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The first two POTa supramolecular frameworks were obtained by using an oxalate-assisted strategy. The frameworks show outstanding proton conductivity. Our strategy opens up a promising avenue for new POTa materials.

A polyoxoniobate-templated silver nanocluster was first obtained. The compound not only shows good chemical stability but also exhibits interesting temperature-dependent luminescent emission.

A rare cadmium-containing windmill-like heteropolyoxoniobate macrocycle has been successfully synthesized with stable 1-D cyclic cluster aggregates.

An oxalate-assisted lanthanide (Ln) incorporation strategy is first demonstrated for creating rare high-nuclearity Ln-containing polyoxoniobates (PONbs). With the strategy, a series of high-nuclearity Ln-containing PONbs of 50-nuclearity

This work demonstrates that the introduction of positive lanthanide (Ln) and transition metal (TM) cations into polyoxotungstates (POTs) to stabilize negative oxoboron clusters is a feasible and ge...

This work demonstrates a feasible strategy for the synthesis of new zeolite-like framework materials. With the strategy of using two different supertetrahedral clusters as secondary building units, two new heterometallic zeolite-like frameworks with isomeric structures but tunable topologies were first made. Besides, the porous nature and the proton conduction performance of the new materials were further studied.

Two 2D similar bamboo-raft-like layered isopolyoxoniobates are constructed from new high-nuclearity {Nb54O151} cluster-based helical nanotubes. Compound 1 exhibits effective base-catalytic performance of chemical warfare agent simulants.

Two new extended polyoxometalate (POM) architectures based on lanthanide-incorporated polyoxoniobate (Ln-incorporated PONb) cages, namely, H

This work reports the interesting and unique cation-exchange behaviors of the first indium-bridged purely inorganic 3D framework based on high-nuclearity polyoxoniobates as building units. Each nanoscale polyoxoniobate features a fascinating near-icosahedral core-shell structure with six pairs of unique inorganic 'molecular tweezers' that have changable opening for binding different metal cations via ion-exchanges and exhibit unusual selective metal-uptake behaviors. Further, the material has high chemical stability so that can undergo single-crystal-to-single-crystal metal-exchange processes to produce a dozen new crystals with high crystallinity. Based on these crystals and time-dependent metal-exchange experiments, we can visually reveal the detailed metal-exchange interactions and mechanisms of the material at the atomic precision level. This work demonstrates a rare systematic and atomic-level study on the ion-exchange properties of nanoclusters, which is of significance for the exploration of cluster based ion-exchange materials that are still to be developed.

Herein, a giant Sb-rich polyoxometalate (POM) {Sb

A 3D Eu-incorporated niobictellurate supramolecular framework with pcu topology is constructed from a sandwich-type cluster [Ln(H2O)3Te6Nb18O64(OH)4]15− and copper–amine complexes with proton conduction and water vapor adsorption properties.

The development of new-type memristors with special performance is of great interest. Herein, an inorganic-organic hybrid crystalline polyoxometalate (POM) with usual dynamic structures is reported and used as active material for fabricating memristor with unique temperature-regulated resistive switching behaviors. The hybrid POM not only exhibits tunable thermochromic properties, but also thermal-induced reversible aggregation and disaggregation reactions, leading to reversible structural transformations in SCSC fashion. Further, the memory device using the hybrid POM as active layer exhibits uncommon performance, which can keep resistive switching silent in the low temperature range of 30-150 °C, but show nonvolatile memory behavior in the high temperature range of 150-270 °C. Particularly, the silent and working states at three special temperatures (30, 150 and 270 °C) can be monitored by chromism. The correlation between structure and resistive switching property of the material has been discussed. The work demonstrates that crystalline inorganic-organic hybrid POMs are promising materials for making memristors with superior performance.

A stable 3

The largest organic–inorganic hybrid Se-4f cluster incorporated polyoxometalate has been synthesized. It exhibits excellent Lewis acid–base catalytic activity and reusability in the gram-scale dehydration condensation reaction of hydrazines and 1,3-diketones.

We demonstrate a remarkable integration of metallacycles and polyoxometalate (POM) macrocycles at the molecular level, forming a series of unprecedented organic–inorganic hybrid POM–metallacycle composite macrocycles with interesting bi-layer and tri-layer cyclic structures, as well various compositions, nuclearities, geometries, and sizes. These molecular composite macrocycles show a fusion of metallacycle and POM chemistry, which opens new perspectives for developing brand-new ring-shaped composite materials.

Two isomeric zeolite-like metal–organic frameworks with the formula of [(CH3)2NH2][Cd(TPO)]·xsolvent were successfully prepared and characterized. Both frameworks are constructed from tetrahedral TPO3− nodes and tetrahedrally connected Cd2+ nodes, representing rare examples of zeolite-like MOFs with an isomeric characteristic. Moreover, one of the frameworks shows mechanically responsive luminescence emission after the crystals are ground for different times. Additionally, it has permanent porosity, and can selectively adsorb CO2 over N2.

A novel pure inorganic cobalt-containing hetero-polyoxoniobate H9KNa2(H2O)10[Co(H2O)2(SiNb18O54)]·15H2O (1-purple) has been constructed from crescent-shaped [SiNb18O54]14− units. In compound 1-purple, the [SiNb18O54]14− units are connected by [Co(H2O)2]2+ ions to form a chiral helical chain. The adjacent helical chains with left/right-handedness are bridged by K+ ions to generate a 2D inorganic layered structure, where the water molecules were trapped by coordination and hydrogen bonds. Compound 1-purple shows reversible chromotropic behaviour in the solid state, changing from purple to dark blue (1-blue) upon heating or desorption. Interestingly, fast reversible blue to purple color transition can only be achieved in the presence of water or vapour. The chromism is demonstrated to stem from the quantitative desorption/adsorption of water by UV-vis-NIR spectroscopy and 2D IR correlation spectroscopy. In addition, the proton conductivity, water vapor adsorption and magnetic properties are also investigated. The dependence of coordinated water molecules with Co(II) centres on the proton conductivity is discussed.

Nanoscale {Nb68O200} cages have been successfully employed as flexible and stable secondary building units to combine with bridging copper–amine complexes to construct two proton conductive polyoxoniobate frameworks, demonstrating a promising strategy for making new porous materials.

A series of 3d-4f heterometallic cluster incorporated polyoxoniobates (PONbs) with different magnetic properties were first made and characterized. This work not only provides a promising strategy to make new heterometallic cluster incorporated PONbs but also demonstrates an ideal model to probe how transition-metal ions influence the magnetic property of PONbs.

Two novel inorganic–organic hybrid 3D TM–Ln incorporated POM-based frameworks, H2[Cu2OL3(H2O)2][Ce(L)(H2O)3(PW11O39)]·17H2O (1) and H4[CuL3]2[Ln(H2O)3(PW11O39)]2·28H2O (2) (L = 4,4′-bipyridine), were hydrothermally synthesized at different temperatures. Structural analysis reveals that both compounds are constructed from [Ln(PW11O39)]4− polyoxoanions and different copper complexes. Interestingly, in compound 1, 2D copper complex layers and 1D chain [Ln(PW11O39)]4− polyoxoanions interconnect to form a 3D framework. In contrast, in compound 2, 1D copper complex chains join the 2D [Ln(PW11O39)]4− layers to give rise to a 3D framework. Both compounds exhibit excellent chemical stability. Furthermore, the dye adsorption and proton conduction properties of both compounds were also investigated. The conductivities of 1 and 2 are 3.175 × 10−4 S cm−1 and 1.750 × 10−4 S cm−1 at 85 °C and 98% RH, respectively. Dye adsorption studies indicate that they can selectively adsorb cationic dyes MB, CV and BR over anionic dyes MO, AO and large cationic RhB.

3d–4f heterometallic supertetrahedral clusters with the formula of Ln4Zn6(μ6-O)L4(CH3COO)6(NO3)4(CH3OH)4(H2O)2 (1-Ln, Ln = Eu, Gd, Tb, H3L = 2-(hydroxymethyl)-2-(pyridin-4-yl)-1,3-propanediol) have been successfully introduced as stable secondary building units (SBUs) to construct new cluster-organic frameworks with tunable emission, demonstrating a promising strategy for developing new optical materials.

Efficient water oxidation remains a particular challenge in water splitting that calls for developing robust and economic water oxidation catalysts (WOCs), preferably based on earth-abundant transition metals. Herein, we report a robust and noble metal-free catalytical system using BiVO4 as an effective light-harvesting material, a cobalt-containing polyoxometalate K4H1.2[Co0.6(H2O)0.6SiW11.4O39.4] (1) as molecular cocatalyst, and NaIO3 as a sacrificial electron acceptor for visible-light-driven water oxidation in a wide pH range 1–7. The combination of 1 + BiVO4 samples gives better oxygen evolution activities than that of pristine BiVO4. A turnover number (TON) of 326.3, apparent quantum efficiency (AQE) of 10.0%, and an O2 yield of 21.8% are obtained under pH 4. This work investigates two kind different catalytic behaviors for 1-cocatalyzed visible light driven water oxidation at pH 1–7 media, which exhibits a pH-induced dynamic change on the catalytic active species. Catalytic behavior, XPS, SEM and TEM collectively testify that 1 remains intact during photocatalytic water oxidation under pH 4–5. Conversely, under pH 1–3 and 6–7, the heterogeneous CoOx originated from 1 is formed on the BiVO4 surface, which is responsible for the enhancement of BiVO4 photocatalytic activity. Our work uncovers the borderline between homogeneous and heterogeneous WOCs using a cobalt-based polyoxometalate at different pH media, which helps to the study of stability for polyoxometalates when semiconducting material is used as the light-harvesting material.

A rare 3D porous inorganic–organic polyoxoniobate framework based on the cubic polyoxoniobate-cupric-complex cage {[Cu(en)2]@{[Cu2(en)2(trz)2]6(Nb68O188)}} (1a), has been successfully synthesized b...

In this work, two rare high-dimensional polyoxoniobates with formulas of H9 [Cu(en)(H2 O)2 ][Cu(en)2 ]8 [Dy(H2 O)4 ]3 [Nb24 -O69 (H2 O)3 ]2 ⋅ 36H2 O (1) and H9 K[Cu(en)2 (H2 O)]5 [Cu(en)2 ]4 -[Eu(H2 O)4 ]3 [Nb24 O69 (H2 O)3 ]2 ⋅ 2en ⋅ 45H2 O (2) have been obtained under hydrothermal conditions. These extended materials are constructed from lanthanide-incorporated triangular-prism-like polyoxoniobate secondary building units (SBUs) {[Ln(H2 O)4 ]3 [Nb24 O69 (H2 O)3 ]2 } (Ln=Dy, Eu). 1 and 2 represent the first examples of high-dimensional polyoxometalate materials based on such lanthanide-incorporated triangular-prism-like polyoxoniobate SBUs. Furthermore, the proton conduction property and the luminescent emission of these materials were evaluated.

A rare 3D porous chiral polyoxoniobate framework, [Cu(en)2(H2O)]2{[Cu(en)]4[Cu(en)2]5 {[Cu(en)2KNb24O72H10]2}·6en·70H2O(1) (en = ethylenediamine) based on two types of isomeric {Cu(en)2KNb24O72H10} clusters (α-CuKNb24 and β-CuKNb24) has been synthesized by a hydrothermal reaction. Interestingly, the α-CuKNb24 and β-CuKNb24 clusters are connected by cupric complexes to form chiral helical pillars with left-handedness (L-α-CuKNb24) and right-handedness (R-β-CuKNb24). To our knowledge, compound 1 is the first polyoxometalate-based MOF with a 4-connected neb-type topology structure within polyoxometalate chemistry. This compound also exhibits proton conduction and strong water vapor adsorption properties.

A series of POM-based all-inorganic open frameworks, H9[Ln9W8(μ4-O)12(μ2-O)24(H2O)24](SiW12O40)3·60H2O (1-Ln, Ln = La, Pr and Nd), have been fabricated and structurally characterized for the first time. The unique architectures are constructed from nanoscale four-shell Ln@W8@Ln8@(SiW12)6 clusters. Additionally, the porous nature of the frameworks has also been investigated.

Two organic–inorganic hybrid polyoxotungstogermanates, HK7(H2O)6(C6H16N2)6-[Fe(C6H14N2)Dy(H2O)2Fe2(B-α-GeW9O34)(GeW7O29)]2·14H2O (1) and (Hphen)2[Fe(phen)3]2[Dy(phen)Fe(B-α-GeW9O34)]2 (2) (C6H14N2 = trans-1,2-cyclohexanediamine, phen = 1,10-phenanthroline), containing organic ligand chelated Fe–Dy heterometallic clusters have been successfully synthesized under hydrothermal conditions. Compound 1 contains a cable-like structural fragment which consists of a centrosymmetric “S”-shaped K7O14 cluster and a centrosymmetric “S”-shaped organic ligand chelated Fe–Dy heterometallic cluster substituted tungstogermanate, {[Fe(C6H14N2)Dy(H2O)2Fe2(B-α-GeW9O34)(GeW7O29)]2}20−. Compound 2 possesses a sandwich structure which contains two trilacunary [B-α-GeW9O34]10− units and one {(phen)DyFeO6}2 cluster in the middle layer. Both compounds have magnetic properties, with compound 1 having frequency dependent magnetic properties.

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

A series of 3D porous lanthanide-substituted polyoxometalate frameworks, Na2[Ln2(H2O)11]2[Ln3(H2O)3(α-SiW11O39)2]2·69H2O (1-Ln, Ln = Sm, Eu, Gd, Tb, and Dy), are built from novel hexadecahedral {Ln6W8O28} heterometallic cage-shaped clusters. Intriguingly, every tetrameric {[Ln3(H2O)3(α-SiW11O39)2]2}14- cage-cluster is linked with another eight tetrameric cage-clusters by Ln3+ cations, leading to a novel 3D inorganic porous framework, which exhibits good thermal and chemical stability, excellent water vapor adsorption capacity, and moderate proton conductive properties. Furthermore, the solid state luminescence spectra demonstrate that 1-Sm, 1-Eu, 1-Tb, and 1-Dy display the lanthanide characteristic emission bands. The temperature-dependent magnetic susceptibility indicates that there are antiferromagnetic interactions in 1-Tb and 1-Dy.

During the past two decades, the search of strategies to introduce polyoxometalate (POM) clusters as secondary building units (SBUs) to construct porous extended POM-organic frameworks (POMOFs) and discrete POM-organic polyhedra (POMOPs) have attracted sustained interests because such materials not only integrate the advantages of both POMs and framework/polyhedra structures, but also exhibit good prospects in photo-/electro-catalysis, separation, molecular recognition, host-guest chemistry and so on. In this review, the recent advancements of POMOFs and POMOPs, including their assembly methodologies, classification and related applications are summarized. Moreover, the current challenges in the design and fabrication of POMOFs and POMOPs as well as the great potential in these two areas are also discussed.