Organic Hybrid Polyoxometalate Research Articles

Highly efficient catalytic reduction of organic dyes, Cr (VI) and 4‐nitrophenol, and photocatalytic degradation of MB by an inorganic–organic hybrid polyoxometalate

It is urgent to remove various pollutants from the water environment. Therefore, an inorganic–organic hybrid polyoxometalate (POM) [PMoVI6MoV2VIV8O44{Co(2,2′‐bipy)2(H2O)}4]‐[PMoVI4MoV4VIV8O44{Co(2,2′‐bipy)2(H2O)}2]·4H2O (PMoVCo) was fully characterized by XRD, XPS, FTIR, SEM, BET and zeta potential techniques, and applied for the catalytic reduction of hazardous methylene blue (MB), methyl orange (MO), rhodamine B (RhB), Cr (VI) and 4‐nitrophenol (4‐NP) in aqueous media over NaBH4 under mild condition. The removal ratios were 99.6% (MB, 2.5 min), 97.0% (MO, 3.0 min), 92.5% (RhB, 2.0 min), 89.2% (Cr (VI), 2.0 min) and 89.6% (4‐NP, 2.5 min), respectively. The pseudo‐first‐order rate constants of the reactions were 1.992 min−1 (MB), 0.810 min−1 (MO), 1.768 min−1 (RhB), 1.186 min−1 (Cr (VI)) and 0.934 min−1 (4‐NP), respectively. Additionally, PMoVCo exhibited satisfactory catalytic activity for the photo‐Fenton‐like degradation of MB at neutral pH under visible light irradiation with a degradation rate up to 99.9% in 480 min. The results of the recycling experiment prove that PMoVCo has high catalytic reusability. Moreover, the possible mechanisms of the catalytic reduction and degradation processes were proposed. The catalytic activities of PMoVCo are better than other inorganic–organic hybrid POMs. All the results of this study indicate that PMoVCo has the potential to be a satisfactory catalyst for wastewater remediation via reduction or photocatalytic degradation.

Polyoxometalate-Dicarboxylate Hybrid Dimers with {SiW10Cr2} Nodes: Syntheses, Structures, and Mass Spectrometric Characterization.

The current study describes a new family of hybrid dimers constructed from secondary building blocks based on a dichromium-substituted silicodecatungstate, {SiW10Cr2}, and flexible dicarboxylate ligands of varied lengths. All five polyoxometalate-organic hybrid compounds exhibit an entropically favored, cyclic dimer motif that contains just two {SiW10Cr2} clusters─the minimum to form a closed loop, linked by two aliphatic dicarboxylates, as revealed by single-crystal X-ray diffraction. Due to the kinetic inertness of such Cr3+-based hybrid dimers, ESI-MS has become a particularly useful technique for the characterization of these paramagnetic, NMR-unfriendly systems.

Polyoxometalate–Organic Hybrid “Calixarenes” as Supramolecular Hosts

AbstractCalixarenes are among the most useful and versatile macrocycles in supramolecular chemistry. The one thing that has not changed in the 80 years since their discovery, despite numerous derivatizations, is their fully organic, covalent scaffolds. Here, we report a new type of organic–inorganic hybrid “calixarenes” constructed by means of coordination‐driven assembly. Replacing acetate ligands on the {SiW10Cr2(OAc)2} clusters with 5‐hydroxyisophthalates allows these 95° inorganic building blocks to be linked into bowl‐shaped, hybrid “calix[n]arenes” (n=3, 4). With a large concave cavity, the metal–organic calix[4]arene can accommodate nanometer‐sized polyoxoanions in an entropically driven process. The development of hybrid variants of calixarenes is expected to expand the scope of their physicochemical properties, guest/substrate binding, and applications on multiple fronts.

Polyoxometalate-Organic Hybrid "Calixarenes" as Supramolecular Hosts.

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

A bifunctional 3D inorganic–organic hybrid framework constructed by [β-Mo8O26]n4n- chains and [Cu(dap)2]2+ cations for efficient electrochemical sensing and photocatalytic reduction of Cr(VI)

Under hydrothermal conditions, a new 3D inorganic–organic hybrid polyoxometalate(POM), {[Cu(dap)2]2[β-Mo8O26]}·H2O (1, dap = 1,2-diaminopropane) was synthesized and characterized. Structural analysis displays that 1 represents an interesting 3D POM-based framework constructed from the 1D infinite inorganic chains [β-Mo8O26]n4n- and [Cu(dap)2]2+ cations. 1 exhibits good electrochemical performance and acts as electrochemical sensor for the detection of Cr(VI) with low limit of detection (LOD) of 0.291 µM, high sensitivity of 0.483 μA μM−1 and good anti-interference. The LOD of Cr(VI) for 1 is lower than the maximum content of Cr(VI) in groundwater required by the World Health Organization (WHO). Interestingly, 1 also displays excellent photocatalytic activity for Cr(VI) reduction. The reduction rate of Cr(VI) by 1 can reach 96% within 80 min under the original pH condition. Furthermore, the photocatalytic process obeys the pseudo-first-order reaction kinetic with the half-life of 16.35 min.

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.

An inorganic–organic hybrid material based on a Keggin‐type polyoxometalate@Dysprosium as an effective and green catalyst in the synthesis of 2‐amino‐4H‐chromenes via multicomponent reactions

A novel inorganic–organic hybrid, [Dy4(PDA)4(H2O)11(SiMo12O40)]·7H2O denoted as (POM@Dy‐PDA), based on a lanthanide cluster, a Keggin‐type polyoxomolybdate, and PDA (1,10‐phenanthroline‐2,9‐dicarboxylic acid) was prepared and fully characterized by elemental analysis, Fourier‐transform infrared and UV–Vis spectroscopies, thermogravimetric analysis, powder X‐ray diffraction (PXRD), and single‐crystal X‐ray diffraction. The structural analysis study showed that the [SiMo12O40]4− ions reside in the interspace between two cationic layers as discrete counterions and are not coordinated to the rare‐earth ions. Significantly, this hybrid catalyst is a rare case of an inorganic–organic hybrid polyoxometalate (POM) with a PDA ligand based on CSD search (CSD version 5.40/November2018). The hybrid catalyst was further characterized via powder X‐ray diffraction (PXRD) pattern at room temperature which indicated the good phase purity of the catalyst. BET and Langmuir surface area analysis indicate surface area of POM@Dy‐PDA 6.6 and 51.3 m2g‐1, respectively. The catalytic activity of the hybrid catalyst was successfully examined in the synthesis of 2‐amino‐4H‐chromene derivatives through a multicomponent reaction. A three‐component, one‐pot reaction involving differently substituted benzaldehydes, resorcinol/α‐naphthol/β‐naphthol/4‐hydroxycoumarin/3‐methyl‐4H‐pyrazole‐5(4H)‐one, and malononitrile or ethyl cyanoacetate in the presence of a catalytic quantity of the aforementioned hybrid catalyst in EtOH/H2O under reflux condition gave the corresponding highly functionalized 2‐amino‐4H‐chromenes in satisfactory yields. The catalyst can be reused several times without appreciable loss in its catalytic activity.

A New 2-D Inorganic–Organic Hybrid Polyoxometalate Based on Mono-Cu-Substituted [CuSiW11O39] n 6n− Chains and [Cu(en)2]2+ Bridges

A new organic–inorganic hybrid polyoxometalate H2[Cu(en)2(H2O)]2[Cu(en)2]{[Cu(en)2]3 (CuSiW11O39)2}·6H2O (1) (en = ethylenediamine) have been hydrothermally synthesized and characterized by IR spectrum, thermogravimetric analysis, power X-ray diffraction and single-crystal X-ray diffraction. Crystal data for 1: monoclinic, P21/c, a = 18.8077(3) A, b = 23.0703(5) A, c = 26.0723(6) A, β = 96.438(2)°, Z = 4. Single-crystal X-ray diffraction analysis revealed that 1 exhibits a 2-dimensional network constructed from mono-Cu-substituted [CuSiW11O39] 6− chains and [Cu(en)2]2+ bridges. A new organic–inorganic hybrid polyoxometalate H2[Cu(en)2(H2O)]2[Cu(en)2]{[Cu(en)2]3(CuSiW11O39)2}·6H2O (1) (en = ethylenediamine) have been hydrothermally synthesized and characterized, which exhibits a 2-dimensional network constructed from mono-Cu-substituted [CuSiW11O39] 6− chains and [Cu(en)2]2+ bridges.

Photoreduction Mechanism of CO2 to CO Catalyzed by a Rhenium(I)–Polyoxometalate Hybrid Compound

The photoreduction mechanism of carbon dioxide to carbon monoxide by the Re–organic hybrid polyoxometalates (POMs) {NaH[PW12O40]3–ReIL(CO)3DMA}n− (L = 15-crown-5 phenanthroline, DMA = N,N-dimethylacetamide) has been investigated by means of DFT and TD-DFT calculations. The reaction mechanism can be divided into several steps, including (i) photoexcitation and charge transfer, (ii) DMA release, (iii) CO2 addition, (iv) protonation, and (v) CO release and regeneration of the catalyst. The charge transfer (CT) states, POM to Re complex, are efficiently induced by metal-centered (MC) excitations occurring on the reduced POM. Once one electron is transferred to the organometallic unit from the excited POM, the Re is able to bind and activate the CO2 substrate. Subsequent steps that involve protonation of CO2 and CO release are favorable thermodynamically and are induced by a second electron transfer from the POM to the Re complex. In this reaction, the POM acts as photosensitizer, electron reservoir, and elect...

Synthesis and Crystal Structure of an Inorganic-Organic Hybrid Material: [1,1′-dibutyl-4,4′-bipyridinium][α-Mo8O26]0.5

A novel inorganic–organic hybrid polyoxometalate, [1,1′-dibutyl-4,4′-bipyridinium,][α-Mo8O26]0.5 (1), has been synthesized by the cation-templated self-assembly with octamolybdate anions under hydrothermal reaction conditions. The structure has been determined by single-crystal X-ray diffraction analysis and further characterized by PXRD, IR spectra, and elemental analysis. The crystal data analysis revealed that the compound was composed of one discrete [1,1′-dibutyl-4′-bipyridinium]2+ cation and 0.5 polyacid anions [Mo8O26]4– interacted by electrostatic interactions. In the compound the anion fraction take on a [α-Mo8O26]4– cluster.

P2V3W15O62]9 − cluster based covalent polyoxometalate-organic hybrid: Synthesis, structure, self-assembly and in vitro antioxidant activities

A new [P2V3W15O62]9− cluster based covalent polyoxometalate-organic hybrid (P1) containing a naphthol-amide-Tris derivative has been synthesized and characterized using standard analytical and spectroscopic techniques including single crystal X-ray diffraction analyses. P1 exhibits interesting self-assembly behaviour leading to the generation of ~200nm spherical aggregates in solutions as revealed by DLS and TEM analyses. Standard in vitro experiments revealed that P1 is capable of exhibiting moderate antioxidant properties under standard experimental conditions.

Supramolecular architectures assembled from amphiphilic hybrid polyoxometalates

Polyoxometalate (POM)-based inorganic-organic molecular hybrid clusters have been recently recognized as good candidates to design novel multi-functional materials. Tremendous efforts have been invested in synthesizing many interesting hybrid structures with exceptional chemical and physical properties. Grafting organic ligands to the POM clusters render these functional clusters amphiphilic properties. Here we summarize the current progresses and provide some perspectives, from colloidal chemists' point of view, on the self-assembly of the amphiphilic POM-organic hybrids in solution and at interfaces, as well as the related consequent novel features such as enhanced fluorescent properties.

Design and Synthesis of “Dumb-bell” and “Triangular” Inorganic-Organic Hybrid Nanopolyoxometalate Clusters and Their Characterisation through ESI-MS Analyses

A series of tris(hydroxymethyl)aminomethane (TRIS)-based linear (bis(TRIS)) and triangular (tris(TRIS)) ligands has been synthesised and were covalently attached to the Wells-Dawson type cluster [P(2)V(3)W(15)O(62)](9-) to generate a series of nanometer-sized inorganic-organic hybrid polyoxometalate clusters. These huge hybrids, with a molecular mass similar to that of small proteins in the range of ≈10-16 kDa, were unambiguously characterised by using high-resolution ESI-MS. The ESI-MS spectra of these compounds revealed, in negative ion mode, a characteristic pattern showing distinct groups of peaks corresponding to different anionic charge states ranging from 3(-) to 8(-) for the hybrids. Each peak in these individual groups could be unambiguously assigned to the corresponding hybrid cluster anion with varying combinations of tetrabutylammonium (TBA) and other cations. This study therefore highlights the prowess of the high-resolution ESI-MS for the unambiguous characterisation of large, nanoscale, inorganic-organic hybrid clusters that have huge mass, of the order of 10-16 kDa. Also, the designed synthesis of these compounds points to the fact that we were able to achieve a great deal of structural pre-design in the synthesis of these inorganic-organic hybrid polyoxometalates (POMs) by means of a ligand design route, which is often not possible in traditional "one-pot" POM synthesis.

Synthesis and characterization of two inorganic–organic hybrid polyoxometalates bridged by Keggin-type building blocks and copper(II) organonitrogen complexes

Two new inorganic–organic hybrid compounds, namely [Cu(dab)2]2[α-SiW12O40]·H2O (dab = 1,2-diaminobenzene) and [Cu(dafo)3]2[Cu(dafo)2(H2O)2][α-PMo12O40]2·4H2O (dafo = 4,5-diaza- fluorene-9-one) have been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction. [Cu(dab)2]2[α-SiW12O40]·H2O exhibits an alternating 2D ladder-like structure built of [α-SiW12O40]4− and [Cu(L)2]2+ units. As the inorganic building block, the Keggin-type polyoxoanion [α-SiW12O40]4− is linked to two metal–organic complexes [Cu(dab)2]2+ through different kinds of oxygen atoms (terminal and bridging). [Cu(dafo)3]2[Cu(dafo)2(H2O)2][α-PMo12O40]2·4H2O shows an extended 3D supramolecular network via hydrogen bonding. Both complexes were characterized by physico-chemical and spectroscopic methods.

A new inorganic–organic hybrid polyoxometalate constructed by [PMo8V6O42] clusters and transition metal complexes

A new compound [Zn(phen)2]2[][Zn(phen)2(H2O)]2[] · 7H2O (phen = phenanthroline) has been synthesized under hydrothermal conditions and characterized by IR, TG analysis and single-crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic system, space group P21/C, a = 21.609(4) Å, b = 16.537(3) Å, c = 21.279(4) Å, α = 90°, β = 100.25(3)°, γ = 90°, V = 7483(3) Å3, Z = 2. The basic building unit in 1 is the [PMo8V6O42] cluster. The most remarkable structural feature of 1 is that there exist two distinct [PMo8V6O42] clusters. One is covalently linked by [Zn(phen)2] complexes to form a 2D covalent layer, the other supports two [Zn(phen)2(H2O)] complexes forming a discrete bisupporting structure. It is interesting that discrete bisupporting clusters locate in the space of two adjacent covalently layers to form a 3D supramolecular framework.

Inorganic–organic hybrid polyoxometalate containing supramolecular helical chains: Preparation, characterization and application in chemically bulk-modified electrode

An inorganic–organic hybrid polyoxometalate (POM) (Hbpy) 4[SiMo 12O 40] ( 1) (bpy = 2,4-bipyridine), has been prepared and characterized. X-ray diffraction study reveals that compound 1 contains interesting organic double helical chains. The hybrid nanoparticles was used as a solid bulkmodifier to fabricate a three-dimensional chemically modified carbon paste electrode ( 1-CPE) by direct mixing. The electrochemical behavior and electrocatalysis of 1-CPE has been studied in detail. The results indicate that 1-CPE has a good electrocatalytic activity toward the reduction of nitrite in 1 M H 2SO 4 aqueous solution. 1-CPE shows remarkable stability that can be ascribed to the interactions existed between POM anions and organic double helical bpy chains, which are very important for practical applications in electrode modification.

Inorganic–organic hybrid polyoxometalate: Preparation, characterization and electrochemistry properties

The solid hybrid material (H 3/4pbpy) 4[PMo 12O 40]·1.25H 2O ( 1) (pbpy=5-phenyl-2-(4-pyridinyl)pyridine) has been prepared and characterized. A structural feature of compound 1 is that the polyoxometalate anions exhibit a one-dimensional inorganic double chain-like structure via weak interactions of O…O. The organic moiety exhibits regular packing with offset aromatic–aromatic interactions between the pbpys, leading to a compact supramolecular framework structure to accommodate the inorganic chains. Compound 1 was employed to fabricate the three-dimensional bulk-modified carbon paste electrode ( 1-CPE) to research on its electrochemistry properties. The results indicate that 1 retained Keggin molybdate anion electrocatalytic activities toward the reduction of chlorate, hydrogen peroxide and nitrite.

Inorganic–organic hybrid polyoxometalate nanoparticle modified wax impregnated graphite electrode: preparation, electrochemistry and electrocatalysis

A kind of inorganic–organic hybrid polyoxometalate (POM) nanoparticle [(CH 3) 4N] 6P 2Mo 18O 62 · 9H 2O has been designed and prepared by solid-state reaction at room temperature and immobilized on the surface of a wax impregnated graphite electrode (WIGE) by the sol–gel technique for the first time. The electrochemical behavior of the [(CH 3) 4N] 6P 2Mo 18O 62 · 9H 2O nanoparticle modified WIGE (P 2Mo 18-WIGE) has been studied in detail, including pH-dependence, solvent effect and stability. The electrocatalytic behavior of the P 2Mo 18-WIGE toward the reduction of chlorate, hydrogen peroxide and nitrite in 1 M H 2SO 4 aqueous solution is reported. The experimental results show that the P 2Mo 18-WIGE not only maintains the electrochemical activity and electrocatalytic properties of the H 6P 2Mo 18O 62, but also shows remarkable stability due to insolubility of the hybrid POM nanoparticles, which is important for practical applications. The significance of our research work is to provide a kind of novel and very stable POM-based solid nano-material applied in electrode modification.