Showing papers on "Polyoxometalate published in 2012"

Recent advances in paramagnetic-TM-substituted polyoxometalates (TM = Mn, Fe, Co, Ni, Cu)

Abstract: During the past decade, research into transition-metal-substituted polyoxometalate self-assembly has been greatly developed. This review summarizes the conventional solution syntheses and hydrothermal syntheses of novel substituted polyoxometalates based on the incorporation of paramagnetic transition metals Mn, Fe, Co, Ni, and Cu, with an emphasis on the variety of nuclearities and configurations of encapsulated transition metal cores and the rich architectures of overall polyoxometalates.

Polyoxometalate-decorated nanoparticles

Abstract: Polyoxometalate cluster anions (POMs) control formation and morphology, and serve as protecting ligands, for structurally and compositionally diverse nanostructures. While numerous examples of POM-protected metal(0) nanoparticle syntheses and reactions can now be found in the literature, the use of POMs to prepare nano-scale analogs of binary inorganic materials, such as metal-oxides, sulfides and halides, is a relatively recent development. The first part of this critical review summarizes the use of POMs as protecting ligands for metal(0) nanoparticles, as well as their use as templates for the preparation of new inorganic materials. Here, key findings that reveal general trends are given additional emphasis. In the second part of the review, new information concerning the structure of POM-protected metal(0) nanoparticles is systematically developed. This information, obtained by the combined use of cryogenic transmission microscopy (cryo-TEM) and UV-vis spectroscopy, provides a new perspective on the formation and structure of POM-decorated nanoparticles, and on the rational design of catalytic and other functional POM-based nano-assemblies.

An ionothermal synthetic approach to porous polyoxometalate-based metal-organic frameworks.

Abstract: Porous materials with regular, bulky, accessible cages and channels have aroused great research interest owing to their potential applications in gas storage, separation, ionexchange, and heterogeneous catalysis. 2] Polyoxometalates (POMs), as a unique class of metal oxide clusters, constitute promising building units for targeting multifunctional materials because of their nanosize, adjustable compositions, abundant topologies, and their oxygen-rich surface with strong coordination abilities. 4] Despite the unparalleled success in the preparation of microporous/mesoporous compounds by covalently linking simple metal ions and organic ligands, attempts to prepare porous POM-based metal– organic frameworks have met with only limited success. Therefore, the synthesis of such frameworks is one of the most challenging issues in synthetic chemistry. Normally, porous materials are prepared by conventional solution synthesis and hydroor solvothermal synthesis. Solvents of these systems have been largely restricted to water and traditional organic solvents, such as methanol, acetonitrile, and acetone. It is undeniable that these solvents have some intrinsic disadvantages: for example, regarding synthesis, their lower boiling points have limited the use of higher temperatures out of safety concerns; furthermore, from the environmental perspective, volatile organic solvents have caused serious health and environmental problems. Therefore, it is very necessary to explore a more effective and environmentally friendly synthetic method to overcome these existing shortcomings. Ionic liquids (ILs), composed of cations and anions, have gained attention owing to their low melting points, high ionic conductivity, non-volatility, nonflammability, high polarity, low toxicity, zero vapor pressure, and relatively low viscosity. Therefore, they may be environmentally friendly alternatives to the traditional solvents. Ionothermal synthesis, with the use of an IL as solvent and structural directing agent, has already been comprehensively discussed in several detailed reviews, and has been successfully applied in the synthesis of zeolites or microporous solids. The remarkable work of Pakhomova and others have also proved the feasibility of such ionothermal methods for preparation of non-porous POM-based materials. Inspired by these recent developments, we present herein the extension of the ionothermal method to the realm of POM-based porous frameworks and demonstrate its capacity to produce such crystalline solids. To our knowledge, no reliable design of POM-based porous materials from this approach has yet been reported to date. In planning the synthesis, we chose a readily available ionic liquid, 1-ethyl-3-methylimidazolium bromide ([Emim]Br) as solvent, the weak coordinating ability of which can facilitate the self-assembly of the polyoxoanions. Meanwhile, to surmount the major obstacle in construction of POM-based solids with extra-large pores, bulky tetrabutylammonium bromide was used. On one hand, it could increase the aperture when it acts as a counterion filling in the cavity; on the other hand, subsequent ion exchange of it with smaller cations would recover the porosity effectively. Indeed, by slightly varying the experimental conditions, three porous POM-based 3D structures have been obtained based on the above design strategy: (TBA)2[Cu (BBTZ)2(xMo8O26)] (x = b for 1, x = a for 2 and 3) (TBA = tetrabutylammonium cation, BBTZ = 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene). Single-crystal X-ray diffraction analysis reveals that the octamolybdate anion in 1 adopts the structural feature of the b-isomer, which consists of eight edge-shared MoO6 octahedra. Each [b-Mo8O26] 4 unit is covalently linked to two [CuBBTZ4] fragments through terminal oxo groups of octahedral Mo sites with Cu O distances of 2.302(4) and 2.302(4) . Each Cu cation adopts an octahedral geometry, defined by four N atoms from four BBTZ organic ligands (Cu1 N5 2.022(5), Cu1 N6 2.036(5)), and two O atoms from the [b-Mo8O26] 4 unit. The BBTZ ligands coordinated to the Cu center adopt a U-type configuration, and thus the CuBBTZ4 fragment has a windmill-type configuration with the four included angles between the four BBTZ ligands coordinated to the Cu centers of 908 (Supporting Information, Figure S1). The Cu centers of the windmills are extended to a 3D covalent net through the [b-Mo8O26] 4 units and the BBTZ ligands. The structure of 1 is very open, and contains three-directional channel systems. These channels intersect with each other and run along three different directions: 1.20 1.20 nm along the [100] direction, and 1.20 1.37 nm along the [011] and [0 11] directions, as shown in Figure 1a. From the topological view, the 3D architecture of 1 can be [*] Dr. H. Fu, Prof. C. Qin, Prof. Y. Lu, Dr. Z.-M. Zhang, Prof. Y.-G. Li, Prof. Z.-M. Su, Dr. W.-L. Li, Prof. E.-B. Wang Key Laboratory of Polyoxometalate Science of Ministry of Education Department of Chemistry, Northeast Normal University Changchun, Jilin 130024 (China) E-mail: qinc703@nenu.edu.cn wangeb889@nenu.edu.cn

Identification of a nonanuclear {Co(II)9} polyoxometalate cluster as a homogeneous catalyst for water oxidation.

Abstract: The polyanion of formula {Co9(H2O)6(OH)3(HPO4)2(PW9O34)3}16– (Co9) contains a central nonacobalt core held together by hydroxo and hydrogen phosphate bridges and supported by three lacunary Keggin-type polyphosphotungstate ligands Our data demonstrate that Co9 is a homogeneous catalyst for water oxidation Catalytic water electrolysis on fluorine-doped tin oxide coated glass electrodes occurs at reasonable low overpotentials and rates when Co9 is present in a sodium phosphate buffer solution at neutral pH We carried out our experiments with an excess of 2,2′-bipyridyl as the chelating agent for free aqueous CoII ions, in order to avoid the formation of a cobalt oxide film on the electrode, as observed for other polyoxometalate catalysts In these conditions, no heterogeneous catalyst forms on the anode, and it does not show any deposited material or significant catalytic activity after a catalytic cycle Co9 is also an extremely robust catalyst for chemical water oxidation It is able to continuously ca

Cyanosilylation of Carbonyl Compounds with Trimethylsilyl Cyanide Catalyzed by an Yttrium‐Pillared Silicotungstate Dimer

Abstract: Cyanohydrins are a very important class of compounds in chemistry as well as biology, and have been widely utilized as important synthetic intermediates for organic compounds, such as a-hydroxy acids, a-hydroxy aldehydes, and b-amino alcohols. For the synthesis of cyanohydrins, various cyanating reagents have been employed, and trimethylsilyl cyanide (TMSCN) is one of the most useful and safe cyanating reagents for nucleophilic addition to carbonyl compounds to give cyanohydrin trimethylsilyl ether. Hence, the development of efficient catalysts for cyanosilylation of carbonyl compounds with TMSCN is a very important subject in current research, and several efficient catalysts have been developed so far. Lewis acid catalysts can act as electrophilic catalysts to activate carbonyl compounds and have been extensively investigated for cyanosilylation (see Table S1 in the Supporting Information). 3] Several nucleophilic catalysts, such as amines, phosphines, phosphazanes, and alkalineearth metal oxides, can activate TMSCN and promote cyanosilylation (Table S1). 3] Asymmetric cyanosilylations have also been successfully developed by employing customly designed chiral ligands. Polyoxometalates (POMs) are a large family of anionic metal–oxygen clusters that consist of Group V and VI metals in their highest oxidation states, and are thermally and oxidatively stable in comparison with commonly utilized organometallic catalysts and organocatalysts. The chemical properties of POMs, for example, redox potentials, (multi)electron-transfer properties, acidities, and solubilities, and negative charges, can be finely tuned by choosing the constituent anion and countercations, and diverse structures can be synthesized. In addition to the above-mentioned properties, the important feature of POMs is the presence of bare nucleophilic surfaces as a result of external oxygen atoms (M O M and M=O species, M = W or Mo), which might act as nucleophilic sites as well as stabilizers of cationic intermediates. 6] In particular, it is expected that POMs with large negative charges can nucleophilically activate TMSCN, thus resulting in promotion of cyanosilylations, as observed for Lewis base catalyzed cyanosilylations. 3h] Initially, the cyanosilylation of 2-adamantanone (1a) with TMSCN was carried out with the 8-charged POM TBA4H4[g-SiW10O36] (SiW10, TBA = tetra-n-butylammonium) in 1,2-dichloroethane at 30 8C. SiW10 promoted the cyanosilylation, giving the corresponding cyanohydrin trimethylsilyl ether 2a in 15% yield after 20 minutes (Scheme 1). In the case of TBA4H4[a-SiW11O39] (SiW11), 2a was also obtained in 16% yield (Table S2). In the absence of the catalysts, cyanosilylation was not observed under the present conditions.

Heterogeneous Selective Oxidation of Sulfides with H2O2 Catalyzed by Ionic Liquid-Based Polyoxometalate Salts

Abstract: A group of ionic liquid (IL)-based polyoxometalate (POM) salts were prepared via anion-exchange of imidazolium IL precursors tethered by different carbon chain alkyls with various Keggin POMs. The ...

Pickering Emulsion Stabilized by Catalytic Polyoxometalate Nanoparticles: A New Effective Medium for Oxidation Reactions

Abstract: Decyl-, dodecyl-, and tetradecyltrimethylammonium cations were combined with the catalytic polyoxometalate [PW12O40]3- anion to give spherical and monodisperse nanoparticles that are able to stabilize emulsions in the presence of water and an aromatic solvent. This triphasic liquid/solid/liquid system, based on a catalytic surfactant, is particularly efficient as a reaction medium for epoxidation reactions that involve hydrogen peroxide. The reactions proceed at competitive rates with straightforward separation of the phases by centrifugation. Such catalytic "Pickering" emulsions combine the advantages of heterogeneous catalysis and biphasic catalysis without the drawbacks (e.g., catalyst leaching or separation time).

Polyoxometalate-Supported 3d–4f Heterometallic Single-Molecule Magnets

Abstract: The reactions of [CuTbLSchiff(H2O)3Cl2]Cl complexes with A- or B-type Anderson polyoxoanions lead to new polyoxometalate-supported 3d–4f heterometallic systems with single-molecule-magnet behavior.

Polyoxometalate-based crystalline tubular microreactor: redox-active inorganic–organic hybrid materials producing gold nanoparticles and catalytic properties

Abstract: Here, we synthesize a novel polyoxometalate-based crystalline tubular inorganic–organic compound, Mn[Zn(im)]2{[Na(H2O)]2[Mn(H2O)2][Zn(im)2][P4Mo6O31H6]2}·8H2O (IFMC-100) (im and IFMC correspond to imidazole and Institute of Functional Material Chemistry, respectively). Au-anchored tubular microreactor, Au@IFMC-100, has been prepared by simple immersion of IFMC-100 in an ethanol solution of HAuCl4 without any extra reducing agents, photochemical and electrochemical auxiliaries. Furthermore, IFMC-100 and Au@IFMC-100 have been employed as catalysts for the reduction of K3Fe(CN)6 and 4-nitrophenol with NaBH4 in aqueous solution, respectively. The results indicate the as-prepared Au@IFMC-100 microtubes exhibit enhanced catalytic performance in redox catalysis.

Water oxidation catalyzed by a new tetracobalt-substituted polyoxometalate complex: [{Co4(μ-OH)(H2O)3}(Si2W19O70)]11-.

Abstract: A new polyoxometalate of earth adundant elements [{Co4(μ-OH)(H2O)3}(Si2W19O70)]11− has been synthesized, characterized and shown to be a water oxidation catalyst. The initial catalytic complex is unstable and slowly undergoes hydrolysis. The hydrolysis products have been isolated and characterized, and their catalytic water oxidation activity is assessed.

Controllable Self-Assembly of Organic-Inorganic Amphiphiles Containing Dawson Polyoxometalate Clusters

Abstract: An organic-inorganic molecular hybrid containing the Dawson polyoxometalate, ((C(4)H(9))(4)N)(5)H[P(2)V(3)W(15)O(59)(OCH(2))(3)CNHCOC(15)H(31)], was synthesized and its surfactant-like amphiphilic properties, represented by the formation of bilayer vesicles, were studied in polar solvents. The vesicle size decreases with both decreasing hybrid concentration and with increasing polarity of the solvent, independently. The self-assembly behavior of this hybrid can be controlled by introducing different counterions into the acetonitrile solutions. The addition of ZnCl(2) and NaI can cause a gradual decrease and increase of vesicular sizes, respectively. Tetraalkylammonium bromide is found to disassemble the vesicle assemblies. Moreover, the original counterions of the hybrid can be replaced with protons, resulting in pH-dependent formation of vesicles in aqueous solutions. The hybrid surfactant can further form micro-needle structures in aqueous solutions upon addition of Ca(2+) ions.

A general green strategy for fabricating metal nanoparticles/polyoxometalate/graphene tri-component nanohybrids: enhanced electrocatalytic properties

Abstract: The well-defined metal NPs@POM–GNS tri-component nanohybrids were synthesized by a green, facile, one-pot method. The obtained nanohybrids exhibited exciting electrocatalytic activity for methanol and formic acid oxidation.

Metal substitution in a Lindqvist polyoxometalate leads to improved photocatalytic performance

Abstract: The photochemical properties of homo- and heterometallic molybdate-based Lindqvist polyoxometalate clusters are investigated in a comparative study and it is shown that vanadium substitution can be used as a facile synthetic tool to optimize the visible light absorption and photocatalytic activity of the cluster. The mono-vanadium substituted unit, [VMo5O19]3− shows light absorption up to 480 nm whereas the light absorption of the molybdate analogue [Mo6O19]2− is mainly in the UV region below 400 nm. The electronic absorption properties of both clusters are further investigated using TD-DFT calculations which show that vanadium incorporation leads to the formation of low-energy O → V LMCT transitions. In comparative photochemical dye decomposition test reactions under UV and Vis irradiation, a higher reactivity is observed for [VMo5O19]3− together with turnover numbers of more than 1600. In addition it is shown that under anaerobic conditions, the photoreaction proceeds faster than in the presence of oxygen, suggesting that oxygen acts as a quencher in one of the photoredox steps.

A stable hybrid bisphosphonate polyoxometalate single-molecule magnet.

Abstract: The long history of polyoxometalate (POM) chemistry initially featured the characterization of diamagnetic species. However, the last few decades have seen the development of several families of paramagnetic POM molecules that display a diverse range of structures and properties. These entities can be of nanosize scale, as exemplified by the discovery of the spin-frustrated Keplerate clusters of general formula {(Mo)Mo5}12M30 (M=Fe , Cr, V). Although of smaller size than these molybdenum compounds, high-nuclearity polyoxovanadate mixed-valent species have also been characterized. The unexpectedly strong magnetic couplings observed in a number of these systems have been studied in detail both experimentally and theoretically. The third— and most extended—magnetic POM family is that of polyoxotungstates. Large clusters in which vacant polyoxotungstate ligands encapsulate 3d or 4f metals have been obtained, and most of these systems are purely inorganic. In particular, very few hybrid polynuclear 3d magnetic polyoxotungstates synthesized under mild conditions have been characterized to date. Moreover, to the best of our knowledge, no general method for the preparation of hybrid, soluble, and stable polyoxotungstates encapsulating magnetic clusters has been proposed. This contrasts with the case of the diamagnetic polyoxotungstates, for which numerous triol-functionalized, organosilyl and organostannic derivatives have been reported. Hybrid molybdenum-based POM chemistry has also been widely developed, but mainly {Mo6} Lindqvist and Anderson-type systems encapsulating a maximum of one 3d cation have been used as a platform for connecting various organic substrates. The establishment of a method allowing the rational synthesis of stable hybrid POMs incorporating several divalent or trivalent 3d metal centers thus remains a challenge. Such materials would be of interest in various fields as they would permit the covalent grafting of POMs containing 3d clusters to a range of organic substrates or surfaces, and thus the elaboration of new functional materials. For example, the covalent connection of photoactive organic groups to multi-electrochromic 3d-substituted inorganic entities may afford optical materials with new properties. Alternatively, Co-substituted polyoxotungstates have been shown to be efficient photocatalysts, which may in itself motivate the search for related hybrid materials. Clearly, hybrid 3d magnetic polyoxotungstates are also interesting in the molecular magnetism field. Since 2008, it is known that 3dor 4f-substituted polyoxotungstates can behave as single molecule magnets (SMMs). Moreover, deposition of POM SMMs on single-wall carbon nanotubes (SWCNTs) has provided evidence that individual POM molecules present a slow relaxation of the magnetization, a crucial point with respect to the potential use of such nanocomposites as information storage devices. However, in such a system, no control of the SWCNT/POM interface is possible. This is due to the purely inorganic nature of the deposited POM—a characteristic of all the 3d POM SMMs species reported to date. Indeed, the reinforcement of the interactions between the two components via covalent grafting or p–p stacking together with the control of the POM/substrate distance obviously implies the elaboration of hybrid POM SMM systems. Herein, we report the characterization of the polyanion [{(B-a-PW9O34)Co3(OH) ACHTUNGTRENNUNG(H2O)2ACHTUNGTRENNUNG(O3PC(O) ACHTUNGTRENNUNG(C3H6NH3)PO3)}2Co] 14 (1), which is built of a heptanuclear Co core sandwiched by two {PW9} units and connected to two bisphosphonato ligands, each possessing a functionalizable alkyl ammonium arm. The stability of this hybrid unit has been unambiguously assessed by using P and H NMR spectroscopy and electrochemical techniques. Single-crystal studies performed on an array of micro-SQUIDs have revealed that the ferromagnetic species 1 exhibits SMM behavior. [a] Dr. H. El Moll, Dr. A. Dolbecq, Dr. J. Marrot, G. Rousseau, Dr. M. Haouas, Dr. F. Taulelle, Prof. P. Mialane Institut Lavoisier de Versailles UMR 8180, Universit de Versailles Saint-Quentin 45 Avenue des Etats-Unis, 78035 Versailles Cedex (France) Fax: (+33)1-39-25-43-81 E-mail : mialane@chimie.uvsq.fr [b] Dr. G. Rogez Institut de Physique et de Chimie des Mat riaux de Strasbourg (IPCMS) UMR 7504, CNRS Universit de Strasbourg 23 rue du Lœss, BP 43, 67034 Strasbourg Cedex 2 (France) [c] Dr. W. Wernsdorfer Institut N el, CNRS et Universit Joseph Fourier BP 166, F-38042 Grenoble Cedex 9 (France) [d] Dr. B. Keita Laboratoire de Chimie Physique Groupe d’Electrochimie et de Photo lectrochimie, UMR 8000, CNRS Universit Paris-Sud, B timent 350, 91405 Orsay cedex (France) E-mail : bineta.keita@lcp.u-psud.fr Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201200140.

{W48} Ring Opening: Fe16‐Containing, Ln4‐Stabilized 49‐Tungsto‐8‐Phosphate Open Wheel [Fe16O2(OH)23(H2O)9(P8W49O189)Ln4(H2O)20]11−

Abstract: Wheely: For the first time and very unexpectedly, a rupture of the very stable {P(8)W(48)} wheel was observed in aqueous solution at pH 4 and 80 °C in the presence of Fe(III), Eu(III)/Gd(III), and H(2)O(2). This inorganic ring opening is unprecedented in polyoxometalate chemistry.

Layer-by-layer inkjet printing of fabricating reduced graphene-polyoxometalate composite film for chemical sensors.

Abstract: Graphene oxide (GO) nanosheets and polyoxometalate such as H3PW12O40 (PTA) are prepared into a multilayer film via a layer-by-layer inkjet printing method. The GO/PTA composite thin film shows linear, uniform and regular layer-by-layer growth. Under UV-irradiation, a photoreduction reaction takes place in the film which converts GO to reduced GO (rGO) due to the photoreduction activity of polyoxometalate clusters. According to the cyclic voltammograms measurement, the rGO/PTA composite film displays good electrocatalytic activity for the oxidation of dopamine (DA). The oxidation peak current (Ipa) increases gradually with increasing the dopamine concentration, which may be used in electrochemical biosensors.

Nature's polyoxometalate chemistry: X-ray structure of the Mo storage protein loaded with discrete polynuclear Mo-O clusters.

Abstract: Some N2-fixing bacteria prolong the functionality of nitrogenase in molybdenum starvation by a special Mo storage protein (MoSto) that can store more than 100 Mo atoms. The presented 1.6 A X-ray structure of MoSto from Azotobacter vinelandii reveals various discrete polyoxomolybdate clusters, three covalently and three noncovalently bound Mo8, three Mo5–7, and one Mo3 clusters, and several low occupied, so far undefinable clusters, which are embedded in specific pockets inside a locked cage-shaped (αβ)3 protein complex. The structurally identical Mo8 clusters (three layers of two, four, and two MoOn octahedra) are distinguishable from the [Mo8O26]4– cluster formed in acidic solutions by two displaced MoOn octahedra implicating three kinetically labile terminal ligands. Stabilization in the covalent Mo8 cluster is achieved by Mo bonding to Hisα156–Ne2 and Gluα129–Oe1. The absence of covalent protein interactions in the noncovalent Mo8 cluster is compensated by a more extended hydrogen-bond network involvin...

Tuning the architectures of polyoxometalate-templated complexes by changing the spacer lengths of bis-pyridyl-bis-amide ligands (L): from 1D chains to 2D networks based on different (CuL)n loops

Abstract: A series of metal–organic complexes based on Keggin-type polyoxometalate (POM) templates and bis-pyridyl-bis-amide ligands with tuned spacer lengths have been hydrothermally synthesized and structurally characterized: [Cu2(L1)3(SiMo12O40)(H2O)6]·2H2O (1), [Cu2(L2)3(SiMo12O40)(H2O)6]·9H2O (2), [Cu2(L2)3(SiW12O40)(H2O)6]·6H2O (3), [Cu2(L3)3(SiMo12O40)(H2O)6]·4H2O (4) and [Cu2(L3)3(SiW12O40)(H2O)6]·4H2O (5) [L1 = N,N′-bis(3-pyridinecarboxamide)-1,2-ethane, L2 = N,N′-bis(3-pyridinecarboxamide)-1,4-butane, L3 = N,N′-bis(3-pyridinecarboxamide)-1,6-hexane]. Single-crystal X-ray analyses reveal that compound 1 is a two-dimensional (2D) supramolecular structure based on one-dimensional (1D) infinite chains containing quadrate Cu2(L1)2 loops and Keggin polyanion templates. Compounds 2 and 3 are isostructural, and they display unusual 1D→2D poly-rotaxane frameworks containing large square Cu2(L2)2 loops, in which the Keggin polyanions are sandwiched between the parallel-packed 2D sheets. Compounds 2 and 3 represent the first POM-templated 2D metal–organic poly-rotaxane networks. Compounds 4 and 5 are isostructural, and they exhibit a 2D metal–organic architecture based on Cu6(L3)6 loops which are large enough to accommodate two Keggin polyanions, in which the polyanions are sandwiched among the stagger-packed cationic sheets. Compounds 1–5 represent examples of introducing flexible bis-pyridyl-bis-amide ligands into POM systems. The electrochemical properties of compounds 1 and 3 and the photocatalytic properties of the title compounds have been reported.

Nanoscale Growth of Molecular Oxides: Assembly of a {V6} Double Cubane Between Two Lacunary {P2W15} Polyoxometalates

Abstract: POM-in-POM: A Wells–Dawson polyoxometalate sandwich compound with a double cubane core consisting of six vanadium atoms has been synthesized (see structure). Cluster formation was followed by mass spectrometry and the reduction of the double cubane was studied by a novel technique combining mass spectrometry and spectroelectrochemistry.

Synthesis and characterization of a new porphyrin–polyoxometalate hybrid material and investigation of its catalytic activity

Abstract: In the present work, the preparation of a new organic–inorganic hybrid material in which tetrakis(p-aminophenylporphyrin) is covalently linked to a Lindqvist structure of polyoxometalate, is reported. This new porphyrin–polyoxometalate hybrid material was characterized by 1H NMR, FT-IR and UV-Vis spectroscopic methods and cyclic voltammetry. These spectro- and electrochemical studies provided spectral data of the synthesis of this compound. Cyclic voltammetry showed the influence of the porphyrin on the redox process of the polyoxometalate. The catalytic activity of this hybrid material was investigated in the alkene epoxidation with NaIO4.

Tuning the photochromic properties of molybdenum bisphosphonate polyoxometalates.

Abstract: Seven hybrid organic–inorganic bisphosphonate molybdenum(VI) polyoxometalate complexes with the general formula [(Mo3O8)4(O3PC(CmH2mNRR′R″)(O)PO3)4]8– (m = 3; R, R′, and R″ = H or CH3) and [(Mo3O8)2(O)(O3PC(CmH2mNRR′R″)(O)PO3)2]6– (m = 3 or 4; R, R′, and R″ = H or CH3) have been synthesized and their structures solved using single-crystal X-ray diffraction. These compounds are made of a {Mo12} or a {Mo6} inorganic core functionalized by various alkylammonium bisphosphonates, with these ligands differing by the length of their alkyl chains and the number of methyl groups grafted on the N atom. The nature of the counter-cations (Na+, K+, Rb+, Cs+, and/or NH4+) constituting these materials has also been modulated. 31P NMR spectroscopic studies in aqueous media have shown that all the dodecanuclear complexes reported here are stable in solution, whereas for the hexanuclear compounds, a dynamic equilibrium between two isomers has been evidenced, and the corresponding standard thermodynamic parameters determine...

pH-Dependent syntheses of copper–quinoxaline–polyoxotungatate hybrids: variable role of Keggin-type polyanion in different pH conditions

Abstract: Four new hybrids based on the Keggin-type polyoxometalate, formulated as (Hbm)3(PW12O40)·4H2O (1) (bm = benzimidazole, which is synthesized in situ by quinoxaline), [Cu6(qx)9(PW12O40)2] (2), [Cu3(qx)5(PW12O40)(H2O)] (3) and [Cu4(qx)4(HPCuIIW11O39)]·1.5H2O (4) (qx = quinoxaline), were hydrothermally synthesized and structurally characterized by routine techniques and single-crystal X-ray diffraction. In 1, the [PW12O40]3− (PW12) clusters only act as counteranions and combine with the protonated organic ligand by electrostatic interactions. In 2, a 63 topological 2D layer is formed with the PW12 as the template. In 3, the PW12 anions link with four metal–organic chains via Cu–O weak interactions to construct a 3D framework. In 4, the Cu(II)-substituted Keggin unit as a hexadentate inorganic ligand coordinates with four Cu(I) ions from metal–organic chains and two O atoms from neighboring POMs to form a sandwich-like 2D layer. The structure difference of compounds 1–4 reveals that the self-assembly process is pH-dependent and the Keggin-type POM plays different role in different pH conditions.

Metastable structures and isotope exchange reactions in polyoxometalate ions provide a molecular view of oxide dissolution

Abstract: Dissolution processes affect the performance of oxides in applications ranging from power generation to catalysis. A study on polyoxometalate ions, which are thought to model oxide surfaces, now suggests that dissolution is controlled by the stability of transient oxygen-stuffed structures.

Assembly of Polyoxometalate-Based Metal–Organic Frameworks with Silver(I)-Schiff Base Coordination Polymeric Chains as Building Blocks

Abstract: Six crystalline polyoxometalate-based three-dimensional (3D) metal–organic frameworks {[AgL4(DMF)][AgL4]2(PMo12O40)·DMF·3H2O}n (1), {[AgL4]3(PW12O40)·6H2O}n (2), {[AgL5]3(PMo12O40)·(CH3CN)3}n (3), {[AgL5(PW12O40)][AgL5(H2O)0.25(MeOH)0.25)][AgL5]0.5·DMF·(H2O)1.5}n (4), {[AgL6]3(PMo12O40)·DMF·H2O}n (5), and {[AgL7]3(PMo12O40)·DMF·(CH3CN)3}n (6) have been successfully synthesized based on one-dimensional (1D) coordination polymers constructed by the coordination of polydentate Schiff-base ligands and silver cations and saturated α-Keggin polyoxoanion [PM12O40]3– (M = W, Mo) as building blocks, where L4, L5, L6, and L7 are 2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene, 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene, 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene, and 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene, respectively. Compounds 1–6 are structurally characterized by elemental analyses, IR spectroscopy, thermogravimetric analyses (TG), powder X-ray diffraction (XRD), and complete single-crystal X-ray diffraction ana...