Interconvertible vanadium-seamed hexameric pyrogallol[4]arene nanocapsules

Two High-Nuclear Wheel-Hub-Shaped Transition-Metal-Doped Polyoxovanadates

The first two unprecedented high-nuclear wheel-hub-shaped transition-metal-doped polyoxovanadates, [M8Mo4W4V20P20] [M = Ni (1), Co (2)], have been assembled under solvothermal conditions. The center of the cluster consists of two {Ni4(oa)4} rings as the center hole, four {MoO4} units acting as the spokes, and four {WV5(PPOA)5} molecular building blocks serving as the tire. Compound 1 exhibits good catalytic properties and recyclability in oxidative desulfurization reactions.

54 K Spin Transition Temperature Shift in a Fe6L4 Octahedral Cage Induced by Optimal Fitted Multiple Guests

Spin-crossover (SCO) coordination cages are at the forefront of research for their potential in crafting next-generation molecular devices. However, due to the scarcity of SCO hosts and their own limited cavities, the interplay between the SCO host and the multiple guests binding has remained elusive. In this contribution, we present a family of pseudo-octahedral coordination cages (M6L4, M = ZnII, CoII, FeII, and NiII) assembled from a tritopic tridentate ligand L with metal ions. The utilization of FeII ion leads to the successful creation of the Fe6L4-type SCO cage. Host-guest studies of these M6L4 cages reveal their capacity to encapsulate four adamantine-based guests. Notably, the spin transition temperature T1/2 of Fe6L4 is dependent on the multiple guests encapsulated. The inclusion of adamantine yields an unprecedented T1/2 shift of 54 K, a record shift in guest-mediated SCO coordination cages to date. This drastic shift is ascribed to the synergistic effect of multiple guests coupled with their optimal fit within the host. Through a straightforward thermodynamic cycle, the binding affinities of the high-spin (HS) and low-spin (LS) states are separated from their apparent binding constant. This result indicates that the LS state has a stronger binding affinity for the multiple guests than the HS state. Exploring the SCO thermodynamics of host-guest complexes allows us to examine the optimal fit of multiple guests to the host cavity. This study reveals that the T1/2 of the SCO host can be manipulated by the encapsulation of multiple guests, and the SCO cage is an ideal candidate for determining the multiple guest fit.

Calix[4]arene-Derived 2D Covalent Organic Framework with an Electron Donor-Acceptor Structure: A Visible-Light-Driven Photocatalyst

The calixarenes are ideal building blocks for constructing photocatalytic covalent organic frameworks (COFs), owing to their electron-rich and bowl-shaped π cavities that endow them with electron-donating and adsorption properties. However, the synthesis and structural confirmation of COFs based on calixarenes are still challenging due to their structural flexibility and conformational diversity. In this study, a calix[4]arene-derived 2D COF is synthesized using 5,11,17,23-tetrakis(p-formyl)-25,26,27,28-tetrahydroxycalix[4]arene (CHO-C4A) as the electron donor and 4,7-bis(4-aminophenyl)-2,1,3-benzothiadiazole (BTD) as the acceptor. The powder X-ray diffraction data and theoretical simulation of crystal structure indicate that COF-C4A-BTD exhibits high crystallinity and features a non-interpenetrating undulating 2D layered structure with AA-stacking. The density functional theory theoretical calculation, transient-state photocurrent tests, and electrochemical impedance spectroscopy confirm the intramolecular charge transfer behavior of COF-C4A-BTD with a donor-acceptor structure, leading to its superior visible-light-driven photocatalytic activity. COF-C4A-BTD exhibits a narrow band gap of 1.99 eV and a conduction band energy of -0.37 V versus normal hydrogen electrode. The appropriate energy band structure can facilitate the participation of ·O2- and h+ . COF-C4A-BTD demonstrates high efficacy in removing organic pollutants, such as bisphenol A, rhodamine B, and methylene blue, with removal rates of 66%, 85%, and 99% respectively.

Synthesis and Structure of High-Nuclearity Carboxylate-Modified Heteropolyoxovanadate Serving as a Heterogeneous Catalyst for Selective Oxidation of Alkylbenzenes

A high-nuclearity carboxylic-modified heteropolyoxovanadate, Na2K10H15[P8VIV24(tart)15(H2O)15(OH)O51]·58H2O [1, tart = C4H2O6], has been successfully synthesized by a conventional aqueous method under mild conditions. The crystallographic study reveals that compound 1 crystallizes in the tetragonal I41/a space group and is composed by a trilayer saddle-like polyoxoanion {P8V24}. Two {V3(tart)(H2O)O11} as linking units bridge the top {P4VIV9(tart)7(H2O)4(OH)O23} and the bottom {P4VIV9(tart)6(H2O)9O22} layers via tartrate ligands and {PO4} tetrahedra, resulting in a 24-nuclearity POV skeleton structure. More interestingly, compound 1 serves as a heterogeneous catalyst for the selective oxidation of diphenylmethanes with 96.2% conversion and 93.6% selectivity under the optimized conditions.

Redox-Controlled Self-Assembly of Vanadium-Seamed Hexameric Pyrogallol[4]Arene Nanocapsules

Here we report the controlled self-assembly of vanadium-seamed metal-organic nanocapsules with specific metal oxidation state distributions. Three supramolecular assemblies composed of the same numbers of components including 24 metal centers and six pyrogallol[4]arene ligands were constructed: a VIII24L6 capsule, a mixed-valence VIII18VIV6L6 capsule, and a VIV24L6 capsule. Crystallographic studies of the new capsules reveal their remarkable structural complexity and geometries, while marked differences in metal oxidation state distribution greatly affect the photoelectric conversion properties of these assemblies. This work therefore represents a significant step forward in the construction of intricate metal-organic architectures with tailored structure and functionality.

Nanocapsules of unprecedented internal volume seamed by calcium ions

The inception of an unprecedented class of voluminous Platonic solids displaying hierarchical geometry based on pyrogallol[4]arene moieties seamed by divalent calcium ion is described. Single-crystal X-ray structural determination has established the highly conserved geometry of two original Ca2+-seamed nanocapsules to be essentially cubic in shape with C-ethylpyrogallol[4]arene units located along the twelve edges of the cube which are then bridged by metallic polyatomic cations ([Ca4Cl]7+ or [Ca(HCO2)Na4]5+) at the six cube faces. The accessible volume of the nanocapsules is ca. 3500 Å3 and 2500 Å3 and is completely isolated from the exterior of the capsules. These remarkable nanocapsule discoveries cast a spotlight on a marginalized area of synthetic materials chemistry and encourage future exploration of diversiform supramolecular assemblies, networks, and capsules built on calcium, with clear benefits deriving from the intrinsic biocompatibility of calcium. Finally, a proof-of-concept is demonstrated for fluorescent reporter encapsulation and sustained release from the calcium-seamed nanocapsules, suggesting their potential as delivery vehicles for drugs, nutrients, preservatives, or antioxidants.

Photo- and Temperature-Induced Reversible Structural Transformation between Dodecanuclear and Pentadecanuclear Gold(I) Sulfido Complexes

Stimuli-responsive structural transformation has attracted much attention for its potential to mimic the behavior of biological transformations and functions. Here, two unprecedented dodecanuclear and pentadecanuclear gold(I) sulfido clusters (denoted trans-Au₁₂ and trans-Au₁₅, respectively) with impressive stimuli-responsive interconversion have been obtained by taking advantage of the judiciously designed tridentate phosphine ligand L_trans as the building block. Both UV light and temperature can be applied to trigger the structural conversions between trans-Au₁₂ and trans-Au₁₅. In addition, NMR, high-resolution electrospray ionization mass spectrometry, and UV-vis absorption spectroscopy have been employed to monitor the transformation process and decipher the mechanism of structural conversion. This work not only provides a paradigm to investigate photo-induced cluster-to-cluster transformation based on polydentate phosphine ligands but also offers a new direction for the construction of the stimuli-responsive materials.

Solvato-Controlled Assembly and Structural Transformation of Emissive Poly-NHC-Based Organometallic Cages and Their Applications in Amino Acid Sensing and Fluorescence Imaging

Stimuli-induced structural transformation of supramolecular cages has drawn increasing attention because of their sensitive feature to external variations as model systems to simulate biological processes. However, combining structural transformation and useful functions has remained a difficult task. This study reports the solvato-controlled self-assembly of two unique topologies with different emission characteristics, a water-soluble Ag₈ L₄ cage (A) and an Ag₄ L₂ cage (B), produced from the same sulfonate-pendant tetraphenylethene (TPE) bridged tetrakis-(1,2,4-triazolium) ligand. Both cages show interesting solvent-responsive reversible structural transformation, and the change of fluorescence signals can efficiently track the process. Additionally, water-soluble cage A exhibits unique properties in thermochromism, thiol amino acid sensing, and subcellular imaging in aqueous media.

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.

Breathable, Moisturizing, Anti-Oxidation SSD-PG-PVA/KGM Fibrous Membranes for Accelerating Diabetic Wound Tissue Regeneration

Diabetic wound tissue repair and regeneration is a multi-step process that includes cell proliferation and migration, gas and moisture management, and inflammatory responses. However, current wound dressing designs lack consideration of the wound microenvironment of diabetic patients, making diabetic wound tissue repair a challenge. Here, we report a wound dressing (SSD-PG-PVA/KGM) with a porous structure and anti-oxidant properties for promoting diabetic wound tissue repair. First, the porous structure created by electrospinning technology encourages cell proliferation and migration in the wound while also providing breathability and moisture retention. Second, adding natural polyphenols (PG) and saikosaponins (SSDs) to the wound reduced reactive oxygen species levels and oxide stress. In vitro cell experiments showed that SSD-PG-PVA/KGM had good biocompatibility. Due to the biocompatibility, anti-oxidation ability, breathability, and moisturizing, SSD-PG-PVA/KGM could effectively promote the repair of diabetic wound tissue (the wound closure rate was 95.6% at 14 days).

Face-Directed Construction of a Metal-Organic Isohedral Tetrahedron for the Highly Efficient Capture of Environmentally Toxic Oxoanions and Iodine

Geometric analysis has been guiding the design and construction of metal-organic polyhedra. Here, a series of isohedral tetrahedra ZrIT-1 and -2 and VIT-1 and -2 were synthesized by a one-pot method relying on trivalent molecular building blocks. Structural analysis shows that the isohedral tetrahedra constructed with {V₆(SO₄)(CO₂)₃} have three different sets of prism lengths, while those constructed with {Zr₃O(CO₂)₃} have two different sets of prism lengths. Comparison of two types of polyhedra reveals that the different sizes and coordination flexibilities of the two MBBs result in different cavity volumes. The environmentally toxic oxoanion trapping ability of ZrIT-1 was explored due to its structural stability and cation cage properties. The results show that ZrIT-1 can capture permanganate and dichromate anions in water with high efficiency and selectivity. Notably, the permanganate adsorption capacity can reach ∼276.6 mg/g, which exceeds those of most metal-organic framework materials. In addition, the adsorption and desorption of iodine showed that ZrIT-1 has a reversible adsorption capacity for iodine.

Stimuli-Responsive and Structure-Adaptive Three-Dimensional Gold(I) Cluster Cages Constructed via "De-aurophilic" Interaction Strategy

Self-assembly of three-dimensional (3D) metallosupramolecular cages has drawn increasing attention for their potential to interconvert between different architectures due to the dynamic and reversible features of the coordination bond. These supramolecular transformations can provide unique approaches for the construction of stimuli-responsive supramolecular model systems to mimic biological transformation processes. While gold(I) clusters have attracted much interest due to their propensity to exhibit aurophilic interactions, the construction of 3D gold(I) cluster cages has remained a challenging and daunting task. Here, we proposed a "de-aurophilic" interaction strategy, which involves the prevention of aurophilic interaction formation between the basic [(μ₃-S)Au₃]⁺ units, to construct 3D gold(I) cluster cages. Through the judicious design of diphosphine ligands, an unprecedented class of gold(I) cluster cages with adaptive structures has been constructed. These gold(I) cluster cages are found to show intriguing stimuli-responsive structure transformation and interconversion. This work not only provides a strategy for the design and construction of novel 3D supramolecular cages based on cluster nodes but also offers a paradigm to study the stimuli-responsive structural interconversion between the unique structures of these gold(I) cluster cages.

Structural Chemistry of Giant Metal Based Supramolecules

The review presents a bird-eye view on the state of research in the field of giant nonbiological discrete metal complexes and ions of nanometer size, which are structurally characterized by means of single-crystal X-ray diffraction, using the crystal structure as a common key feature. The discussion is focused on the main structural features of the metal clusters, the clusters containing compact metal oxide/hydroxide/chalcogenide core, ligand-based metal-organic cages, and supramolecules as well as on the aspects related to the packing of the molecules or ions in the crystal and the methodological aspects of the single-crystal neutron and X-ray diffraction of these compounds.

A tris-oxovanadium pyrogallate complex: synthesis, structure, and magnetic and electronic properties

With the aim of identifying new cation-phenolate complexes, we herein investigated the reactivity of pyrogallol (H₃pgal) with vanadium salts. A trimetallic anionic complex was identified, and found to be formed under a broad set of reaction conditions. This complex, with the formula V₃O₃(pgal)₃^3-, consists of three oxovanadium(IV) units connected together by three pyrogallate ligands to afford a bowl-shaped species presenting a pseudo 3-fold symmetry axis. Its crystal structure is reported, as well as its characterisation by a broad set of techniques, including powder X-ray diffraction, thermogravimetric analysis, infrared and Raman spectroscopy, and solid state UV-visible diffuse reflectance. Its redox activity both in solution and in the solid state is described, together with its magnetic behavior. Finally, the relevance of this trimetallic unit in the field of phenolic-based biocoatings and Metal Organic Framework (MOF) synthesis is briefly discussed.

Coordination Polymers Constructed from Pyrogallol[4]arene-Assembled Metal-Organic Nanocapsules

Coordination polymers, commonly known as infinite crystalline lattices, are versatile networks and have diverse potential applications in the fields of gas storage, molecular separation, catalysis, optics, and drug delivery, among other areas. Secondary building blocks, mainly incorporating rigid polydentate organic linkers and metal ions or clusters, are commonly employed to construct coordination polymers. Recently, novel building blocks such as coordination polyhedra have been utilized as metal nodes to fabricate coordination polymers. Benefiting from the rigid porous structure of the coordination polyhedron, prefabricated designer "pores" can be incorporated in this type of coordinate polymer. In this Account, coordination polymers built by pyrogallol[4]arene-assembled metal-organic nanocapsules are summarized. This class of metal-organic nanocapsule possesses the following advantages that make them excellent candidates in the construction of coordination polymers: (i) Various geometrical shapes with different volumes of the inner cavities can be obtained from these capsules. Among them, the two main categories illustrated are dimeric and hexameric capsules, which comprise two and six pyrogallol[4]arenes units, respectively. (ii) A wide range of possible metal ions ranging from main group metals to transition metals and even lanthanides have been demonstrated to seam the capsules. Therefore, these coordination polymers can be endowed with fascinating functionalities such as magnetism, semiconductivity, luminescence, and radioactivity. (iii) Up to 24 metal ions have been successfully embedded on the surface of the nanocapsule, each a potential reaction site in the construction of coordination polymers, opening up pathways for the formation of multidimensional frameworks.In this Account, we focus primarily on the synthesis and the structural information on pyrogallol[4]arene-derived coordination polymers. Coordination polymers can be formed by introducing linkers with two coordination sites, using pyrogallol[4]arenes with coordination sites on the tail, or even via metal ions cross-linking with each other. Machine learning was recently developed to help us predict and screen the structures of the coordination polymers. With single crystal analysis in hand, detailed structural information provides a molecular-level perspective. Significantly, following the formation of coordination polymers, the overall shape and structure of the discrete metal-organic nanocapsules remains essentially unchanged, with full retention of the prefabricated pores. If a rigid linker is used to connect capsules, more than one lattice void with different volumes can be found within the framework. Thus, molecules with different sizes could potentially be encapsulated within these coordination polymers. In addition, flexible ligands can also be employed as linkers. For example, polymers have been employed as large linkers that transform the crystalline coordination polymers into polymer matrices, paving the way toward the synthesis of advanced functional materials. Overall, coordination polymers constructed with pyrogallol[4]arene-assembled metal-organic nanocapsules show wide diversity and tunability in structure and fascinating properties, as well as the promise of built-in functionality in the future.

Two new calix[4]resorcinarene-based coordination cages adjusted by metal ions for the Knoevenagel condensation reaction

Two new calix[4]resorcinarene-based coordination cages, namely, [Zn4(TPC4R)(PDC)4]·2DMF·6H2O (1-Zn) and [In11(TPC4R)2(PDC)16(μ2-OH)2(H2O)2]·[(CH3)2NH2]·8DMF·20H2O·EtOH (2-In), have been synthesized via solvothermal reactions (TPC4R = tetra(2-(4H-pyrazol-3-yl)pyridine)calix[4]resorcinarene, H2PDC = 3,5-pyridinedicarboxylic acid, DMF = N,N'-dimethylformamide). By carefully tuning different metal ions, two structurally different cages 1-Zn and 2-In were achieved. The former shows a bowl-shaped structure, while the latter features a dumbbell-like structure. After activation, they exhibited unsaturated Zn(ii) or In(iii) Lewis acid sites and the free nitrogen Lewis base sites of the PDC2-. Therefore, they were employed as catalysts for the Knoevenagel condensation reaction in the absence of a solvent. Particularly, 1-Zn featured high structural stability and enhanced the catalytic activity.

Efficient ethylene purification by a robust ethane-trapping porous organic cage

The removal of ethane (C₂H₆) from its analogous ethylene (C₂H₄) is of paramount importance in the petrochemical industry, but highly challenging due to their similar physicochemical properties. The use of emerging porous organic cage (POC) materials for C₂H₆/C₂H₄ separation is still in its infancy. Here, we report the benchmark example of a truncated octahedral calix[4]resorcinarene-based POC adsorbent (CPOC-301), preferring to adsorb C₂H₆ than C₂H₄, and thus can be used as a robust absorbent to directly separate high-purity C₂H₄ from the C₂H₆/C₂H₄ mixture. Molecular modelling studies suggest the exceptional C₂H₆ selectivity is due to the suitable resorcin[4]arene cavities in CPOC-301, which form more multiple C–H···π hydrogen bonds with C₂H₆ than with C₂H₄ guests. This work provides a fresh avenue to utilize POC materials for highly selective separation of industrially important hydrocarbons.

The removal of ethane from ethylene is of importance in the petrochemical industry, but similar physicochemical properties of these molecules makes separation a challenging task. Here, the authors demonstrate that a robust octahedral calix[4]resorcinarene-based porous organic cage can separate high-purity ethylene from ethane/ethylene mixtures.

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.

Ionothermal Synthesis of Uranyl Vanadate Nanoshell Heteropolyoxometalates

Two uranyl vanadate heteropolyoxometalates (h-POMs) have been synthesized by ionothermal methods using the ionic liquid 1-ethyl-3-methylimidazolium diethyl phosphate (EMIm-Et₂PO₄). The hybrid actinide-transition metal shell structures have cores of (UO₂)₈(V₆O₂₂) and (UO₂)₆(V₃O₁₂), which we designate as {U₈V₆} and {U₆V₃}, respectively. The diethyl phosphate anions of the ionic liquids in some cases terminate the core structures to form actinyl oxide clusters, and in other cases the diethyl phosphate oxyanions link these cluster cores into extended structures. Three compounds exist for the {U₈V₆} cluster core: {U₈V₆}-monomer, {U₈V₆}-dimer, and {U₈V₆}-chain. Tungsten atoms can partially substitute for vanadium in the {U₆V₃} cluster, which results in a chain-based structure designated as {U₆V₃}-W. Each of these compounds contains charge-balancing EMIm cations from the ionic liquid. These compounds were characterized crystallographically, spectroscopically, and by mass spectrometry.

An octahedral polyoxomolybdate-organic molecular cage

An unprecedented Mo-organic molecular cage built on interesting {MoVI2O5} secondary building blocks and BTC ligands, which has been successfully synthesized and systematically characterized, presents the first example of an isopolyoxomolybdates(vi)-organic molecular cage. An investigation into the related Cs+-exchange experiment was performed in detail.

Guest-Reaction Driven Cage to Conjoined Twin-Cage Mitosis-Like Host Transformation

We report here a guest-reaction-induced mitosis-like host transformation from a known Pd₄ L₂ cage 1 to a conjoined Pd₆ L₃ twin-cage 2 featuring two separate cavities. The encapsulation of 1-hydroxymethyl-2-naphthol (G1), a known ortho-quinone methide (o-QMs) precursor, within the hydrophobic cavity of cage 1 is found crucial to realize the cage to twin-cage conversion. Confined G1 molecules within the nanocavity undergo self-coupling dimerization reaction to form 2,2'-dihydroxy-1,1'-dinaphthylmethane (G2) which then triggers the cage to twin-cage mitosis. The same conversion also proceeds, in a much faster rate, via the direct templation of G2, confirming the induced-fit transformation mechanism. The structure of the (G2)₂ ⊂2 host-guest complex has been established by X-ray crystallographic study, where cis- to trans- conformational switch on one bridging ligand is revealed.

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.

The rise of metal-organic polyhedra

Metal-organic polyhedra are a member of metal-organic materials, and are together with metal-organic frameworks utilized as emerging porous platforms for numerous applications in energy- and bio-related sciences. However, metal-organic polyhedra have been significantly underexplored, unlike their metal-organic framework counterparts. In this review, we will cover the topologies and the classification of metal-organic polyhedra and share several suggestions, which might be useful to synthetic chemists regarding the future directions in this rapid-growing field.

Equi-size nesting of Platonic and Archimedean metal-organic polyhedra into a twin capsid

Inspired by the structures of virus capsids, chemists have long pursued the synthesis of their artificial molecular counterparts through self–assembly. Building nanoscale hierarchical structures to simulate double-shell virus capsids is believed to be a daunting challenge in supramolecular chemistry. Here, we report a double-shell cage wherein two independent metal–organic polyhedra featuring Platonic and Archimedean solids are nested together. The inner (3.2 nm) and outer (3.3 nm) shells do not follow the traditional “small vs. large” pattern, but are basically of the same size. Furthermore, the assembly of the inner and outer shells is based on supramolecular recognition, a behavior analogous to the assembly principle found in double-shell viruses. These two unique nested characteristics provide a new model for Matryoshka–type assemblies. The inner cage can be isolated individually and proves to be a potential molecular receptor to selectively trap guest molecules.

Supramolecular constructs that mimic complex biological assemblies are synthetically challenging. Here, the authors present a double-shell cage wherein two independent metal-organic polyhedra are nested together in a manner analogous to that found in double-shell virus capsids.

Metal-Deficient Supramolecule Based on a Fivefold-Symmetric Building Block

An unprecedented cationic supramolecule [(Cp''Fe(η5 -P5 ))12 {CuNCMe}8 ]8+ 2.66 nm in diameter was selectively isolated as a salt of the weakly coordinating anion [Al{OC(CF3 )3 }4 ]- for the first time and characterized by X-ray structure analysis, PXRD, NMR spectroscopy, and mass spectrometry. Its metal-deficient core contains the lowest possible number of Cu atoms to connect 12 pentaphosphaferrocene units, providing a supramolecule with fullerene topology which, topologically, also represents the simplest homologue in the family of metal-deficient pentaphosphaferrocene-based supramolecules [{CpR Fe(η5 -P5 )}12 (CuX)20-n ]. The 12 vacant metal sites between the cyclo-P5 rings, the largest number attained to date, make this compound a facile precursor for potential inner and outer modifications of the core as well as for functionalization via the substitution of labile acetonitrile ligands.

Inorganic-Organic Hybrid Polyoxoniobates: Polyoxoniobate Metal Complex Cage and Cage Framework

The combination of polyoxoniobates (PONbs) with 3d metal ions, azoles, and organoamines is a general synthetic procedure for making unprecedented PONb metal complex cage materials, including discrete molecular cages and extended cage frameworks. By this method, the first two PONb metal complex cages K₄ @{[Cu₂₉ (OH)₇ (H₂ O)₂ (en)₈ (trz)₂₁ ][Nb₂₄ O₆₇ (OH)₂ (H₂ O)₃ ]₄ } and [Cu(en)₂ ]@{[Cu₂ (en)₂ (trz)₂ ]₆ (Nb₆₈ O₁₈₈ )} have been made. The former exhibits a huge tetrahedral cage with more than 120 metal centers, which is the largest inorganic-organic hybrid PONb known to date. The later shows a large cubic cage, which can act as building blocks for cage-based extended assembly to form a 3D cage framework {[Cu(en)₂ ]@{[Cu₂ (trz)₂ (en)₂ ]₆ [H₁₀ Nb₆₈ O₁₈₈ ]}}. These materials exhibit visible-light-driven photocatalytic H₂ evolution activity and high vapor adsorption capacity. The results hold promise for developing both novel cage materials and largely unexplored inorganic-organic hybrid PONb chemistry.

One-Pot and Postsynthetic Phenol-Thermal Synthesis toward Highly Stable Titanium-Oxo Clusters

The synthetic approach plays a crucial role for the exploration and optimization of functional materials. As the molecular models of titanium dioxide, polyoxo-titanium clusters have undergone rapid development over past decade. Unfortunately, many of them are unstable, especially in aqueous environments, greatly limiting their applications in catalysis and environmental fields. In this work, we report a novel phenol-thermal approach toward the construction of highly stable polyoxo-titanium clusters. In addition to the traditional one-pot procedure, the phenol-thermal synthesis can also be used as a postsynthetic pathway to modify the alcohol terminated titanium-oxo clusters. During the modification in phenol, Ti-O core structures consisting entirely of 6-coordinated Ti^IV centers can be retained. Nevertheless, isopropanol terminated 5-coordinated Ti^IV centers are not stable and reconstructed to 6-coordinated Ti^IV centers during the phenol-thermal modification to form new Ti-O clusters. Physical attribute studies confirm that the obtained phenolic clusters generally display much better stability and stronger visible light absorption than isopropanol stabilized clusters with identical or similar cores. Therefore, phenol can not only offer a suitable solution environment for the construction of new cluster structures but also provide robust protection for the cluster cores and also an efficient method to enhance their visible light responses.