Thiacalixarene-based nanoscale polyhedral coordination cages

Thiacalixarene-supported M20V8 (M = Fe, Co, Ni) square pyramid nanocages for visible light photothermal catalysis

We rationally designed and synthesized a series of square pyramid nanocages (M20V8, M = Fe, Co, Ni) based on M4-TC4A (H4TC4A = p-tert-butylthiacalix[4]arene) polynuclear secondary building units (PSBUs) and vanadate anion units in {5+8} condensation modes. Among them, the Fe20V8 cage exhibited significant photothermal conversion efficiency (up to 80%) and photothermal catalytic performance for the oxidation desulfurization of thioether.

A [CuII24] truncated octahedron and its [CuII8] building block

Reaction of CuCl2·2H2O with p-tert-butylthiacalix[4]arene (H4TC[4]A) affords a [CuII24] cage whose metallic skeleton conforms to a truncated octahedron in which the metal ions are strongly antiferromagnetically coupled. A structurally related [CuII8] cluster can be made using CuBr2 in an otherwise identical reaction.

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.

Interplay between conformational flexibility, intermolecular H-bonding and 3d-metal cation extraction ability in a series of thiacalix[4]arene lower rim disubstituted Schiff base derivatives

The rational design of organic ligands with the aim to control their binding abilities towards different metal ions can be considered as one of the key concepts in supramolecular coordination chemistry. Regarding the macrocyclic compounds of thiacalix[4]arene family, this can be achieved via the targeted modulation of macrocyclic platform rigidity as well as the proper choice of appended binding sites. Four macrocyclic salen-type ligands based on lower rim disubstituted thiacalix[4]arene derivatives, adopted in a cone conformation, bearing highly coordinating iminophenolic or catecholic groups and two -CH2- moieties as spacers but presenting different abilities to form H-bonds, were chosen to elucidate the interplay between the conformational flexibility of the macrocyclic ligands, propensity to participate in the intermolecular H-bonding and the extraction ability of 3d-metal cations. X-ray diffraction analysis, theoretical DFT calculations, IR and Raman spectroscopies, and dynamic light scattering (DLS) studies performed in combination with liquid-liquid metal extraction study revealed that compounds 4, and 6, based on a thiacalix[4]arene macrocyclic platform, display a higher extraction ability towards all studied 3d-metal ions, caused by enhanced conformational flexibility. This is in good accordance with the ability of 6 to form H-bonded supramolecular assemblies in solution and crystalline phases due to recognition between the catecholic moieties.

Advancements in Atomically Precise Nanocluster Protected by Thiacalix[4]arene

Coinage metal nanoclusters (NCs), comprising a few to several hundred atoms, are prized for their size-dependent properties crucial in catalysis, sensing, and biomedicine. However, their practical application is often hindered by stability and reactivity challenges. Thiacalixarene, a macrocyclic ligand, shows promise in stabilizing silver, copper, and bimetallic NCs, enhancing their structural integrity and chemical stability. This investigation delves into the unique properties of thiacalix[4]arene and their role in bolstering NC stability, catalytic efficiency, and sensing capabilities. The current challenges and future prospects are critically evaluated, underscoring the transformative impact of thiacalix[4]arene in nanoscience. This review aims to broaden the utilization of atomically precise coinage metal NCs, unlocking new avenues across scientific and industrial applications.

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.

Three in One: Three Different Molybdates Trapped in a Thiacalix[4]arene Protected Ag72 Nanocluster for Structural Transformation and Photothermal Conversion

Polyoxometalates (POMs) represent crucial intermediates in the formation of insoluble metal oxides from soluble metal ions, however, the rapid hydrolysis-condensation kinetics of MoVI or WVI makes the direct characterization of coexisted molecular species in a given medium extremely difficult. Silver nanoclusters have shown versatile capacity to encapsulate diverse POMs, which provides an alternative scene to appreciate landscape of POMs in atomic precision. Here, we report a thiacalix[4]arene protected silver nanocluster (Ag72b) that simultaneously encapsulates three kinds of molybdates (MoO4 2- , Mo6 O22 8- and Mo7 O25 8- ) in situ transformed from classic Lindqvist Mo6 O19 2- , providing more deep understanding on the structural diversity and condensation growth route of POMs in solution. Ag72b is the first silver nanocluster trapping so many kinds of molybdates, which in turn exert collective template effect to aggregate silver atoms into a nanocluster. The post-reaction of Ag72b with AgOAc or PhCOOAg produces a discrete Ag24 nanocluster (Ag24a) or an Ag28 nanocluster based 1D chain structure (Ag28a), respectively. Moreover, the post-synthesized Ag28a can be utilized as potential ignition material for further application. This work not only provides an important model for unlocking dynamic features of POMs at atom-precise level but also pioneers a promising approach to synthesize silver nanoclusters from known to unknown.

Al12Co4: a pioneering heterometallic aluminum oxo cluster with surface-exposed Co sites for the oxygen evolution reaction

We report an unprecedented heterometallic aluminum oxo cluster (AlOC) containing four surface-exposed CoII sites, designated as Al12Co4, protected by four t-butylcalix[4]arene (TBC[4]) molecules. The Al12Co4 nanocluster represents a significant advancement on multiple innovative fronts. First, it stands as an pioneering example of an AlIII-based metallocalixarene nanocluster. It is also the first instance of heterometallic AlOCs shielded by macrocyclic ligands. Notably, this cluster also holds the distinction of being the highest nuclearity Al-Co bimetallic nanocluster known to date. Additionally, by depositing Al12Co4 on carbon nanotubes (CNTs) as a supported catalyst, we investigated its electrocatalytic performance for the oxygen evolution reaction in alkaline media. To reach a 10 mA cm-2 current density in alkaline solution, the Al12Co4@CNT electrode needs overpotential as low as 320 mV.

Dynamic Interconversion and Induced-Fit Guest Binding with Two Macrocycle-Based Coordination Cages

We report the syntheses and host-guest chemistry of two interconvertible coordination cages, Pd₂L₂ and Pd₁L₁, from a dynamic macrocycle ligand (L) and a cis-blocking (tmen)Pd(NO₃)₂ (tmen = tetramethylethylenediamine) unit (Pd). The water-soluble macrocyclic L, which can bind various polycyclic aromatic hydrocarbon (PAH) guests in its cis-conformation, was constructed via four pyridinium bonds between two 2,4,6-tri(4-pyridyl)-1,3,5-triazine [TPT] panels and two p-xylene bridges. We selectively formed each cage either by changing the reaction concentration/solvent/temperature or through induced-fit guest encapsulation, while direct assembly of L and Pd resulted in a mixture of Pd₂L₂ and Pd₁L₁ in equilibrium. X-ray structures of the free ligand and the host-guest complexes confirmed the induce-fit adaptive changes in the ligand's conformation and the cage's cavity. This work demonstrates a useful strategy for designing multistimuli-responsive supramolecular hosts by coordination self-assembly with macrocyclic ligands featuring rich conformational freedom.

Atomically accurate structural tailoring of thiacalix[4]arene-protected copper(II)-based metallamacrocycles

Accurate manipulation of ligands at specific sites in robust clusters is attractive but difficult, especially for those ligands that coordinate in intricate binding patterns. By linking the shuttlecock-like {Cu₄(μ₄-Cl)TC4A} motif and the phenylphosphate (PhPO₃^2-) ligand, we elaborately design and synthesize two Cu(II)-thiacalix[4]arene metallamacrocycles (MMCs), namely Cu₁₂L₃ and Cu₁₆L₄, which have regular triangular and quadrilateral topologies, respectively. While keeping the core intact, the Cl^- and PhPO₃^2- in those two MMCs, which coordinated in a μ₄-bridging fashion, can be accurately substituted with salicylate ligands. Theoretical calculations have been carried out to reveal the effect of ligand tailoring on the electronic structure of clusters. Structural regulation can affect the catalytic activity of these clusters, which has been verified by using the clusters as catalysts for selective sulfide oxidation.

Thiacalixarene Appended Azo-based Supramolecular Systems: Self-assembly and Photo Tuning Reversible Liquid Crystalline Properties

Four new azo-based supramolecular materials containing thiacalixarene core substituted by variable alkoxy groups (TFA₁ -TFA₄ ) have been designed and synthesized for the mesomorphic and photoswitching properties. The liquid crystalline behavior were accomplished by using DSC, POM, and XRD studies. All azo-based thiacalixarene based materials with short and higher chain length display columnar hexagonal mesophase with broad temperature range. The thermal behavior of all the materials was investigated by DSC and TGA study. The structural and conformational study of the lower rim functionalized materials was confirmed by using different techniques. These thiacalixarene moulded liquid crystalline compounds shows columnar self-assembly type behavior and higher thermal stability. The introduction of bi-substituted azo-ester network towards the lower rim of thiacalixarene core has impact on the electron delocalization and liquid crystalline properties. The photoswitching properties suggested cis and trans azo-isomerization under radiation of UV light and higher thermal back relaxation time. The mesogenic behaviour of compound TFA₂ and TFA₄ were demolished by the influence of cis and trans isomerization. The structure-property correlation is studied to understand the variation in mesogenic properties with the substitution of variable alkoxy side chain.

Platonic and Archimedean solids in discrete metal-containing clusters

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

Thiacalix[4]arene-Sandwiched Sandglass-like Ln9 Clusters (Ln = Tb and Eu): Insights into the Selective Luminescence Quenching Properties by p-Nitrobenzene Derivatives

Nonanuclear lanthanide clusters Ln₉ (Ln = Tb and Eu) based on p-tert-butylthiacalix[4]arene (H₄TC4A) have been synthesized by the solvothermal reaction and were structurally determined by single-crystal X-ray diffraction. The framework of Ln₉ can be termed as a sandglass-like structure whose two Ln₄-TC4A polynuclear secondary building units are bridged by one octa-coordinate {Ln(μ₃-O)₈} unit. Efficient TC4A-to-Ln energy transfer was observed for Tb₉ but not for Eu₉. The luminescence quantum yield (QY) of Tb₉ in the solid state at room temperature was determined to be 17.6%, while its highest QY in a methanolic solution (2 × 10^-5 mol/L) is 59.2% upon excitation at 318 nm. The luminescence of Tb₉ was quenched selectively by derivatives of p-nitrobenzene, as demonstrated by the results of photoluminescence and UV-vis titration experiments and supported by density functional theory calculations. We believe that the interactions between the analyte molecules and the pocket of Tb₉ are primarily responsible for the observed quenching. As such, this work represents one of the few examples of utilizing structurally interesting lanthanide cluster complexes as a sensory platform for the recognition of meaningful analytes and portends the further development of lanthanide-calixarene-complex-based functional materials.

Advances in the Electrocatalytic Hydrogen Evolution Reaction by Metal Nanoclusters-based Materials

With the development of renewable energy systems, clean hydrogen is burgeoning as an optimal alternative to fossil fuels, in which its application is promising to retarding the global energy and environmental crisis. The hydrogen evolution reaction (HER), capable of producing high-purity hydrogen rapidly in electrocatalytic water splitting, has received much attention. Abundant research about HER has been done, focusing on advanced electrocatalyst design with high efficiency and robust stability. As potential HER catalysts, metal nanoclusters (MNCs) have been studied extensively. They are composed of several to a hundred metal atoms, with sizes being comparable to the Fermi wavelength of electrons, that is, < 2.0 nm. Different from metal atoms/nanoparticles, they exhibit unique catalytic properties due to their quantum size effect and low-coordination environment. In this review, the activity-enhancing approaches of MNCs applied in HER electrocatalysis are mainly summarized. Furthermore, recent progress in MNCs classified with different stabilization strategies, that is, the freestanding MNCs, MNCs with organic, metal and carbon supports, are introduced. Finally, the current challenges and deficiencies of these MNCs for HER are prospected.

Ancillary ligand-regulated Ti(IV)-based metallocalixarene coordination cages for photocatalytic H2 evolution

High-valence Ti(IV)-based metallocalixarene coordination cages that are linked by oriented ancillary ligands are unknown so far. Herein, the first family of tunable calixarene-based coordination cages of Ti(IV) with a framework formula [Ti₁₂(OⁱPr)₁₂(TBC[4])₆L₆] have been assembled from six {Ti₂(OⁱPr)₂(TBC[4])}²⁺ nodes and six pyridinedicarboxylic ligands. Furthermore, the {Ti12L6} cage showed strong photocatalytic H₂ evolution activity, and DFT studies were performed to explore its electronic structure.

An ultrastable Ti-based metallocalixarene nanocage cluster with photocatalytic amine oxidation activity

Polyhedral metallocalixarene nanocage clusters based on pure Ti(IV) ions are to our knowledge unknown hitherto. Herein we report the first Ti(IV)-based metallocalixarene nanocage cluster by assembling a [Ti₁₃O₁₄] cage with six t-butylcalix[4]arene molecules. Notably, the cluster exhibits extraordinary stability in high-concentration acid/alkali solutions and can act as a stable photocatalyst to catalyze the oxidation of ammonia to imines.

Stepwise Assembly of Ag42 Nanocalices Based on a MoVI-Anchored Thiacalix[4]arene Metalloligand

Metalloligand strategy has been well recognized in the syntheses of heterometallic coordination polymers; however, such a strategy used in the assembly of silver nanoclusters is not broadly available. Herein, we report the stepwise syntheses of a family of halogen-templated Ag₄₂ nanoclusters (Ag42c-Ag42f) based on Mo^VI-anchored p-tert-butylthiacalix[4]arene (H₄TC4A) as a metalloligand (hereafter named MoO₃-TC4A). X-ray crystallography demonstrates that they are similar C₃-symmetric silver-organic nanocalices capped by six MoO₃-TC4A metalloligands, which are evenly distributed up and down the base of 42 silver atoms. These nanoclusters can be disassembled to six bowl-shaped [Ag₁₁(MoO₃-TC4A)(RS)₃] secondary building units (SBUs, R = Et or ⁿPr), which are fused together in a face-sharing fashion surrounding Cl^- or Br^- as a central anion template. The electrospray mass spectrometry (ESI-MS) indicates their high stabilities in solution and verifies the formation of the MoO₃-TC4A metalloligand, thereby rationalizing the overall stepwise assembly process for them. Moreover, Ag42c shows lower cytotoxicity and better activity against the HepG-2 cell line than MCF-7 and BGC-823. These results not only exemplify the effectiveness of a thiacalix[4]arene-based metalloligand in the assembly of silver nanoclusters but also give us profound insight about the step-by-step assembly process in silver nanoclusters.

A coordination cage hosting ultrafine and highly catalytically active gold nanoparticles

Ultrafine metal nanoparticles (MNPs) with size <2 nm are of great interest due to their superior catalytic capabilities. Herein, we report the size-controlled synthesis of gold nanoparticles (Au NPs) by using a thiacalixarene-based coordination cage CIAC-108 as a confined host or stabilizer. The Au NPs encapsulated within the cavity of CIAC-108 (Au@CIAC-108) show smaller size (∼1.3 nm) than the ones (∼4.7 nm) anchored on the surface of CIAC-108 (Au/CIAC-108). The cage-embedded Au NPs can be used as a homogeneous catalyst in a mixture of methanol and dichloromethane while as a heterogeneous catalyst in methanol. The homogeneous catalyst Au@CIAC-108-homo exhibits significantly enhanced catalytic activities toward nitroarene reduction and organic dye decomposition, as compared with its larger counterpart Au/CIAC-108-homo and its heterogeneous counterpart Au@CIAC-108-hetero. More importantly, the as-prepared Au@CIAC-108-homo possesses remarkable stability and durability.

The size-controlled synthesis of Au NPs was achieved by using a coordination cage CIAC-108 as a support. The Au NPs encapsulated within the cavity of CIAC-108 show smaller size (∼1.3 nm) than the ones (∼4.7 nm) anchored on the surface of CIAC-108.

Porous nickel and cobalt hexanuclear ring-like clusters built from two different kind of calixarene ligands – new molecular traps for small volatile molecules

The formation and structural analysis of porous hexanuclear ring-like cluster complexes built from two different kind of calixarene ligands is presented, together with their stability and vapor solvent sorption properties.

Impact of flexible succinate connectors on the formation of tetrasulfonylcalix[4]arene based nano-sized polynuclear cages: structural diversity and induced chirality study

The formation of three types of supramolecular coordination cages is described. Tetrasulfonylcalixarene, combined with metallic salts (Ni, Co and Zn) and the flexible succinate ligand, led to cages. H bonded induced chirality was observed for both isomorphous cages.

Assembly of cobalt-p-sulfonatothiacalix[4]arene frameworks with phosphate, phosphite and phenylphosphonate ligands

Three cobalt-calixarene coordination frameworks, namely, {[Co4Cl(H4TC4AS)]4(HPO3)8}4− (CIAC-253), {[Co4Cl(H4TC4AS)]4(PO4)8}12− (CIAC-254) and {[Co4Cl(H4TC4AS)]3(Ph-PO3)6}3− (CIAC-255) were obtained by solvothermal reaction of a cobalt salt, sodium p-sulfonatothiacalix[4]arene (Na4H4TC4AS) and phosphate, phosphite and phosphonate ligands. In CIAC-253 and CIAC-254, the shuttlecock-like Co4Cl-(TC4AS) secondary building units (SBUs) are bridged by HPO3 2− or PO4 3− anions into two quadrilateral frameworks while in CIAC-255, the Co4Cl-(TC4AS) SBUs are linked into a triangular framework by phenylphosphonate anions. The supramolecular interactions between the phenyl groups of phosphonate and TC4AS play a crucial role in the formation of the triangle. Magnetic measurements revealed that all the cobalt(II) centers exhibit antiferromagnetic interactions.

Fascinating interlocked triacontanuclear giant nanocages

We report herein three air, thermal and solvent stable interlocked triacontanuclear giant nanocages, generated using a node and spacer concept. Interestingly, the crystal structures of the cages are not only nano-dimensional but also exist in the nano-dimension range, which was corroborated with microscopic images. The combination of microscopic and crystallographic data, in effect, led us to a unique advantageous situation of generating nanomaterials with hard-to-come-by structural information at the molecular level.

Functional supramolecular systems: design and applications

The interest in functional supramolecular systems for the design of innovative materials and technologies, able to fundamentally change the world, is growing at a high pace. The huge array of publications that appeared in recent years in the global literature calls for systematization of the structural trends inherent in the formation of these systems revealed at different molecular platforms and practically useful properties they exhibit. The attention is concentrated on the topics related to functional supramolecular systems that are actively explored in institutes and universities of Russia in the last 10–15 years, such as the chemistry of host–guest complexes, crystal engineering, self-assembly and self-organization in solutions and at interfaces, biomimetics and molecular machines and devices.

The bibliography includes 1714 references.

Synthesis of Azacalixarenes and Development of Their Properties

This review focuses on the synthesis, structure, and interactions of metal ions, the detection of some weak interactions using the structure, and the construction of supramolecules of azacalixarenes that have been reported to date. Azacalixarenes are characterized by the presence of shallow or deep cavities, the simultaneous presence of a basic nitrogen atom and an acidic phenolic hydroxyl group, and the ability to introduce various side chains into the cyclic skeleton. These molecules can be given many functions by substituting groups on the benzene ring, modifying phenolic hydroxyl groups, and converting side chains. The author discusses the evidence of azacalixarene utilizing these characteristics.

Decahexanuclear Zinc(II) Coordination Container Featuring a Flexible Tetracarboxylate Ligand: A Self-Assembly Supermolecule for Highly Efficient Drug Delivery of Anti-Inflammatory Agents

The application of a coordination container in biomedicine is hindered by single binding domains and unsatisfactory biostability and biocompatibility. Herein, we designed a sulfonylcalix[4]arene-based decahexanuclear zinc(II) coordination container employing a flexible tetracarboxylate ligand as a linker and utilized it as a novel drug delivery system. The coordination container consisting of one endo and four exo cavities provides multiple binding domains for efficient encapsulation of drug molecules as clearly revealed by systematic host-guest studies using NMR techniques of ¹H NMR titration experiments and 2D NOESY and diffusion-ordered NMR spectroscopy studies. Incorporation of a flexible p-phenylene-bis(methanamino) spacer into the container via the carboxylate linker allowed a stepwise drug loading process through sequential binding at endo and exo cavities, as well as enabling pH-responsive stepwise drug release. The drug-loaded coordination container not only exhibits excellent biostability and biocompatibility but also provides encouraging therapeutic efficiency toward inflammatory macrophages as revealed by in vitro studies. The novel strategy for engineering the endo cavity of a coordination container provides a new approach to achieving controlled drug delivery and opens up new opportunities for designing novel functional supramolecular materials.

Co9 S8 @CN Composites Obtained from Thiacalix[4]arene-Based Coordination Polymers for Supercapacitor Applications

Metal sulfides have been recognized as promising electrodes for electrochemical energy storage owing to their remarkable electrochemical properties. Here, we demonstrate the preparation of Co₉ S₈ nanoparticles anchored on a carbon matrix (denoted as Co₉ S₈ -X@CN (X=1, 2)) from precursor sources, two 1D infinite coordination polymers 1 and 2. The two polymers were assembled by linking Co₄ -TC4A secondary building blocks (SBUs) with ligands L₁ and L₂ , respectively (H₄ TC4A=p-tert-butylthiacalix[4]arene, L₁ =1,4-bis(2H-tetrazol-5-yl)benzene, L₂ =1,3-bis(2H-tetrazol-5-yl)benzene). The composites obtained from 1D polymers showed different morphologies, that is, the Co₉ S₈ nanoparticles of Co₉ S₈ -1@CN are octahedral with a size of ca. 140 nm, while the lamellar Co₉ S₈ nanoparticles in Co₉ S₈ -2@CN possess different sizes (50-150 nm). The Co₉ S₈ -2@CN immobilized on nickel foam (Co₉ S₈ -2@CN/NF) show better supercapacitive performance than that of Co₉ S₈ -1@CN. Co₉ S₈ -2@CN showed exceptionally high activities, combining higher specific capacitances (445.2 F g^-1 at 2 A g^-1 and 393.9 F g^-1 and 5 A g^-1 ), rate capacity (94.5% retention at 2 A g^-1 ), and long-term stability (79.2% retention at 5 A g^-1 over 1000 cycles). The smaller size and larger BET surface area of Co₉ S₈ -2@CN nanoparticles can improve the electrical conductivity and provide facile pathways for charge transport, thus leading to conspicuous electrochemical performance of Co₉ S₈ -2@CN compared with its Co₉ S₈ -1@CN counterpart.

A novel series of giant cobalt-calixarene macrocycles: ring-expansion and modulation of pore apertures through recrystallization

The design and synthesis of metallomacrocycles can be quite challenging because the assemblies of such molecular cycles are difficult to control and the products are usually unpredictable. In this work, a novel series of metallomacrocycles, denoted as {Co30-A}, {Co30-B} and {Co32-A} have been synthesized via self-assembly of p-tert-butylthiacalix[4]arene (H4TC4A) and 3,5-pyrazoledicarboxylic acid (H3pdc) with Co2+ ions under solvothermal conditions. Recrystallization of {Co32-A} under different conditions was found to form {Co32-B} and {Co32-C} that have a similar ring structure to that of {Co32-A} but have different molecular packing modes in the lattices, as well as a 40-membered ring {Co40}. These complexes represent the highest-nuclearity metallocalixarene coordination wheels reported to date. Crystallographic studies indicate that all these metallomacrocycles feature wheel-like structures with apertures varing from 11.4 to 20.3 Å. It is noteworthy that {Co32-A} exhibited good efficiency in removing RhB even at low initial concentration (10 ppm) and also excellent adsorption selectivity towards RhB over Na2Fl (RhB = Rhodamine B, Na2Fl = disodium fluorescein). This work not only makes a breakthrough in the synthesis of metallocalixarene macrocycles with high nuclearity and large apertures, but also provides a simple recrystallization approach to realize the ring-expansion and regulation of molecular packing modes of the metallomacrocycles.

Calixarene-Protected Titanium-Oxo Clusters and Their Photocurrent Responses and Photocatalytic Performances

Three photosensitive tert-butylcalix[n]arene (TBC[n], n = 4, 6, 8)-protected titanium-oxo clusters (TOCs), formulated as [Ti₄(μ₃-O)₂(TBC[4])₂(OⁱPr)₄(DEF)₂]·DEF (1, TBC[4]-Ti₄, DEF = N,N-diethylformamide), [Ti₄(μ₄-O)TBC[6](OCH₃)₉]·H₂O (2, TBC[6]-Ti₄), and [Ti₄(μ₃-O)₂(OⁱPr)₄TBC[8](DEF)₂]·DEF (3, TBC[8]-Ti₄), were successfully synthesized and characterized. Because of the generation of charge transfer from TBC[n] to the TiO core, the three TBC[n]-decorated TOCs show a broadened visible-light absorption and narrowed optical band gap based on the UV-visible spectra and density functional theory calculations. The corresponding photosensitive electrodes prepared using these three TOCs exhibit stable photocurrent responses. Furthermore, their photocatalytic performances for hydrogen evolution and methylene blue degradation were evaluated, and all of the materials display excellent photocatalytic activity and stability. The calixarene-Ti coordination is therefore an effective strategy to enlarge the visible-light absorption band of Ti-O materials and improve their photoelectric/photocatalytic performances.

Thiacalix[4]arene-supported molecular clusters for catalytic applications

Thiacalixarenes are intriguing ligands that have attracted sustained interest because of their changeable conformations and excellent coordination ability. Thiacalix[4]arene analogues, which can bind metal ions to form modular second building units, are capable of constructing molecular-based functional materials with defined structures and various applications via directional coordination assembly. Due to rich metal-sulfur bonds, thiacalix[4]arene-based molecular clusters also exhibit diverse properties compared to other clusters. In particular, the combination of thiacalixarenes with currently popular molecular architectures, such as high-nuclearity clusters and coordination cages, has shown special catalytic performances. In this perspective, the latest advances in catalytic applications of thiacalix[4]arene-based molecular clusters, including molecular clusters themselves as catalysts and coordination cages serving as reaction vessels encapsulating metal nano-components for catalysis, are highlighted.

Assembly of {Co14} nanoclusters from adenine-modified Co4-thiacalix[4]arene units

An adenine-modified Co₄-thiacalix[4]arene unit can serve as a second building unit for fabrication of three Co₁₄ clusters with different structures.

Coordination-Assembled Molecular Cages with Metal Cluster Nodes

Molecular cages have attracted great attention because of their fascinating topological structures and well-defined functional cavities. These discrete cages were usually fabricated by coordination assembly approach, a process employing directional metal-ligand coordination bonds due to the nature of the divinable coordination geometry and the required lability to encode dynamic equilibrium/error-correction. Compared to these coordination molecular cages with mononulcear metal-nodes, an increasing number of molecular cages featuring dinuclear and then polynuclear metal-cluster nodes have been synthesized. These metal-cluster-based coordination cages (MCCCs) combine the merits of both metal clusters and the cage structure, and exhibit excellent performances in catalysis, separation, host-guest chemistry and so on. In this review, we highlight the syntheses of MCCCs and their potential functions that is donated by the metal-cluster nodes.

Monocarboxylate-driven structural growth in Calix[n]arene-polyoxotitanate hybrid systems: utility in hydrogen production from water

A carboxylate-driven assembly strategy has been developed for the first time to build calix[n]arene-based polyoxotitanate clusters with tuneable nuclearity and structures. Photocatalytic studies revealed that these clusters exhibit structural-dependent H₂ evolution ability with a maximum rate up to 415.11 μmol h^-1 g^-1, which is almost the highest recorded in polyoxotitanate clusters.

Cooperative Binding and Stepwise Encapsulation of Drug Molecules by Sulfonylcalixarene-Based Metal-Organic Supercontainers

The cooperative binding behavior of a face-directed octahedral metal-organic supercontainer featuring one endo cavity and six exo cavities was thoroughly examined in chloroform solution through ultraviolet-visible (UV-Vis) titration technique using two representative drug molecules as the guests. The titration curves and their nonlinear fit to Hill equation strongly suggest the efficient encapsulation of the guest molecules by the synthetic host, which exhibit interesting cooperative and stepwise binding behavior. Based on the control experiments using tetranuclear complex as a reference, it is clear that two equivalents of the guest molecules are initially encapsulated inside the endo cavity, followed by the trapping of six additional equivalents of the drug molecules through six exo cavities (1 eq. per exo cavity), and the remaining guests are entrapped by the external pockets. The results provide an in-depth understanding of the cooperative binding behavior of metal-organic supercontainers, which opens up new opportunities for designing synthetic receptors for truly biomimetic functional applications.

Formation of Unsymmetrical Trinuclear Metallamacrocycles Based on Two Different Cone Calix[4]arene Macrocyclic Rings

A combination of tetrasulfonylcalix[4]arene (3-4H) together with a calix[4]arene dicarboxylate derivative 2-4H led, in the presence of MII(NO3)2 (M = Co, Ni, Zn), to the formation of three novel isostructural metallomacrocycles of formula [M3(DMF)2(μ3-H2O)-(2-2H)-3]. The structure of the prepared coordination compounds was studied in the solid state using single crystal/powder X-ray diffraction studies. The X-ray diffraction on single crystal revealed that the structure of the obtained supramolecular complexes is composed of a trinuclear metallic cluster [M3]+6 held between one di-deprotonated molecule of (2-2H)2− offering two carboxylate groups for binding metal cations and one tetra-deprotonated compound 34−, where four oxygen atoms, belonging to four deprotonated phenolic moieties and three oxygen atoms coming from three SO2 groups, are coordinated with the cluster core. Thus, an example of an easily reproducible molecular recognition pattern involving two different types of calix[4]arene based ligands, displaying different coordination moieties, and trinuclear metallic clusters, is reported here. In addition, it has been shown that the cone moieties of the calixarene also encapsulate solvent molecules.

A Brucite-Like Mixed-Valent Cluster Capped by [MnIIIp-tBu-calix[4]arene]− Moieties

p-tBu-calix[4]arene (H4TBC[4]) has proven to be an incredibly versatile ligand for the synthesis of 3d- and 3d/4f- clusters, in particular those containing mixed-valent Mn ions. These are of interest to the magnetochemist for the diversity of magnetic behaviours that can be shown, along with a huge variety of nuclearities and topologies accessible, which allow one to outline magneto-structural correlations and a quantitative understanding of their properties. This contribution reports the synthesis, analysis and magnetic properties of a Brucite-like Mn-oxo/hydroxo octanuclear fragment encapsulated within/capped by four [MnIII-TBC[4]]− moieties. A diol coligand in the reaction mixture plays a seemingly important role in determining the outcome, though it is not incorporated in the final structure.

Mixed Tb/Dy coordination ladders based on tetra(carboxymethyl)thiacalix[4]arene: a new avenue towards luminescent molecular nanomagnets

The macrocyclic ligand calix[4]arene (L1) and its sulphur-containing analogue thia[4]calixarene (L2) are promising precursors for functional molecular materials as they offer rational functionalization with various organic groups. Here, we present the first example of lanthanide-based coordination polymers built from the macrocyclic thiacalix[4]arene backbone bearing four carboxylic moieties, namely, ligand H₄L3. The combination of H₄L3 with the Tb³⁺ and Dy³⁺ cations led to the formation of 1D ladder-type coordination polymers with the formula [Ln^IIIHL3DMF₃]·(DMF) (where DMF = dimethylformamide and Ln = Tb or Dy, denoted as HL3–Tb and HL3–Dy), which resulted from the coordination of the lanthanide cations with the partially deprotonated ligand HL3³⁻ that behaved as a T-shape connector. The coordination sphere around the metal was completed by the coordinated DMF solvent molecules. By combining both Tb³⁺ and Dy³⁺ cations, isostructural heterobimetallic solid solutions HL3–Tb_1−xDy_x were also prepared. HL3–Tb and HL3–Dy showed visible light photoluminescence originating from the f–f electronic transitions of pale green emissive Tb³⁺ and pale yellow emissive Dy³⁺ with efficient sensitization by the functionalized thia[4]calixarene ligand HL3. In the HL3–Tb_1−xDy_x solid solutions, the Tb/Dy ratio governed both the emission colour as well as the emission quantum yield, which reached even 28% at room temperature for HL3–Tb. Moreover, HL3–Dy exhibited a slow magnetic relaxation effect related to the magnetic anisotropy of the dodecahedral Dy³⁺ complexes, which were well isolated in the crystal lattice by expanded organic spacers.

The single crystals of the two isostructural Tb³⁺- and Dy³⁺-based coordination polymers (HL3–Tb and HL3–Dy) were structurally characterized, and their photophysical properties were investigated, together with their corresponding solid solutions.

Mercaptothiacalixarenes Steer 24 Copper(I) Centers to form a Hollow-Sphere Structure Featuring Cu2 S2 Motifs with Exceptionally Short Cu⋅⋅⋅Cu Distances

Tetramercaptotetrathiacalix[4]arene (LH₄) can be used as a coordination platform to bind four Cu^I ions at the thiolate and thioether S atoms. Donor ligands such as phosphanes can stabilize the resulting [LCu₄] units, which then remain monomeric ([(Ph₃PCu)₄L]). In the absence of donor ligands, they aggregate, providing a hexamer ([LCu₄]₆) in high yields, with a hollow‐sphere structure formed by an unprecedented Cu₂₄S₄₈ cage that is surrounded by the organic framework of the calixarene chalices. Preliminary NMR experiments with regard to the host‐guest chemistry in solution showed that the compound represents a polytopic host for acetonitrile and methane.