Polyoxometalate Chemistry Research Articles

Medium and high temperature H2S removal via phosphazene polyoxometalate ionic liquids: Performance evaluation and mechanism exploration

The development of non-aqueous solvent desulfurizer is crucial to addressing the challenges associated with traditional liquid-phase wet desulfurization technologies. Based on this, we prepared a series of phosphazene polyoxometalate ionic liquids (PPILs) based of 1-butyl-3-methylimidazolium chloride using different kinds of phosphazenes (PNs) combined with polyoxometalate (POM), and used for hydrogen sulfide (H2S) dynamic absorption experiments. The effects of PN type and ratio, temperature and desulfurizer concentration on the desulfurization performance of different PPILs were explored. Among them, PPILs@IBuPN-9 as the optimal desulfurizer could keep almost 100 % desulfurization efficiency in the medium and high temperature range (100–200 °C). The results showed that the combination of PNs with POM significantly improved and widened the H2S removal performance and the operational temperature window of the desulfurizer. Besides, PPILs@IBuPN-9 required only air regeneration to maintain relatively stable cycle performance for at least four times and the sulfur capacity could be efficiently increased during multiple regenerations. It was found that the hydrogen bonding sites on IBuPN network formed significantly enhanced the H2S capture ability of PPILs and the sulfur capacity was substantially improved by S2− substitution of oxygen atoms in the POM according to the characterization results and density functional theory calculations. This study promotes the deep integration of polyoxometalate chemistry with ionic liquids in the field of gas purification and promotes the development of non-aqueous phase desulfurization process.

2,5-Thiophenedicarboxylic Acid Bridging Hexameric CeIII-Substituted Selenotungstate and Its Application for Detecting Mucin 1.

The development of polyoxometalate chemistry not only is derived from the continuous discovery of novel polyoxometalates (POMs) but also stems from the exploitation of their new functionalities. In this work, we obtained a rigid sulfur-containing heterocyclic ligand-linking aggregate [N(CH3)4]10Na6H6[Ce8(H2O)26W8(HTDA)2(TDA)2O20][SeW4O18]2[SeW9O33]4·112H2O (1) (H2TDA = 2,5-thiophenedicarboxylic acid). Its polyanionic unit consists of one [Ce4(H2O)13W4O10(HTDA)(TDA)O10]18+ cluster and two kinds of Keggin-type [SeW4O18] and [SeW9O33] segments. It is noteworthy that H2TDA ligands not only work as connectors to link two symmetrical {[Ce4(H2O)13W4(HTDA)(TDA)O10][SeW4O18][SeW9O33]2}11- units but also function as ornaments to graft to the polyanionic backbone. Furthermore, 1 and 3,4-ethylenedioxythiophene (EDOT) were deposited on the glassy carbon electrode (GCE) by the electropolymerization (EPM) method, resulting in a 1-poly(3,4-ethylenedioxythiophene) (1-PEDOT) composite film, which can provide sufficient binding sites to immobilize Au nanoparticles (Au NPs). Hereafter, the Au NPs-immobilized 1-PEDOT modified electrode (Au/1-PEDOT/GCE) was used to construct an electrochemical aptasensor to detect mucin 1, showing a low detection limit of 29.5 fM in the Tris solution. This work not only demonstrates that rigid heterocyclic ligands are beneficial for the creation of novel rare-earth-substituted selenotungstate hybrids but also provides more enlightenment for POM-based materials used for electrochemical detection of cancer markers.

A New Avenue in Hybrid Polyoxometalate Chemistry: Synthesis and Characterization of Mn (II) Functionalized POM Based Ionic Liquids

The synthesis of novel hybrid materials, combining the properties of organic and inorganic components in one compound, results in materials with unique physical and chemical properties. The organic-functionalization of POMs with covalently or non-covalently linked organic species opens a large spectrum of possibilities and research challenges. The development of such novel systems for metal−organic architectures is an attractive research field. Lacunary polyoxometalates (POMs) offer structurally well-defined coordination sites with various coordination directions; thus, lacunary POMs are ideal building blocks for inorganic−organic architectures. Here, we report the successful self-assembly of transition metal substituted anionic POM along with a new generation POM based ionic liquid. We know that the counter-cations in polyoxometalate chemistry play immense role beyond charge balance. That is why the resultant structure is furthermore utilized as a stable and reactive building block to synthesize POM based ionic liquid (POM-IL), an inorganic−organic architecture comprising 3d-metal substituted mono-lacunary POM and tetrabutyl ammonium (TBA) ligands.

Commentary on the role of polyoxometalates in nature cybernetic loop

AbstractThe interplay between extraterrestrial, atmospheric, aqueous, interfacial, and hydrothermal processes is crucial for Earth's prebiotic chemistry. Volcanic terrains contain polyoxometalates (POMs). Some polyoxocuprates were identified as building blocks of fumarole minerals produced from high‐temperature gases. The existence of polyoxovanadate anions in acidified reducing volcanic aquifers cannot be excluded. At present, it can only be speculated whether life arose around natural POM deposits and/or around their aqueous phase chemistry through acid‐base and/or redox reactions. This Commentary spans different fields of sciences in nature cybernetic loop to provide impetus to explore gas‐phase chemical reactions of multiply charged POM ions, catalysis by POM‐containing mineral phases, the behavior of POMs under plasma‐initiated ultraviolet photolysis, interactions of POMs with microorganisms, bioorthogonal chemistry of POMs, and engineering POM‐based bionic functions inspired by living organisms.

Bioorthogonal chemistry of polyoxometalates - challenges and prospects.

Bioorthogonal chemistry has enabled scientists to carry out controlled chemical processes in high yields in vivo while minimizing hazardous effects. Its extension to the field of polyoxometalates (POMs) could open up new possibilities and new applications in molecular electronics, sensing and catalysis, including inside living cells. However, this comes with many challenges that need to be addressed to effectively implement and exploit bioorthogonal reactions in the chemistry of POMs. In particular, how to protect POMs from the biological environment but make their reactivity selective towards specific bioorthogonal tags (and thereby reduce their toxicity), as well as which bioorthogonal chemistry protocols are suitable for POMs and how reactions can be carried out are questions that we are exploring herein. This perspective conceptualizes and discusses advances in the supramolecular chemistry of POMs, their click chemistry, and POM-based surface engineering to develop innovative bioorthogonal approaches tailored to POMs and to improve POM biological tolerance.

Aryl selenonium vs. aryl sulfonium counterions in polyoxometalate chemistry: the impact of Se+ cationic centers on the photocatalytic reduction of dichromate.

A selenonium organic counter ion has been used in polyoxometalate chemistry to develop a new aryl selenonium polyoxometalate (POM) hybrid, and its photocatalytic properties have been explored in comparison with an aryl sulfonium POM-hybrid counterpart for the first time. The chalcogenonium counterions, namely, methyldiphenylsulfonium trifluoromethane sulfonate (MDPST) and methyldiphenylselenonium trifluoromethane sulfonate (MDPSeT), and their octamolybdate ([Mo8O26]4-) hybrids, 1 and 2, with the general formula (C13H13X)4[Mo8O26] (where X = S for 1 and Se for 2) were synthesized and characterized. Hybrids 1 and 2 vary in their chalcogenonium cationic center (S+vs. Se+), which enabled a direct comparison of their photocatalytic properties as a function of the cationic center. The photocatalytic activities of hybrids 1 and 2 were tested using the reduction of dichromate (Cr2O72-) as a model reaction under UV irradiation. A 99% photocatalytic reduction of Cr2O72- with a rate constant of 0.0305 min-1 was achieved with hybrid 2, while only a 67% reduction with a rate constant of 0.0062 min-1 was observed with hybrid 1 in 180 minutes. The better catalytic performance of hybrid 2 may be correlated to the larger atomic radii of Se than S, which helps in better stabilizing the photogenerated electron-hole (e--h+) pair on the POM cluster by polarizing its lone pair more efficiently compared to S. The catalytic recyclability was tested for up to 4 cycles using hybrid 2, and up to 98% reduction was obtained even after the 4th cycle. Recyclability tests and control experiments also indicated the generation of some elemental Se through possible cleavage of some C-Se bonds of MDPSe under prolonged UV exposure during catalysis, and the Se thus generated was found to contribute to the catalytic reduction of dichromate. This study, therefore, opens new avenues for aryl selenonium moieties and their POM hybrids for potential catalytic applications.

Heteroelements in polyoxometalates: a study on the influence of different group 15 elements on polyoxometalate formation.

In the field of polyoxometalate (POM) chemistry, different heteroelements are integrated into the cage-like structures, to obtain different structural types of so-called heteropolyanions (HPAs). While it is generally accepted, that some elements favor certain types of structure, a systematic study is still missing. In this article, we present a systematic investigation of the influence of the group 15 elements nitrogen, phosphorous, arsenic, and antimony on the formation of different POM structure types. Our study is comprised of DFT calculations and corresponding experimental structural analysis. In this context, the DFT study establishes the thermodynamics of formation of different coordination geometries with various heteroelements on two POM structure types, the Keggin and the Anderson-Evans structures. Our POM synthesis experiments were performed at two different pH values (1 and 5) and resulted in a variety of heteropolytungstates, which were identified and characterized by elemental analysis as well as single crystal X-ray diffraction and vibrational spectroscopy. With these methods, we were able to establish a clear trend, showing that heavier elements lead to formation of different structure types than lighter elements. These results signify a large step towards a better understanding of POM formation specifically with respect to the choice of heteroelement.

{Ti12} Cluster-Added Poly(polyoxometalate) Containing Mixed Trivacant Keggin and Dawson Fragments.

A new high-nuclear Ti-oxo-cluster-added poly(polyoxometalate) Cs2Na19H12[(Cs@Ti12O18)@{(A-α-SiW9O34) (P2W15O56)3}]·29H2O (1) has been made by reacting two types of trivacant precursors with TiOSO4 under hydrothermal conditions. The polyoxoanion of 1 contains one Keggin-type [A-α-SiW9O34]10- and three Dawson-type [P2W15O56]12- fragments that synergistically induce the Ti4+ ions to aggregate at vacant sites, resulting in a large {Ti12}-oxo-cluster cavity sealing a Cs+ ion. It is worth noting that the {Ti12} cluster is built by three edge-shared Ti3O13 ({Ti3}1) cores and one corner-shared Ti3O15 ({Ti3}2) core bridged via 6 μ2-O, which has never been seen before in polyoxometalate chemistry. Significantly, 1 represents the first example of [A-α-SiW9O34]10- and [P2W15O56]12- simultaneously participating in making poly(polyoxometalate).

10-Molybdo-2-vanadophosphoric acid derived (V) MoS2 microflowers @ V2CTx MXene designed 3D@2D nanoarchitecture for high-performance aqueous supercapacitors

Polyoxometalates (POMs) are emerging redox active materials having great potential for energy storage. Normally, POMs are directly anchored to substrates, however we looked into a novel feature of POM chemistry by employing them as precursor for metal sulphide 3D microflower arrangements without the use of a template. High surface area, outstanding electrical conductivity, and exceptional structural stability are all characteristics of 2D materials like MXenes; nevertheless, their direct use is constrained by poor specific capacitance as a result of layer restacking. Transition Metal sulphides (TMDs), on the other hand, have a high surface area but a poor conductivity. Layer restacking will be prevented by an MXene-TMDs nanocomposite, which will also increase TMDs' conductivity. Here, we report MXene-TMDs nanocomposite (MV) with MXene intercalated vanadium molybdenum sulphide (VMD) microflowers using 10-molybdo-2-vanadophosphoric acid. Due to faster ionic diffusion, higher electrochemically active surface area, and more active sites, MV exhibits good electrochemical performance. Additionally, the MV||MV cell offers outstanding cycling stability (96 % capacitance retention after 8000 cycles @ 2 A g−1) and performs well up to 0.9 V, delivering a maximum energy density of 28.96 Wh kg−1 @ 232.35 W kg−1. This research investigates how POMs affect the atomic ratio and morphology of final product.

Space-Confined Nucleation of Semimetal-Oxo Clusters within a [H7P8W48O184]33– Macrocycle: Synthesis, Structure, and Enhanced Proton Conductivity

Spatially confined assembly of semimetallic oxyanions (AsO33- and SbO33-) within a [H7P8W48O184]33- (P8W48) macrocycle has afforded three nanoscale polyanions, [{AsIII5O4(OH)3}2(P8W48O184)]32- (As10), [(SbIIIOH)4(P8W48O184)]32- (Sb4), and [(SbIIIOH)8(P8W48O184)]24- (Sb8), which were crystallized as the hydrated mixed-cation salts (Me2NH2)13K7Na2Li10[{AsIII5O4(OH)3}2(P8W48O184)]·32H2O (DMA-KNaLi-As10), K20Li12[(SbIIIOH)4(P8W48O184)]·52H2O (KLi-Sb4), and (Me2NH2)8K6Na5Li5[(SbIIIOH)8(P8W48O184)]·65H2O (DMA-KNaLi-Sb8), respectively. A multitude of solid- and solution-state physicochemical techniques were employed to systematically characterize the structure and composition of the as-made compounds. The polyanion of As10 represents the first example of a semimetal-oxo cluster-substituted P8W48 and accommodates the largest AsIII-oxo cluster in polyoxometalates (POMs) reported to date. The number of incorporated SbO33- groups in Sb4 and Sb8 could be customized by a simple variation of SbIII-containing precursors. Encapsulation of semimetallic oxyanions inside P8W48 sets out a valid strategy not only for the development of host-guest assemblies in POM chemistry but also for their function expansion in emerging applications such as proton-conducting materials, for which DMA-KNaLi-As10 showcases an outstanding conductivity of 1.2 × 10-2 S cm-1 at 85 °C and 70% RH.

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 PIII and TeIV synergistically controlling octa-CeIII-encapsulated heteropolyoxotungstate [H2N(CH3)2]11K2Na6H11[Ce8(CH3COO)2(HPIIIO3)2W8O20(H2O)12(B-β-TeW8O30)2(B-α-TeW8O31)4]·64H2O (1). Its distinctive anion skeleton [Ce8(CH3COO)2(HPIIIO3)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(HPIIIO3)2W8O20(H2O)12]26+ {Ce8P2W8} cluster core. Interestingly, {Ce8P2W8} is assembled from four [W2O11]10- groups and two [HPIIIO3]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.

A Novel Tri-Coordination Zinc Complex Functionalized Silicotungstate with ROS Catalytic Ability and Anti-Tumor Cells Activity

Reactive oxygen species (ROS) can be used as an effective method to treat tumors. Artificial oxidase has received increasing attention as a catalyst for ROS generation in fields ranging from bioinorganic chemistry to pharmaceutical chemistry. In this study, an artificial oxidase based on a binuclear zinc complex and Keggin-type silicotungstate [Zn2(4,4′-bpy)(Phen)2][SiW12O40] (ZSW) (4,4′-bpy = 4,4′-bipyridine; Phen = 1,10-phenanthroline) was synthesized and structurally featured in terms of its X-ray photoelectron spectrum (XPS), bond valence sum (Σs) calculation, IR spectra, and single-crystal X-ray diffraction (SXRD). ZSW is an ionic compound in which the cation is a binuclear zinc complex [Zn2(4,4′-bpy)(Phen)2]4+ and the anion is a α-Keggin-type silicotungstate [SiW12O40]4– cluster. Notably, the Zn ions in the [Zn2(4,4′-bpy)(Phen)2] exist in tri-coordination, which was first obtained in polyoxometalate (POM) chemistry. It was also demonstrated that ZSW is capable of efficiently catalyzing the production of ROS, which, according to the computational calculations, may be due to the synergistic action of zinc complexes and POM building blocks. Furthermore, ZSW exhibited inhibition ability toward ROS-sensitive tumor cells, such as PC12 cells.

Anion-π stacks of Lindqvist superoctahedra [Mo6O19]2− supported by caffeinium and theophyllinium cations

Ionic lattices of two new Lindqvist polyoxometalates (HCaf)2[Mo6O19]⋅2EtOH (1) and (HThe)2[Mo6O19]⋅H2O (2) [Caf = caffeine, The = theophylline] reveal extensive anion⋅⋅⋅π interactions, which result in the generation of dense stacks of the electron deficient aromatic cations to the faces of metal-oxide polyhedra with interplanar distances of 2.989(5)-3.048(4) Å and interplanar angles of 2.60(13)-7.35(13)o. These interactions are applicable to the construction of purine/ polyoxometalate solids as special kinds of supramolecular synthons providing linkage of metal-oxide polyhedra through anion⋅⋅⋅π⋅⋅⋅anion links. Hirshfeld surface analysis for the individual anions in 1 and 2 as well as for related structures in CSD supports the relevance of this new interaction for crystal chemistry of polyoxometalates. The total interaction energies of the {(Cation)4[Mo6O19]}2+ synthons are evaluated and compared by using DFT calculations, which suggest larger stability of the (HCaf)+ complexes (–290.3 kcal/mol for 1 and –250.9 for 2) conditioned by additional CH···O contacts involving the methyl groups and the O-atoms of the [Mo6O19]2− anions. Interesting supramolecular assemblies in compounds 1 and 2 have been also rationalized by using molecular electrostatic potential (MEP) surface plots and the noncovalent interaction plot (NCIplot) index. The present structures provide reliable molecular models for geometries and energetics of the stacks subtended by purine bases and polyoxometalate anions that could be relevant for specific targeting of POMs in biomedical systems.

Bouquet-like uranium-containing selenotungstate consisting of two different Keggin-/Anderson-type units with excellent photoluminescence quantum yield

We present the synthesis, characterization and photoluminescence properties of uranium-containing selenotungstate, [(UO2)3(SeO3)3Na5(H2O)6(SeW6O21)(SeW9O33)3]21–, which was isolated by a one-pot reaction of uranium nitrate with sodium tungstate and sodium selenite in a pH 5.2 aqueous solution at 90 °C. In this study, the effect of the introduction of lone-electron pair containing heteroatoms on the structure is demonstrated, a three-layered heterometallic {Se3U3Na5} cluster is encapsulated by two different anionic building block units: three trivacant Keggin {B-α-SeW9O33} and one Anderson {SeW6O21}. To our knowledge, the {Se3U3Na5} cluster has never been observed in the polyoxometalate chemistry. The solid-state photoluminescence properties and lifetime decay behaviours of the title compound (1) have been measured at room temperature, and the photoluminescence spectrum displays the characteristic emission bands of corresponding uranyl cations. In addition, the photoluminescence quantum yield of 1 is 72%, which is almost three times that of starting material UO2(NO3)2·6H2O (27%). By using this strategy, we envision that an increasing number of assemblies with ‘open’ clusters may be designed and obtained, in which the exposed oxygen atoms show strong affinity towards metal ions, providing new opportunities to generate bigger clusters or to tune existing properties.

Giant Ln 30 -Cluster-Embedded Polyoxotungstate Nanoclusters with Exceptional Proton-Conducting and Luminescent Properties

Giant Ln ₃₀ -Cluster-Embedded Polyoxotungstate Nanoclusters with Exceptional Proton-Conducting and Luminescent Properties

Polyoxometalates as chemically and structurally versatile components in self-assembled materials.

Polyoxometalates (POMs) are anionic molecular metal oxides with expansive diversity in terms of their composition, structure, nuclearity and charge. Within this vast collection of compounds are dominant structural motifs (POM platforms), that are amenable to significant chemical tuning with minimal perturbation of the inorganic oxide molecular structure. Consequently, this enables the systematic investigation of these compounds as inorganic additives within materials whereby structure and charge can be tuned independently i.e. [PW12O40]3−vs. [SiW12O40]4− while also investigating the impact of varying the charge balancing cations on self-assembly. The rich surface chemistry of POMs also supports their functionalisation by organic components to yield so-called inorganic–organic hybrids which will be the key focus of this perspective. We will introduce the modifications possible for each POM platform, as well as discussing the range of nanoparticles, microparticles and surfaces that have been developed using both surfactant and polymer building blocks. We will also illustrate important examples of POM-hybrids alongside their potential utility in applications such as imaging, therapeutic delivery and energy storage.

Three Lanthanide-Functionalized Antimonotungstate Clusters with a {Sb4O4Ln3(H2O)8} Core: Syntheses, Structures, and Properties.

Three lanthanide (Ln)-functionalized antimonotungstate (AT) clusters with a {Sb4O4Ln3(H2O)8} core [H2N(CH3)2]14Na8H16[Sb4O4Ln3(H2O)8W2O4(H2O)2(B-α-SbW9O33)4]2·87H2O [Ln = Dy3+ (1), Ho3+ (2), Y3+ (3)] were synthesized in an acidic aqueous solution. Their molecular structural unit comprises two {Sb4O4Ln3(H2O)8}-core-incorporated tetrameric [Sb4O4Ln3(H2O)8W2O4(H2O)2 (B-α-SbW9O33)4]19- polyanionic units, each of which is assembled from an unprecedented [Sb4O4Ln3(H2O)8W2O4(H2O)2]17+ heteroatom cluster surrounded by four trivacant [B-α-SbW9O33]9- subunits. What is noteworthy is that a tetrahedral {Sb4O4} cluster is located at the center of the polyanionic unit, as far as we know, which is very infrequent in multi-Ln-functionalized polyoxometalate chemistry. Solid-state luminescent properties and energy migration of AT ligands to Dy3+ and Ho3+ cations in 1 and 2 have been intensively probed at ambient temperature. By varying the exciting wavelength from 250 to 450 nm, the emitting color could vary from blue to yellow for 1 and blue to green-yellow for 2, separately. In addition, high catalytic activities and good reusability of 2 as a heterogeneous catalyst for oxygenation reaction of sulfides have been systematically performed.

Frontiers and applications of polyoxometalates-based porous ionic crystals

<p indent="0mm">Polyoxometalates (denoted as POMs) are discrete metal-oxide anions of V, Mo, W, etc., with variable structures and sub-nanometer sizes. Plenty of POMs and their derivatives have been reported due to their oxygen-enriched surface and abundant substitutional chemistry. However, few studies have focused on the modulation of the counter cations so far. Different from common cations, such as Na⁺, NH₄⁺ and other organic ammonium ions (tetramethylammonium, tetrabutylammonium, etc.), cation clusters with larger size can also be used as counter ions of POMs. They are arranged alternately through ionic bonds or hydrogen bonds to form the solid ionic crystal materials with special properties, which are named POM-based porous ionic crystals (PPICs). The use of cation clusters with different compositions greatly enriches the structure and type of PPICs, which further boosts the development of polyoxometalates chemistry. The POMs anions and large metal complex cations in PPICs are regularly arranged into a porous honeycomb or layered structure. Some PPICs also contain monovalent cations such as H⁺ and alkali metal ions to balance their extra negative charges. The use of ion clusters facilitates the formation of pore structures in the PPICs lattice because they can reduce the electrostatic interaction between cations and anions. Thus, the pore structure of PPICs is much larger than that of POMs. Note that the pore size in PPICs can be easily adjusted by changing the shape, size and charges of cation and anions. Apart from the electrostatic interaction, anisotropic π-π stacking and hydrogen bonding network among the components of PPICs also contribute to their assembly. All these interaction modes will affect the arrangement of anions and cations in the PPICs lattice, resulting in the formation of different hole sizes and various channels characteristics in the crystal lattice, such as hydrophilic, hydrophobic and amphiphilic pores. In addition, the long-range Coulomb interaction works isotropically, leading to the easy transformation of the flexible PPICs structure. Hence, the adjustment of the channel provides a useful strategy for constructing PPICs with unique structures. Most importantly, PPICs show better performance than individual components because they inherit the advantages from both anions and cations. Briefly, PPICs not only retain good redox reversibility, rich multi-electron transfer characteristics and strong Brønsted acidity of POMs, but also reserve the magnetic properties of large cation clusters. Therefore, the physical and chemical properties of PPICs can be modulated by the rational design of each component. The future research on PPICs should not be limited to expanding the categories of cations, and the innovative structural type of POMs is also an important aspect. In addition to the Keggin POMs, other POMs structures, such as Dawson, Anderson, and Preyssler, can also be used in PPICs, resulting in some unique properties. Besides, various POM-based materials (modified POMs or POM-based composites, etc.) can also be adopted to fabricate PPICs, which may bring unexpected performance. Thus, changing anions and cations makes PPICs have great potential in many interdisciplinary fields such as chemistry, materials science, and biomedicine. This review systematically summarizes the structural characteristics and composition of PPICs, which is essential for understanding the characteristics of PPICs, such as adjustable pore structure, unique redox behavior, strong acidity and magnetic properties. In general, PPICs with different properties can be constructed by using diverse POMs and distinct cation clusters, which will be widely applied in many fields such as guest adsorption, ion exchange, photoelectric catalysis, bioimaging and medical materials.

Nanoblackberries of {W72Fe33} and {Mo72Fe30}: Electrocatalytic Water Reduction.

The reversible self-assembly of a {Mo72Fe30} cluster into nanoblackberries in a dilute solution of the relevant crystalline compound [Mo72Fe30O252(CH3COO)12{Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O)91]·150H2O ({Mo72Fe30}cryst) was demonstrated by Liu, Müller, and their co-workers as a landmark discovery in the area of polyoxometalate chemistry. We have described, in the present work, how these ∼2.5 nm nano-objects, {M72Fe30} (M = W, Mo) can be self-assembled into nanoblackberries irreversibly, leading to their solid-state isolation as the nanomaterials Fe3[W72Fe30O252(CH3COO)2(OH)25(H2O)103]·180H2O ({W72Fe33}NM) and Na2[Mo72Fe30O252(CH3COO)4(OH)16(H2O)108]·180H2O ({Mo72Fe30}NM), respectively (NM stands for nanomaterial). The formulations of these one-pot-synthesized nanoblackberries of {W72Fe33}NM and {Mo72Fe30}NM have been established by spectral analysis including Raman spectroscopy, elemental analysis including ICP metal analysis, volumetric analysis (for iron), microscopy techniques, and DLS studies. The thermal stability of the tungsten nanoblackberries {W72Fe33}NM is much higher than that of its molybdenum analogue {Mo72Fe30}NM. This might due to the extra three ferric (Fe3+) ions per {W72Fe30} cluster in {W72Fe33}NM, which are not part of the {W72Fe30} cluster cage but are placed between two adjacent clusters (i.e., each cluster has six surrounding 0.5Fe3+) to form this self-assembly. The isolated blackberries behave like an inorganic acid, a water suspension of which shows pH values of 3.9 for {W72Fe33}NM and 3.7 for {Mo72Fe30}NM because of the deprotonation of the hydroxyl groups in them. We have demonstrated, for the first time, a meaningful application of these inexpensive and easily synthesized nanoblackberries by showing that they can act as electrocatalysts for the hydrogen evolution reaction (HER) by reducing water. We have performed detailed kinetic studies for the electrocatalytic water reduction catalyzed by {W72Fe33}NM and {Mo72Fe30}NM in a comparative study. The relevant turnover frequencies (TOFs) of {W72Fe33}NM and {Mo72Fe30}NM (∼0.72 and ∼0.45 s-1, respectively), the overpotential values of {W72Fe33}NM and {Mo72Fe30}NM (527 and 767 mV, respectively at 1 mA cm-2), and the relative stability issues of the catalysts indicate that {W72Fe33}NM is reasonably superior to {Mo72Fe30}NM. We have described a rationale of why {W72Fe33}NM performs better than {Mo72Fe30}NM in terms of catalytic activity and stability.

Tricarboxylic-Ligand-Decorated Lanthanoid-Inserted Heteropolyoxometalates Built by Mixed-Heteroatom-Directing Polyoxotungstate Units: Syntheses, Structures, and Electrochemical Sensing for 17β-Estradiol.

Organic-inorganic hybrid metal-oxide clusters have been pursued for many years, benefiting from their abundant structures and prominent performances. Upon our exploration, a family of unusual mixed-heteroatom (SbIII, PIII)-directing lanthanoid (Ln)-inserted heteropolyoxotungstates (Ln-HPOTs), [(CH3)2NH2]2Na7H3[Ln4(HPIII)W8(H2O)12(H2ptca)2O28][SbIIIW9O33]2·27H2O [Ln = Ce3+ (1), La3+ (2), Pr3+ (3)], functionalized by 1,2,3-propanetricarboxylic acid (H3ptca) was achieved. The intriguing trimeric [Ln4(HPIII)W8(H2O)12(H2ptca)2O28][SbIIIW9O33]212- polyanion was established by two trivacant [B-α-SbIIIW9O33]9- segments mounted on both sides and one rare [HPIIIW4O18]8- segment at the bottom, which are bridged via an organic-inorganic hybrid [W4Ln4(H2O)12O10(H2ptca)2]14+ central moiety. Such Ln-HPOTs involving dual-heteroatom-directing mixed building blocks, and even simultaneously modified by tricarboxylic ligands, are rather unseen in polyoxometalate chemistry. Moreover, the detection of 17β-estradiol through a 1-based electrochemical biosensor has been explored, demonstrating a low detection limit (7.08 × 10-14 M) and considerable stability.