Zeolitic Polyoxometalate-Based Metal−Organic Frameworks (Z-POMOFs): Computational Evaluation of Hypothetical Polymorphs and the Successful Targeted Synthesis of the Redox-Active Z-POMOF1

Atomically Precise Single-Site Catalysts via Exsolution in a Polyoxometalate-Metal-Organic-Framework Architecture

Single-site catalysts (SSCs) achieve a high catalytic performance through atomically dispersed active sites. A challenge facing the development of SSCs is aggregation of active catalytic species. Reducing the loading of these sites to very low levels is a common strategy to mitigate aggregation and sintering; however, this limits the tools that can be used to characterize the SSCs. Here we report a sintering-resistant SSC with high loading that is achieved by incorporating Anderson-Evans polyoxometalate clusters (POMs, MMo6O24, M = Rh/Pt) within NU-1000, a Zr-based metal-organic framework (MOF). The dual confinement provided by isolating the active site within the POM, then isolating the POMs within the MOF, facilitates the formation of isolated noble metal sites with low coordination numbers via exsolution from the POM during activation. The high loading (up to 3.2 wt %) that can be achieved without sintering allowed the local structure transformation in the POM cluster and the surrounding MOF to be evaluated using in situ X-ray scattering with pair distribution function (PDF) analysis. Notably, the Rh/Pt···Mo distance in the active catalyst is shorter than the M···M bond lengths in the respective bulk metals. Models of the active cluster structure were identified based on the PDF data with complementary computation and X-ray absorption spectroscopy analysis.

Lanthanide-Anderson Polyoxometalates Frameworks: Efficient Sulfide Photooxidation

Three polyoxometalate-based metal-organic frameworks were synthesized by the thermal reaction of pyridyl-Anderson polyoxometalate linker and lanthanide ions. With the help of [Ru(bpy)₃]²⁺ photosensitizer, these frameworks exhibited excellent photocatalytic sulfide oxidation performance with sulfoxide selectivity. The reactive oxygen species as well as the photooxidation mechanism were also explored.

Demystifying the roles of single metal site and cluster in CO2 reduction via light and electric dual-responsive polyoxometalate-based metal-organic frameworks

Photo- or electroreduction of carbon dioxide into highly valued products offers a promising strategy to achieve carbon neutrality. Here, a series of polyoxometalate-based metal-organic frameworks (M-POMOFs) were constructed by metalloporphyrins [tetrakis(4-carboxyphenyl)-porphyrin-M (M-TCPPs)] and reductive POM for photo- and electrocatalytic carbon dioxide reductions (PCR and ECR, respectively), and the mysteries between the roles of single metal site and cluster in catalysis were disclosed. Iron-POMOF exhibited an excellent selectivity (97.2%) with high methane production of 922 micromoles per gram in PCR, together with superior Faradaic efficiency for carbon dioxide to carbon monoxide (92.1%) in ECR. The underlying mechanisms were further clarified. Photogenerated electrons transferred from iron-TCPP to the POM cluster for methane generation under irradiation, while the abundant electrons flowed to the center of iron-TCPP for carbon monoxide formation under the applied electric field. The specific multielectron products generated on iron-POMOF through switching driving forces to control electron flow direction between single metal site and cluster catalysis.

Assembly of ϵ-Keggin Polyoxometalate from Molecular Crystal to Zeolitic Octahedral Metal Oxide

Zeolitic octahedral metal oxides are inorganic crystalline microporous materials with adsorption and redox properties. New ϵ-Keggin nickel molybdate-based zeolitic octahedral metal oxides have been synthesized. ³¹ P NMR spectroscopy shows that reduction of Mo^VI -based molybdates forms an ϵ-Keggin polyoxometalate that immediately transfers to the solid phase. Investigation of the formation process indicates that a low Ni concentration, insoluble reducing agent, and long synthesis time are the critical factors for obtaining the zeolite octahedral metal oxides rather than the ϵ-Keggin polyoxometalate molecule. The synthesized zeolitic nickel molybdate with Na⁺ is used as the adsorbent, which effectively separates C₂ hydrocarbon mixtures.

Designed Syntheses of Three {Ni6PW9}-Based Polyoxometalates, from Isolated Cluster to Cluster-Organic Helical Chain

Three new hexa-Ni-substituted Keggin-type polyoxometalates (POMs), [Ni6(OH)3- (DACH)3(H2O)6(PW9O34)]·31H2O (1), [Ni(DACH)2][Ni6(OH)3(DACH)3(HMIP)2(H2O)2(PW9O34)]·56 H2O (2), and [Ni(DACH)2][Ni6(OH)3(DACH)2(AP)(H2O)5(PW9O34)]·2H2O (3) (DACH = 1,2-Diami- nocyclohexane, MIP = 5-Methylisophthalate, AP = Adipate) were successfully made in the presence of DACH under hydrothermal conditions. 1 is an isolated hexa-Ni-substituted Keggin unit decorated by DACH. In order to further construct POM cluster-organic frameworks (POMCOFs) on the basis of 1, by analyzing the steric hindrances and orientations of the POM units, the rigid HMIP and flexible AP ligands were successively incorporated, and another anionic monomeric POM 2 and the new 1D POM cluster organic chain (POMCOC) 3 were obtained. HMIP ligand still acts as a decorating group on the Ni6 core of 2 but results in the different spatial arrangement of the {Ni6PW9} units. AP ligands in 3 successfully bridge adjacent isolated POM cluster units to 1D POMCOC with left-hand helices. The AP in 3 is the longest aliphatic carboxylic acid ligand in POMs, and the 1D POM cluster-AP helical chain represents the first 1D POMCOC with a helical feature.

Designable assembly of atomically precise Al4O4 cubane supported mesoporous heterometallic architectures

Heterometallic cluster-based framework materials are of interest in terms of both their porous structures and multi-metallic reactivity. However, such materials have not yet been extensively investigated because of difficulties in their synthesis and structural characterization. Herein, we reported the designable synthesis of atomically precise heterometallic cluster-based framework compounds and their application as catalysts in aldol reactions. By using the synergistic coordination protocol, we successfully isolated a broad range of compounds with the general formula, [Al₄M₄O₄(L)₁₂(DABCO)₂] (L = carboxylates; DABCO = 1,4-diazabicyclo[2.2.2]-octane; M²⁺ = Co²⁺, Mn²⁺, Zn²⁺, Fe²⁺, Cd²⁺). The basic heterometallic building blocks contain unprecedented main-group γ-alumina moieties and surrounding unsaturated transition metal centers. Interestingly, the porosity and interpenetration of these frameworks can be rationally regulated through the unprecedented strategy of increment of the metal radius in addition to general introduction of sterically bulky groups on the ligand. Furthermore, these porous materials are effective catalysts for aldol reactions. This work provides a catalytic molecular model platform with accurate molecular bonding between the supporters and catalytically active metal ions.

A Novel Anderson-Evans Polyoxometalate-based Metal-organic Framework Composite for the Highly Selective Isolation and Purification of Cytochrome C from Porcine Heart

Anderson-Evans type polyoxometalate group (Na₆[TeW₆O₂₄]·22 H₂O, TeW₆) was combined with porous metal-organic framework ZIF-8 by electrostatic interaction to obtain a novel Anderson-Evans polyoxometalate-based metal-organic framework composite, TeW₆ @ZIF-8. FT-IR, Raman, XRD, TG, DSC, SEM, and TEM were used to characterize the composite. It was proved that the Anderson-Evans type polyoxometalate group TeW₆ was successfully hybridized with metal-organic framework ZIF-8, and the composite possesses good stability. Based on the potential interaction between TeW₆ and proteins and the coordination between imidazole groups in ZIF-8 and proteins with a porphyrin ring structure, the adsorption selectivity towards different proteins on the TeW₆ @ZIF-8 composite was studied in this work. The experiment results showed that the TeW₆ @ZIF-8 composite was selectively adsorbed to cytochrome C. At pH 11.0, the adsorption efficiency of 94.01% was obtained for processing 1.0 mL 100 μg mL^-1 cytochrome C with 3.0 mg TeW₆ @ZIF-8 composite. The adsorption behavior of cytochrome C fits well with the Langmuir adsorption model, corresponding to a theoretical adsorption capacity of 232.56 mg g^-1. The retained cytochrome C could be readily recovered by 1% SDS (m/m), giving rise to a recovery of 65.6%. Circular dichroism spectra indicate no conformational change for cytochrome C after the adsorption and desorption processes, demonstrating the favorable biocompatibility of TeW₆ @ZIF-8 composite. In applying practical samples, SDS-PAGE results showed that cytochrome C was successfully isolated and purified by TeW₆ @ZIF-8 composite from porcine heart protein extract, which is further identified with LC-MS/MS. Thus, a new strategy for separating and purifying cytochrome C from the porcine heart using TeW₆ @ZIF-8 composite as an adsorbent was established.

An unprecedented fully reduced {MoV 60} polyoxometalate: from an all-inorganic molecular light-absorber model to improved photoelectronic performance

Fully reduced polyoxometalates are predicted to give rise to a broad and strong absorption spectrum, suitable energy levels, and unparalleled electronic and optical properties. However, they are not available to date. Here, an unprecedented fully reduced polyoxomolybdate cluster, namely Na8[MoV 60O140(OH)28]·19H2O {MoV 60}, was successfully designed and obtained under hydrothermal conditions, which is rare and is the largest fully reduced polyoxometalate reported so far. The MoV 60 molecule describes one Keggin {ε-Mo12} encapsulated in an unprecedented {Mo24} cage, giving rise to a double truncated tetrahedron quasi-nesting architecture, which is further face-capped by another four {Mo6} tripods. Its crystalline stability in air, solvent tolerance, and photosensitivity were all shown. As a cheap and robust molecular light-absorber model possessing wide light absorption, MoV 60 was applied to build a co-sensitized solar cell photoelectronic device along with N719 dyes and the optimal power conversion efficiency was 28% higher than that of single-dye sensitization. These results show that MoV 60 polyoxometalate could serve as an ideal model for the design and synthesis of all-inorganic molecular light-absorbers for other light-driven processes in the future.

Assembly of a coordination polymer with sulphate-capped pentamolybdate units and copper: Synthesis, Structure, Magnetic and Catalytic studies

A new coordination polymer based upon the sulphate-capped pentamolybdate unit has been synthesized from the reaction of {Mo3S7Br6}2- with copper(II) bromide and pyridine, in DMF. The as-synthesized compound, formulated as...

Carbazole-based bis-imidazole ligand-involved synthesis of inorganic–organic hybrid polyoxometalates as electrochemical sensors for detecting bromate and efficient catalysts for selective oxidation of thioether

Considering the potential application on preparing electrode and catalyst materials of inorganic–organic hybrid polyoxometalates, a bis-imidazole ligand with carbazole as a connector, 3,6-di(1H-imidazol-1-yl)-9H-carbazole (L), was used for preparing inorganic–organic hybrid polyoxometalates. As a result, three complexes formulated by [NiL₂(Mo₂O₇)] (1), [Cu(H₂O)₂(HL)₂ (β-Mo₈O₂₆)]·H₂O (2) and [Ni₂(H₂O)₄L₂ (CrMo₆(OH)₅O₁₉)]·6H₂O (3) were obtained successfully. Structural analysis indicated that the different polyoxoanions and metal ions showed important influences on the formation of structures. In the presence of Ni²⁺ ions and heptamolybdate, a 2D network constructed from Ni²⁺ ions and L ligands was formed in complex 1, in which the [Mo₄O₁₄]⁴⁻ polyoxoanions were encapsulated. But the use of Cu²⁺ ions led to a 1D chain of complex 2, which was composed of [β-Mo₈O₂₆]⁴⁻ polyoxoanions and mononuclear {CuL₂} units. By utilizing [CrMo₆(OH)₅O₁₉]⁴⁻ as the inorganic building block, complex 3 showed a 2D (4, 4)-connected layer. Complexes 1–3 could be employed as electrode materials for sensing bromate with the limits of detection of 0.315 μM for 1, 0.098 μM for 2 and 0.551 μM for 3. Moreover, these complexes showed efficient catalytic activity for the selective oxidation of thioethers.

Three inorganic–organic hybrid polyoxometalates were prepared using a bis-imidazole ligand featuring carbazole as a connector, exhibiting not only diverse structures, but also good electrochemical sensing activities for bromate, as well as efficient catalytic performances for oxidation of thioether.

Redox induced controlling microporosity of zeolitic transition metal oxides based on ε‑Keggin ironmolybdate in an ultra-fine level

Tuning microporosity of crystalline microporous materials is critical for achieving good application performance. Zeolitic ironmolybdate shows both redox property and microporosity, and a redox-triggered microporosity change is investigated. The micropore...

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

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

Implanting Polypyrrole in Metal-Porphyrin MOFs: Enhanced Electrocatalytic Performance for CO2RR

Metal-organic frameworks (MOFs) with plenty of active sites and high porosity have been considered as an excellent platform for the electroreduction of CO₂, yet they are still restricted by the low conductivity or low efficiency. Herein, we insert the electron-conductive polypyrrole (PPy) molecule into the channel of MOFs through the in situ polymerization of pyrrole in the pore of MOF-545-Co to increase the electron-transfer ability of MOF-545-Co and the obtained hybrid materials present excellent electrocatalytic CO₂RR performance. For example, FE_CO of PPy@MOF-545-Co can reach up to 98% at -0.8 V, almost 2 times higher than that of bare MOF-545-Co. The high performance might be attributed to the incorporation of PPy that can serve as electric cables in the channel of MOF to facilitate electron transfer during the CO₂RR process. This attempt might provide new insights to improve the electrocatalytic performance of MOFs for CO₂RR.

Lanthanide Polyoxometalate Based Water-Jet Film with Reversible Luminescent Switching for Rewritable Security Printing

Luminescent security printing is of particular importance in the information era. However, the use of conventional paper still carries a lot of economic and environmental issues. Therefore, developing new environmentally friendly security printing material with a low cost is imperative. To achieve the aforementioned goals, novel lanthanide polyoxometalate doped gelatin/glycerol films with high transparency, high strength, and good flexibility have been developed via a solution-casting method. The electrostatic interaction between zwitterionic gelatin and polyoxometalate was confirmed by attenuated total reflection Fourier transform infrared spectroscopy. Luminescent spectra and digital images indicated that the films exhibited reversible luminescent switching properties through association and dissociation of hydrogen bonds between glycerol and water molecules, allowing its potential application as water-jet rewritable paper for luminescent security printing. Furthermore, the printed information can be conveniently "erased" by heating, and the film can be reused for printing. The film exhibited excellent ability to be both rewritten and re-erased. A QR code pattern and hybrid printing were employed to improve the security of information. In addition, the rewritable films possessed excellent regeneration ability and low toxicity, as well as good stability against UV irradiation and organic solvents. The water-jet rewritable film based on lanthanide polyoxometalate for luminescent security printing, to the best of our knowledge, has not yet been reported up to date. This work provides an attractive alternative strategy on fabricating rewritable films for luminescent security printing in terms of cutting down the cost, simplifying the preparation process, and protecting the environment.

Hexameric to Trimeric Lanthanide-Included Selenotungstates and Their 2D Honeycomb Organic-Inorganic Hybrid Films Used for Detecting Ochratoxin A

Two types of organic-inorganic hybrid structure-related lanthanide (Ln)-included selenotungstates (Ln-SeTs) [H₂N(CH₃)₂]₁₁Na₇[Ce₄(H₂PTCA)₂(H₂O)₁₂(HICA)]₂[SeW₄O₁₇]₂[W₂O₅]₄[SeW₉O₃₃]₄·64H₂O (1, H₃PTCA = 1,2,3-propanetricarboxylic acid, H₂ICA = itaconic acid) and [H₂N(CH₃)₂]₆Na₄[Ln₄SeW₈(H₂O)₁₄(H₂PTCA)₂O₂₈] [SeW₉O₃₃]₂·31H₂O [Ln = Pr³⁺ (2), Nd³⁺ (3)] were obtained by Ln nature control. The primary frameworks of 1-3 are composed of trivacant Keggin-type [B-α-SeW₉O₃₃]^8- and [SeW₄O_m]^n- [Ln = Ce³⁺ (1), m = 17, n = 6; Ln = Pr³⁺ (2), Nd³⁺ (3), m = 18, n = 8] fragments bridged by organic ligands and Ln clusters. Intriguingly, Ln nature results in the degradation of hexameric 1 to trimeric 2-3. Besides, 1@DMDSA and 3@DMDSA composites (DMDSA·Cl = dimethyl distearylammonium chloride) were prepared through the cation exchange method, which were then reorganized to form two-dimensional (2D) honeycomb thin films by the breath figure method. Using these honeycomb thin films as electrode materials, the aptasensors were further established by utilizing methylene blue as an indicator and cDNA and Au nanoparticles as signal amplifiers to enhance the response signal so as to realize the purpose of ochratoxin A (OTA) detection. This work provides a new platform for detecting OTA and explores the application potential of POM-based composites in biological and clinical analyses.

Construction of the POMOF@Polypyrrole Composite with Enhanced Ion Diffusion and Capacitive Contribution for High-Performance Lithium-Ion Batteries

Polyoxometalate (POM) as an "electronic sponge" can store a great number of electrons; however, shortcomings of poor conductivity and solubility in electrolytes cause a significant decrease in specific capacity and poor rate capability. To address the aforementioned disadvantages, a dual strategy was proposed, including coating the conductive polypyrrole (PPy) and utilizing nitrogenous ligands (1,10-phenanthroline monohydrate = 1,10-phen) for metal-organic frameworks (MOFs) to fabricate a [Cu(1,10-phen)(H₂O)₂]₂[Mo₆O₂₀]@PPy (Cu-POMOF@PPy) composite, effectively confining the POM in MOFs to avoid dissolution of POM in the electrolyte and improve electrochemical stability. Simultaneously, the PPy shell could improve the conductivity, contribute extra capacity, and alleviate volume variation of Cu-POMOF during cycling. Therefore, the final Cu-POMOF@PPy composite provides an excellent specific capacity of around 769 mA h g^-1 at 0.1 A g^-1 after 160 cycles and good rate performance, associated with great cycling stability (319 mA h g^-1 at 2 A g^-1 after 500 cycles). Moreover, the electrochemical reaction mechanism of Cu-POMOF@PPy was investigated by ex situ XPS measurements, indicating that storage of electrons results from the reduction/oxidation of Mo atoms (Mo⁶⁺ ↔ Mo⁴⁺) and Cu atoms (Cu²⁺ ↔ Cu⁰). As a consequence, this work not only proposes a novel method for preparing POM-based lithium-ion batteries but also expands the variety of anode materials.

Recent progress and perspectives on the structural design on metal-organic zeolite (MOZ) frameworks

As a typical group of coordination polymers, metal-organic zeolite (MOZs) frameworks inherit the topological and structural advantages of inorganic zeolites and display great application potential in many areas, including gas adsorption/separation, catalysis, luminescence and chemical sensing. In this review, we outline the recent progress in the synthesis, functionalization and application of metal-organic zeolite frameworks, mainly focusing on the basic structural design principle and synthesis strategy on 4-connect inorganic nodes and 2-connect organic linkers. Employing different valent metals, small inorganic TO₄^2- units and high-nuclear clusters as 4-connect nodes, we derived multi-types of MOZs with a modified framework charge, improved stability and enhanced photo-/eletrocatalytic activity. Besides, the selection, functionalization and defect-engineering on the 2-connect ligands generated different topological and functional MOZs. Finally, the future trends and some perspectives in this area are outlined.

Preparation of zeolitic bismuth vanadomolybdate using a ball-shaped giant polyoxometalate for olefin epoxidation

Bismuth vanadomolybdate-based zeolitic octahedral metal oxide was synthesized from {Mo72V30} and used as a heterogeneous catalyst for olefin epoxidation.

Polyoxometalate-based metal–organic frameworks for heterogeneous catalysis

POM-based MOFs simultaneously possessing the virtues of POMs and MOFs exhibit excellent heterogeneous catalytic properties.

Electrochemical Applications of Ferrocene-Based Coordination Polymers

Ferrocene and its derivatives, especially ferrocene-based coordination polymers (Fc-CPs), offer the benefits of high thermal stability, two stable redox states, fast electron transfer, and excellent charge/discharge efficiency, thus holding great promise for electrochemical applications. Herein, we describe the synthesis and electrochemical applications of Fc-CPs and reveal how the incorporation of ferrocene units into coordination polymers containing other metals results in unprecedented properties. Moreover, we discuss the usage of Fc-CPs in supercapacitors, batteries, and sensors as well as further applications of these polymers, for example in electrocatalysts, water purification systems, adsorption/storage systems.

The Surface Chemistry of Metal Oxide Clusters: From Metal-Organic Frameworks to Minerals

Many metal-organic frameworks (MOFs) incorporate nodes that are small metal oxide clusters. Some of these MOFs are stable at high temperatures, offering good prospects as catalysts-prospects that focus attention on their defect sites and reactivities-all part of a broader subject: the surface chemistry of metal oxide clusters, illustrated here for MOF nodes and for polyoxocations and polyoxoanions. Ligands on MOF defect sites form during synthesis and are central to the understanding and control of MOF reactivity. Reactions of alcohols are illustrative probes of Zr₆O₈ node defects in UiO-66, characterized by the interconversions of formate, methoxy, hydroxy, and linker carboxylate ligands and by catalysis of alcohol dehydration reactions. We posit that new reactivities of MOF nodes will emerge from incorporation of a wide range of groups on their surfaces and from targeted substitutions of metals within them.

A Rare 3D Porous Inorganic-Organic Hybrid Polyoxometalate Framework Based on a Cubic Polyoxoniobate-Cupric-Complex Cage with a High Water Vapor Adsorption Capacity

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 by a hydrothermal method. The cubic cages 1a are connected with 4-(tetrazol-5-yl)pyridine to form a 1D pillar-like chain structure, and every 1D pillar-like chain is further linked with four adjacent pillar-like chains by the [Cu(en)₂]²⁺ complex to form a 3D porous inorganic-organic polyoxoniobate framework with 4-connected CdSO₄-type topology. To our knowledge, it is the first time that three different types of organic ligands are simultaneously introduced into one polyoxoniobate. This material also exhibits a high vapor adsorption capacity and good ionic conductivity properties.

Proton-conducting layered structures based on transition metal oxo-clusters supported by Sb(iii) tartrate scaffolds

Two transition metal-antimony oxo-cluster based compounds, H₅{MCd(H₂O)₆[M(H₂O)₃Co₃Sb^VSb(μ₃-O)₈(l-tta)₆]}·7H₂O (1) (M = Cd_0.5 + Co_0.5) and H₃K₅(H₂O)₁₁{Cd(H₂O)₄[Cd(H₂O)Fe₄Cd₂Sb₆(μ₄-O)₅(μ₃-O)₃(l-tta)₆][Cd(H₂O)₂Fe₄Cd₂Sb₆(μ₄-O)₄(μ₃-O)₄(l-tta)₆][Cd(H₂O)₂Fe₄Cd₂Sb₆(μ₄-O)₄(μ₃-O)₄(l-tta)₆Cd(H₂O)₅]}·17H₂O (2) (L-H₄tta = l-tartaric acid) were hydrothermally synthesized and characterized. Compound 1 features a [MCo₃Sb^VSb(μ₃-O)₈(l-tta)₆(H₂O)₃]^9- cluster, while compound 2 contains three types of clusters, namely, [Cd(H₂O)Fe₄Cd₂Sb₆(μ₄-O)₅(μ₃-O)₃(l-tta)₆]^4-, [Cd(H₂O)₂Fe₄Cd₂Sb₆(μ₄-O)₄(μ₃-O)₄(l-tta)₆]^4- and [Cd(H₂O)₂Fe₄Cd₂Sb₆(μ₄-O)₄(μ₃-O)₄(l-tta)₆Cd(H₂O)₅]^2-. All the clusters are of sandwich-type with {Sb₃(μ₃-O)(l-tta)} scaffolds on the top and bottom. The Cd (and M in 1) ions interconnect the clusters into layered structures in both compounds. To the best of our knowledge, this is the first report of transition metal-antimony oxo-clusters that simultaneously contain the first-row and second-raw transition metal ions, and compound 1 represents the first example of such type of clusters that contain Sb(v). The two compounds exhibit proton conductivity with the values of 2.43 × 10^-3 and 2.95 × 10^-3 S cm^-1 at 85 °C under 98% relative humidity, respectively.

A bi-polyoxometallate-based host-guest metal-organic framework

Anionic POMs prefer to bond with positive metal cations instead of neutral or negative organic ligands. Therefore, it is challenging to synthesize POM-based MOFs, let alone bi-POM-based host-guest MOFs. In this work, an unprecedented bi-POM-based host-guest MOF, Na[Ni(enMe)2]4[Ni(enMe)2(H2O)2]2{[Ni6(μ3-OH)3(enMe)3 (SIP)1.5(B-α-PW9O34)]2[H3PNiW11O40]}·5enMe·33H2O (1), with Ni6-capped [PW9O34] as the node of the host framework and Keggin-type [PNiW11O40] units as the guest was synthesized. 1 showed excellent chemical stability towards aqueous solutions of pH 2-12 at both ambient and boiling temperature, providing opportunities for its application in fresh water harvesting from air.

A rare 4-connected neb-type 3D chiral polyoxometalate framework based on {KNb24O72} clusters

A rare 3D porous chiral polyoxoniobate framework has been constructed from two types of isomeric {Cu(en)₂KNb₂₄O₇₂} clusters with a 4-connected neb-type topology. This compound exhibits proton conduction and high water vapor adsorption properties.

Metal–organic frameworks with different spatial dimensions for supercapacitors

Recent progress in MOF materials for SCs with different spatial dimensions, such as 2D MOFs, including conductive MOFs and nanosheets, and 3D MOFs, categorized as single metallic and multiple metallic MOFs, are reviewed.

Insights into the lithium diffusion process in a defect-containing porous crystalline POM@MOF anode material

A crystalline POM@MOF material with high Li-ion storage capacity with surface uncoordinated N atoms (defect sites) is reported. The Li-ion diffusion sites are confirmed via ex situ XPS and off-line XRD measurements.

3D Ni and Co redox-active metal–organic frameworks based on ferrocenyl diphosphinate and 4,4′-bipyridine ligands as efficient electrocatalysts for the hydrogen evolution reaction

New 3D Ni and Co redox-active metal–organic frameworks based on ferrocenyl diphosphinate and 4,4′-bipyridine ligands have been explored as efficient electrocatalysts with superior long-term durability in a hydrogen evolution reaction.

A polyoxometalate-encapsulated nanocage cluster organic framework built from {Cu4P2} units and its efficient bifunctional electrochemical performance

The first polyoxometalate-encapsulated twenty-four-nucleus organophosphorus-copper nanocage cluster organic framework has been constructed and it is shown to exhibit highly efficient bifunctional electrochemical performance.

Two new isolated Zn-ε-Keggin clusters modified by conjugated organic ligands with decent electrocatalytic and third-order NLO properties

Compound 2 is the first isolated Zn₅PMo₁₂ cluster, and the two Zn-ε-Keggin-based compounds display excellent electrocatalytic and third-order NLO properties.

A heterometallic D–A hybrid heterostructural framework with enhanced visible-light photocatalytic properties

A heterometallic D–A hybrid heterostructural framework from the ternary combination of CuI, lanthanide cations and viologen tectons exhibited enhanced photocatalytic activities for degradation of organic dyes.

Hydrophobic Polyoxometalate-Based Metal-Organic Framework for Efficient CO2 Photoconversion

A novel polyoxometalate (POM)-based metal-organic framework, TBA₅[P₂Mo₁₆^VMo₈^VIO₇₁(OH)₉Zn₈(L)₄] (NNU-29), was in situ synthesized and applied into CO₂ photoreduction. The selection of porous material containing a reductive POM cluster is considered to be helpful for CO₂ reduction; meanwhile, a hydrophobic-group-modified organic ligand enables NNU-29 to exhibit good chemical stability and restrains hydrogen generation to some extent. In the photocatalytic CO₂ reduction, the yield of HCOO^- reached 35.2 μmol in the aqueous solution with selectivity of 97.9% after 16 h.

Multielectron transportation of polyoxometalate-grafted metalloporphyrin coordination frameworks for selective CO2-to-CH4 photoconversion

Photocatalytic CO₂ reduction into energy carriers is of utmost importance due to the rising concentrations of CO₂ and the depleting energy resource. However, the highly selective generation of desirable hydrocarbon fuel, such as methane (CH₄), from CO₂ remains extremely challenging. Herein, we present two stable polyoxometalate-grafted metalloporphyrin coordination frameworks (POMCFs), which are constructed with reductive Zn-ϵ-Keggin clusters and photosensitive tetrakis(4-carboxylphenyl)porphyrin (H₂TCPP) linkers, exhibiting high selectivity (>96%) for CH₄ formation in a photocatalytic CO₂-reduction system. To our knowledge, the high CH₄ selectivity of POMCFs has surpassed all of the reported coordination-framework-based heterogeneous photocatalysts for CO₂-to-CH₄ conversion. Significantly, the introduction of a Zn-ϵ-keggin cluster with strong reducing ability is the important origin for POMCFs to obtain high photocatalytic selectivity for CH₄ formation, considering that eight Mo^V atoms can theoretically donate eight electrons to fulfill the multielectron reduction process of CO₂-to-CH₄ transformation.

Zn and Co redox active coordination polymers as efficient electrocatalysts

New redox active 1D helical coordination polymers M(fcdHp) (M(ii) = Zn(1), Co(2)) have been obtained.