Polyoxometalate-based Metal Organic Framework Research Articles

Ultrafine Co-MoC particles in porous carbon derived from polyoxometalate-based metal organic framework for efficient hydrogen evolution reaction

Accurately regulating ultrafine molybdenum carbide (MoC)-based catalysts is a significant challenge in the rational design of hydrogen evolution reaction (HER) electrocatalysts. Herein, under the guidance of the first principle calculations, we proposed an in-situ polyoxometalate-confined strategy for creating uniformly distributed ultrafine Co-MoC bimetallic nanoparticles in porous carbon nanostars, with the assistance of precisely designed metal–organic framework (MOF). The Co-MoC@C electrocatalyst has a high specific surface area of 969 m2·g−1 because of the conductive carbon substrate with abundant mesopores, which makes for exposing more active sites of Co-MoC nanocrystals (∼1.5 nm) and facilitating electron/ion transport. Thus, Co-MoC@C electrocatalyst shows the excellent electrochemical activity with overpotentials of 88.4 mV and 66.6 mV at a current density of 10 mA·cm−2 under acidic and alkaline conditions, respectively. The in-situ polyoxometalate-confined strategy will provide a new guideline for the design and preparation of efficient HER electrocatalysts.

Exploring Electron Transfer Mechanism in Synergistic Interactional Reduced Polyoxometalate-Based Cu(I)-Organic Framework for Photocatalytic Removal of U(VI).

Photocatalytic reduction of U(VI) is a promising method for removing uranium containing pollutants. However, using polyoxometalate-based metal-organic frameworks (POMOFs) for photoreduction of U(VI) is rare, and the relevant charge transfer pathway is also not yet clear. In this article, we demonstrate a highly efficient strategy and revealed a clearly electron transfer pathway for the photoreduction of U(VI) with 99% removal efficiency by using a novel POMOF, [Cu(4,4'-bipy)]5·{AsMo4VMo6VIV2VO40(VIVO)[VIVO(H2O)]}·2H2O (1), as catalyst. The POMOF catalyst was constructed by the connection of reduced {AsMo10V4} clusters and Cu(I)-MOF chains through Cu-O coordination bonds, which exhibits a broader and stronger light absorption capacity due to the presence of reduced {AsMo10V4} clusters. Significantly, the transition of electrons from Cu(I)-MOF to {AsMo10V4} clusters (Cu → Mo/V) greatly inhibits the recombination of photogenerated carriers, thereby advancing electron transfer. More importantly, the {AsMo10V4} clusters are not only adsorption sites but also catalytically active sites. This causes the fast transfer of photogenerated electrons from Mo/V to UO22+(Mo/V → O → U) via the surface oxygen atoms. The shorter electron transmission distance between catalytic active sites and UO22+ achieves faster and more effective electron transport. All in all, the highly effective photocatalytic removal of U(VI) using the POMOF as a catalyst is predominantly due to the synergistic interaction between Cu(I)-MOFs and reduced {AsMo10V4} clusters.

Tandem catalysis of furfural to γ-valerolactone over polyoxometalate-based metal-organic frameworks: Exploring the role of confinement in the catalytic process

Polyoxometalate-based metal-organic frameworks (POMOFs) with bifunctional Lewis-Brønsted acid were designed by confining polyoxometalates (POMs: phosphotungstic acid (PW), phosphomolybdic acid (PMo) or silicotungstic acid (SiW)) within the Zr-MOFs. The confined POMs not only have their own Brønsted acid, but can also regulate the Lewis acid strength of the POMOFs via charge regulation, ultimately allowing the POMOFs to display superior catalytic performance in the tandem catalysis of furfural (FAL) to γ-valerolactone (GVL). Among the three catalysts (POMOF-PW, POMOF-PMo and POMOF-SiW), a complete conversion of FAL was achieved, while POMOF-PW exhibited the highest GVL yield (58.1 %) at 160 °C within 23 h. The leaching experiment and structural characterization of the catalyst before and after recycling confirmed the stability of the catalyst structure. The humin originates from the polymerization of furan ring-containing compounds driven by Brønsted acid. The adsorption configuration of the substrate molecules on the catalyst offers a new explanation for the tandem reaction process, i.e. that perpendicular adsorption performs only the first step of the tandem reaction, while the coexistence of perpendicular and horizontal adsorption permits the entire reaction process. This work gives unique insights into the tandem reaction of FAL and can guide the design of efficient tandem reaction catalysts.

Rapid, Massive, and Green Synthesis of Polyoxometalate-Based Metal-Organic Frameworks to Fabricate POMOF/PAN Nanofiber Membranes for Selective Filtration of Cationic Dyes.

Developing high-efficiency membrane materials for the rapid removal of organic dyes is crucial but remains a challenge. Polyoxometalates (POMs) clusters with anionic structures are promising candidates for the removal of cationic dyes via electrostatic interactions. However, their shortcomings, such as their solubility and inability to be mass-produced, hinder their application in water pollution treatment. Here, we propose a simple and green strategy utilizing the room temperature stirring method to mass produce nanoscale polyoxometalate-based metal-organic frameworks (POMOFs) with porous rhomboid-shaped dodecahedral and hexagonal prism structures. The products were labeled as POMOF1 (POMOF-PW12) and POMOF2 (POMOF-PMo12). Subsequently, a series of x wt% POMOF1/PAN (x = 0, 3, 5, and 10) nanofiber membranes (NFMs) were prepared using electrospinning technology, where polyacrylonitrile (PAN) acts as a "glue" molecule facilitating the bonding of POMOF1 nanoparticles. The as-prepared samples were comprehensively characterized and exhibited obvious water stability, as well as rapid selective adsorption filtration performance towards cationic dyes. The 5 wt% POMOF1/PAN NFM possessed the highest removal efficiency of 96.7% for RhB, 95.8% for MB, and 86.4% for CV dyes, which realized the selective separation over 95% of positively charged dyes from the mixed solution. The adsorption mechanism was explained using FT-IR, SEM, Zeta potential, and adsorption kinetics model, which proved that separation was determined via electrostatic interaction, hydrogen bonding, and π-π interactions. Moreover, the POMOF1/PAN membrane presented an outstanding recoverable and stable removal rate after four cycles. This study provides a new direction for the systematic design and manufacture of membrane separation materials with outstanding properties for contaminant removal.

Vanadate-based Fe-MOFs as promising negative electrode for hybrid supercapacitor device

In the supercapacitor field, negative electrodes are mainly concentrated in carbon-based materials, such as activated carbon, carbon nanotubes, graphene, and so forth. However, materials based on metal–organic frameworks (MOFs) as negative active components are relatively rare. Herein, a series of composite materials based on graphene oxide (GO) and vanadate-based Fe-organic frameworks have been prepared by hydrothermal method namely GO/Fe-VO4-BIPY. The deposition amount of polyoxometalate-based metal–organic frameworks (POMOFs) on the surface of graphene is adjusted by changing the content of POMOFs. Through the deposition, it can effectively reduce the accumulation between graphene, and increase the dispersion of POMOFs. As a result, the charge storage performance of the as-obtained materials is greatly improved. Among these materials, GO/Fe-VO4-BIPY-1 has the most prominent performance, with a specific capacitance of 190 F g−1 at 0.5 A g−1, which is attributed to the excellent synergistic effect between the Faraday chemical reaction and electric double-layer capacitance. In comparison with pristine Fe-VO4-BIPY, GO/Fe-VO4-BIPY-1 delivers more excellent surface area and therefore exhibits abundant redox reaction sites, achieving better electrochemical performance the best. After assembly with the positive Ni(OH)2 electrode, the maximum energy density of 46.84 W h kg−1 at a power density of 850 W kg−1 is achieved.

Zirconium-rich magnetic polyoxometalate-based metal–organic framework: Tailored for phosphopeptide analysis from lung cancer A549 cells

Polyoxometalate-based metal–organic frameworks (POMOFs) have become a promising affinity material for separation and enrichment. The analysis of protein phosphorylation represents a challenge for the development of efficient enrichment materials. Here, a novel zirconium-rich magnetic POMOF was successfully designed and prepared for the enrichment of phosphopeptides. The binding affinity of the nanomaterial partly came from Fe–O clusters in the MOF. The Lewis acid–base interactions between V–O clusters and zirconium ions in V10O28-Zr4+ and phosphate groups in phosphopeptides further strengthened the enrichment ability. The zirconium-rich magnetic POMOF was employed to capture phosphopeptides from non-fat milk, human saliva, and serum. Additionally, 748 unique phosphopeptide peaks were detected from the tryptic digests of lung cancer A549 cell proteins with a high specificity (86.9 %). POMOFs will become an active competitor for the design of protein affinity materials and will provide a new approach for phosphopeptide analysis.

Revealing the roles of the dual active-sites on a polyoxometalate-based metal–organic framework in catalyzing Knoevenagel condensations

The efficient catalysis of Knoevenagel condensations under mild conditions is a significant way for obtaining olefin compounds, which can be used to produce a wide range of biologically active heterocyclic chemicals and fine chemical raw materials. Herein, a novel polyoxometalate-based metal–organic framework (POMOF), [Co(bix)(H2O)]{V2O6} (VMOF-1, bix = 1,4-bis(imidazol-1-ylmethyl)benzene), is synthesized and structurally characterized. After removal of the coordinated water molecules of CoII ions by vacuum drying, VMOF-1a with both Lewis acid and Lewis base catalytic active-centers is achieved. VMOF-1a as the heterogeneous catalyst for the conversion of benzaldehyde and malononitrile to high value-added olefinic compounds under mild conditions, exhibits excellent conversion and selectivity, good recyclability and broad substrate applicability. Experimental and theoretical studies have revealed that CoII ion and {V2O6}2− unit in VMOF-1a synergistically catalyze the Knoevenagel condensation reaction: (1) {V2O6}2− is used as a Lewis base to pull out the proton of the active methylene group on malononitrile; (2) CoII ion acts as a Lewis acid to activate the carbonyl oxygen on benzaldehyde. Furthermore, it is demonstrated for the first time that the Lewis acid sites in POMOF can play the role of stabilize the alcohol hydroxyl anion intermediates generated during the reaction process, which further elucidates the reason for the high catalytic activity of VMOF-1a in the Knoevenagel condensation. This study provides theoretical guidance for the design of efficient and sustainable catalysts for Knoevenagel condensation.

A novel amine-functionalized polyoxometalate-based metal-organic framework: A reusable heterogeneous nanocomposite for selective oxidation of alcohols

Keggin-type H5PMo10V2O40 (PMoV2) immobilized onto amine-functionalized UiO-66-NH2 via acid-base interaction to create a highly efficient catalyst, called PMoV2@UiO-66-NH2, using post-synthetic modification. This POM-based MOF nanocomposite was used to synthesize carbonyl compounds from alcohols using H2O2 as an oxidant in a green oxidation process. The PMoV2 was successfully immobilized on the amine-functionalized MOF surface through electrostatic interaction, as confirmed by standard characterization methods including FT-IR, EDX, TGA, FE-SEM, MAP images, XRD, and ICP-OES. PMoV2@UiO-66-NH2 exhibited remarkable catalytic activity, with complete conversion of benzyl alcohol and high selectivity towards benzaldehyde. The superior catalytic performance of PMoV2@UiO-66-NH2 can be attributed to its large surface area, uniform dispersion of PMoV2, and the presence of V5+/V4+ redox pairs. The catalyst exhibited attractive yields, required minimal packing, and retained its catalytic activity for up to six cycles.

Drawing Inspiration from Nature: Trinitarian Strategies for Designing Polyoxometalates and Metal-Organic Framework-Based Biomimetic Microhoneycomb Electromagnetic Wave-Absorbing Materials.

Trinitarian designs in the morphology, components, and microstructure remain challenging for advanced electromagnetic wave absorption (EMWA) materials with light weight, strong absorption, and well-defined structure-function relationships. Herein, a series of X-doped MoS2/Cu9S5 with multilevel honeycomb structures (X-MoS2/Cu9S5 MHs, X = P, Si, Ge) were designed by space-confined growth and in situ sulfidation of a polyoxometalate-based metal-organic framework. X-MoS2/Cu9S5 MHs possess low density, high surface area, and abundant cation-cuprum and anion-sulfur double vacancies (VCu and VS) simultaneously that are unmatched by conventional EMWA materials. Also, the systematic investigation of the doping effect of various polyoxometalate heteroatoms on VCu and VS in the microhoneycomb has been conducted. Experimental results and density functional theory calculations reveal that the excellent EMWA performance (-56.21 dB) results from the synergistic effect of morphology design, component optimization, and vacancy regulation. This study not only provides an important opportunity to understand a morphology-component-microstructure strategy in electromagnetic wave absorption but also builds a noteworthy bridge between bioinspired engineering and microscale absorbers.

Advancing biomedical applications of polyoxometalate-based metal–organic frameworks: from design to therapeutic potential

The review covers POMOF materials synthesis, modification, and unique properties, focusing on biomedical sensors and therapies. Finally, the review summarises the challenges and developments of POMOFs in biomedicine.

Anderson-type polyoxometalate-based metal-organic framework as an efficient heterogeneous catalyst for selective oxidation of benzylic C-H bonds.

Oxidative transformation of benzylic C-H bonds into functional carbonyl groups under mild conditions represents an efficient method for the synthesis of aromatic carboxylic acids and ketones. Here we report a high-efficiency catalyst system constructed from an Anderson-type polyoxometalate-based metal-Organic framework (POMOF-1) and N-hydroxyphthalimide (NHPI) for selective oxidation of methylarenes and alkylarenes under 1 atm O2 atmosphere. POMOF-1 exerted a synergistic effect originating from the well-aligned Anderson {CrMo6} clusters and Cu centers within the framework, and this entailed good cooperation with NHPI to catalyze the selective oxidation. Accordingly, the reactions exhibit good tolerance and chemical selectivity for a wide range of substrates bearing diverse substituent groups, and the corresponding carboxylic acids and ketones were harvested in good yields under mild conditions. Mechanism study reveals that POMOF-1 worked synergistically with NPHI to activate the benzylic C-H bonds of substrates, which are sequentially oxidized by oxygen and HOO˙ to give rise to the products. This work may pave a way to design high-efficiency catalysts by integration of polyoxometalate-based materials with NPHI for challenging C-H activation.

Photocatalytic oxidative coupling of terminal alkynes with p-benzoquinone to diaryl ketones by the Cu(I)-PS-POM assembling system through synergistic effect

Photocatalytic C–C bonds formation is an effective approach to synthesize the significant drug intermediates diaryl ketones. Herein, a new polyoxometalate-based metal–organic framework (POMOF), CuW6–TPT, was synthesized by assembling an oxidation catalyst [W6O19]2− into photoactive MOF constructed by photosensitizer (PS) 4,6-tri(4-pyridyl)-1,3,5-triazine (TPT) and binuclear Cu(I) units. CuW6–TPT exhibits excellent light absorption ability and unique conductivity due to the coordination bond, strong π∙∙∙π interactions and H-bonding among Cu(I) ions, TPT moieties and [W6O19]2− in the defined spatial. The abundant exposed Cu(I) catalytic centres are conductive to activate phenylacetylene in situ formation Cu(I)-phenylacetylide, which then undergoes a reductive single electron transfer (SET) process to obtain the key intermediate Cu(II)-phenylactetylide for the Paterno-Buchi (2+2) cycloaddition with benzoquinone to form the labile Cu(II)-oxetane ring. It is a direct route to synthesize diaryl ketones with a hydroxyl group from simple starting materials such as terminal alkynes with p-benzoquinone.

One-Step Synthesis of Hollow CoS2 Spheres Derived from Polyoxometalate-Based Metal-Organic Frameworks with Peroxidase-like Activity.

In this work, hollow CoS2 particles were prepared by a one-step sulfurization strategy using polyoxometalate-based metal-organic frameworks as the precursor. The morphology and structure of CoS2 have been monitored by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray powder diffraction. The mechanism for the formation of CoS2 is discussed. The reaction time and sulfur content are found to be important factors that affect the morphology and pure phase formation of CoS2, and a hollow semioctahedral morphology of CoS2 with open voids was obtained when the sulfur source was twice as large as the precursor and the reaction time was 24 h. The CoS2 (24 h) particles show an excellent peroxidase-like activity for the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized (oxTMB) by hydrogen peroxide. The polyoxometalate used as a precursor helps to stabilize oxTMB during catalytic oxidation, forming a stable curve platform for at least 8 min. Additionally, the colorimetric detection of hydroquinone is developed with a low detection limit of 0.42 μM. This research provides a new strategy to design hollow materials with high peroxidase-mimicking activity.

Assembly of Lanthanide-Containing 3D [MnMo9O32]6--Based Metal-Organic Frameworks and Oxidative Desulfurization Performance.

Lanthanide-containing polyoxometalate-based metal-organic frameworks (POMOFs) not only enjoy intriguing architectures but also have good application prospects as catalysts. Herein, three novel three-dimensional (3D) POMOFs with the formulas of {H[Ln3(2,6-pydc)2(H2O)10(MnMo9O32)]·2H2O}n (Ln = La(1), Pr(2), Nd(3)) have been synthesized based on Waugh-type [MnMo9O32]6- anions and pyridine-2,6-dicarboxylate (2,6-H2pydc). Compounds 1-3 are isomorphic, and there are two kinds of one-dimensional (1D) helical chains with opposite handedness staggered into two-dimensional (2D) layers. Interestingly, the coordinated L- and R-[MnMo9O32]6- anions are encapsulated in 1D chains with the same chirality and are further expanded into 3D structures. The catalytic tests indicate that compounds 1-3 exhibit high-efficiency heterogeneous catalytic activity in the oxidative desulfurization reaction for catalyzing the oxidation of sulfides to sulfoxides using tert-butyl hydrogen peroxide (TBHP) as the oxidant. Moreover, a series of control experiments have been conducted to investigate the influence of various parameters such as temperature, time, solvent, catalyst, and substrate on the reaction. Significantly, compound 2, as an example, exhibits good reusability and structural stability in the oxidative desulfurization reaction. It is worth noting that investigations on the oxidative desulfurization of [MnMo9O32]6- anions are scarce. Moreover, their electrochemical properties are also explored.

Improved supercapacitors and water splitting performances of Anderson-type manganese(III)-polyoxomolybdate through assembly with Zn-MOF in a host–guest structure

Enhancing performance through the combination of polyoxometalates (POMs) clusters with metal–organic frameworks (MOFs) that contain various transition metals is a challenging task. In this study, we synthesized a polyoxometalate-based metal–organic framework (POMOF) named HRBNU-5 using a solvothermal method. HRBNU-5 is composed of Zn[N(C4H9)4][MnMo6O18{(OCH2)3CNH2}2]@Zn3(C9H3O6)2·6C3H7NO, which includes two components: Zn[N(C4H9)4][MnMo6O18{(OCH2)3CNH2}2]·3C3H7NO ({Zn[MnMo6]}) and Zn3(C9H3O6)2·3C3H7NO (Zn-BTC). Structural characterization confirmed the host–guest structure, with Zn-BTC encapsulating {Zn[MnMo6]}. In a three-electrode system, HRBNU-5 exhibited a specific capacitance of 851.3 F g−1 at a current density of 1 A/g and retained high stability (97.2 %) after 5000 cycles. Additionally, HRBNU-5 performed well in aqueous-symmetric/asymmetric supercapacitors (SSC/ASC) in terms of energy density and power density in a double-electrode system. Moreover, it demonstrated excellent catalytic performance in a 1.0 M KOH solution, with low overpotentials and Tafel slopes for hydrogen and oxygen evolution reactions: 177.1 mV (η10 HER), 126.9 mV dec–1 and 370.3 mV (η50 OER), 36.3 mV dec–1, respectively, surpassing its precursors and most reported studies. HRBNU-5′s positive performance is attributed to its host–guest structure, high electron-transfer conductivity, and porous structure that enhances efficient mass transport. This work inspires the design of Anderson-type POMOF electrode materials with multiple active sites and a well-defined structure.

Effective Enrichment of Phosphopeptides Using Magnetic Polyoxometalate-Based Metal-Organic Frameworks.

In this study, magnetic polyoxometalate-based metal-organic frameworks (Fe3O4-POMOFs) were designed and applied to the enrichment of phosphopeptides. Thanks to the abundant metal oxide and metal ion sites, the material had a strong affinity for phosphopeptides. Simultaneously, the high amount of amino and guanidyl groups provided hydrophilicity and positive charge for phosphopeptide capture. By coupling with MS detection, the established platform possessed good reusability, high sensitivity (0.01 fmol), and high selectivity (α-casein/β-casein/bovine serum albumin = 1:1:5000). Furthermore, the method was successfully used for the detection of phosphopeptides in nonfat milk, human serum, saliva, and A549 cell lysate, showing great potential for practical application.

Ni3P2W18O62-Ni3(BTC)2 composite of Ni3P2W18O62 coated on the surface of the Ni3(BTC)2 with supercapacitor and H2O2 sensing properties was prepared by simple grinding strategy

Polyoxometalate-based metal-organic frameworks (POMOFs) as energy and catalytic materials have attracted considerable attention. Hence, Ni3P2W18O62-Ni3(BTC)2 (BTC=1,3,5-benzene-tricarboxylic acid) composite was successfully synthesized by a simple grinding strategy. IR, XRD, SEM, TEM and HRTEM results show that Ni3P2W18O62 is successfully coated on the surface of the Ni3(BTC)2. The specific capacitance of Ni3P2W18O62-Ni3(BTC)2 (460 F g−1 at 1 A g−1) is higher than that of precursors and reported supercapacitors when nickel foam is used as a collector. And the stability of Ni3P2W18O62-Ni3(BTC)2 is excellent after 5000 cycles. The symmetrical supercapacitor (SSC) was assembled with the Ni3P2W18O62-Ni3(BTC)2 as the electrode material and the energy density can reach 28.6 Wh kg−1 with a power density of 600 W kg−1. Ni3P2W18O62-Ni3(BTC)2 as a H2O2 sensor not only has a wide linear range (0.5 μM to 0.25 mM) and a low detection limit (0.17 μM), but also has strong stability and anti-interference ability, and can be used to detect H2O2 in real blood serum specimens. The improved capacitance and sensing properties are mainly attributed to the increased active site and faster electron/charge migration rate of the Ni3P2W18O62-Ni3(BTC)2. This study overcomes the shortcomings of traditional synthesis methods and provides new ideas for their application in electrochemistry.

Synergy effect of highly dispersed palladium and Ni-SiW polyoxometalate-based metal-organic framework (POMOF) for highly efficient and selective nitroaromatics hydrogenation

The Pd/Ni-SiW catalysts with different Pd loadings (weight percent-0.77%, 1.41%, and 2.52%) are prepared by room-temperature precipitation method, which are with the Pd nanoclusters highly dispersed in Ni-SiW POMOF. These as-prepared catalysts show high catalytic activity for the hydrogenation of nitroaromatics under mild condition (hydrogen pressure-3.0 MPa and reaction temperature-40 ℃). Among them, the 1.41%Pd/Ni-SiW catalyst has 99% conversion, 100% selectivity and 255.5 h−1 TOF for p-nitroacetophenone hydrogenation to p-aminoacetophenone. The Pd nanoclusters are highly dispersed in the pores of Ni-SiW POMOF, resulting in appropriate size of the Pd nanoclusters making H2 much better dissociation, and the substrate is easily adsorbed at the Ni-SiW POMOF by the interaction of Ni-SiW POMOF-NO2 group. There is a synergistic effect between the Pd and Ni-SiW, which the existence of a two-dimensional framework composed of 4,4′-bipyridine and nickel nodes increases the adsorption capacity of nitro groups, thus preferentially adsorbing nitro groups.

Two 3D Two-Fold Interpenetrated Dia-Like Polyoxometalate-Based Metal-Organic Frameworks: Synthesis and Sulfide Selective Oxidation Activity.

Two new three-dimensional (3D) polyoxometalate-based metal-organic frameworks (POMOFs), [M2(btap)4(H2O)4(HPMo10VI Mo2VO40)] (M = Co (1) and Cd (2); btap = 3, 5-bis(1', 2', 4'-triazol-1'-yl)pyridine), have been synthesized under mild hydrothermal conditions and characterized in detail. Single-crystal X-ray diffraction (SXRD) analysis indicates that 1 and 2 are isostructural. In complexes 1 and 2, the metal ion is coordinated with the ligand to form two different left and right helical one-dimensional chains, which are alternately connected in a twisted form to build a two-fold interpenetrated three-dimensional structure, and the polyoxometalate is encapsulated into in the pores generated by the interpenetrating structure. It is noteworthy that 1 and 2, as recyclable catalysts, possess favorable heterogeneous catalytic activity and excellent sulfoxide selectivity in sulfide oxidation reactions, with H2O2 as an oxidant. By reason of the high dispersion of polyoxometalate with good intrinsic activity in the skeleton structure, the title complex has high activity. In addition, no obvious decrease of sulfoxide yield is observed after at least five cycles. These results indicate the excellent catalytic activity and sustainability of 1 and 2.

Coordination Defect-Induced Frustrated Lewis Pairs in Polyoxometalate-Based Metal-Organic Frameworks for Efficient Catalytic Hydrogenation.

Precise control of the structure and spatial distance of Lewis acid (LA) and Lewis base (LB) sites in a porous system to construct efficient solid frustrated Lewis pair (FLP) catalyst is vital for industrial application but remains challenging. Herein, we constructed FLP sites in a polyoxometalate (POM)-based metal-organic framework (MOF) by introducing coordination-defect metal nodes (LA) and surface-basic POM with abundant oxygen (LB). The well-defined and unique spatial conformation of the defective POM-based MOF ensure that the distance between LA and LB is at ~4.3 Å, a suitable distance to activate H2. This FLP catalyst can heterolytically dissociate H2 into active Hδ-, thus exhibiting high activity in hydrogenation, which is 55 and 2.7 times as high as that of defect-free POM-based MOF and defective MOF without POM, respectively. This work provides a new avenue toward precise design multi-site catalyst to achieve specific activation of target substrate for synergistic catalysis.