Functionalized polyoxometalates enable fast ion transport in solid-state batteries at room temperature.

The coupling of functionalized inorganic polyoxometalates with polymer electrolytes leads to considerably enhanced mechanical properties and faster ion transport (1.1 × 10-4 S cm-1) at room temperature. The assembled Li/Li symmetric cell displays excellent stability in a 3000 h cycling test and a Li/LiFePO4 cell exhibits superior cycling performance over 250 cycles.

Polyoxometalate-Organic Hybrid "Calixarenes" as Supramolecular Hosts.

Calixarenes are among the most useful and versatile macrocycles in supramolecular chemistry. The one thing that has not changed in the 80 years since their discovery, despite numerous derivatizations, is their fully organic, covalent scaffolds. Here, we report a new type of organic-inorganic hybrid "calixarenes" constructed by means of coordination-driven assembly. Replacing acetate ligands on the {SiW10 Cr2 (OAc)2 } clusters with 5-hydroxyisophthalates allows these 95° inorganic building blocks to be linked into bowl-shaped, hybrid "calix[n]arenes" (n=3, 4). With a large concave cavity, the metal-organic calix[4]arene can accommodate nanometer-sized polyoxoanions in an entropically driven process. The development of hybrid variants of calixarenes is expected to expand the scope of their physicochemical properties, guest/substrate binding, and applications on multiple fronts.

Atomically Precise Silver Clusters Stabilized by Lacunary Polyoxometalates with Photocatalytic CO2 Reduction Activity.

The syntheses of atomically precise silver (Ag) clusters stabilized by multidentate lacunary polyoxometalate (POM) ligands have been emerging as a promising but challenging research direction, the combination of redox-active POM ligands and silver clusters will render them unexpected geometric structures and catalytic properties. Herein, we report the successful construction of two structurally-new lacunary POM-stabilized Ag clusters, TBA6 H14 Ag14 (DPPB)4 (CH3 CN)9 [Ag24 (Si2 W18 O66 )3 ] ⋅ 10CH3 CN ⋅ 9H2 O ({Ag24 (Si2 W18 O66 )3 }, TBA=tetra-n-butylammonium, DPPB=1,4-Bis(diphenylphosphino)butane) and TBA14 H6 Ag9 Na2 (H2 O)9 [Ag27 (Si2 W18 O66 )3 ] ⋅ 8CH3 CN ⋅ 10H2 O ({Ag27 (Si2 W18 O66 )3 }), using a facile one-pot solvothermal approach. Under otherwise identical synthetic conditions, the molecular structures of two POM-stabilized Ag clusters could be readily tuned by the addition of different organic ligands. In both compounds, the central trefoil-propeller-shaped {Ag24 }14+ and {Ag27 }17+ clusters bearing 10 delocalized valence electrons are stabilized by three C-shaped {Si2 W18 O66 } units. The femtosecond/nanosecond transient absorption spectroscopy revealed the rapid charge transfer between {Ag24 }14+ core and {Si2 W18 O66 } ligands. Both compounds have been pioneeringly investigated as catalysts for photocatalytic CO2 reduction to HCOOH with a high selectivity.

A Macrocyclic Polyoxomolybdate with Phosphate and Phosphonate Linkers: Synthesis, Structure, and Proton Conductivity.

A coordination macrocycle composed of eight identical [PMo8O27]- ({PMo8}) clusters connected by both organic tetraphosphonates and inorganic phosphates, (C3N2H5)29(NH4)6H12[(PMo8O27)8(C10P4O12N2H20)4(PO4)4Cs(Mo4O10(H2O)4)] (C3N2H5+ = imidazolium), is presented here. The primary building block, {PMo8}, is a tetravacant Keggin-type phosphomolybdate that has never been observed before. The compound shows a high proton conductivity of 9.70 × 10-3 S cm-1 at 373 K and 98% relative humidity. Control experiments on an imidazolium-free sample demonstrate the critical role of the imidazolium counterions as mobile proton carriers. The contribution of imidazolium necessitates a high activation energy (Ea = 0.502 eV) for proton conduction via the vehicle mechanism.

{Mo126 W30 }: Polyoxometalate Cages Shaped by π-π Interactions.

Here we report the formation of giant {Mo126 W30 } polyoxometalate cages templated by π-conjugated planar ligands. Their inorganic shells incorporate arrays of 18 stacked aromatic carboxylates, such as 1,3,5-benzenetricarboxylate or 5-nitroisophthalate, and the assembly is stabilized by multiple π-π interactions. NMR data confirmed that the cages are stable in solution and the inner aromatic templates can be postsynthetically replaced by selected aliphatic dicarboxylates, paving the way for endo-functionalization and exploration of the reactivities within the cage cavities.

A bimodal type of AgPd Plasmonic Blackbody Nanozyme with boosted catalytic efficacy and synergized photothermal therapy for efficacious tumor treatment in the second biological window.

Nanozymes are promising for precise cancer treatment, but are typically limited in terms of the low catalytic efficiency and the complexity in tumor microenvironment (TME). Herein, we describe a bimodal type of AgPd plasmonic blackbody (AgPd PB) nanozyme of compact sizes (< 30 nm), which presents not only boosted enzyme efficacy but also efficient photothermal therapy (PTT) for synergized therapy through tissue-penetrating light in the second biological window (1000-1700 nm). The synthesized hyperbranched AgPd PB nanozymes possess intense and broadband localized surface plasmonic resonance absorption of 400-1300 nm, entailing prominent photothermal efficiency (η = 45.1% at 1064 nm) for PTT. Importantly, PTT was found to significantly boost the nanozyme efficacy of both catalase (CAT) and peroxidase (POD) processes, which correspondingly decompose H2O2 to into O2 to relieve tumor hypoxia, and activate H2O2 to generate oxidative •OH radical. While the generated •OH was found to be able to minimize heat shock proteins (HSPs), which plays a vital role to counterbalance PTT effect both in vitro and in vivo. As compared to control ground without treatment, the synergized nanozyme and PTT activities resulted in about 7-fold reduction of tumor volume, thus elevating the survival rate from 0 to 80% at 30 days posttreatment. Besides the synergistic therapy, the AgPd PB nanozyme were shown to own fluorescence, computed tomography (CT), and photoacoustic (PA) imaging abilities, thus having implications for uses in imaging-guided precise cancer therapy. This study provides a paradigm of TME responsive theranostics under NIR-II light irradiation.

Timing matters: pre-assembly versus post-assembly functionalization of a polyoxovanadate-organic cuboid.

The pre-assembly and post-assembly approaches in the functionalization of a polyoxovanadate-organic cuboid, [{V6S}8(QPTC)8{V3}2]10-, are discussed. We have shown that the two pathways have led to distinctly different systems, with either an expanded or contracted interior void space, when phenylphosphonate is introduced at different stages of the self-assembly. One leaves the cuboid framework largely intact, whereas the other results in a compact, twisted cuboid. Kinetic factors will have to be considered in the equilibrium of these complex processes. Furthermore, the exceptional stability of these polyoxometalate-organic systems facilitates mass spectrometric characterization, which confirms the composition of the complexes and also indicates that the methoxide groups on the vanadium cluster nodes are labile. The results will help deepen the mechanistic understanding of the formation mechanisms of polyoxovanadate-based metal-organic cages and other functionalized polyoxovanadate clusters in general.

Metal-Organic Cages with {SiW9 Ni4 } Polyoxotungstate Nodes.

A tritopic, Ni-substituted Keggin cluster, {SiW9 Ni4 }, assembles with rigid dicarboxylate linkers to give rise to a set of discrete, POM2n L3n -type structures (POM={SiW9 Ni4 }) with defined interior voids. The outcome of coordination-driven self-assemblies of these polyhedral cages-from fused dimers to trigonal prisms-was found to be sensitive to bend angles of the ditopic ligands, which vary from 122° to 180°. These polyoxotungstate-based metal-organic polyhedra, when coupled with [Ru(bpy)3 ]Cl2 as a photosensitizer and triethanolamine as the electron donor, serve as highly effective catalysts for CO2 reduction, with turnover numbers up to 328 and CO selectivity as high as 96.2 %. The inner cavities of such cage structures, if functionalized or of sufficient size to encapsulate targeted guest molecules, could present a new strategy towards functional materials for potential applications.

Macrocyclic Polyoxometalates: Selective Polyanion Binding and Ultrahigh Proton Conduction.

The rational development of an anion templation strategy for the construction of macrocycles has been historically limited to small anions, but large polyoxoanions can offer unmatched structural diversity and ample binding sites. Here we report the formation of a {Mo22 Fe8 } macrocycle by using the Preyssler anion, [NaP5 W30 O110 ]14- ({P5 W30 }), as a supramolecular template. The {Mo22 Fe8 } macrocycle displays selective anion binding behavior in solution. In the solid state, the 1 : 2 host-guest complex, {P5 W30 }2 ⊂{Mo22 Fe8 }, transports protons more effectively, through an extended hydrogen-bonding network, than a related 1 : 1 complex where the guest is completely encapsulated. The results highlight the great potential this anion templation approach has in producing macrocyclic systems for selective anion recognition and proton conduction purposes.

High-Sensitivity Sensing of Divalent Copper Ions at the Single Upconversion Nanoparticle Level.

Single-nanoparticle-level sensing allows us to measure individual molecular interactions and probe environmental stimuli at nanometer-scale resolution. Despite these premises, limited success has been met hitherto due to the demanding challenge to distinguish a dimmed signal from a noisy background. Here, we describe an approach for high-sensitivity single-nanoparticle-level sensing of divalent copper (Cu2+) ions through near-infrared-to-visible upconversion luminescence against a near-null background. This nanosensor utilizes ytterbium- (Yb3+) and erbium (Er3+)-doped sodium yttrium fluoride (NaYF4) upconversion nanoparticles (UCNPs) (maximal emission at 540 nm when excited at 980 nm) as an energy donor, of which the surface attaches Cu2+-dependent DNAzymes labeled with BHQ1 dye (Black Hole Quencher 1, maximal absorption at 548 nm) as energy acceptors. Adding a hint amount of Cu2+ ions resulted in the cleavage of a BHQ1-containing moiety in DNAzymes, thus turning on upconversion luminescence for sensitive detection. Indeed, this approach allows us to perform single-nanoparticle-level detection of Cu2+ ions with extraordinary signal-to-noise ratios (SNRs, >277) for all measured concentrations that cover 3 orders of magnitude (from sub-nM to µM). Importantly, a limit of detection of 220 pM was achieved, about sevenfold lower than the one at the ensemble level. Moreover, a stochastic particle-to-particle sensing behavior was also identified, featuring single-nanoparticle-level detection. This work untaps the usage of UCNPs for high-sensitivity single-nanoparticle-level biosensing.

How to not build a cage: endohedral functionalization of polyoxometalate-based metal-organic polyhedra.

Introducing functionalities into the interior of metal-organic cage complexes can confer properties and utilities (e.g. catalysis, separation, drug delivery, and guest recognition) that are distinct from those of unfunctionalized cages. Endohedral functionalization of such cage molecules, for decades, has largely relied on modifying their organic linkers to covalently append targeted functional groups to the interior surface. We herein introduce an effective coordination method to bring in functionalities at the metal sites instead, for a set of polyhedral cages where the nodes are in situ formed polyoxovanadate clusters, [VIV 6O6(OCH3)9(µ6-SO4)(COO)3]2-. Replacing the central sulfates of these hexavanadate clusters with more strongly coordinating phosphonate groups allows the installation of functionalities within the cage cavities. Organophosphonates with phenyl, biphenyl, and terphenyl tails were examined for internalization. Depending on the size/shape of the cavities, small phosphonates can fit into the molecular containers whereas larger ones inhibit or transform the framework architecture, whereby the first non-cage complex was isolated from a reaction that otherwise would lead to entropically favored regular polyhedra cages. The results highlight the complex and dynamic nature of the self-assembly process involving polyoxometalates and the scope of molecular variety accessible by the introduction of endo functional groups.

Pentadecanuclear Fe-Containing Polyoxometalate Catalyst for Visible-Light-Driven Generation of Hydrogen.

The structurally new, carbon-free pentadecanuclear Fe-containing polyoxometalate, Na21[NaFe15(OH)12(PO4)4(A-α-SiW9O34)4]·85H2O (Na21-Fe15P4(SiW9)4), was synthesized using a facile one-pot, solution-based synthetic approach and systematically characterized by various spectroscopic techniques. Single-crystal X-ray diffraction reveals that the title complex is composed of two [Fe4(A-α-SiW9O34)] fragments and two [Fe3.5(A-α-SiW9O34)] fragments stabilized by four PO4 linkers in a tetrameric style with idealized Td point group symmetry. When coupling with (4,4'-ditert-butyl-2,2'-dipyridyl)-bis(coumarin)-iridium(III) hexafluorophosphate ([Ir(coumarin)2(dtbbpy)][PF6]) photosensitizer and triethanolamine (TEOA) sacrificial electron donor, polyoxoanion Fe15P4(SiW9)4 effectively catalyzed hydrogen production with a minimally optimized TON of 986, which represents, to our knowledge, one of the highest values among known Fe-substituted POM-catalyzed hydrogen production systems. Both a mercury-poisoning test and FT-IR characterizations proved the structural stability of Fe15P4(SiW9)4 catalyst under photocatalytic conditions. The photocatalytic mechanism of the present hydrogen-evolving system was investigated by time-solved luminescence and static emission quenching measurements.

Bridging Polyoxometalate-Based Mn4 Cubane Clusters with Inorganic Phosphates: Structural Transformation and Magnetic Properties.

The mixed-valent tetramanganese MnIII3MnIV (Mn4) cubane clusters have been at the forefront of molecular magnetism and biomimetic catalysis research for decades. Incorporating robust polyoxometalates to Mn4 cubanes significantly improves their stability and aqueous solubility, while providing a great platform for studying their deposition onto selected surfaces during device fabrication. In this work, we discovered that the terminal carboxylate ligands in these polyoxometalate-based [MnIII3MnIVO4] magnetic clusters can be partially or completely replaced by inorganic phosphate/polyphosphate groups. This replacement leads to oligomeric aggregates of the Mn4 clusters. The magnetic data of the monomeric and oligomeric Mn4 clusters suggested that the introduction of inorganic phosphate bridges may not alter the S = 9/2 ground state of individual Mn4 clusters, although different magnetic behaviors, especially at low temperatures, were observed primarily because of intercluster interactions.

In situ self-assembled cationic lanthanide metal organic framework membrane sensor for effective MnO4- and ascorbic acid detection.

Developing portable membrane sensors to accurately detect the biomolecule ascorbic acid (AA) is extremely important for food safety and human health. Herein, we successfully design and synthesize a novel cationic metal organic framework (Eu-pbmc, Hpbmc = 2-(pyridine-2-yl)-1H-benzimidazole-5-carboxylic acid) and assemble polyacrylonitrile/Eu-pbmc membrane (PEM) by an in-situ growth strategy. Benefiting from the appreciable loading of Eu-pbmc nanoparticles and high water permeation flux, PEM possesses effective detection for MnO4- with a limit of detection (LOD) of 17 nM. Utilizing the cationic porous framework, we load MnO4- into PEM and construct a "on-off-on" system for effective AA detection. The oxidative MnO4- can be reduced by AA and the resulting turn-on luminescence can reflect the concentration of AA. Compared with pure Eu-pbmc crystals, PEM exhibits improved AA detection performance with LOD of 48 nM and detection time of 1 min via a concise detection operation. The stable membrane sensor realizes an accurate detection in real biological samples, meeting the practical requirement. Moreover, an IMP logic gate is helpful to analyze MnO4- and AA in water. The proposed novel luminescence platform as well as reasonable "on-off-on" luminescence mode provide a promising method for AA detection.

Highly Stable Zinc-Based Metal-Organic Frameworks and Corresponding Flexible Composites for Removal and Detection of Antibiotics in Water.

Antibiotic contamination of water bodies is a major environmental concern. Exposure to superfluous antibiotics is an ecological stressor correlated to the development of antibiotic resistance. Thus, it is imperative that effective methods are developed to simultaneously detect and remove such antibiotics so as to avoid inadvertent release. Herein, two flexible three-dimensional (3D) zinc-based metal-organic frameworks (MOFs) {[Zn2(bcob)(OH)(H2O)]·DMA}n (ROD-Zn1) and {[Zn(Hbcob)]·(solvent)}n (ROD-Zn2) (H3bcob = 1,3-bis((4'-carboxylbenzyl)oxy)benzoic acid) with rod second building units (SBUs) are successfully prepared. Their exceptional water and chemical stabilities (toward both acid and base), fast sorption kinetics, and unique framework endow the MOFs with excellent uptake capacity toward various antibiotics in the aqueous environment. The adsorption performance was further optimized by one-pot preparation of MOF-melamine foam (MF) hybrid composites, resulting in a hierarchical microporous-macroporous MOF@MF system (ROD-Zn1@MF and ROD-Zn2@MF), which are readily recyclable after adsorptive capture. The mechanisms of adsorption have been deeply investigated by static and competitive adsorption experiments. In addition, the MOFs exhibit excellent fluorescent properties and quenched by trace amounts of antibiotics in water solution. Therefore, ROD-Zn1 and ROD-Zn2 present a dual-functional performance, being promising candidates for detection and removal of antibiotics.

Chain length effect in the functionalization of polyoxometalates with α,ω-alkyldiphosphonates.

Altering the organic spacers in hybrid complexes of polyoxotungstates and long-chain α,ω-alkyldiphosphonates (Ln), by a single CH2 group (e.g.L6vs.L5), can steer the self-assembly processes into different paths. Even homologous hybrids of L5 and L4 have seen the spin ground states switch from S = 0 to S = 9 upon shortening the chain length (L5vs.L4).

{Mo24Fe12} macrocycles: anion templation with large polyoxometalate guests.

POM and circumstance: Nanometer-sized polyoxometalates (POMs) bring a new direction to anion-templated supramolecular chemistry. The Keggin (left) and Dawson-type (right) polyoxoanions direct the assembly of giant metallomacrocycles through an array of weak hydrogen-bonding interactions. The concerted action of multiple hydrogen bonds keeps the templating guests embedded within the hosts, even in the solution state.

The self-assembly of a macroion with anisotropic surface charge density distribution.

A macroion, having anisotropic surface charge density distribution, shows unique self-assembly behaviour in polar solvents. Regular "blackberry"-like assemblies form in methanol-water mixtures due to counter-ion mediated attraction and the strong contribution of hydrogen bonding. However, rod-like assemblies form in acetone-water mixtures as the charge inhomogeneity effect overcomes the non-directional hydrogen bonding.