Polyoxometalate Hybrid Research Articles

Hybrid Polyoxometalate Salt Adhesion by Butyltin Functionalization.

Polyoxometalate (POM)-based ionic liquids, with nearly infinite compositional variations to fine-tune antimicrobial and physical properties, function as water purification filters, anticorrosion/antibacterial coatings for natural stones, self-repairing acid-resistant coatings, catalysts, and electroactive, stable solvents. By combining hydrophobic quaternary ammonium cations (QACs; tetraheptylammonium and trihexyltetradecylammonium) with butyltin-substituted polyoxotungstates [(BuSn)3(α-SiW9O37)] via repeated solvent extraction-ion exchange, we obtained phase-pure hybrid POM salts (referred to as such because they melt above room temperature). If the solvent extraction process is performed only once, then solids with high salt contamination and considerably lower melting temperatures are obtained. Solution-phase behavior, based on POM-QAC interactions, was similar for all formulations in polar and nonpolar organic solvents, as observed by X-ray scattering and multinuclear magnetic resonance spectroscopy. However, solid thin films of the butyltin-functionalized hybrid POM salts were significantly more stable and adhesive than their inorganic analogues. We attribute this to the favorable hydrophobic interactions between the butyltin groups and the QACs. All synthesized hybrid POM salts display a potent antimicrobial activity toward Escherichia coli. These studies provide fundamental form-function understanding of hybrid POM salts, based on interactions between ions in these complex hybrid phases.

Synthesis and Characterization of Polyvanadium and Heteropoly-Tungsten Based Inorganic Wells Dawson Polyoxometalates Hybrids

The two new Wells-Dawson type polyoxometalatehybrids named as [(C4H9)4N]10H2[{C7H14O4C(CH2O)3P2V3W15O59] (D.Poms@Lig1), [(C4H9)4N)]5H2[C2H4OC(CH2O)3 P2V3W15O59] (D.Poms@Lig-2) have been synthesized with good percentage yields (65 and 75%, respectively). The newly prepared hybrids were characterized successfully by FT-IR, 1H, 13C, 31P, 51V NMR and UV-Visible spectroscopic methods. Parent Dawson polyoxometalates and ligands molecules display the strong metal-oxo (V–O) vibrational bands at 700 cm–1. After interaction, there is a little fluctuations in these vibrational bands and appeared at 757 and 750 cm–1 for V–O of D. Poms@Lig-1 and D.Poms@Lig-2, respectively. The strong peaks appeared at 824, 718 and 803, 754 cm–1 are assigned for ν(W–O–W) D.Poms@Lig-1 and D.Poms@Lig-2, respectively. In 1H NMR, the chemical shift value 2.95–2.94 ppm was observed C–CH2–O for D.Poms@Lig-1 and D.Poms@Lig-2, respectively. In 13C NMR, signal appears at 62.92 and 62.75 ppm are assigned for –CH2–C–CH2– for D.Poms@Lig-1, D.Poms@Lig-2, respectively. 51V NMR spectra showed peaks at –541.00 and –541.87 ppm for D.Poms@Lig-1 and D.Poms@Lig-2, respectively. 31P NMR spectra showed two peaks at δ = [–13.44, –7.19] ppm and [–13.44, –7.25] ppm for D.Poms@Lig-1, and D.Poms@Lig-1, respectively. The UV-Visible absorption spectra showed that there is just a little bit change in the intensity of the absorption bands among the absorption spectra of the ligands, hybrid compounds and parent Dawson POM.

Aerobic photoxidation of sulfides using unique hybrid polyoxometalate under visible light

A unique hybrid Polyoxometalate was synthesized, which can absorb visible light and perform photocatalytic activity. This Organic-Inorganic hybrid material was synthesized through attaching the organotin compound to the vacant polyoxometalate. Interestingly, this hybridization brought an outstanding decrement in the polyoxometalate band gap and turned this hybrid polyoxometalate to a photocatalytic compound, which can conduct catalytic reactions under visible light. In this line, we devised photoxidation of sulfides using this photocatalyst and under O2 atmosphere as a sustainable and environmental friendly oxidant. Various kinds of sulfides were investigated under optimum reaction conditions and the corresponding sulfoxide products were synthesized in good to high yields.

On‐POM Ring‐Opening Polymerisation of N‐Carboxyanhydrides

AbstractThe ring‐opening polymerisation of α‐amino acid N‐carboxyanhydrides (NCAs) offers a simple and scalable route to polypeptides with predicted and narrow molecular weight distributions. Here we show how polyoxometalates (POMs)—redox‐active molecular metal‐oxide anions—can serve as inorganic scaffold initiators for such NCA polymerisations. This “On‐POM polymerisation” strategy serves as an innovative platform to design hybrid materials with additive or synergistic properties stemming from the inorganic and polypeptide component parts. We have used this synthetic approach to synthesise a library of bactericidal poly(lysine)–POM hybrid derivatives that can be used to prevent biofilm formation. This versatile “On‐POM polymerisation” method provides a flexible synthetic approach for combining inorganic scaffolds with amino acids, and the potential to tailor and improve the specificity and performance of hybrid antimicrobial materials.

On‐POM Ring‐Opening Polymerisation of N‐Carboxyanhydrides

The ring-opening polymerisation of α-amino acid N-carboxyanhydrides (NCAs) offers a simple and scalable route to polypeptides with predicted and narrow molecular weight distributions. Here we show how polyoxometalates (POMs)-redox-active molecular metal-oxide anions-can serve as inorganic scaffold initiators for such NCA polymerisations. This "On-POM polymerisation" strategy serves as an innovative platform to design hybrid materials with additive or synergistic properties stemming from the inorganic and polypeptide component parts. We have used this synthetic approach to synthesise a library of bactericidal poly(lysine)-POM hybrid derivatives that can be used to prevent biofilm formation. This versatile "On-POM polymerisation" method provides a flexible synthetic approach for combining inorganic scaffolds with amino acids, and the potential to tailor and improve the specificity and performance of hybrid antimicrobial materials.

Interactions of aromatic rings in the crystal structures of hybrid polyoxometalates and Ru clusters

Computational analysis for π–π interaction energies of {(arene)Ru}2+ containing complexes and relative group 5 hybrid polyoxometalates reveals different frameworks. Some perspectives on πOF materials processing and crystal engineering were discussed.

Polarizability is a key parameter for molecular electronics.

Identifying descriptors that govern charge transport in molecular electronics is of prime importance for the elaboration of devices. The effects of molecule characteristics, such as size, bulkiness or charge, have been widely reported. Herein, we show that the molecule polarizability can be a crucial parameter to consider. To this end, platinum nanoparticle self-assemblies (PtNP SAs) are synthesized in solution, including a series of polyoxometalates (POMs). The charge of the POM unit can be modified according to the nature of the central heteroatom while keeping its size constant. POM hybrids that display remote terminal thiol functions strongly anchor the PtNP surface to form robust SAs. IV curves, recorded by conductive AFM, show a decrease in Coulomb blockade as the dielectric constant of the POMs increases. In this system, charge transport across molecular junctions can be interpreted as variations in polarizability, which is directly related to the dielectric constant.

Dipyridine Amine Octamolybdates Hybrid Material Effectively Catalyzed Oxidation of Sulfide Derivatives with Hydrogen Peroxide

With the increasing interest in polyoxometalates (POMs) materials over the past few decades, scientific researchers have focused their attention on the fruitful utilization of POMs hybrids as efficient catalysts in many organic reactions. In this paper, dipyridine amine (dpa) organic ligand hybrid polyoxomolybdate material was solvothermally synthesized and structurally identified by elemental analysis, X-ray diffraction and infrared spectrum. Structural refinement of the hybrid polyoxomolybdate compound 1 with general formula [Hdpa]4Mo8O26 · 2DMF (DMF = N,N-dimethylformamide) shows that compound 1 presents in the space group P-1 with triclinic system, and is built up from a well-known β-[Mo8O26]4– anionic cluster, four free protonated dpa cations and two free DMF molecules. Remarkably, the β-Mo8O26-based hybrid material was further applied as the catalyst in the conversion of sulfides utilizing hydrogen peroxide (30%) as green terminal oxidant and exhibited efficient catalytic activities for selective oxidation of sulfides.

Photocurrent generation from visible light irradiation of covalent polyoxometalate–porphyrin copolymers

Four hybrid polyoxometalate–porphyrin copolymer films were obtained by the electrooxidation of zinc-β-octaethylporphyrin (ZnOEP) or 5,15-ditolylporphyrin (H2T2P) in the presence of organosilyl functionalized Keggin-type POMs TBA3[PW11Si2O40C26H16N2] (abbreviated Py-PW11Si2-Py) and Dawson-type POMs TBA6[P2W17Si2O62C26H16N2] (abbreviated Py-P2W17Si2-Py) bearing two remote pyridyl groups. The electropolymerization process of the four copolymers was monitored by EQCM. The obtained copolymers were characterized by UV/Vis spectroscopy, X-ray photoelectron spectroscopy, electrochemistry, and AFM. Their impedance properties (EIS) were studied and their photovoltaic performances were also investigated by photocurrent transient measurements under visible light irradiation. These studies showed a correlation between impedance and photovoltaic performances, the films based on Dawson type POMs and Zn porphyrins giving the best results. This last system displayed one of the best photocurrent efficiency for a reported POM photosensitized hybrid.

A silicododecamolybdate/pyridinium-tetrazole hybrid molecular salt as a catalyst for the epoxidation of bio-derived olefins

The hybrid polyoxometalate (POM) salt (Hptz)4[SiMo12O40]∙nH2O (1) (ptz = 5-(2-pyridyl)tetrazole) has been prepared, characterized by X-ray crystallography, and examined as a catalyst for the epoxidation of cis-cyclooctene (Cy) and bio-derived olefins, namely dl-limonene (Lim; a naturally occurring monoterpene found in the rinds of citrus fruits), methyl oleate and methyl linoleate (fatty acid methyl esters (FAMEs) obtained by transesterification of vegetable oils). The crystal structure of 1 consists of α-Keggin-type heteropolyanions, [SiMo12O40]4-, surrounded by space-filling and charge-balancing 2-(tetrazol-5-yl)pyridinium (Hptz+) cations, as well as by a large number of water molecules of crystallization (n = 9). The water molecules mediate an extensive three-dimensional (3D) hydrogen-bonding network involving the inorganic anions and organic cations. For the epoxidation of the model substrate Cy in a nonaqueous system (tert-butylhydroperoxide as oxidant), the catalytic performance of 1 (100% epoxide yield at 24 h, 70 °C) was superior to that of the tetrabutylammonium salt (Bu4N)4[SiMo12O40] (2) (63% epoxide yield at 24 h), illustrating the role of the counterion Hptz+ in enhancing catalytic activity. The hybrid salt 1 was effective for the epoxidation of Lim (69%/85% conversion at 6 h/24 h) and the FAMEs (87–88%/100% conversion at 6 h/24 h), leading to useful bio-based products (epoxides, diepoxides and diol products).

Special-selective C–H oxidation of toluene to benzaldehyde by a hybrid polyoxometalate photocatalyst including a rare [P6W48Fe6O180]30– anion

It is a challenge to develop new photocatalysts for high selective oxidation of primary carbon-hydrogen (C–H) bonds with O2 under mild condition. Herein, a novel hybrid K6(H2O)8H24(C26H16N4O4)8[P6W48Fe6O180]·6H2O (FeW–DPNDI) was firstly synthesized by incorporating a rare Fe-substituted trimeric Dawson derivative and photosensitizer N,N'-bis(4-pyridylmethyl)naphthalene diimide (DPNDI) via solvothermal method. In FeW–DPNDI, [P6W48Fe6O180]30– and DPNDI are orderly arranged in the three-dimensional framework by the anion···π interaction and C–H···O hydrogen bonds, that is beneficial to promote the electron transfer among components. FeW–DPNDI is a typical n-type semiconductor with the calculated energy level at 2.22 V vs. NHE of the highest occupied molecular orbital (HOMO) and – 0.57 vs. NHE of the lowest unoccupied molecular orbital (LUMO), which is theoretically feasible for the reduction O2 to O2•– because of the more negative potential of CB than the standard redox potential (E(O2•–/O2) = – 0.33 V vs. NHE). The proton conductivity of FeW–DPNDI is 2.0 × 10–4 S cm−1 at 98% relative humidity and 358 K. FeW–DPNDI exhibits special selectivity for generating benzaldehyde in the photocatalytic oxidation of stubborn C–H bond of toluene under mild condition. Moreover, FeW–DPNDI can be easily isolated from the products and reused. FeW–DPNDI is the first example of the trimmer of Fe-substituted Dawson derivative, but also the first hybrid POM explored in the activating C–H bond of toluene under white light irradiation.

Covalent Grafting of Polyoxometalate Hybrids onto Flat Silicon/Silicon Oxide: Insights from POMs Layers on Oxides.

Immobilization of polyoxometalates (POMs) onto oxides is relevant to many applications in the fields of catalysis, energy conversion/storage, or molecular electronics. Optimization and understanding the molecule/oxide interface is crucial to rationally improve the performance of the final molecular materials. We herein describe the synthesis and covalent grafting of POM hybrids with remote carboxylic acid functions onto flat Si/SiO2 substrates. Special attention has been paid to the characterization of the molecular layer and to the description of the POM anchoring mode at the oxide interface through the use of various characterization techniques, including ellipsometry, AFM, XPS, and FTIR. Finally, electron transport properties were probed in a vertical junction configuration and energy level diagrams have been drawn and discussed in relation with the POM molecular electronic features inferred from cyclic-voltammetry, UV-visible absorption spectra, and theoretical calculations. The electronic properties of these POM-based molecular junctions are driven by the POM LUMO (d-orbitals) whatever the nature of the tether or the anchoring group.

Stable aqueous Zn−Ag and Zn−polyoxometalate hybrid battery driven by successive Ag+ cation and polyoxoanion redox reactions

Hybrid batteries with multiple electrochemical reactions that integrate respective advantages and remedy intricate shortages of disparate batteries are both fundamentally interesting and practically attractive. Here, an aqueous hybrid battery combining electrochemical features of Zn−Ag battery and Zn−POM battery is for the first time proposed, which is actuated by successive Ag+ cation and polyoxoanion redox reactions in an insoluble polyoxometalate (POM)-based cathode. The unique POM-based composite material constructed from loose stacking high-nuclearity polyoxovanadate clusters and crystalline Ag nanoparticles not only provides plentiful Zn2+ storage sites but also presents fast ion / electron diffusion kinetics. Meanwhile, both the severe migration of Ag+ ions and the dissolution of POM clusters in aqueous electrolyte are effectively inhibited. The as-fabricated hybrid battery with POM-based cathode exhibits a reversible capacity of 200 mAh g–1 at 10 A g–1 with outstanding capacity retention (97.4% over 7000 cycles) and superior rate capability. Moreover, the stable hybrid energy storage mechanism is revealed in detail. The work presents a promising strategy for the application of POM-based electrode in aqueous batteries and provides heuristic thinking for further developing novel energy storage systems.

Characterization and Kinetic Studies on Photocatalytic Degradation of Phenol in Aqueous Solution

Recently, many researchers tend to study the performance of hybrid polyoxometalates (HPOM) as photocatalyst due to its greater performance in photocatalytic degradation. The process that based on the light enhanced generation of reactive OH radical that plays an important role in order to convert organic compound completely into water, CO2 and inorganic compounds. In this research, the photocatalytic degradation of phenol was studied using HPOM as photocatalyst. The HPOM was synthesized and used to study its effect on photocatalytic degradation of phenol. The synthesized HPOM were characterized using SEM and FTIR. It was found that the surface morphology of the synthesized HPOM le displayed an irregular spherical-like shape, granular structure with different size and least distribution of non-agglomerated rod-like nanoparticles. The present of WO6 octahedral and PO4 octahedral indicated that Keggin type structure of synthesized hybrid polyoxometalates. The kinetics of photocatalytic degradation of phenol via hybrid polyoxometalates follows pseudo first order kinetic reaction.

Selective aerobic oxidation of allyl phenyl ether to methyl ketone by palladium–polyoxometalate hybrid catalysts

In this study, we report that selective aerobic oxidation of allyl phenyl ethers is attained by a Pd catalyst/polyoxometalate hybrid system to yield corresponding methyl ketones in water-enriched acetonitrile. The Pd(OAc)2/H5PV2Mo10O40 system exhibits higher conversions and yields of corresponding methyl ketone by Wacker-type oxidation of allyl phenyl ether as compared with the conventional PdCl2/CuCl2 system. The higher yields are attributed to the efficient re-oxidation of Pd0 to Pd2+ by H5PV2Mo10O40 using O2 as an oxidant as evidenced by electrochemical measurements. A reduced species of H5PV2Mo10O40 by Pd0 during the catalytic oxidation is revealed by UV–vis spectral measurements. The use of PdCl2 in place of Pd(OAc)2 in combination with [PV2Mo10O40]5− bearing tetraalkylammonium counter cations has also exhibited comparable conversions and product yields in the Wacker-type oxidation of allyl phenyl ethers. Para-substituted allyl phenyl ether derivatives are successfully oxidized in the Pd catalyst/polyoxometalate system to yield corresponding methyl ketones. The initial rate of products of para-substituted methyl ketones depended on the electronic effect of the substituents in which allyl phenyl ethers with electron-donating groups have accelerated the initial rate in the Pd catalyst/polyoxometalate system.

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.

An organic–inorganic hybrid nanoscale phosphotungstate with reactive oxygen species catalytic ability

An organic-inorganic hybrid polyoxometalate (POM) based on bi-nuclear copper complexes and Dawson-type phosphotungstate (POT) [CuL(H2O)][CuL]2[P2W18O62]·3H2O (abbreviated as CPW) (L = 2-(1H-pyrazol-3-yl)pyridine) was synthesized and structurally characterized by IR spectrum, and single-crystal X-ray diffraction. Structural analysis indicated that CPW is nanoscale molecule and extends into a two-dimensional layer, in which three bi-nuclear copper complexes are substituted at different sites of Dawson-type POT and joined adjacent POT fragments together. Notably, CPW can efficiently catalyze the production of reactive oxygen species.

Redox‐Active Hybrid Polyoxometalate‐Stabilised Gold Nanoparticles

AbstractWe report the design and preparation of multifunctional hybrid nanomaterials through the stabilization of gold nanoparticles with thiol‐functionalised hybrid organic–inorganic polyoxometalates (POMs). The covalent attachment of the hybrid POM forms new nanocomposites that are stable at temperatures and pH values which destroy analogous electrostatically functionalised nanocomposites. Photoelectrochemical analysis revealed the unique photochemical and redox properties of these systems.

Redox-Active Hybrid Polyoxometalate-Stabilised Gold Nanoparticles.

We report the design and preparation of multifunctional hybrid nanomaterials through the stabilization of gold nanoparticles with thiol‐functionalised hybrid organic–inorganic polyoxometalates (POMs). The covalent attachment of the hybrid POM forms new nanocomposites that are stable at temperatures and pH values which destroy analogous electrostatically functionalised nanocomposites. Photoelectrochemical analysis revealed the unique photochemical and redox properties of these systems.

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.