Recent advances on high-nuclear polyoxometalate clusters

Biomimetic Hierarchical Construction of Anti-Tumor Polyoxopalladates for Cancer Therapy

Inspired by the construction scheme of biomacromolecules, a hierarchical assembly based on the lacunary polyoxopalladate (POP) of [SrPd12O6(OH)3(PhAsO3)6(OAc)3]4- (SrPd12) has been achieved. As a structurally programmable molecular building block, SrPd12 is used to evolve from monomer via dimer to supramolecular aggregates in a controlled manner. In such process, the open-shell-type monomers are covalently integrated into bowl- or cage-like dimers via a direct or indirect splicing strategy. Upon that, hydrogen bond and hydrophobic effects are further hired to fabricate supramolecular aggregates of varied host-guest archetypes, thereby completing a hierarchical construction. In consideration of the combined advantages of noble metals and polyoxometalates in cancer treatment, both in vitro and in vivo anti-tumor assays of these SrPd12-derived POPs were studied in detail. A structure-dependent anti-tumor activitywas observed, originating from an imbalance of damage and repair of DNA as anti-tumor mechanism.

A tetranuclear Pr-W heterometal cluster-imbedded antimotungstate for the catalytic synthesis of benzimidazoles

A novel organic-inorganic Pr-W heterometal cluster-imbedded antimotungstate, [(CH3)2NH2]4Na20.5{[(OAc)Pr4W6O12(tar)3](SbW9O33)4(H2O)10}Cl0.5·ca. 40.3H2O (Pr-1), was synthesized via a one-step in situ assembly strategy. Pr-1 features a distinctive tetranuclear Pr-based organic-inorganic hybrid structure stabilized by polycarboxylic acid ligands, which efficiently regulate the hydrolysis of Pr3+ to facilitate the assembly of Pr-W heterometallic clusters. Notably, this structure includes abundant Lewis acid sites from Pr3+, making it highly promising for catalytic applications. Pr-1 has been successfully demonstrated as an environmentally friendly, heterogeneous catalyst in synthesizing benzimidazoles from o-phenylenediamines and benzaldehydes. The high catalytic activity, excellent structural stability, and recyclability over five cycles highlight the potential of Pr-1 as an efficient and sustainable catalyst for N-containing heterocyclic organic synthesis.

Hydrolytic Degradation of Key Plastic Pollutant Model Systems by a Discrete Metal-Oxo Cluster: A Combined Theoretical and Experimental Study

Degradation of plastic materials represents one of the major challenges faced by the modern world. In this study, computational and experimental techniques have been employed to investigate the hydrolysis of most commonly used plastic materials poly(ether urethane) (PEU) and polyethylene terephthalate (PET) and their commercially available models ethyl N-phenylcarbamate (ENP) and ethylene glycol dibenzoate (EGD), respectively, by a discrete metal-oxo cluster, Zr-substituted Keggin-type polyoxometalate, (Et2NH2)8[Zr(μ-O)(H2O)(PW11O39)] (ZrK), in which the Zr(IV) catalytic site is stabilized by coordination to a robust metal-oxo core. The all-atom molecular dynamics simulations predicted that all substrates interact with ZrK through water-mediated interactions. The quantum mechanics/molecular mechanics (QM/MM) calculations showed that the lengths of scissile ester and amide bonds of PEU/ENP and the ester bond of PET/EGD are quite similar, and the hydrolysis of PEU and ENP and PET and EGD occurs with similar energetics. According to the most plausible mechanisms, the cleavage of the ester and amide bonds of PEU/ENP takes place with a barrier of 16.5/16.6 and 19.0/20.4 kcal/mol, respectively. However, the scissile ester bond of PET/EGD is hydrolyzed with a barrier of 16.7/16.5 kcal/mol. This computed difference in the rate-limiting barrier of 3.9 kcal/mol between the amide bond of ENP and the ester bond of EGD is supported by the experimentally observed sluggish hydrolysis of ENP in comparison to EGD. While both ENP and EGD were successfully hydrolyzed by ZrK in DMSO solvent at 100 °C, EGD hydrolysis has proven to be much more efficient, with 99% yield obtained within 18 h compared to 48% of ENP hydrolysis observed after 162 h. The combined theoretical and experimental results presented here contribute to the development of potent and robust all-inorganic cluster-based catalysts for the degradation of PEU and PET and suggest that ENP and EGD can be used as excellent model substrates in this endeavor.

Synthesis, Structure and Dye Adsorption Properties of Wine-Rack-Type Supramolecular Macrocycles Based on Polyoxovanadate

The precise construction and programmable assembly of structures with specific topologies remain persistent challenges in crystal engineering, primarily constrained by the limited availability of building blocks. Utilizing a synergistic approach that combines an in situ-formed concave polyoxovanadate (POV) cluster {VV4} with specifically designed 120° ditopic carboxylic acid bridging ligands, we successfully synthesized a series of wine-rack-type supramolecular macrocycles characterized by the general formula [(V5O9Cl)4(L)8]8-. The experimental results demonstrate that the introduction of sulfonic acid groups enables controlled structural extension into 1D chain and 2D layer architectures, manifesting the unique advantages of POV-based wine-rack units in constructing framework-based porous materials. This work significantly contributes to the structural diversity of wine-rack-type supramolecular architectures while simultaneously highlighting the great potential of polyoxometalate-driven supramolecular assemblies in materials science.

Polyoxometalates for the catalytic reduction of nitrogen oxide and its derivatives: from novel structures to functional applications

Nitrogen oxide and its derivatives, including nitroaromatic hydrocarbons and various other nitro compounds, are commonly used in industrial applications such as synthesizing drugs, dyes, pesticides, and explosives. However, these compounds are also highly toxic to the environment. Their long-term accumulation can significantly affect air and water quality and disrupt ecosystems. Thus, efficiently converting these harmful compounds into more valuable products through catalytic processes is an urgent challenge in chemical catalysis. In this regard, polyoxometalates (POMs) have emerged as promising inorganic molecular catalysts for the reduction of nitrogen oxide and its derivatives. Their unique structure, excellent redox properties, and versatile catalytic abilities contribute to their effectiveness. This review provides an overview of recent advancements in the POM-catalyzed reduction of nitrogen oxide and its derivatives, focusing on reducing nitroaromatic hydrocarbons and nitrogen oxides. Additionally, we discuss the reaction mechanisms involved in the catalytic process, explore the potential of POMs' structural features for the rational design and optimization of catalytic performance, and highlight future directions for developing POM-based catalysts.

Aminobenzoic Acid Covalently Modified Polyoxotungstates Based on {XW6} Clusters with Proton Conductivity Property

Three cases of aminobenzoic acid hybrid polyoxotungstates, Na3(H3O)2[(HPW6O21) (O2CC6H4NH2)3]·7H2O (1), K2(H3O)4[(AsW6O21)(O2CC6H4NH2)3]·4H2O (2), and [(H2N(CH3)2]3Na2(H3O)[(SbW6O21) (O2CC6H4NH2)3]·7H2O (3), were successfully synthesized. This is the first report of the successful assembly of the hexanuclear {XW6} (X = HPIII, AsIII, or SbIII) clusters and organic carboxylic acid (para aminobenzoic acid) ligands. All three hybrids feature a common {XW6} unit composed of a six-membered {WO6} octahedral ring capped by one {XO3} trigonal pyramid. Furthermore, these hybrids possess an extensive three-dimensional network of hydrogen bonds, which not only provide high thermal stability but also contribute to excellent proton conductive performances. Simultaneously, based on the Hirshfeld partition analysis, combined with the interaction between POMs and water molecules, the proton transport mechanisms of three hybrids were highlighted.

A Wavy Multiple Tm(III)-Containing Open Wells-Dawson Silicotungstate: Synthesis, Structure, and Catalytic Application

A Tm(III)-rich silicotungstate Na{Tm3(H2O)17[Tm2(H2O)7(Si2W18O66)]}·35H2O (Tm5Si2W18) based on the open Wells-Dawson-type [Si2W18O66]16- building unit was synthesized by the reaction of Na10[α-SiW9O34]·18H2O, itaconic acid, and TmCl3 in a HAc/NaAc buffer solution. Five kinds of Tm(III) ions were found in this compound and further linked the {Tm2Si2W18} subunit to form an interesting wavy 1D chain structure, which achieved the introduction of more lanthanide (Ln) ions into the [Si2W18O66]16- unit for the first time. Tm5Si2W18 contains multiple exposed Tm-metal active sites, making it an efficient catalyst for the acetalization of 2-aminobenzamides/2-aminobenzenesulphonamides with aldehydes. A series of 2,3-dihydroquinazolinones and 3,4-dihydro-2H-1,2,4-benzothiadiazine-1,1-dioxides could be obtained in excellent yields under green and mild conditions.

Assembly of the Skirt-Like Giant Molybdenum Blue Cluster {Mo158} from Dimerization of {Mo79} Featuring an Octameric Skeleton

Cyclic compounds are appealing owing to their intrinsic porous structures and facile accessibility as building blocks (BBs) for fabricating high-order assemblies. Nevertheless, the modular synthesis of such molecular entities and their subsequent controlled assembly are still very challenging. Herein, we report the synthesis of a gigantic molybdenum blue (MB) wheel {Mo158} (1), featuring a skirt-shaped structure dimerized from {Mo79}. {Mo79} exhibits an unprecedented octameric architecture built from eight sets of {Mo8} BBs, and the controlled assembly of this smallest member in the MB library is achieved by proper wheel contraction induced by {Mo1} and edge-sharing {Mo2} BBs. Moreover, {Mo158} can function as a 4-connected giant synthon, connecting with adjacent four clusters in a controlled manner via four Mo-O-Mo bridges, resulting in a high-order architecture with a 2D layer structure. In addition to single-crystal X-ray diffraction, {Mo158} is fully characterized by a variety of spectroscopies, allowing for the unambiguous determination of its structure and formula. This work not only enriches the family of gigantic clusters but also demonstrates their potential for constructing more complex assemblies.

Atomically Precise Metal-Metal Oxide Interface in Polyoxometalate-Noble Metal Hybrid Clusters

Metal-metal oxide hybrid materials, typically composed of metal nanoparticles anchored on metal oxides matrix, are devoted enormous attentions as famous heterogeneous catalysts. The interactions between noble metals and metal oxides as well as their interfaces have been proven to be the origin of their excellent catalytic performance. Deep understandings on the interactions between noble metals and metal oxides at atomic precision, thus to precisely assess their contributions to catalysis, can serve as basic principles for catalyst design. In recent years, polyoxometalates (POMs), which in principle can be regarded as atomically precise metal oxide clusters, have been shown to have strong affinity to noble metals, thus forming diverse kinds of POM-noble metal hybrid clusters. Their well-resolved atomically precise structures and hybrid nature promise them as ideal platforms to understand the interfaces and interactions between noble metals and metal oxides. In this review, metal-metal oxide interface is classified into different categories based on the different configurations of hybrid clusters, and aims to understand the interface structures and electronic correlations between POMs and noble metals at the atomic precision. Based on these basic understandings, the study provides the perspectives on the challenges and research efforts to be paid in the future.

Single-Atom Pt Anchored Polyoxometalate as Electron-Proton Shuttle for Efficient Photoreduction of CO2 to CH4 Catalyzed by NiCo Layered Doubled Hydroxide

The crucial role of active hydrogen (H*) in photocatalytic CO2 methanation has long been overlooked, although recently, accelerating proton-coupled electron transfer (PCET) processes to enhance CH4 productivity and selectivity has garnered significant attention. Herein, a single-atom Pt-anchored H3PMo12O40 (Pt1-PMo12) is applied as an efficient proton-electron shuttle to facilitate the photocatalytic performance of NiCo layered double hydroxide (NiCo-LDH). The resultant Pt1-PMo12@NiCo-LDH exhibited superior CH4 productivity (723 µmol g-1 h-1) with CH4 selectivity of 82.3%, showcasing a 24.9 times productivity enhancement over NiCo-LDH (29 µmol g-1 h-1). Systematic investigations revealed that abundant H* is generated by the dissociation of H2O on Pt1 sites and stored within Pt1-PMo12. Subsequently, the multiple H* rapidly migrated from Pt1-PMo12 to the catalytic sites on NiCo-LDH by the engineered strong Mo─O─Ni/Co bonds, thereby significantly expediting the PCET process. The in situ DRIFTS and theoretical calculations elucidated that the Pt1-PMo12 decreased the energy barrier for *CO protonation to *CHO (0.38-0.18 eV) and optimized the rate-determining step of *CH3 to *CH4 (0.64 eV), thus promoting highly active and selective CH4 generation. This work provided novel insights into achieving efficient photocatalytic CO2 methanation by modulating the fast generation and transport of active H*.

A Novel Banana-Shaped Mixed-Metal Co/Fe Polyoxometalate Cluster

The synthesis and characterization of a Co/Fe mixed-metal banana-shaped polyoxometalate with the formula [(Co2.5Fe0.5(H2O)PW9O34)2(PW6O26)]16- (Co5Fe) is reported. This transition-metal-substituted polyoxometalate readily assembles from its components in a one-pot reaction and crystallizes in the monoclinic space group P21/c. The structure of Co5Fe can be considered a double sandwich composed by two B-α-{Co2.5Fe0.5PW9O40} Keggin units, in which one coordinatively saturated octahedral metal position is equally occupied by Co(II) and Fe(III) ions with a 50 % of site occupancy. These Keggin units are linked via a hexalacunary Keggin unit {PW6O26}. Single crystal X-ray diffraction and magnetic measurements support the proposed atom arrangement within the crystal structure. Magnetic measurements of these double trimeric unit {Co2.5Fe0.5O13}2 show a combination of antiferromagnetic interactions, the presence of spin frustration, and the first-order spin-orbit coupling of Co(II) ions. Electrocatalytic water oxidation measurements show that Co5Fe displays low stability in both homogeneous and heterogeneous conditions. This is evidenced by the constant increase on the catalytic currents over time together with the appearance of polyoxometalate-derived electrode-bound species that can be responsible for the observed catalytic activity.

A Two-Dimensional Layered Heteropolyoxoniobate Based on Cubic Sn(IV)-Containing {Sn12Nb56O200} Cages with Good Proton Conductivity Property

The first example of a Sn(IV)-containing heteropolyoxoniobate K6H18[Cu(en)2]8{[Sn(OH)2]12 (HNb7O22)8}·2en·88H2O (1) is built from nanoscale high-nuclearity cubic {[Sn(OH)2]12(HNb7O22)8} cluster and [Cu(en)2]2+ complexes. The cubic {[Sn(OH)2]12(HNb7O22)8} cage is composed of eight {Nb7O22} clusters and 12 SnO6 octahedrons. The eight {Nb7O22} fragments are situated at the vertices of the cubic cage, while the 12 SnO6 octahedrons are positioned along the edges of the cubic cage. The [Cu(en)2]2+ complexes link the {[Sn(OH)2]12(HNb7O22)8} clusters into two-dimensional (2D) (4,4) grid-like layers. The N-H···O hydrogen bonds between the [Cu(en)2]2+ complexes and the {[Sn(OH)2]12(HNb7O22)8} clusters link the layers to form a 3D supramolecular structure. Compound 1 exhibits a good proton conductivity of 3.1 × 10-2 S cm-1 at 85 °C and 98% relative humidity.

Multinuclear Antimony-Bismuth-Lanthanide Cluster-Connected Polyoxometalate for the Detection of 5-Hydroxyindoleacetic Acid via Luminescence

The judicious selection and combination of multicomponents provide great potential for the further exploration of new polyoxometalate (POM) materials. Here, a delicate control on tungstate, SbIII and BiIII sources, Eu3+ ions, and organic molecules led to the discovery of a novel multimetal cluster-embedded POM [H2N(CH3)2]9Na8H5{[Eu4(H2O)6Sb4Bi2W2O12](SbW9O33)2(SbW8O31)2}·78H2O (1). The polyoxoanion of 1 was constructed from four in situ-formed [SbW8O31]11- and [SbW9O33]9- building blocks connected by two hexa-metallic [Eu2(H2O)3Sb2BiWO6]9+ clusters, to be a rare member of Sb- and Bi-coexisting POM. The most impressive characteristic of 1 is the intricate [Eu2(H2O)3Sb2BiWO6]9+ cluster linker, which contains a SbIII-BiIII coinserted [Sb2BiWO6]3+ core grasping one [Eu1(H2O)2]3+ cation and one [Eu2(H2O)]3+ cation on both sides through Sb-O-Eu and Bi-O-Eu bonds. Functionalized by luminescence centers of Eu3+ ions, 1 can emit intense emission in water and be capable of detecting the biomarker of carcinoids, 5-hydroxyindoleacetic acid (5-HIAA) with a low limit of detection of 0.43 μM, high selectivity, and excellent anti-interference, as well as fast response (12 s). The high detectability of 1 for 5-HIAA is relevant to the underlying dynamic quenching and energy-transfer mechanism. In urine conditions, remarkable recognition of 1 for 5-HIAA and satisfactory recoveries were achieved, indicative of the possibility of 1 in detecting 5-HIAA in a real environment. This work reveals the special clustering effect of SbIII and BiIII atoms in the assembly of neoteric POM species and also promotes the application of POMs as potential diagnostic tool in the early detection of carcinoids.

Electrochemical Biosensor Based on Dual-Ligand Functionalized Lanthanide-Encapsulated Polyoxometalate Conductive Polymer Film for Detecting Broad-Spectrum Tumor Marker MicroRNA-155

In this work, a dual-ligand functionalized lanthanide-encapsulated selenotungstate [H2N(CH3)2]16Na2H10[Ho6(H2O)10(HPACA)4W10O28(Ac)2][SeW9O33]6 · 60H2O (1, HPACA = 2-pyrazinecarboxylic acid, HAc = acetic acid) was successfully acquired by simultaneously incorporating rigid HPACA and flexible Ac- ligands to one reaction system. Interestingly, the polyanion [Ho6(H2O)10(HPACA)4W10O28(Ac)2][SeW9O33]628- of 1 is composed of six trivacant Keggin-type [B-α-SeW9O33]8- units interconnected through an organic-inorganic hybrid dual-ligand bimetallic [Ho6(H2O)10(HPACA)4W10O28(Ac)2]20+ cluster. Moreover, the 1@PNMPy film (PNMPy = poly(N-methylpyrrole)) was successfully prepared through an electrochemical polymerization strategy. The doping of 1 significantly narrows the bandgap in the 1@PNMPy film, which enables the 1@PNMPy film to exhibit remarkable conductivity and rapid electron transfer capability. Then, the 1@PNMPy film-modified glassy carbon electrode was used to construct a 1@PNMPy-based electrochemical biosensor (ECBS), which achieves sensitive electrochemical detection (a low limit of detection of 0.108 fM and a wide concentration detection range of 10-8-10-15 M) for broad-spectrum tumor marker microRNA-155. Also, the 1@PNMPy-based ECBS has a good specific recognition performance for microRNA-155 in a variety of interfering media. The research not only contributes to a deeper understanding of the synthetic chemistry of multicomponent polyoxometalate (POM)-based materials but also can further expand innovative applications of multicomponent POM-based materials in electrochemical detection and electrochemical devices.

Mixed Carboxylate Ligands Bridging Tetra-Pr3+-Encapsulated Antimonotungstate: Syntheses, Structure, and Catalytic Activity for Imidazoles Synthesis

Multinuclear Pr-containing antimonotungstate [Pr4(H2O)10W6O13(mal)2(OAc)(B-α-SbW9O33)4]21- (Pr-1, mal = malate anion, OAc = acetate anion), bridged by organic carboxylic acid, was synthesized through a one-pot assembly reaction and structurally characterized. Pr-1 is composed of four [B-α-SbW9O33]9- fragments fused together by an organic-inorganic hybrid central [Pr4(H2O)10W6O13(mal)2(OAc)]15+ cluster core through 24 μ2-O atoms. Notably, the central cluster comprises unprecedented decanuclear Pr4(H2O)10W6O13 jointly decorated by two types of carboxylic acid ligands. This integration of rare earth-containing antimonotungstate with mixed organic carboxylate ligands is very rare in POMs chemistry. Pr-1 exhibits excellent catalytic activity in the cyclo-condensation reaction involving benzil, aldehyde, and NH4OAc. A series of 2,4,5-trisubstituted imidazoles were synthesized in remarkable yields using iPrOH as a green solvent.

Unprecedented Organogermanium Functionalized GeIV-SbIII-Templating Polyoxotungstate Nanocluster for Photothermal-Chemodynamic Cancer Therapy

The function-oriented synthesis of polyoxometalate (POM) nanoclusters has become an increasingly important area of research. Herein, the well-known broad-spectrum anticancer drug Ge-132 which contains GeIV as potential heteroatoms and carboxyl coordination sites, is introduced to the POM system, leading to the first organogermanium functionalized GeIV-SbIII-templating POM nanocluster Na4[H2N(CH3)2]16 H18[Sm4(H2O)12W4O14Ge(CH2CH2COOH)]2[SbW9O33]4[Ge(CH2CH2COOH) SbW15O54]2·62H2O (1). An unprecedented organogermanium templating Dawson-like [Ge(CH2CH2COOH)SbW15O54]12- building block is discovered. To take advantage of the potential pharmaceutical activity of such an organogermanium-functionalized POM cluster, 1 is further composited with gold nanoparticles (NPs) to prepare 1-Au NPs, which doubles the blood circulation time of 1-based nanodrug. Efficient separation of photogenerated charges in 1-Au NPs largely boosts the photothermal conversion efficiency (PCE = 55.0%), which is nearly 2.1 times that of either single 1 (PCE = 26.7%) or Au NPs (PCE = 26.2%), and simultaneously facilitate the generation of toxic activate reactive oxygen species in tumor microenvironment. Based on these findings, it is demonstrated that 1-Au NPs are a multifunctional and renal clearable nanomedicine with great potential in photoacoustic imaging guiding photothermal-chemodynamic therapy for breast cancer.

A uranium-bridged dimeric Keggin-type polyoxometalate and its proton conductive properties

A novel dimeric structure based on trilacunary Keggin-type [SbW9O33]9- was synthesized and comprehensively characterized. Different from the conventional dimeric structures, the compound (NH4)10[(SbW9O33)2(UO2)2(H2O)2(SbOH)2]·7H2O ({U2Sb4}) features two additional Sb3+ cations. The successful synthesis of {U2Sb4} reveals the significant role of heteroatoms in structural modulation. The dimer forms a hydrogen-bonded network with water molecules and NH4+ and is therefore expected to exhibit remarkable proton conductivity. Proton conduction studies revealed that {U2Sb4} was a temperature and humidity-dependent proton conductor with conductivity reaching up to 2.50 × 10-2 S cm-1 at 85 °C and 85% RH.

Assembled Structures and Electrical Conductivities of Salts Comprised of Cationic Sandwich Complexes and Polyoxometalates

Polyoxometalates (POMs) are recognized for their diverse structures and catalytic properties, yet their organometallic salts have not been thoroughly investigated. In this study, we synthesized salts of a Keggin-type POM with cationic sandwich complexes featuring various substituents, [X]2[SMo12O40] [X = Ru(C5H5)(C6H5R); R = H (1a), Me (1b), Bu (1c)], [Co(C5H5)2 (2), and Co(C5Me5)2 (3)]. These salts exhibited similar structural characteristics, with each anion surrounded by 10 cations, forming two-dimensional sheet arrangements through O···O anion-anion contacts, except for the salt of 1c, which exhibited one-dimensional contact owing to the larger cation substituent. Additionally, [2](THA)[Mo6O19], [3]2[Mo6O19], and [3](THA)[SMo12O40], containing the Lindqvist-type POM [Mo6O19] and/or tetrahexylammonium (THA) cation, were obtained, with the packing structure of [3]2[Mo6O19] closely resembling that of [X]2[SMo12O40]. Solvate crystals of [1a]3[PMo12O40] were also prepared. [1a]2[SMo12O40] exhibits an electrical conductivity σ of 1.4 × 10-7 S cm-1 at 373 K, which is 2 orders of magnitude higher than those of (THA)2[SMo12O40] and [1a]PF6.

Dy/Ho-encapsulated tartaric acid-functionalized tungstoantimonates: heterogeneous catalysts for isoindolinone synthesis

Two novel rare earth-substituted tungstoantimonates [H2N(CH3)2]8Na12[Dy2(H2O)6(tar)(Sb2W21O72)]2·40H2O (DySbW) and [H2N(CH3)2]6Na14[Ho2(H2O)6(tar)(Sb2W21O72)]2·25H2O (HoSbW) (H4tar = tartaric acid) were synthesized. The meso-polyanions are alternately linked by {Na3(H2O)3} clusters and DL-tar ligands to form 1D chains. Notably, HoSbW exhibits excellent catalytic activity and high stability for the synthesis of isoindolinones using EtOH as a green solvent.

Making an inverted Keggin ion lacunary

The century-old inverted Keggin ion has been revisited in an effort to unleash its potential in the structural engineering and functional development of polyoxomolybdates (POMos). Over the past hundred years, attempts to program the metal-oxo scaffold of inverted Keggins have been conducted continually but without any success. In this work, a structurally inert, inverted Keggin-type POMo could finally be altered by means of a binary heterogroup-templated approach, resulting in the successful isolation of two lacunary species. The local structure and charge distribution of these species are adjustable, and hence they serve as available building blocks for the subsequent controlled assembly of a CeIII-incorporated derivative. From the plenary to the lacunary, the enclosed structure of the inverted Keggin has been opened up significantly, resulting in less steric hindrance, along with a transition from an electron neutral species to a negatively charged species. Owing to these beneficial properties, the emerging defect-containing polyanions demonstrated outstanding Lewis acid-base catalytic activity in the high efficiency production of pyrazoles.

Cylindrical HPIII-SbIII-Templated Five-Layer Polyoxotungstate with Conspicuous Photochromism Triggered by UV or Visible Light

The heteroanion (HA) component plays an important role in the templating of heteropolyoxometalate (HPA) structures, but polyoxometalates (POMs) formed from two different templates are rarely reported. Herein, we present a five-layer POM [H2N(CH3)2]14{[(HPO3)4W6O10][HPSbW15O54]2}·16H2O (1) prepared by two kinds of different HA templates. The multilayer heteropolyanion {[(HPO3)4W6O10][HPSbW15O54]2}14- in 1 consists of two trivacant diheteroatom-templated ([HPO3]2- and [SbO3]3-) [HPSbW15O54]11- subunits linked by one unusual [(HPO3)4W6O10]8+ subcluster via twelve corner-sharing oxygen atoms. Compound 1 was systematically characterized by IR, UV, PXRD, TGA, XPS, and Raman spectra. Compound 1 exhibits good photochromism under UV irradiation with a half-life (t1/2) of 42.5 s, and it also exhibits noteworthy photochromism under visible light irradiation with a half-life (t1/2) of 157.2 s. The possible photochromic mechanism is proposed and verified by the experimental results.

Indium-Assisted Construction of {SiNb18O54}-Based Aggregates and Their Assembly into Extended Polyoxoniobate Architectures

In this research, indium ions were introduced into polyoxoniobates (PONbs) reaction systems to facilitate the construction of different {SiNb18O54}-based aggregates, including an {In(en)2{SiNb18O54}2} (en = ethylenediamine) dimer, an {[InO2][In2(en)O3]2{SiNb18O54}3} trimer, and an {[In(en)2][InO2][In7(en)5O9]{SiNb18O54}4} tetramer. Interestingly, these aggregates were further assembled into three uncommon extended PONb architectures in the presence of [Cu(en)2]2+ complexes, namely, H3[Cu(en)2(H2O)][Cu(en)2]6[Cu(en)2]2{[In(en)2][K2{SiNb18O54}(H2O)6]2}·1.5en·16H2O, H9{[Cu(en)2]6{[Cu(en)2]3[Cu(en)2(H2O)][In(H2O)2][In2(en)(H2O)2(OH)]2{SiNb18O54}3}·5en·29H2O, and H14[Cu(en)2]0.5[Cu(en)2(H2O)]{[Cu(en)2]2{[Cu(en)2]3[Cu(en)2(H2O)]5[K(H2O)2][In(H2O)2][In(en)2][In7(OH)9(en)5]{SiNb18O54}4}·7en·39H2O. In addition, all of them have good water vapor adsorption capacities and moderate proton transport capabilities. The above results indicate that introducing suitable heteroatoms to induce the aggregation PONb building blocks and further assembling them into new structures is an effective strategy to enrich the PONbs' structural diversity and develop new functional materials.

Antitumor effects of a Sb-rich polyoxometalate on non-small-cell lung cancer by inducing ferroptosis and apoptosis

Polyoxometalates (POMs) are a class of anionic metal-oxygen clusters with versatile biological activities. Over the past decade, an increasing number of POMs, especially Sb-rich POMs, have been proven to exert antitumor activity. However, the antitumor effects and mechanisms of POMs in the treatment of non-small cell lung cancer (NSCLC) remain largely unexplored. This study employed a Sb-rich {Sb21Tb7W56} POM (POM-1) for NSCLC therapy and investigated its mechanism of action. Our results demonstrated that POM-1 exhibited cytotoxicity against H1299 and A549 cells with IC50 values of 3.245 μM and 3.591 μM, respectively. The migration and invasion were also inhibited by 28.05% and 76.18% in H1299 cells, as well as 36.88% and 36.98% in A549 cells at a concentration of 5 μM. In a tumor xenograft mouse model, POM-1 suppressed tumor growth by 76.92% and 84.62% at doses of 25 and 50 mg kg-1, respectively. Transcriptomic analysis indicated the alteration of ferroptosis and apoptosis signaling pathways in POM-treated NSCLC cells. Subsequent experimentation confirmed the induction of ferroptosis, evidenced by 5.6-fold elevated lipid peroxide levels with treatment of 5 μM POM-1, alongside increased expression of ferroptosis-associated proteins. Additionally, the apoptosis induced by POM-1 was also validated by the 19.67% and 30.1% increase in apoptotic cells in H1299 and A549 cells treated with 5 μM POM-1, respectively, as well as the upregulated activation of caspase-3. In summary, this study reveals, for the first time, ferroptosis as the antitumor mechanism of Sb-rich POM, and that synergism with ferroptosis and apoptosis is a highly potent antitumor strategy for POM-based antitumor therapy.

Synthesis of Isotypic Giant Polymolybdate Cages for Efficient Photocatalytic C-C Coupling Reactions

The construction of isotypic high-nuclearity inorganic cages with identical pristine parent structure and increasing nuclearity is highly important for molecular growth and structure-property relationship study, yet it still remains a great challenge. Here, we provide an in situ growth approach for successfully synthesizing a series of new giant hollow polymolybdate dodecahedral cages, Mo250, Mo260-I, and Mo260-E, whose structures are growth based on giant polymolybdate cage Mo240. Remarkably, they show two pathways of nuclear growth based on Mo240, that is, the growth of 10 and 20 Mo centers on the inner and outer surfaces to afford Mo250 and Mo260-I, respectively, and the growth of 10 Mo centers both on the inner and outer surfaces to give Mo260-E. To the best of our knowledge, this is the first study to display the internal and external nuclear growth of a giant hollow polyoxometalate cage. More importantly, regular variations in structure and nuclearity confer these polymolybdate cages with different optical properties, oxidative activities, and hydrogen atom transfer effect, thus allowing them to exhibit moderate to excellent photocatalytic performance in oxidative cross-coupling reactions between different unactivated alkanes and N-heteroarenes. In particular, Mo240 and Mo260-E with better comprehensive abilities can offer the desired coupling product with yield up to 92% within 1 h.

Development of non-closed silver clusters by transition-metal-coordination-cluster substituted polyoxometalate templates

Nature seems to favor the formation of closed anion-templated silver clusters. How precisely to create non-closed sliver clusters remains an interesting challenge. In this work, we propose that the use of transition-metal-coordination-cluster substituted polyoxometalates (TMCC-substituted POMs) as templates is an effective synthetic strategy for creating the non-closed silver clusters, as demonstrated by the obtainment of four types of rare non-closed silver cluster species of Ag38-TM (TM = Co, Ni or Zn), Ag37-Zn, {Ag37-Zn}∞ and Ag36-TM (TM = Co, Ni). The idea of the strategy is to employ the TMCC-substituted POMs containing cluster modules with different bond interactions with Ag+ ions as templates to guide the formation of the non-closed silver clusters. For example, TMCC-substituted POM clusters are used as templates in this work, which contain POM modules that can coordinate with the Ag+ ions and TMCC moieties that are difficult to coordinate with the Ag+ ions, leading to the Ag+ ions being unable to form closed clusters around TMCC-substituted POM templates. The work demonstrates a promising approach to developing intriguing and unexplored non-closed silver clusters.

Hybrid Membrane of Sulfonated Poly(aryl ether ketone sulfone) Modified by Molybdenum Clusters with Enhanced Proton Conductivity

Developing novel proton exchange membranes (PEMs) with low cost and superior performance to replace Nafion is of great significance. Polyoxometalate-doped sulfonated poly(aryl ether ketone sulfone) (SPAEKS) allows for the amalgamation of the advantages in each constituent, thereby achieving an optimized performance for the hybrid PEMs. Herein, the hybrid membranes by introducing 2MeIm-{Mo132} into SPAEKS are obtained. Excellent hydrophilic properties of 2MeIm-{Mo132} can help more water molecules be retained in the hybrid membrane, providing abundant carriers for proton transport and proton hopping sites to build successive hydrophilic channels, thus lowering the energy barrier, accelerating the proton migration, and significantly fostering the proton conductivity of hybrid membranes. Especially, SP-2MIMo132-5 exhibits an enhanced proton conductivity of 75 mS cm-1 at 80 °C, which is 82.9% higher than pristine SPAEKS membrane. Additionally, this membrane is suitable for application in proton exchange membrane fuel cells, and a maximum power density of 266.2 mW cm-2 can be achieved at 80 °C, which far exceeds that of pristine SPAEKS membrane (54.6 mW cm-2). This work demonstrates that polyoxometalate-based clusters can serve as excellent proton conduction sites, opening up the choice of proton conduction carriers in hybrid membrane design and providing a novel idea to manufacture high-performance PEMs.

Advances in polyoxometalate-based electrochemical sensors in the last three years

As a famous subclass of metal-oxide cluster materials, polyoxometalates (POMs) feature variable architectures, reversible multi-electron transport capability, catalytic activity, and redox capacity. These attributes endow POMs with great potential as promising electrode materials in electrochemical sensors (ECSs). Up to now, POM-based ECSs have been passionately studied, and diverse POM-based redox ECSs, aptasensors and immunosensors have emerged. And these POM-based ECSs generally demonstrate fast response, low detection limit, strong selectivity and high antijamming capability. This review mainly focuses on the remarkable advancement of POM-based ECSs in environmental monitoring, food safety and biomedicine from 2021, aiming to furnish theoretical insights that inform the design and development of innovative sensors.

Two Mn(II)-Bridged Silverton-Type [UMo12O42]8- Polyoxometalates with Catalytic Activity for the Synthesis of Pyrazoles

Two Mn(II)-bridged Silverton-type {UMo12O42}-based polyoxomolybdates with different three-dimensional structures, Na6(H2O)12[Mn(UMo12O42)] (NaMn) and (NH4)2[K2Na6(μ4-O)2(H2O)1.2Mn(UMo12O42)]·4.6H2O (KMn), were hydrothermally synthesized and further characterized, demonstrating a feasible strategy for the assembly of Silverton-type polyoxomolybdates. Additionally, NaMn is demonstrated to be a good heterogeneous catalyst in the condensation cyclization reaction of hydrazines and 1,3-diketones, and a range of valuable pyrazoles were produced in up to 99% yield.

Prussian blue nanoparticle-based pH-responsive self-assembly for enhanced photothermal and chemotherapy of tumors

In recent years, there has been growing interest in size-transformable nanoplatforms that exhibit active responses to acidic microenvironments, presenting promising prospects in the field of nanomedicine for tumor therapy. However, the design and fabrication of such size-adjustable nanotherapeutics pose significant challenges compared to size-fixed nanocomposites, primarily due to their distinct pH-responsive requirements. In this study, we developed pH-activated-aggregating nanosystems to integrate chemotherapy and photothermal therapy by creating size-transformable nanoparticles based on Prussian blue nanoparticles (PB NPs) anchored with acid-responsive polyoxometalates (POMs) quantum dots via electrostatic interactions (PPP NPs). Subsequently, we utilized doxorubicin (DOX) as a representative drug to formulate PPPD NPs. Notably, PPPD NPs exhibited a significant response to acidic conditions, resulting in changes in surface charge and rapid aggregation of PPP NPs. Furthermore, the aggregated PPP NPs demonstrated excellent photothermal properties under near-infrared laser irradiation. Importantly, PPPD NPs prolonged their retention time in tumor cells via a size-transformation approach. In vitro cellular assays revealed that the anticancer efficacy of PPPD NPs was significantly enhanced. The IC50 values for the PPPD NPs groupand the PPPD NPs + NIR group were 50.11 μg/mL and 30.9 μg/mL. Overall, this study introduces a novel strategy for cancer therapy by developing size-aggregating nano-drugs with stimuli-responsive properties, holding promise for improved therapeutic outcomes in future combination approaches involving photothermal therapy and chemotherapy.

Evaporation-induced self-assembly of Janus pyramid molecules from fractal network to core-shell nanoclusters evidenced by small-angle X-ray scattering

Self-assembly of nanoclusters (NCs) is an effective synthetic method for preparing functionalized nanomaterials. However, the assembly process and mechanisms in solutions still remain ambiguous owing to the limited strategies to monitor intermediate assembled states. Herein, the self-assembly process of amphiphilic molecule 4POSS-DL-POM (consisting of four polyhedral oligomeric silsesquioxanes, a dendritic linker, and one polyoxometalate) by evaporation of acetone in a mixed acetone/n-decane solution is monitored by time-resolved synchrotron small-angle X-ray scattering (SAXS). Scattering data assessments, including Kratky analysis, pair distance distribution function, and model fitting, track the self-assembly process of 4POSS-DL-POM from a fractal network to compact NCs, then to core-shell NCs, and finally to superlattice structure. The calculated average aggregation number of a core-shell NC is 11 according to the parameters obtained from core-shell model fitting, in agreement with electron microscopy. The fundamental understanding of the self-assembly dynamics from heterocluster into NCs provides principles to control building block shape and guide target aggregation, which can further promote the design and construction of highly ordered cluster-assembled functional nanomaterials.

Structural and vibrational properties of lanthanide Lindqvist polyoxometalate complexes

Molecular spin qubits have demonstrated immense potential in quantum information science research due to the addressability of electron spins using microwave frequencies, and the scalability and tunability of molecular systems. Exemplary in this regard is the holmium polyoxometalate, [Na9Ho(W5O18)2]·35H2O (HoW10), which features an accessible atomic clock transition at 9.4 GHz; however, the coherence time of this molecule is limited by spin-phonon coupling driven decoherence processes. To limit these decoherence pathways, materials need to be designed to reduce energy overlap between spin and phonon states, and this necessitates developing a better understanding on how structural modifications impact the vibrational landscape for classes of complexes. Herein we conducted a full investigation into the fundamental structural and vibrational properties of the lanthanide Lindqvist polyoxometalate series, [Na9Ln(W5O18)2]·xH2O (Ln = La(III)-Lu(III), except Pm(III)) (LnW10), to assess how structural changes effect vibrational characteristics and to elucidate pathways to improve the coherence properties of HoW10. Single crystal X-ray diffraction results revealed four distinct structural polymorphs in complexes 1-14 wherein first coordination spheres were identical, and differences manifested as changes in lattice packing. Interestingly, the subtle changes in packing exhibited by the four polymorphs were found to impact distortions away from ideal D4d symmetry for each of the LnW10 complexes. Raman and far-infrared (FIR) spectra of complexes 1-14 were collected to identify vibrational modes present in low energy regions and peak fitting assignments were made according to literature precedents. Qualitative and Partial least squares (PLS) analysis show correlations between complex structural parameters with the low energy Raman and FIR vibrational modes of interest. Overall, this investigation shows that the second coordination sphere plays an integral role in modulation of the structural and vibrational characteristics of LnW10 complexes, which makes it a viable route for tuning spin and vibrational manifolds of species within this series.

A Spectroscopic Method for Distinguishing Two Novel Sandwich-Type Tungsten Oxide Cluster Compounds

This study introduces two novel sandwich-type tungsten-oxygen cluster compounds synthesized by hydrothermal methods, H4(C6H12N2H2)3{Na(H2O)2[Mn2(H2O)(GeW9O34)]}2 (Compound 1) and H2(C6H12N2H2)3.5{Na3(H2O)4[Co2(H2O)(GeW9O34)]2}·17H2O (Compound 2). The two compounds comprise cluster anions [GeW9O34]10- coordinated with transition metal atoms, either Mn or Co, and are stabilized by organic ligands. These compounds are crystallized in the hexagonal crystal system and P63/m space group. The two compounds were characterized through various techniques. Fourier transform infrared (IR) spectroscopy showed absorption peaks of anionic backbone vibrations of the Keggin cluster at 500-1000 cm-1, IR spectral peaks of δ(N-H) and νas(C-N) of the ligand triethylenediamine at 1000-2000 cm-1, and IR spectral peaks of the ligand νas(N-H) and νas(O-H) of water at 3000-3500 cm-1. Despite similar one-dimensional (1D) IR spectra due to the same cluster anions and similar molecular structures, the two compounds exhibited distinct responses in two-dimensional correlation spectroscopy with IR under magnetic and thermal perturbations. Under magnetic perturbation, Compound 1 showed a strong response peak for νas(W-Ob-W), while Compound 2 exhibited a strong response peak for νas(W=Od), possibly linked to differing magnetic particles. Similarly, Compound 1 displayed a strong response peak under thermal perturbation for νas(W-Oc-W). In contrast, Compound 2 showed a strong response peak for νas(W=Od); these results may be attributed to the different hydrogen bonding connections between the two compounds, which affect the groups in distinct ways through vibration and transmit these vibrations to the W-O bonds. The research presented in this paper expands the theoretical and experimental data of 2D correlation IR spectroscopy.

Two Different Three-Dimensional Uranium-Containing Polymolybdates Based on Zn(II) for the Heterogeneous Catalytic Construction of C-N Bond

The introduction of transition metal (TM) ions into polyoxometalates (POMs) cannot only bring about interesting structural diversities but also enable changes in properties. However, TM-containing Silverton-type polyoxomolybdates are still lacking in terms of structural diversity and application development. Herein, two Zn(II)-containing Silverton-type {UMo12O42}-based polyoxomolybdates, H1.89Na4.11(H2O)9Zn[UMo12O42]·4.5H2O (Zn-1) and H1.8Na4.2(H2O)12Zn[UMo12O42] (Zn-2) were hydrothermally synthesized, demonstrating a practical strategy to assembly of TM-containing Silverton-type POMs. Zn-1 is proven to be an excellent and recyclable heterogeneous catalyst in cross-dehydrogenation coupling of 1,4-naphthoquinones with amines reactions, and a series of 2-amino-1,4-naphthoquinones with potential medicinal value have been constructed.

Tetra-Ln3+-Implanted Tellurotungstates Covalently Modified by dl-Malic Acid: Proton Conduction and Photochromic Properties

Three unique dl-malic acid covalently modified tetra-Ln3+-implanted tellurotungstates [H2(CH3)2]9NaH9[Ln4(H2O)14W6O13(OH)5(Mal)2(B-α-TeW9O33)4]·48H2O [Ln = La3+ (1), Ce3+ (2), Pr3+ (3); H3Mal = dl-malic acid] were fabricated by reacting Na2TeO3, Na2WO4·2H2O, Mal, and LnCl3·6H2O with dimethylamine hydrochloride in an aqueous solution. The most prominent architectural feature of these compounds is the covalent connection mode of an organic ligand and a polyoxometallate backbone, which is relatively rare in the realm of polyoxotungstates. The tetrameric polyanion can be deemed as four [TeW9O33]8- fragments fused together via an intriguing hexanuclearity [W6O13(OH)5(Mal)2Ln4(H2O)14]13+ cluster. Impedance measurements manifest that all three complexes display splendid proton conduction properties, with an exceptional conductivity for 2 up to 2.48 × 10-2 S·cm-1 under 85 °C and 95% relative humidity. Moreover, compounds 1 and 3 exhibited fast reversible photochromic properties with allochroic half-life periods t1/2 of 1.046 and 0.544 min, respectively.

A New Molybdenum Blue Structure Type: How Uranium Expands this Family of Polyoxometalates

The assembly of molybdenum polyoxometalates (POMs) has afforded large discrete nanoclusters with varied degrees of reduction such as the ~20 % reduced molybdenum blues. While many heterometals have been incorporated into these clusters to afford new properties, uranium has yet to be reported. Here we report the first uranium containing molybdenum blue clusters and the unique properties exhibited by this incorporation. The uranyl ion (UO2 2+) directs formation of Mo72U8, a square POM comprised of two faces connected by eight edge-sharing molybdenum dimers. Mo72U8, a chiral cluster, crystallizes as a racemic mixture and, in the solid state, has a 'negative' charge localized on one face of the cluster opposite the 'positively' charged face of another cluster. Using U(IV) as both heterometal and molybdenum reductant afforded crystals of Mo97U10, a wheel cluster with a heptamolybdate cap on one face. Mo97U10 dissociates in solution, losing the heptamolybdate, to form Mo90U10. Using more solvent during synthesis afforded crystals of Mo90U10S4 which, instead of heptamolybdate, contains four sulfate ions. Crystals of Mo90U10S4 undergo a dehydration induced phase change where clusters form a sheet through oxide bridges. Half of the bridges are cation-cation interactions between the uranyl oxygen atom and molybdenum, the first reported of this kind.

An Innovative SbIII-WVI-Cotemplated Antimonotungstate with Potential in Sensing Paroxetine Electrochemically

Advances in polyoxometalate (POM) self-assembly chemistry are always accompanied by new developments in molecular blocks. The exploration and discovery of uncommon building blocks offer great possibilities for generating unprecedented POM clusters. An intriguing SbIII-WVI-cotemplated antimonotungstate [H2N(CH3)2]11Na[SbW9O33]Er2(H2O)2Sb2[SbWVIW15O57]·22H2O (1) was synthesized, which comprises a classical trivacant Keggin [SbW9O33]9- ({SbW9}) fragment and an unclassical lacunary Dawson-like [SbWVIW15O57]15- ({SbWVIW15}) subunit. Notably, the Dawson-like {SbWVIW15} subunit is the first example of a [SbO3]3- and [WVIO6]6- mixed-heteroatom-directing POM segment. Hexacoordinated [WVIO6]6- can not only serve as the heteroatom function but its additional oxygen sites can also link to lanthanide, main-group metal, and transition-metal centers to form the innovative structure. {SbWVIW15} and {SbW9} subunits are joined by the heterometallic [Er2(H2O)2Sb2O17]22- cluster to give rise to an asymmetric sandwich-type architecture. To further realize its potential application in electrochemical sensing, a conductive 1@rGO composite was obtained by the electrochemical deposition of 1 with graphene oxide (GO). Using a 1@rGO-modified glassy carbon electrode as the working electrode, an electrochemical biosensor for detecting the antidepressant drug paroxetine (PRX) was successfully constructed. This work can provide a viable strategy for synthesizing mixed-heteroatom-directing POMs and demonstrates the application of POM-based materials for the electrochemical detection of drug molecules.

Photocatalytic Reduction of Nitrobenzene to Aniline by an Intriguing {Ru(C6H6)}-Based Heteropolytungstate

In this paper, we have successfully synthesized a structurally novel heteropolytungstate via coordination of four {Ru(C6H6)} and trivacant {TeW9O33} clusters, formulated as Cs4Na2H2[Te2W20O72(H2O){(C6H6)Ru}4]·12H2O (1). Compound 1 inherited the strong absorption of [Ru(C6H6)Cl2]2 in the visible region and {TeW9O33} in the UV region, providing a good basis for photocatalysis. As expected, compound 1 showed good photocatalytic activity in the visible-light-driven reduction of nitrobenzene using N2H4·H2O as a reductant with a yield of 99.8%, a high turnover number (TON = 330), and a high turnover frequency (TOF = 24 h-1). The cyclic experiment of nitrobenzene reduction indicated that compound 1 was an effective and stable heterogeneous catalyst. Finally, the nitrobenzene reduction pathway was affirmed using condensation with azobenzene as a reaction intermediate based on control experiments.

{Mo4}-directed structural evolution of highly reduced molybdenum red clusters for efficient proton conduction

A series of highly reduced Mo red clusters {Mo28} (1), {Mo30} (2), and {Mo40} (3) are synthesized from the rational assembly of planar {MoV4} building blocks and employed for proton conduction. 3 exhibits the best conductivity of 7.56 × 10-3 S cm-1 under optimal conditions due to the most efficient hydrogen-bonding network.

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.

Gold Nanoparticles Capped with a Novel Titanium(IV)-Containing Polyoxomolybdate Cluster: Selective and Enhanced Bactericidal Effect Against Escherichia coli

Bacterial infections are a public health threat of increasing concern in medical care systems; hence, the search for novel strategies to lower the use of antibiotics and their harmful effects becomes imperative. Herein, the antimicrobial performance of four polyoxometalate (POM)-stabilized gold nanoparticles (Au@POM) against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as Gram-negative and Gram-positive bacteria models, respectively, is studied. The bactericidal studies performed, both in planktonic and sessile forms, evidence the antimicrobial potential of these hybrid nanostructures with selectivity toward Gram-negative species. In particular, the Au@GeMoTi composite with the novel [Ti2 (HGeMo7 O28 )2 ]10- POM capping ligand exhibits outstanding bactericidal efficiency with a minimum inhibitory concentration of just 3.12 µm for the E. coli strain, thus outperforming the other three Au@POM counterparts. GeMoTi represents the fourth example of a water-soluble TiIV -containing polyoxomolybdate, and among them, the first sandwich-type structure having heteroatoms in high-oxidation state. The evaluation of the bactericidal mechanisms of action points to the cell membrane hyperpolarization, disruption, and subsequent nucleotide leakage and the low cytotoxicity exerted on five different cell lines at antimicrobial doses demonstrates the antibiotic-like character. These studies highlight the successful design and development of a new POM-based nanomaterial able to eradicate Gram-negative bacteria without damaging mammalian cells.

Polyoxometalates as Potential Artificial Enzymes toward Biological Applications

Artificial enzymes, as alternatives to natural enzymes, have attracted enormous attention in the fields of catalysis, biosensing, diagnostics, and therapeutics because of their high stability and low cost. Polyoxometalates (POMs), a class of inorganic metal oxides, have recently shown great potential in mimicking enzyme activity due to their well-defined structure, tunable composition, high catalytic efficiency, and easy storage properties. This review focuses on the recent advances in POM-based artificial enzymes. Different types of POMs and their derivatives-based mimetic enzyme functions are covered, as well as the corresponding catalytic mechanisms (where available). An overview of the broad applications of representative POM-based artificial enzymes from biosensing to theragnostic is provided. Insight into the current challenges and the future directions for POMs-based artificial enzymes is discussed.

Water-Soluble Polyoxometal Clusters of Molybdenum (V) with Pyrazole and Triazole: Synthesis and Study of Cytotoxicity and Antiviral Activity

Among well-studied and actively developing compounds are polyoxometalates (POMs), which show application in many fields. Extending this class of compounds, we introduce a new subclass of polyoxometal clusters (POMCs) [Mo12O28(μ-L)8]4- (L = pyrazolate (pz) or triazolate (1,2,3-trz or 1,2,4-trz)), structurally similar to POM, but containing binuclear Mo2O4 clusters linked by bridging oxo- and organic ligands. The complexes obtained by ampoule synthesis from the binuclear cluster [Mo2O4(C2O4)2(H2O)2]2- in a melt of an organic ligand are soluble and stable in aqueous solutions. In addition to the detailed characterization in solid state and in aqueous solution, the biological properties of the compounds on normal and cancer cells were investigated, and antiviral activity against influenza A virus (subtype H5N1) was demonstrated.

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).

Combination of covalent organic frameworks (COFs) and polyoxometalates (POMs): the preparation strategy and potential application of COF-POM hybrids

Both covalent organic frameworks (COFs) and polyoxometalates (POMs) show excellent properties and application potential in many fields, thus receiving widespread attention. In recent years, COF-POM hybrid materials were prepared by combining COFs and POMs through physical or chemical methods. COF-POM hybrids have shown high performance in many fields, such as catalysis, sensing, energy storage, and biomedicine. In this review, we introduced the preparation strategy and application of COF-POM hybrids in detail. We believe that the combination of COFs and POMs will provide more abundant functions and broad application prospects.

Ni/Mn-Complex-Tethered Tetranuclear Polyoxovanadates: Crystal Structure and Inhibitory Activity on Human Hepatocellular Carcinoma (HepG-2)

Polyoxometalates (POMs) exhibit unique structural characteristics and excellent physical and chemical properties, which have attracted significant attention from scholars in the fields of anticancer research and chemotherapy. Herein, we successfully synthesized and structurally characterized two novel polyoxovanadates (POVs), denoted as POVs-1 and POVs-2, where [M(1-vIM)4]2[VV4O12]·H2O (M: NiII and MnII, 1-vinylimidazole abbreviated as 1-vIM) serve as ligands. The two POVs are isomeric and consist of fundamental structural units, each comprising one [V4O12]4- cluster, two [M(1-vIM)4]2+ cations, and one water molecule. Subsequently, we evaluated the cell viability of human hepatocellular carcinoma (HepG-2) cells treated with the synthesized POVs using the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazoliumbromide) assay. And the changes in cell nucleus morphology, mitochondrial membrane potential (Δψm), and reactive oxygen species levels in HepG-2 exposed to POVs were monitored using specific fluorescent staining techniques. Both hybrid POVs showed potent inhibitory activities, induing apoptosis in HepG-2 cells along with significant mitochondria dysfunction and a burst of reactive oxygen species. Notably, the inhibitory effects of POVs-2 were more pronounced than those of POVs-1, which is primarily attributed to the different transition metal ions present. These findings underscore the intricate relationship between the metal components, structural characteristics, and the observed antitumor activities in HepG-2 cells.

Cerium-Encapsulated SbIII-SeIV-Templating Polyoxotungstate for Electrochemically Sensing Human Multidrug Resistance Gene Segment

A tower-like SbIII-SeIV-templating polyoxotungstate [H2N(CH3)2]12Na7H3[Ce0.5/Na0.5(H2O)5]2[SbSe2W21O75]2·50H2O (1) was synthesized, whose skeleton is assembled from two prolonged lacunary Dawson [SbSe2W21O75]13- units and two [Ce0.5/Na0.5(H2O)5]2+ linkers. The uncommon [SbSe2W21O75]13- unit can be viewed as a combination of one [SeW6O21]2- group grafted onto a trivacant Dawson [SbSeW15O54]11- subunit. The conductive composite 1-Au@rGO containing 1, gold nanoparticles, and reduced graphene oxide (rGO) was conveniently prepared, using which the 1-Au@rGO-based electrochemical genosensor was constructed for detecting human multidrug resistance gene segment. This work enriches structural types of dual-heteroatom-inserted polyoxometalates and promotes the application of polyoxometalates in genosensors.

Fabrication of Polyoxometalate-Based Metal-Organic Frameworks Integrating Paddlewheel Rh2(OAc)4 for Visible-Light-Driven Oxidative Coupling of Amines

The development of visible-light-responsive, environmentally friendly, and reusable photocatalysts for organic oxidation reactions is of vital significance. Herein, four polyoxometalate-based metal-organic frameworks (POMOFs) were synthesized and systematically characterized by assembling the paddlewheel complex Rh2(OAc)4 and various polyoxometalates (POMs). Single-crystal X-ray diffraction analysis revealed that the four POMOFs were isomorphic and possessed rare structural features among the POMOFs, with POMs as nodes and Rh2(OAc)4 as linkers. As expected, the activities of the four POMOFs for the photocatalytic oxidative coupling of benzylamine were better than that of Rh2(OAc)4 or POMs individually, which was ascribed to the synergistic effect between them, and the intrinsic reasons for the difference in the activity were explained via electrochemical measurements. In particular, the product imine yield reached 96.1% with NaRh-SiW12 as the catalyst and a turnover number and a turnover frequency of 480.5 and 120.5 h-1, respectively, while the product yield remained as high as 92% after three repetitions, evidencing its high stability. Moreover, the higher activities of the four POMOFs for the selective epoxidation of various alkenes reaffirm the synergistic effect between Rh2(OAc)4 and POMs.

Recent Advances in Confining Polyoxometalates and the Applications

Polyoxometalates (POMs) are widely used in catalysis, energy storage, biomedicine, and other research fields due to their unique acidity, photothermal, and redox features. However, the leaching and agglomeration problems of POMs greatly limit their practical applications. Confining POMs in a host material is an efficient tool to address the above-mentioned issues. POM@host materials have received extensive attention in recent years. They not only inherent characteristics of POMs and host, but also play a significant synergistic effect from each component. This review focuses on the recent advances in the development and applications of POM@host materials. Different types of host materials are elaborated in detail, including tubular, layered, and porous materials. Variations in the structures and properties of POMs and hosts before and after confinement are highlighted as well. In addition, an overview of applications for the representative POM@host materials in electrochemical, catalytic, and biological fields is provided. Finally, the challenges and future perspectives of POM@host composites are discussed.

Polyoxometalate-based frameworks for photocatalysis and photothermal catalysis

Polyoxometalate-based frameworks (POM-based frameworks) are extended structures assembled from metal-oxide cluster units and organic frameworks that simultaneously possess the virtues of POMs and frameworks. They have been attracting immense attention because of their diverse architectures and charming topologies and also due to their probable application prospects in the areas of catalysis, separation, and energy storage. In this review, the recent progress in POM-based frameworks including POM-based metal organic frameworks (PMOFs), POM-based covalent organic frameworks (PCOFs), and POM-based supramolecular frameworks (PSFs) is systematically summarized. The design and construction of a POM-based framework and its application in photocatalysis and photothermal catalysis are introduced, respectively. Finally, our brief outlooks on the current challenges and future development of POM-based frameworks for photocatalysis and photothermal catalysis are provided.

Structural Regulation of Two Polyoxometalate-Based Metal-Organic Frameworks for the Heterogeneous Catalysis of Quinazolinones

Two dimeric {ε-Zn₄PMo₁₂}-based metal-organic frameworks (MOFs), [ε-PMo₈^VMo₄^VIO₃₄(OH)₆Zn₄][LO] (SDUT-21, LO = [5-((4'-carboxybenzyl)oxy)isophthalic acid]) and [TBA]₃[ε-PMo₈^VMo₄^VIO₃₇(OH)₃Zn₄][LN] (SDUT-22, TBA⁺ = tetrabutylammonium ion, LN = [5-((4-carboxybenzyl)imino)isophthalic acid]), combining the advantages of polyoxometalates (POMs) and MOFs, were synthesized by the one-pot assembly strategy. The dimeric {ε-Zn₄PMo₁₂} units act as nodes that are linked by the flexible ligands and extended into two- or three-dimensional frameworks. The cyclic voltammetry and proton conductivity measurements of SDUT-21 and SDUT-22 were performed and indicated the high electron and proton transfer abilities. These materials also e xhibited the catalytic performance for the synthesis of quinazolinones in the heterogeneous state, and the different binding capacities toward the substrates caused the catalytic activity of SDUT-21 to be higher than that of SDUT-22 under the same conditions. In addition, the used catalysts could be readily recovered for five successive cycles and maintained high catalytic efficiency.