Organoboron-Functionalization Enables the Hierarchical Assembly of Giant Polyoxometalate Nanocapsules

A Cubic Tinkertoy-like Heterometallic Cluster with a Record Magnetocaloric Effect

Clusters showing a giant magnetocaloric effect (MCE) are of interest as molecular coolants for magnetic refrigeration. Herein, we report two heterometallic clusters, denoted as Gd152Ni14@Cl24 and Sm152Ni8, just to highlight their inorganic core motifs, obtained by ligand-controlled co-hydrolysis of Ni2+ and Ln3+ (Ln = Gd, Sm) in the presence of N-(2-hydroxyethyl)iminodiacetic acid (H2HEIDA). Both clusters display fascinating cubic Tinkertoy-like structures, with the core motifs being built of multiple metallic shells of Platonic and Archimedean polyhedra. The isothermal magnetic entropy change─a direct measurement of MCE─was determined to be 52.65 J·kg-1·K-1 at 2.5 K and 7.0 T for the Gd-containing cluster; this value is the highest known for any molecular clusters so far reported.

A Giant Heterometallic Polyoxometalate Nanocluster for Enhanced Brain-Targeted Glioma Therapy

Giant heterometallic polyoxometalate (POM) clusters with precise atom structures, flexibly adjustable and abundant active sites are promising for constructing functional nanodrugs. However, current POM drugs are almost vacant in orthotopic brain tumor therapy due to the inability to effectively penetrate the blood-brain barrier (BBB) and low drug activity. Here, we designed the largest (3.0 nm × 6.0 nm) transition-metal-lanthanide co-encapsulated POM cluster {[Ce10 Ag6 (DMEA)(H2 O)27 W22 O70 ][B-α-TeW9 O33 ]9 }2 88- featuring 238 metal centers via synergistic coordination between two geometry-unrestricted Ce3+ and Ag+ linkers with tungsten-oxo cluster fragments. This POM was combined with brain-targeted peptide to prepare a brain-targeted nanodrug that could efficiently traverse BBB and target glioma cells. The Ag+ active centers in the nanodrug specifically activate reactive oxygen species to regulate the apoptosis pathway of glioma cells with a low half-maximal inhibitory concentration (5.66 μM). As the first brain-targeted POM drug, it efficiently prolongs the survival of orthotopic glioma-bearing mice.

Hydrogenation Catalysis by Hydrogen Spillover on Platinum-Functionalized Heterogeneous Boronic Acid-Polyoxometalates

The activation of molecular hydrogen is a key process in catalysis. Here, we demonstrate how polyoxometalate (POM)-based heterogeneous compounds functionalized with Platinum particles activate H2 by synergism between a hydrogen spillover mechanism and electron-proton transfer by the POM. This interplay facilitates the selective catalytic reduction of olefins and nitroarenes with high functional group tolerance. A family of polyoxotungstates covalently functionalized with boronic acids is reported. In the solid-state, the compounds are held together by non-covalent interactions (π-π stacking and hydrogen bonding). The resulting heterogeneous nanoscale particles form stable colloidal dispersions in acetonitrile and can be surface-functionalized with platinum nanoparticles by in situ photoreduction. The resulting materials show excellent catalytic activity in hydrogenation of olefins and nitrobenzene derivatives under mild conditions (1 bar H2 and room temperature).

Computational Study into the Effects of Countercations on the [P8W48O184]40- Polyoxometalate Wheel

Porous metal oxide materials have been obtained from a ring-shaped macrocyclic polyoxometalate (POM) structural building unit, [P8W48O184]40-. This is a tungsten oxide building block with an integrated "pore" of 1 nm in diameter, which, when connected with transition metal linkers, can assemble frameworks across a range of dimensions and which are generally referred to as POMzites. Our investigation proposes to gain a better understanding into the basic chemistry of this POM, specifically local electron densities and locations of countercations within and without the aforementioned pore. Through a rigorous benchmarking process, we discovered that 8 potassium cations, located within the pore, provided us with the most accurate model in terms of mimicking empirical properties to a sufficient degree of accuracy while also requiring a relatively small number of computer cores and hours to successfully complete a calculation. Additionally, we analyzed two other similar POMs from the literature, [As8W48O184]40- and [Se8W48O176]32-, in the hopes of determining whether they could be similarly incorporated into a POMzite network; given their close semblance in terms of local electron densities and interaction with potassium cations, we judge these POMs to be theoretically suitable as POMzite building blocks. Finally, we experimented with substituting different cations into the [P8W48O184]40- pore to observe the effect on pore dimensions and overall reactivity; we observed that the monocationic structures, particularly the Li8[P8W48O184]32- framework, yielded the least polarized structures. This correlates with the literature, validating our methodology for determining general POM characteristics and properties moving forward.

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.

Two Types of Subgroup-Valence Heteroatoms (PIII, TeIV) Synergistically Controlling Octa-CeIII-Encapsulated Heteropolyoxotungstate and Its Electrochemical Recognition Properties

Rapid development of the synthetic chemistry of polyoxometalates (POMs) has greatly driven the generation of structurally variable innovative POM-based materials. Herein, we synthesized a novel P^III and Te^IV synergistically controlling octa-Ce^III-encapsulated heteropolyoxotungstate [H₂N(CH₃)₂]₁₁K₂Na₆H₁₁[Ce₈(CH₃COO)₂(HP^IIIO₃)₂W₈O₂₀(H₂O)₁₂(B-β-TeW₈O₃₀)₂(B-α-TeW₈O₃₁)₄]·64H₂O (1). Its distinctive anion skeleton [Ce₈(CH₃COO)₂(HP^IIIO₃)₂W₈O₂₀(H₂O)₁₂(B-β-TeW₈O₃₀)₂(B-α-TeW₈O₃₁)₄]^30- is built by two tetra-vacancy [B-β-TeW₈O₃₀]^8- and four tetra-vacancy [B-α-TeW₈O₃₁]^10- moieties linked through an inorganic-organic hybrid [Ce₈(CH₃COO)₂(HP^IIIO₃)₂W₈O₂₀(H₂O)₁₂]²⁶⁺ {Ce₈P₂W₈} cluster core. Interestingly, {Ce₈P₂W₈} is assembled from four [W₂O₁₁]^10- groups and two [HP^IIIO₃]^2- anions and eight Ce³⁺ ions. Besides, 1 was further composited with carboxylated multiwalled carbon nanotube (CMCN), resulting in a bi-component 1/CMCN nanocomposite. An electrochemical recognition platform (named as 1/CMCN/GCE) was built by modifying 1/CMCN on a glassy carbon electrode (GCE) for electrochemical detection of dopamine (DPA) at physiological pH (pH = 7.0). The findings have shown that 1/CMCN/GCE exhibits a good detection limit of 4.95 nM for DPA. This work provides considerable inspiration to promote innovative and rational structure designs of POM-based materials and expand their applications to electrochemical and biological detection fields.

Organophosphonic Acid-Regulating Assembly of PV-SbIII Polyoxotungstate and Its Potential in Building a Dual-Signal Readout Electrochemical Aptasensor for Carcinogen Detection

Template-directed assembly of giant cluster-based nanomaterials is an everlasting theme in cluster science. In this work, ethylenediamine tetramethylphosphonic acid [H₈EDTPA = (POCH₂(OH)₂)₄C₂H₄N₂] and [B-α-SbW₉O₃₃]^9- were, respectively, used as an organic template and an inorganic template to prepare an organophosphonic acid-regulating P^V-Sb^III-heteroatom-inserted polyoxotungstate aggregate [H₂N(CH₃)₂]₅Na₁₁H₉[CeW₄O₁₀(HEDTPA)SbW₁₅O₅₀][B-α-SbW₉O₃₃]₂·36H₂O (1). Noteworthily, organophosphonic acid ligand not only works as an organic template leading to the assembly of a [HEDTPASbW₁₅O₅₀]^14- building block but also further bridges the sandwich-type [CeW₄O₁₀(B-α-SbW₉O₃₃)₂]^11- entity. To extend its potential application in electrochemical sensing properties, we prepared a three-dimensional 1@EGO composite (EGO = reduced graphene oxide functionalized by ethylenediamine) with porous architecture and a prominent conducting ability. Furthermore, the 1@EGO composite was explored as a modification material for glassy carbon electrodes to build a dual-signal readout electrochemical aptasensor for carcinogens, which shows much better detection performance for aflatoxin B1 compared with traditional single-signal biosensors.

The largest Se-4f cluster incorporated polyoxometalate with high Lewis acid-base catalytic activity

A 4p-4f cluster incorporated polyoxometalate (POM), namely, H₁₈{[(H₄pic)₄Eu₁₀Se₁₃O₂₈(H₂O)₁₂](α-GeW₉O₃₄)₄·40H₂O (1-Eu, H₄pic = isonicotinic acid), has been first synthesized and characterized. 1-Eu features an interesting four-shell structure, representing the largest Se-4f cluster incorporated POM known to date. Besides, 1-Eu exhibits excellent Lewis acid-base catalytic activity and reusablity in catalyzing the gram-scale dehydration condensation reaction of hydrazines and 1,3-diketones to synthesize polysubstituted pyrazoles.

Polyoxometalate Ionic Sponge Enabled Dendrite-Free and Highly Stable Lithium Metal Anode

Metallic lithium batteries are holding great promises for revolutionizing the current energy storage technologies. However, the formation of dendrite-like morphology of lithium deposition caused by uneven distribution of Li⁺ might cause severe safety concerns of batteries. In this study, a polyoxometalate (POM) cluster, H₅ PMo₁₀ V₂ O₄₀ (PMo₁₀ V₂ ), is added to the conventional electrolyte that can construct a lithium-rich layer and inhibit the growth of Li dendrites effectively. The Li-rich layer can fill any lack of lithium ions on the surface of the metal anode, making the electric field strength consistent across the anode surface, thereby inhibiting the formation of lithium dendrites. Consequently, a significantly prolonged cyclic lifespan is obtained for both Li/Li symmetric cells and Li/LiCoO₂ (Li/LCO) full cells. The cells with LCO positive maintains a high reversible specific capacity of 108.5 mAh g^-1 after 300 cycles when electrolyte with PMo₁₀ V₂ additive is used, compared to 31.5 mAh g^-1 for the untreated electrolyte. The findings indicate that POMs endowed as "ionic sponge" can be widely deployed in lithium metal batteries.

Two Giant Calixarene-Like Polyoxoniobate Nanocups {Cu12 Nb120 } and {Cd16 Nb128 } Built from Mixed Macrocyclic Cluster Motifs

Cup-shaped molecules are of great interest due to their appealing architectures and properties. Compared with widely studied calixarenes, polyoxometalate-based cup-shaped molecules currently remain a virgin land waiting for exploration. In this work, we report the first discovery of two giant cup-shaped inorganic-organic hybrid polyoxoniobates (PONbs) of {Cu₁₂ Nb₁₂₀ } and {Cd₁₆ Nb₁₂₈ }. The former integrates three tricyclic Nb₂₄ clusters and a hexacyclic Nb₄₈ cluster into a cup-shaped molecule via a Cu₁₂ metallacalixarene, while the latter unifies two tricyclic Nb₂₄ clusters and a brand-new pentacyclic Nb₄₀ cluster into another cup-shaped molecule via a hybrid Cd₁₆ unit. With 132 and 144 metal centers, {Cu₁₂ Nb₁₂₀ } and {Cd₁₆ Nb₁₂₈ } show the largest two inorganic-organic hybrid PONbs known to date.

Supramolecular assemblies of organo-functionalised hybrid polyoxometalates: from functional building blocks to hierarchical nanomaterials

This review provides a comprehensive overview of recent advances in the supramolecular organisation and hierarchical self-assembly of organo-functionalised hybrid polyoxometalates (hereafter referred to as hybrid POMs), and their emerging role as multi-functional building blocks in the construction of new nanomaterials. Polyoxometalates have long been studied as a fascinating outgrowth of traditional metal-oxide chemistry, where the unusual position they occupy between individual metal oxoanions and solid-state bulk oxides imbues them with a range of attractive properties (e.g. solubility, high structural modularity and tuneable properties/reactivity). Specifically, the capacity for POMs to be covalently coupled to an effectively limitless range of organic moieties has opened exciting new avenues in their rational design, while the combination of distinct organic and inorganic components facilitates the formation of complex molecular architectures and the emergence of new, unique functionalities. Here, we present a detailed discussion of the design opportunities afforded by hybrid POMs, where fine control over their size, topology and their covalent and non-covalent interactions with a range of other species and/or substrates makes them ideal building blocks in the assembly of a broad range of supramolecular hybrid nanomaterials. We review both direct self-assembly approaches (encompassing both solution and solid-state approaches) and the non-covalent interactions of hybrid POMs with a range of suitable substrates (including cavitands, carbon nanotubes and biological systems), while giving key consideration to the underlying driving forces in each case. Ultimately, this review aims to demonstrate the enormous potential that the rational assembly of hybrid POM clusters shows for the development of next-generation nanomaterials with applications in areas as diverse as catalysis, energy-storage and molecular biology, while providing our perspective on where the next major developments in the field may emerge.

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.

Covalent Linkage of BODIPY-Photosensitizers to Anderson-Type Polyoxometalates Using CLICK Chemistry

The covalent attachment of molecular photosensitizers (PS) to polyoxometalates (POMs) opens new pathways to PS‐POM dyads for light‐driven charge‐transfer and charge‐storage. Here, we report a synthetic route for the covalent linkage of BODIPY‐dyes to Anderson‐type polyoxomolybdates by using CLICK chemistry (i. e. copper‐catalyzed azide‐alkyne cycloaddition, CuAAC). Photophysical properties of the dyad were investigated by combined experimental and theoretical methods and highlight the role of both sub‐components for the charge‐separation properties. The study demonstrates how CLICK chemistry can be used for the versatile linkage of organic functional units to molecular metal oxide clusters.

High Proton-Conductivity in Covalently Linked Polyoxometalate-Organoboronic Acid-Polymers

The controlled bottom-up design of polymers with metal oxide backbones is a grand challenge in materials design, as it could give unique control over the resulting chemical properties. Herein, we report a 1D-organo-functionalized polyoxometalate polymer featuring a purely inorganic backbone. The polymer is self-assembled from two types of monomers, inorganic Wells-Dawson-type polyoxometalates, and aromatic organo-boronates. Their covalent linkage results in 1D polymer strands, which combine an inorganic oxide backbone (based on B-O and Nb-O linkages) with functional organic side-chains. The polymer shows high bulk proton conductivity of up to 1.59×10-1  S cm-1 at 90 °C and 98 % relative humidity. This synthetic approach could lead to a new class of organic-inorganic polymers where function can be designed by controlled tuning of the monomer units.

Multinuclear transition metal-containing polyoxometalates constructed from Nb/W mixed-addendum precursors: synthesis, structures and catalytic performance

Four new transition metal-containing Nb/W mixed-addendum POM trimers with the formula H19[M4(H2O)x(P2W15Nb3O62)3]·m(HCOOH)·nH2O (M = Cu, x = 15, m = 0, and n = 21, Cu-POM; M = Co, x = 7, m = 0, and n = 15, Co-POM; M = Mn, x = 7, m = 6, and n = 18, Mn-POM; and M = Zn, x = 7, m = 0, and n = 23, Zn-POM) have been synthesized by a solvothermal method in a water-ethanol mixed solvent. All the four compounds were characterized by single-crystal X-ray diffraction, powder X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). These compounds can serve as efficient heterogeneous catalysts for the cyanosilylation of different carbonyl compounds under ambient temperature and solvent-free conditions, and Cu-POM shows much better catalytic performance than the other three compounds. The cycle experiment showed that Cu-POM can be reused for at least five cycles without significant loss of catalytic activity. The IR spectroscopy and XRD analysis revealed that Cu-POM can retain its integrity after catalysis.

Multicomponent Self-Assembly of a Giant Heterometallic Polyoxotungstate Supercluster with Antitumor Activity

The hierarchical aggregation of molecular nanostructures from multiple components is a grand synthetic challenge, which requires highly selective linkage control. We demonstrate how two orthogonal linkage groups, that is, organotin and lanthanide cations, can be used to drive the aggregation of a giant molecular metal oxide superstructure. The title compound {[(Sn(CH3 )2 )2 O]4 {[CeW5 O18 ] [TeW4 O16 ][CeSn(CH3 )2 ]4 [TeW8 O31 ]4 }2 }46- (1 a) features dimensions of ca. 2.2×2.3×3.4 nm3 and a molecular weight of ca. 25 kDa. Structural analysis shows the hierarchical aggregation from several independent subunits. Initial biomedical tests show that 1 features an inhibitory effect on the proliferation of HeLa cells based on an apoptosis pathway. In vivo experiments in mice reveal the antiproliferative activity of 1 and open new paths for further development of this new compound class.

Core–shell carbon colloid sphere@phosphotungstic acid/CdS as a Z-scheme heterojunction with synergistic adsorption, photothermal and photocatalytic performance

Core–shell carbon colloid sphere@phosphotungstic acid/CdS exhibits excellent visible-light-driven photocatalytic performance, which is due to the Z-scheme heterojunction favoring the charge transfer and spatial charge separation and the photothermal effect.

Post-functionalization through covalent modification of organic counter ions: a stepwise and controlled approach for novel hybrid polyoxometalate materials

Post-functionalization of Class I type polyoxometalate-organic hybrids through covalent modification of the organic counter ions in a step-wise and controlled manner is reported for the first time. The properties of the post-functionalized hybrids have been studied and compared with those of their parent hybrids revealing marked differences in properties.

Organoboron-Functionalization Enables the Hierarchical Assembly of Giant Polyoxometalate Nanocapsules

The aggregation of molecular metal oxides into larger superstructures can bridge the gap between molecular compounds and solid-state materials. Here, we report that functionalization of polyoxotungstates with organo-boron substituents leads to giant polyoxometalate-based nanocapsules with dimensions of up to 4 nm. A "lock and key" mechanism enables the site-specific anchoring of aromatic organo-boronic acids to metal-functionalized Dawson anions [M₃ P₂ W₁₅ O₆₂ ]^9- (M=Ta^V or Nb^V ), resulting in unique nanocapsules containing up to twelve POM units. Experimental and theoretical studies provide initial insights into the role of the organo-boron moieties and the metal-functionalized POMs for the assembly of the giant aggregates. The study therefore lays the foundations for the design of organo-POM-based functional nanostructures.

Five Keggin-based compounds modified by bis- and mono-[1,3,4]triazole ligands: characterization, and selective photocatalytic and electrochemical properties

By using three kinds of triazole-containing ligands under hydrothermal conditions, five kinds of 0D to 3D POM-based compounds were successfully synthesized. These compounds have good photocatalytic selectivity and electrocatalytic activity.