, and nitrophenols.

Solvent-responsive cavitand lanthanum complex

A new, solvent responsive tetra-phosphonate cavitand lanthanum complex forms a dimer in acetonitrile, interconverts into a monomeric complex in acetone and is disassembled in methanol.