Dawson Anions Research Articles

(Invited) Computational Modelling of Super-Reduced Polyoxometalates for Energy Storage

It is well know that polyoxometalates can be reduced at relatively potentials and can act as reservoir of electrons. Very recently, it has been reported that polyoxometalates clusters like Li6[P2W18O62] can achieve very high proton–electron storage capacities in aqueous solution. DFT calculations in combination with classical MD and CPMD simulations were able to substantiate that the physical properties of classical polyoxotungstates, like those of the prototypical Dawson anion [P2W18O62]6-, strongly depend on the presence of collective forces associated to POM concentration, pH and countercation nature. At low POM concentration and neutral pH only four electrons are reversibly incorporated to the POM. However, in acidic media, the POM framework begins to protonate after the third electron reduction. The salt concentration is also very relevant, since it favours the POM aggregation, which induces an additional stabilization of molecular orbitals. These and another features of reduced polyoxometales will be discussed in the present communication.

Preparation of polyoxometalate ionic liquids (POM‐ILs) coated on metal coins for anticorrosion activity

Corrosion is globally a serious problem for metallic structure and materials in recent decades. When there is interaction between acid and metallic structure, a large amount of corrosion produced. Herein, we have synthesized two energetic polyoxometalates (POMs) based ionic liquids by ion exchange method of smaller cations with larger cations tetraalkyl ammonium (CnH2n+1)4N+(n = 7). FT-IR, SEM, Electrochemical Impedance Spectroscopy (EIS), Optical Imaging Microscopy(OIM), Rheological analysis, 1HNMR and TGA techniques were used to characterize the corresponding ionic liquids. Metals can easily be protected by using hydrophobic polyoxometalate-ionic liquids (POM-ILs). At room-temperature the metallic coins were coated with W17@POM-IL andV3W15@POM-IL, comprising of Dawson anions and quaternary tetraheptylammonium cations (Q7). The acid resistant V3W15@POM-IL and W17@POM-IL were used for coating of coins samples. The un-coated coins have shown corrosion with holes production when treated with HCl while POM-ionic liquid coated coins expressed excellent resistant against corrosion and obviously, no cracking was observed. TGA results of W17@POM-IL revealed minimum weight loss of 4.3% and V3W15@POM-IL has maximum weight loss (9.2%) at highest temperature (500 °C). We have analyzed from the results that coins without coating of POM-ILs have demonstrated the weight loss of 14.3% while the coins coated with V3W15@POM-IL and W17@POM-ILs expressed less weight lost with 3.7% and 1.7% respectively. Furthermore, electrochemical impedance measurement (EIS) has charge transfer ratio of 7.03 Ω, 5.23 Ω and 3.78 Ω for W17@POM-IL, V3W15@POM-IL and un-coated coins respectively. Rheological analysis with highest elastic modulus (103 Pa) and viscous modulus (103 Pa) of W17@POM-IL has given best coating properties. Hence, the POM-ILs have variety of applications as coherent, adherent, chemical stability. Comparison of V3W15@POM-IL with W17@POM-IL inferring us that later is best for protection of metal coins against corrosion and damage production with highest thermal stability.

Supramolecular Aggregation Control in Polyoxometalates Covalently Functionalized with Oligoaromatic Groups.

CLICK-chemistry has become a universal route to covalently link organic molecules functionalized with azides and alkynes, respectively. Here, we report how CLICK-chemistry can be used to attach oligoaromatic organic moieties to Dawson-type polyoxometalates. In step one, the lacunary Dawson anion [α2 -P2 W17 O61 ]6- is functionalized with phosphonate anchors featuring peripheral azide groups. In step two, this organic-inorganic hybrid undergoes microwave-assisted CLICK coupling. We demonstrate the versatility of this route to access a series of Dawson anions covalently functionalized with oligoaromatic groups. The supramolecular chemistry and aggregation of these systems in solution is explored, and we report distinct changes in charge-transfer behavior depending on the size of the oligoaromatic π-system.

Synthesis, Characterization, Electrochemistry, Photoluminescence and Magnetic Properties of a Dinuclear Erbium(III)-Containing Monolacunary Dawson-Type Tungstophosphate: [{Er(H2O)(CH3COO)(P2W17O61)}2]16−

Reaction of the trilacunary Wells−Dawson anion {α-P2W15O56}12− with ErIII ion in a 1 M LiOAc/HOAc buffer (pH 4.8) solution produces a dinuclear erbium(III) substituted sandwich-type structure [{Er(H2O)(CH3COO)(P2W17O61)}2]16− (1). The isolated compound was structurally characterized using single crystal and powder X-ray diffraction, FTIR spectroscopy, mass spectrometry and thermogravimetric analysis. The electrochemical, electrocatalytic, photoluminescence and magnetic properties of 1 were investigated.

Cyclodextrin-Assisted Hierarchical Aggregation of Dawson-type Polyoxometalate in the Presence of {Re6Se8} Based Clusters

The association of metallic clusters (CLUS) and polyoxometalates (POM) into hierarchical architectures is achieved using γ-cyclodextrin (γ-CD) as a supramolecular connector. The new self-assembled systems, so-called CLUSPOM, are formed from Dawson-type polyoxometalate [P2W18O62]6- and electron-rich rhenium clusters. It is worth noting that a cluster-based cation [{Re6Se8}(H2O)6]2+ on one hand and a cluster-based anion on the other hand [{Re6Se8}(CN)6]4- can be associated with the anionic POM. In the absence of the supramolecular connector, a "CLUSPOM salt" was obtained from aqueous solution of the cationic cluster and the polyoxometalate. In this solid, the arrangement between the polymetallic building blocks is mainly governed by long-range Coulombic interactions. In the presence of γ-CD, the Dawson anion and the cationic cluster are assembled differently, forming a hierarchical supramolecular solid, K2[{Re6Se8}(H2O)6]2{[P2W18O62]@2γ-CD}·42H2O, where the organic macrocycle acts as a ditopic linker between the inorganic building blocks. In such an edifice, the short-range molecular recognition dominates the long-range Coulombic interactions leading to a specific three-dimensional organization. Interestingly, the assembling of anionic POM [P2W18O62]6- with the anionic rhenium cluster [{Re6Se8}(CN)6]4- is also achieved with γ-CD despite the repulsive forces between the nanosized anions. The resulting solid, K10{[{Re6Se8}(CN)6]@2γ-CD}[P2W18O62]·33H2O, is built from 1:2 inclusion complexes {[{Re6Se8}(CN)6]@2γ-CD}4- linked by a POM unit interacting with the exterior wall of the organic macrocycle. Multinuclear NMR and small-angle X-ray scattering investigations support supramolecular preorganization in aqueous solution prior to crystallization.

Organoboron-Functionalization Enables the Hierarchical Assembly of Giant Polyoxometalate Nanocapsules.

The aggregation of molecular metal oxides into larger superstructures can bridge the gap between molecular compounds and solid‐state materials. Here, we report that functionalization of polyoxotungstates with organo‐boron substituents leads to giant polyoxometalate‐based nanocapsules with dimensions of up to 4 nm. A “lock and key” mechanism enables the site‐specific anchoring of aromatic organo‐boronic acids to metal‐functionalized Dawson anions [M3P2W15O62]9− (M=TaV or NbV), resulting in unique nanocapsules containing up to twelve POM units. Experimental and theoretical studies provide initial insights into the role of the organo‐boron moieties and the metal‐functionalized POMs for the assembly of the giant aggregates. The study therefore lays the foundations for the design of organo‐POM‐based functional nanostructures.

Construction of Mono-, Bi- and Trinuclear Clusters to Modify Wells–Dawson Anions through Using Different Transition Metals and Flexible Bis(Pyrazole) Ligands

Three new Wells–Dawson compounds, namely [CoII(edpz)(H2bdpm)3][(H4P2W18O62)] (1), [CdII2(mpz)(H2bhpe)2.5(H2O)(H2P2W18O62)] · (ppz) · 6H2O (2) and [CuII3(ppz)(H2bhpe)2(P2W18O62)(H2O)3] · 2H2O (3) (edpz = 4-ethyl-3,5-dimethyl-1H-pyrazole, H2bdpm = 1,1'-bis(3,5-dimethyl-1H-pyrazolate)methane, mpz = 4-methyl-4H-pyrazole, H2bhpe = 1,2-bis(1H-pyrazolyl)ethane, ppz = 4-propyl-1H-pyrazole), have been hydrothermally synthesized by using flexible bis(pyrazole) ligands and characterized by single-crystal X-ray diffraction analysis, IR spectra and elemental analyses. In compound 1, there are two discrete subunits: a mono-nuclear [Co(edpz)(H2bdpm)3]2+ cluster and a Wells–Dawson anion. The hydrogen bonding interactions between these subunits induce a 2D supramolecular structure. In compound 2, two Cd ions are fused by one mpz and five H2bhpe ligands to construct a bi-nuclear Cd cluster. The [P2W18O62]6– anions link bi-nuclear Cd clusters to form a 3D framework. In compound 3, four H2bhpe ligands fuse three CuII ions to construct a planar tri-nuclear cluster, with one ppz ligand vertical with this tri-nuclear cluster. The [P2W18O62]6– anions connect adjacent tri-nuclear clusters to form a 3D framework. Moreover, we also investigated the electrochemical and photocatalytic properties of compounds 1−3.

Synthesis of an environmental nano-polyoxometalate (α2P2W17CoO61)8− as catalyst for dyes degradation: A comparative study oxidation of indigoid and azo dyes

A nanopolyoxometalate (nano-POM) compound consisting of saturated Dawson anions (α2P2W17CoO61)8− has been synthesized and characterized by various analytical methods, UV–vis spectroscopy, FT-IR spectroscopy, single crystal X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive X-ray analysis (EDX).The separately oxidative degradation of indigo carmine and methyl orange dyes in aqueous solution by KMnO4 using (α2P2W17CoO61)8− as catalyst was investigated. The full Decolorization was attained during the first minutes of oxidation process by this new homogeneous system (dye/KMnO4/α2P2W17O61Co). The experimental results showed that the catalyst greatly affected the discoloration efficiency; it was up to 75.4 % and 66.1 % respectively for IC and MO under these optimum conditions: an initial potassium permanganate concentration of 0.02 mM, a catalyst concentration of 0.2 mM and initial concentration dyes of 5 mg/L at pH 3 and room temperature (25 °C).The effect of other Dawson type polyoxometalates on the dyes oxidation under the same conditions was evaluated. After four consecutive reaction cycles, the catalyst (α2P2W17CoO61)8− exhibited a good recyclability and reusability without significant loss of activity. The precedents analytical methods indicated that this recovered catalyst has effectively a good stability. This nano-POM function as a recyclable efficient catalyst for the rapid removal of various anionic textile dyes from aqueous solutions.

Inhibition of Na+/K+- and Ca2+-ATPase activities by phosphotetradecavanadate

Polyoxometalates (POMs) are promising inorganic inhibitors for P-type ATPases. The experimental models used to study the effects of POMs on these ATPases are usually in vitro models using vesicles from several membrane sources. Very recently, some polyoxotungstates, such as the Dawson anion [P2W18O62]6−, were shown to be potent P-type ATPase inhibitors; being active in vitro as well as in ex-vivo. In the present study we broaden the spectrum of highly active inhibitors of Na+/K+-ATPase from basal membrane of epithelial skin to the bi-capped Keggin-type anion phosphotetradecavanadate Cs5.6H3.4PV14O42 (PV14) and we confront the data with activity of other commonly encountered polyoxovanadates, decavanadate (V10) and monovanadate (V1). The X-ray crystal structure of PV14 was solved and contains two trans-bicapped α-Keggin anions HxPV14O42(9-x)-. The anion is built up from the classical Keggin structure [(PO4)@(V12O36)] capped by two [VO] units. PV14 (10 μM) exhibited higher ex-vivo inhibitory effect on Na+/K+-ATPase (78%) than was observed at the same concentrations of V10 (66%) or V1 (33%). Moreover, PV14 is also a potent in vitro inhibitor of the Ca2+-ATPase activity (IC50 5 μM) exhibiting stronger inhibition than the previously reported activities for V10 (15 μM) and V1 (80 μM). Putting it all together, when compared both P-typye ATPases it is suggested that PV14 exibited a high potential to act as an in vivo inhibitor of the Na+/K+-ATPase associated with chloride secretion.

Synthesis, characterization, Hirshfeld surface analysis and theoretical calculation of new organic–inorganic hybrid material: (C4H7N2)6[As2W18O62]·4H2O

New hybrid arsenotungstates based on Dawson polyanions [C4H7N2]6[As2W18O62]·4H2O (1) have been isolated by conventional solution method and characterized by single-crystal X-ray diffraction, infrared spectrum and UV–visible spectroscopies and thermogravimetric analysis. Hirshfeld surface analysis was performed to study the intermolecular interactions. Compound 1 crystallizes in hexagonal system, in a P-3 space group, with cell parameters a = 20.2904(2) A, b = 20.2904(2) A, c = 16.8246(2) A, and a V = 5998.38(11) A3. Compound 1 exhibits a three-dimensional chain constructed from Well–Dawson anions linked together with (C4H7N2)+ cations and water molecules.

Use of symmetrical and pendant pyrazole derivatives for the construction of two polyoxometalate-based complexes as electrochemical sensors

Through the use of two pyrazole derivatives, one symmetrical, namely 1,1′-bis(3,5-dimethyl-1H-pyrazol-4-yl)methane (H2bdpm), and one asymmetrical, namely 4-propyl-4,5-dihydro-1H-pyrazole (pdp), two polyoxometalate (POM)-based complexes constructed from saturated Wells–Dawson and mono-Cu(II)-substituted Keggin anions, respectively, were hydrothermally synthesized and structurally characterized as [(Cu2(H2bdpm)2)[H2P2W18O62]0.5]·2H2O (1) and [(Cu3(pdp)6Cl2)(H5PMo11CuO39)2]·12H2O (2). In complex 1, the bidentate H2bdpm ligands link CuI centers to form a 1D wave-like metal–organic chain. Adjacent chains are parallel with each other, with Wells–Dawson anions occupying the gaps. In complex 2, six pdp ligands are coordinated to three CuII centers to form a trinuclear cluster. Two Cl− anions are also coordinated to the copper centers. The mono-Cu(II)-substituted Keggin anions connect the trinuclear clusters to construct a 2D grid-like structure. Both 1 and 2 are semiconducting in nature, with Eg valves of 2.61 and 2.81, respectively. The electrochemical behavior of both complexes has been studied. Carbon paste electrodes of both can be used as electrochemical sensors for the detection of hydrogen peroxide, bromate and nitrite.

Decorated Dawson Anion by Two Different Complex Fragments of Phenanthroline and Isonicotinic Acid: Synthesis and Properties

An unreported inorganic–organic hybrid compound [{Cu2(phen)2(ina)2(H2O)}{Cu(phen)2}(H2P2W18O62)]·10H2O(1) (phen = 1,10-phenanthroline, ina = isonicotinate anion) was hydrothermally synthesized and characterized with elemental analysis, IR spectroscopy, thermal analysis, luminescent spectroscopy, UV/Vis diffuse reflection spectroscopy, magnetic measurement. The crystal structure was determined with X-ray single-crystal diffraction. [Cu(phen)2]2+and [Cu2(phen)2(ina)2(H2O)]2+ units are grafted on the Dawson anion [P2W18O62]6− via the terminal oxygen atoms of two WO6 octahedra. In [Cu2(phen)2(ina)2(H2O)]2+ unit Cu2+ ions displays a square-pyramidal geometry, and in [Cu(phen)2]2+ unit the geometry of Cu2+ ion is more close to triangle bipyramidal geometry including a terminal oxygen atom. Hydrogen bonds exist between the decorated Dawson anions and water molecules. The compound 1 has a narrow band gap of 2.05 eV and strong emission at 437 nm. Variable-temperature magnetic measurement of 1 shows a typical antiferromagnetic interaction in the 2–300 K temperature range.

Asymmetrically fused polyoxometalate-silver alkynide composite cluster.

We demonstrate that an asymmetric composite cluster, [Ag25{C≡CC(CH3)3}16(CH3CN)4(P2W15Nb3O62)] (1), consisting of directly fused polyoxometalate and silver alkynide moieties can be facilely synthesized by a one-pot reaction between a Nb-substituted Dawson-type polyoxometalate, H4[α-P2W15Nb3O62](5-), and the mixture of (CH3)3CC≡CAg and CF3SO3Ag. Single-crystal X-ray diffraction revealed the structure of 1, where Ag atoms are selectively attached to the Nb-substituted hemisphere of the pedestal Dawson anion. Its structural integrity in the solution was demonstrated by (31)P NMR spectroscopy and analytical ultracentrifugation. The latter method also unveiled the stepwise formation mechanism of 1.

Reversible photodimerization of coumarin-modified Wells–Dawson anions

The light-driven reversible dimerization of a coumarin-functionalized organic–inorganic hybrid polyoxometalate anion and the resulting changes in their aggregation and redox-behaviour are reported.

Three 2-(4-thiazolyl)benzimidazole-based supramolecular assemblies oriented by Keggin and Wells–Dawson anions

Three polyoxometalate supramolecular assemblies based on rigid 2-(4-thiazolyl)benzimidazole (L) and two types of polytungstate anions, [CuII2Cl(L)4(PW12O40)]·3H2O (1), [CuII(L)2(H2O)]2[P2W18O62]·(HL)2·6H2O (2), and [ZnII(L)3]4[H(KPW12O40)3] (3), have been synthesized and characterized by single-crystal X-ray diffraction, elemental analyses, and IR spectra. Compound 1 contains binuclear copper clusters {Cu2L4Cl}3+ with Cl– as bridges. These binuclear clusters and [PW12O40]3– anions construct a supramolecular 2-D layer through hydrogen-bonding interactions. In 2, the [CuL2(H2O)]2+ subunits and Wells–Dawson anions build a 1-D supramolecular chain. In 3, the [PW12O40]3– anions are covalently linked by K+ to form an inorganic chain. These chains and discrete [ZnII(L)3]2+ subunits construct a 3-D supramolecular structure. The electrochemical and photocatalytic properties of 1–3 have been studied.

Two new 1-D and 3-D Wells–Dawson structures assisted by alkali metals

Two new Wells–Dawson based compounds containing alkali metals, [Ag(H2biim)2]2·[Ag5(H2biim)10Na2(H2O)2(H3/2P2W18O62)2]·12H2O (1) and [Cd(H2biim)2 K(P2W18O62)1/2] (2) (H2biim = 2,2′-biimidazole), have been synthesized under hydrothermal conditions. In 1, two-supporting Wells–Dawson anions are linked by a [Ag(H2biim)2]+ subunit to form a dimer. The adjacent dimers are further connected by Na+ through (POM)O-Na-O(POM) bonds to build a 1-D chain. In 2, adjacent anions are linked by two [Cd2(H2biim)2]4+ subunits and a 1-D chain is formed. Furthermore, the anion in the chain is fused by six K+ ions and a 3-D framework is obtained. The alkali metals exhibit crucial influence on the conversion of dimensionality assisting anions and Ag-H2biim subunits to construct 1-D and 3-D frameworks. The electrochemical and photocatalytic properties of 1 and 2 have been investigated.

Syntheses, structures and photoluminescence of two Dawson-based hybrid materials with polynuclear silver clusters

Abstract Two new Dawson-based hybrids, namely, [Ag6(H L)4(H2O)6(P2W18O62)]·4H2O (1) and [Ag4(H2biim)4][K2(H2O)3(P2W18O62)]·H2O (2) (HL = 5-(4-imidazol-1-yl-phenyl)-2H-tetrazole, H2biim = 2,2′-biimidazole), have been hydrothermally synthesized and characterized. X-ray diffraction analysis reveals that compound 1 is a 3D structure based on infinite organic–metal chains {Ag6(HL)4}n and Wells–Dawson anions. Compound 2 displays a 3D framework based on potassium-Dawson inorganic sheets and dinuclear silver-H2biim units. The luminescent properties of compounds 1 and 2 have also been investigated.

Syntheses, structures and magnetic properties of two unprecedented hybrid compounds constructed from open Wells–Dawson anions and high-nuclear transition metal clusters

Two new inorganic-organic hybrid compounds Na2(C3N2H12)4{[Ni5(OH)3(H2O)4(CH3CO2)][Si2W18O66]}·12.5H2O (1) and (C3N2H12)3{[Co(II)2Co(III)4(OH)5(H2O)2(CH3CO2)][Si2W18O66]}·6H2O·(C3N2H10) (2), based on lacunary polyoxometalates and high-nuclear transition-metal clusters, have been synthesized by a new method (solvothermal method). Single crystal XRD, magnetic measurements, nonlinear-optical (NLO) measurements, thermogravimetric (TG) measurements, and IR spectra were performed to analyze the structures and properties of 1 and 2. XRD analyses reveal that compound 1 consists of an open Wells-Dawson anion [Si2W18O66](16-), a five-nuclear cationic cluster [Ni5(OH)3(H2O)4(CH3CO2)](6+), free Na(+) cations, and protonated 1,3-diaminopropanes. Compound 2 has a similar structure to 1, while a six-nuclear cationic cluster [Co(II)2Co(III)4(OH)5(H2O)2(CH3CO2)](10+) replaces the five-nuclear cationic cluster [Ni5(OH)3(H2O)4(CH3CO2)](6+) in 1. Magnetic susceptibility measurements indicate antiferromagnetic interactions in 1, and the chirality of compound 2 may bring potential properties of catalysis and optical nonlinearity.

A polyoxometalate-based ionic crystal assembly from a heterometallic cluster and polyoxoanions with visible-light catalytic activity

A polyoxometalate-based inorganic–organic hybrid [WO4{Ni(en)2(H2O)}3] [Ni(en)3]{P2W18O62}·[Ni(en)3]CO3·H2O (1) (en = ethanediamine), was synthesized under hydrothermal conditions, and characterized by IR, elemental analyses, XPRD, UV diffuse reflectance spectroscopy and single crystal X-ray diffraction analyses. Compound 1 consists of a heterometallic cluster [WO4{Ni(en)2(H2O)}3]4+, two [Ni(en)3]2+ groups, one [CO3]2− group, one water molecule and a Wells–Dawson anion [P2W18O62]6− ({P2W18}), which represents the first POM-based ionic crystal with the heterometallic macrocation cluster. Photocatalytic studies indicate that compound 1 is not only actively photocatalytic for degradation of methylene blue (MB) under visible light irradiation, but very stable and easily separated from the reaction system for reuse as well.

An unprecedented trimer based on monovacant Dawson anion: [(α2-P2W17O61)Ln(H2O)4]321− (Ln = LaIII, CeIII and PrIII)

Three unprecedented trimers based on monovacant Dawson-type polyoxotungstates Na12[Ln(H2O)9]2[(α2-P2W17O61H4)La(H2O)4]6·100H2O (Ln = LaIII (1)) and Na24[Ln(H2O)8]2[(α2-P2W17O61H2)Ln(H2O)4]6·56H2O (Ln = CeIII (2), and PrIII (3)) have been successfully synthesized by straightforward “self assembly” processes starting from a 1 : 4 ratio of the saturated Dawson precursor [α-P2W18O62]6− and Ln ions in aqueous solution, which were further characterized by elemental analyses, X-ray powder diffraction (XRPD), IR spectra, thermogravimetric (TG) analyses, electrospray ionization mass spectrometry (ESI-MS) and single-crystal X-ray diffraction. The common feature of 1–3 is that they all consist of the trimeric triangular [(α2-P2W17O61)Ln(H2O)4]321− subunit, as we know, the trimeric [(α2-P2W17O61)Ln(H2O)4]321− polyoxoanion is firstly discovered. Furthermore, all three compounds can further generate three dimensional channel architectures through Na+ cations. Meanwhile, the multinuclear solution 31P NMR spectrum of 1 at 300 K in D2O has been investigated, the results are further demonstrated by the technologies of ESI-MS.