Showing papers on "Polyoxometalate published in 2006"

New polyoxometalate compounds built up of lacunary Wells-Dawson anions and trivalent lanthanide cations.

Abstract: Five new polyoxometalate compounds built on lacunary Wells−Dawson anions and trivalent lanthanide cations, KNa3[Nd2(H2O)10(α2-P2W17O61)]·11H2O (1), (H3O)[Nd3(H2O)17(α2-P2W17O61)]·6.75H2O (2), (H2bpy)2[Nd2(H2O)9 (α2-P2W17O61)]·4.5H2O (3), (H2bpy)2[La2(H2O)9(α2-P2W17O61)]·4.5H2O (4), and (H2bpy)2[Eu2(H2O)9(α2-P2W17O61)]·5H2O (5), have been synthesized and characterized by elemental analysis, IR, TG, and single-crystal X-ray diffraction. Compound 1 shows a bisupporting polyoxometalate cluster structure where two {Nd(H2O)7}3+ fragments are supported on the polyoxometalate dimer [{Nd(H2O)3(α2-P2W17O61)}2]14-; this represents the first bisupporting polyoxometalate compound based on a polyoxometalate dimer. Compound 2 displays a 1D chain structure built up of bisupporting polyoxoanions [{Nd(H2O)7}2{Nd(H2O)3(α2-P2W17O61)}2]8- and Nd3+ ions. Compounds 3−5 are isostructural and show a 2D structure constructed of 1D polyoxometalate chains of [Ln(H2O)2(α2-P2W17O61)]n7n- linked by Ln3+ ions. Compounds 2−5 represent th...

Self-Assembly of Extended High-Dimensional Architectures from Anderson-type Polyoxometalate Clusters

Abstract: Three unusual compounds based on polyoxometalate building blocks, [(C6H5NO2)2Ln(H2O)4]2[IMo6O24][NO3]·4H2O (Ln = Ce 1 and La 2) and [(H2O)4Ag3][Cr(OH)6Mo6O18]·3H2O 3, have been synthesized and characterized by elemental analysis, IR and X-ray photoelectron spectroscopy, thermogravimetry analysis, and single-crystal X-ray diffraction. Compounds 1 and 2 are isostructural and possess a unique two-dimensional (2D) network, which is composed of rare earth coordination polymer chains joint together by [IMo6O24]5- polyoxoanions, representing the first example of 2D inorganic−organic hybrid compounds based on A-type Anderson polyoxoanions. Compound 3 is constructed from B-type Anderson polyoxoanions [Cr(OH)6Mo6O18]3- and silver (I) ions to yield a three-dimensional (3D) open framework containing “guest” water molecules. To our best knowledge, it is the first time Anderson-type polyoxometalate motifs have been connected with silver ions to construct a 3D covalent framework.

[γ‐1,2‐H2SiV2W10O40] Immobilized on Surface‐Modified SiO2 as a Heterogeneous Catalyst for Liquid‐Phase Oxidation with H2O2

Abstract: An organic-inorganic hybrid support has been synthesized by covalently anchoring an N-octyldihydroimidazolium cation fragment onto SiO 2 (denoted as 1-SiO 2 ). This modified support was characterized by solid-state 13 C, 29 Si, and 31 P NMR spectroscopy, IR spectroscopy, and elemental analysis. The results showed that the structure of the dihydroimidazolium skeleton is preserved on the surface of SiO 2 . The modified support can act as a good anion exchanger, which allows the catalytically active polyoxometalate anion [γ-1,2-H 2 SiV 2 W 10 O 40 ] 4- (I) to be immobilized onto the support by a stoichiometric anion exchange (denoted as 1/1-SiO 2 ). The structure of anion I is preserved after the anion exchange, as confirmed by IR and 51 V NMR spectroscopy. The catalytic performance for the oxidation of olefins and sulfides, with hydrogen peroxide (only one equivalent with respect to substrate) as the sole oxidant, was investigated with I/1-SiO 2 . This supported catalyst shows a high stereospecificity, diastereoselectivity, regioselectivity, and a high efficiency of hydrogen peroxide utilization for the oxidation of various olefins and sulfides without any loss of the intrinsic catalytic nature of the corresponding homogeneous analogue of I (i.e., the tetra-n-butylammonium salt of I, TBA-I), although the rates decreased to about half that with TBA-I. The oxidation can be stopped immediately by removal of the solid catalyst, and vanadium and tungsten species can hardly be found in the filtrate after removal of the catalyst. These results rule out any contribution to the observed catalysis from vanadium and tungsten species that leach into the reaction solution, which means that the observed catalysis is truly heterogeneous in nature. In addition, the catalyst is reusable for both epoxidation and sulfoxidation without any loss of catalytic performance.

Synthesis, Crystal Structure, and Optical Properties of a Polyoxometalate-Based Inorganic−Organic Hybrid Solid, (n-Bu4N)2[Mo6O17(≡NAr)2] (Ar = o-CH3OC6H4)

Abstract: A novel organic−inorganic hybrid solid, (n-Bu4N)2[Mo6O17(NAr)2] (Ar = o-CH3OC6H4) 1, has been prepared by refluxing of (n-Bu4N)2[Mo6O19] and appropriate o-anisidine in acetonitrile with N-N‘-dicyclohexylcarbodiimide (DCC) as the dehydrating agent. Compound 1 has been characterized by single-crystal X-ray diffraction. Both of the two terminal o-anisidido ligands are linked, respectively, to an Mo atom of the hexamolybdate in a terminal fashion and exhibit an almost linear coordination mode of the Mo⋮N triple bond character. The two o-anisidido aryl rings on the hexamolybdate cluster lie in the cis position, allowing π−π stacking of phenyl ring among the anions. In the crystal, the cluster anions of 1 aggregate into an interesting 1D double chain along the a-axis through π−π stacking and C−H···O hydrogen-bonding interactions. Compared to the hexamolybdate parent, this solid has a smaller optical band gap of 2.25 eV from UV−visible-near-IR reflectance spectroscopy studies. It has also been characterized by 1...

Synthesis and Structure of Asymmetric Zirconium-Substituted Silicotungstates, [Zr6O2(OH)4(H2O)3(β-SiW10O37)3]14- and [Zr4O2(OH)2(H2O)4(β-SiW10O37)2]10-

Abstract: The reaction of ZrCl4 with [γ-SiW10O36]8- in a potassium acetate buffer results in two different products depending on the reactant ratios. The trimeric species [Zr6O2(OH)4(H2O)3(β-SiW10O37)3]14- (1) consists of three β23-SiW10O37 units linked by an unprecedented Zr6O2(OH)4(H2O)3 cluster with C1 point group symmetry. The dimeric species [Zr4O2(OH)2(H2O)4(β-SiW10O37)2]10- (2) consists of β22- and β12-SiW10O37 units sandwiching a Zr4O2(OH)2(H2O)4 cluster, which also has C1 symmetry. Polyanion 1 contains more zirconium centers than any other polyoxometalate known to date.

Rapid Synthesis of Amino Acid Polyoxometalate Nanotubes by One-Step Solid-State Chemical Reaction at Room Temperature†

Abstract: A novel and convenient method—solid-state chemical reaction at room temperature—is reported for the synthesis of amino acid polyoxometalate nanotubes. As a convenient synthesis method for nanomaterials, it may open up a new pathway for the fabrication of organic–inorganic hybrid materials with nanotubular structure. Here, three novel tyrosine (Tyr) polyoxometalate nanotubes, (HTyr)3PMo12O40 · 3H2O, (HTyr)3PW12O40 · 3H2O, and (HTyr)4SiW12O40 · 5H2O are successfully synthesized via a one-step solid-state chemical reaction at room temperature. Elemental analysis confirms the rationality of composition for the samples. Infrared spectroscopy, X-ray diffraction, and 31P magic-angle spinning NMR results prove that the samples still possess Keggin-type structures. Scanning and transmission electron microscopies suggest that the three samples are comprised of nanotubes with remarkably uniform shape and size, with diameters from 50 to 150 nm and lengths of up to several micrometers. Cyclic voltammograms of samples in 1 mol L–1 H2SO4 indicate that three redox waves correspond to three two-electron processes resulting from the reduction/oxidation of the heteropoly anion.

Synthesis and Structure of Dilacunary Decatungstogermanate, [γ-GeW10O36]8-

Abstract: The dilacunary decatungstogermanate [γ-GeW10O36]8- (1) has been synthesized and structurally characterized in solution and in the solid state. Reaction of germanium dioxide with sodium tungstate in aqueous acidic medium results in the formation of [β2-GeW11O39]8- (2), which is then used as a precursor for the synthesis of 1. The 183W spectrum of 2 shows the expected 11 peaks of equal intensity, whereas that of 1 exhibits the expected three peaks with relative intensities 2:2:1. Polyanion 1 represents a novel lacunary polyoxometalate, giving rise to a multitude of derivatives by reaction with transition metals, lanthanides, and other electrophiles.

Characterization of manganese(V)-oxo polyoxometalate intermediates and their properties in oxygen-transfer reactions.

Abstract: A manganese(III)-substituted polyoxometalate, [α2-P2MnIII(L)W17O61]7- (P2W17MnIII), was studied as an oxidation catalyst using iodopentafluorobenzene bis(tifluoroacetate) (F5PhI(TFAc)2) as a monooxygen donor. Pink P2W17MnIII turns green upon addition of F5PhI(TFAc)2. The 19F NMR spectrum of F5PhI(TFAc)2 with excess P2W17MnIII at −50 °C showed the formation of an intermediate attributed to P2W17MnIII−F5PhI(TFAc)2 that disappeared upon warming. The 31P NMR spectra of P2W17MnIII with excess F5PhI(TFAc)2 at −50 and −20 °C showed a pair of narrow peaks attributed to a diamagnetic, singlet manganese(V)−oxo species, P2W17MnVO. An additional broad peak at −10.6 ppm was attributed to both the P2W17MnIII−F5PhI(TFAc)2 complex and a paramagnetic, triplet manganese(V)−oxo species. The electronic structure and reactivity of P2W17MnVO were modeled by DFT calculations using the analogous Keggin compound, [PMnVOW11O39]4-. Calculations with a pure functional, UBLYP, showed singlet and triplet ground states of similar energ...

Micelle directed synthesis of polyoxometalate nanoparticles and their improved catalytic activity for the aerobic oxidation of sulfides.

Abstract: Micelle directed polyoxometalate nanoparticles were synthesized by depositing H3+xPVxMo12-xO40 (x = 0, 2) by precipitation on micelles prepared from cesium dodecyl sulfate. The cryo-TEM image showed particles of about ∼10 nm roughly consistent with the particle size computed from an idealized model. HRTEM coupled with EELS imaging to map the distribution of the elements also supported the formation of micelle directed polyoxometalate nanoparticles. In the aerobic oxidation of various sulfides to sulfoxides and sulfones, the clustered polyoxometalate assemblies supported on hydrophilic silica showed significantly higher catalytic activity versus that of nonclustered assemblies.

Synthesis, Structural Characterization, and Catalytic Performance of Dititanium-Substituted γ-Keggin Silicotungstate

Abstract: A novel titanium-substituted silicotungstate cluster of [{γ-SiTi2W10O36(OH)2}2(μ-O)2]8- (1) is synthesized by the introduction of titanium(IV) ions into a divacant lacunary γ-Keggin-type silicotungstate of [γ-SiW10O36]8-. This titanium-substituted polyoxometalate, 1, exhibits a dimeric structure. One half of the γ-Keggin fragment of 1 contains a dinuclear titanium center bridged by two hydroxo groups, and the resulting Ti2(μ-OH)2 core connects to the other Ti2(μ-OH)2 core of the paired γ-Keggin subunit through Ti−O−Ti linkages. The Ti2(μ-OH)2 core of 1 reacts with MeOH to form the corresponding alkoxo derivative, [{γ-SiTi2W10O36(OH)(OMe)}2(μ-O)2]8- (2). Two of four hydroxo groups of the Ti2(μ-OH)2 cores in 1 are replaced by methoxo groups to give the Ti2(μ-OH)(μ-OMe) core, and the Ti−O−Ti linkages connecting two γ-Keggin subunits are maintained in 2. The γ-Keggin dititanium-substituted silicotungstate 1 catalyzes mono-oxygenation reactions, such as the epoxidation of olefins and sulfoxidation of sulfides ...

Regular Two-Dimensional Molecular Array of Photoluminescent Anderson-type Polyoxometalate Constructed by Langmuir−Blodgett Technique

Abstract: A regular two-dimensional photoluminescent array of Anderson-type polyoxometalates (POMs) was constructed as built-up Langmuir-Blodgett (LB) films. LB films of hexatungstoantimonate (SbW(6)) and -manganate (MnW(6)) were successfully fabricated by using dimethyldioctadecylammonium (DODA) as cationic partner, while hexamolybdochromate (CrMo(6)) was unsuccessful. Specular X-ray reflectivity (SXR) and grazing incidence X-ray diffraction (GIXD) measurements revealed that both SbW(6)/DODA and MnW(6)/DODA LB films exhibited well-ordered layers consisting of periodic arrangement of the planar-structured Anderson-type molecules. Surprising periodicity was observed in SbW(6)/DODA LB film, in which the distance between SbW(6) and DODA layers was 4.40 nm, and SbW(6) anions would form a two-dimensional square lattice with a length of 1.4 nm. SbW(6)/DODA LB films exhibited photoluminescence at 77 K, while emission spectra were observed at room temperature for SbW(6) solid.

Analysis of weak interactions in the crystal packing of inorganic metalorganic hybrids based on keggin polyoxometalates and dinuclear copper(II)-acetate complexes

Abstract: Reaction of in situ generated copper-monosubstituted Keggin polyoxometalate (POM) and copper-phenanthroline complexes in potassium or sodium acetate buffers led to the formation of the potassium salt of [{SiW 11 O 39 Cu(H 2 O)}{Cu 2 (phen) 2 (H 2 O)(ac) 2 }] 4 - (1) and [{Si 2 W2 2C u 2 O 78 (H 2 O)}{Cu 2 (phen) 2 (H 2 O)(ac) 2 } 2 ] 8- (2, where phen = phenanthroline and ac = acetate) hybrid polyanions, respectively. Both compounds are the first discrete mono- and bimolecular transition-metal-substituted Keggin POMs that support a binuclear copper-acetate complex. Despite the different nature of the POMs, the crystal packing of the two compounds is closely related, being formed of hybrid parallel layers that give rise to an alternate sequence of inorganic and metalorganic regions. This packing type seems to be determined by the extensive network of weak intermolecular interactions established by the dicopper complexes, as a Hirshfeld surface analysis shows. Electron paramagnetic resonance studies indicate that both the supported [Cu 2 (ac) 2 (phen) 2 (H 2 O)] 2+ complexes and the copper(ll)-monosubstituted POMs are magnetically isolated.

A Novel Copper(I) Halide Framework Templated by Organic–Inorganic Hybrid Polyoxometalate Chains Formed In Situ: A New Route for the Design and Synthesis of Porous Frameworks

Abstract: A 1D organic–inorganic hybrid polyoxometalate chain has been used as a non-coordinating anionic template for the construction of a novel 3D copper halide 4,4′-bipy framework, namely [Cu3ICl(4,4′-bipy)4][CuII(1,10-phen)2Mo8O26]. X-ray diffraction experiments revealed that the title compound consists of chloride-bridged trinuclear CuI units linked by neutral organic 4,4′-bipy groups into a 3D framework with hexagon-like channels in which 1D organic–inorganic hybrid polyoxometalate chains reside. This is the first example of a 1D organic–inorganic hybrid polyoxometalate chain functioning as a novel anionic template for the construction of a 3D framework. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Highly reactive catalysts for aerobic thioether oxidation the Fe-substituted polyoxometalate/hydrogen dinitrate system

Abstract: A new type of polyoxometalate (POM), one with a hydrogen dinitrate group associated with a d-electron-substituted polyoxometalate, FeIII[H(ONO2)2]PW11O395− (1), has been developed that catalyzes highly effective aerobic sulfoxidation (RR′S + 0.5 O2 → RR′SO) under ambient conditions (1 atm of air at room temperature). Comparison of the rates for aerobic sulfoxidation of the mustard simulant 2-chloroethyl ethyl sulfide (CEES) catalyzed by 1 and several other species reported to be catalysts for this class of reactions, including NO+, NO2, (NH4)2CeIV(NO3)6 and AuIIICl2NO3(CH3CN) indicate that 1 is clearly the most effective catalyst. Conversions and selectivities for the desired sulfoxide decontamination product (CEESO in these studies) are both effectively quantitative. The low or nonexistent catalytic activity of FeII(NO)PW11O396−, Fe(NO3)3 and HNO3 argues strongly that nitrosyl and nitrate derivatives of the Fe polyoxometalate and nitric acid are not species important in catalytic turnover. The techniques of single crystal X-ray diffraction, solution NMR, FTIR, TGA, DSC, cyclic voltammetry, elemental and wet chemical analyses were applied to the characterization of 1 and these are collectively consistent with the α-Keggin structure with a strongly associated hydrogen dinitrate group and a more weakly associated nitrate of crystallization.

An example of lipophiloselectivity: the preferred oxidation, in water, of hydrophobic 2-alkanols catalyzed by a cross-linked polyethyleneimine-polyoxometalate catalyst assembly.

Abstract: A cross-linked polyethyleneimine polymer containing the [ZnWZn2(H2O)2(ZnW9O34)2]12- polyoxometalate was prepared from branched polyethyleneimine (Mw = 600), the polyoxometalate, and a n-octylamine-epichlorohydrin cross-linking reagent. This catalytic assembly was active for the selective oxidation of 2-alkanols to 2-alkanones with aqueous H2O2 with reactions presumably occurring at a hydrophobic domain. Most importantly, the catalyst showed distinctive lipophiloselectivity, that is selectivity as a function of the lipophilic nature of a reaction substrate. The lipophiloselectivity was proportional to the relative partition coefficient (1-octanol/water) of the substrates.

Thermotropic Mesomorphic Behavior of Surfactant-Encapsulated Polyoxometalate Hybrids

Abstract: We investigate in detail novel organic−inorganic hybrid liquid crystalline materials, the complexes of surfactant-encapsulated polyoxometalate clusters (SECs), using thermal, X-ray diffraction, and FT-IR spectroscopic analyses. The differential scanning calorimetry measurements reveal four phase transitions under heating processes. We employ FT-IR spectroscopy to understand these phase behaviors. On the basis of vibration spectral assignments, the evidence suggests that the first two phase transitions are associated with the increase of gauche conformers and the disruption of alkyl chains packing in the heating run; the third phase transition is due to the full conformational disorder of alkyl chains covered on the polyoxometalates (PMs); no significant C−H stretching or wagging vibrations are observed with the fourth transition. We find that the fourth endothermic peak is sensitive to the charges of the PMs, and the transition temperature decreases from 185, 177, to 164 °C with decreasing PM charges from...

Bio-inspired oxidations with polyoxometalate catalysts

Abstract: Transition metal substituted polyoxometalates (TMS-POM) provide a redox-active metal center, (Fe, Ru, Mn or else), with a totally inorganic ligand system, featuring rigid polydentate binding sites, high electron-acceptor character, extreme robustness and interesting structural and coordination properties, in some cases, mimicking the coordination geometry of natural oxygenase enzymes. Their synthesis and reactivity can be promoted by microwave (MW) induced dielectric heating. In particular, MW irradiation induces a very efficient and selective hydrothermal synthesis of the diamagnetic, air-stable [Ru II (DMSO)PW 11 O 39 ] 5− . Its catalytic activity has been screened with shunt oxidants like NaIO 4 and KHSO 5 and PyCl 2 NO. Under dioxygen and MW irradiation, [Ru II (DMSO)PW 11 O 39 ] 5− catalyzes the oxidation of DMSO to DMSO 2 in water. Fe III -POMs with nuclearities 1–4, namely [α-Fe(H 2 O)SiW 11 O 39 ] 5− (FeSiW 11 ), [γ-Fe 2 (H 2 O) 2 SiW 10 O 38 ] 6− (Fe 2 SiW 10 ) , [α-Fe 3 (H 2 O) 3 SiW 9 O 37 ] 7− (Fe 3 SiW 9 ) and [β-Fe 4 (H 2 O) 10 (XW 9 O 33 ) 2 ] n− (Fe 4 X 2 W 18 , X = Se IV , Te IV ; As III , Sb III ; n = 4, 6) were also found to catalyze the MW assisted cyclohexane oxygenation with high turnover frequencies. Preliminary results indicate that the Krebs-type Fe polyoxotungstates can also promote the oxidative cleavage of 3,5-ditert-butylcatechol with molecular oxygen.

From Molecular Double‐Ladders to an Unprecedented Polycatenation: A Parallel Catenated 3D Network Containing Bicapped Keggin Polyoxometalate Clusters

Abstract: A new three-dimensional coordination polymer, {Cu3(4,4′-bpy)3(H2O)[PMo12O40(VO)2]·5H2O}n (1) (4,4′-bpy = 4,4′-bipyridine), which represents the first example of 3D polycatenation generated by unprecedented parallel catenation of the 1D double ladders, has been hydrothermally synthesized. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Luminescent Polyoxotungstoeuropate Anion‐Pillared Layered Double Hydroxides

Abstract: Novel luminescent polyoxometalate anion-pillared layered double hydroxides (LDHs) were prepared by aqueous ion exchange of a Zn–Al LDH precursor in nitrate form with the europium-containing polyoxotungstate anions [EuW10O36]9–, [Eu(BW11O39)(H2O)3]6– and [Eu(PW11O39)2]11–. The host–guest interaction has a strong influence on the nature of the final intercalated species, as evidenced by elemental analysis, powder X-ray diffraction (XRD), infra-red (IR) and Raman spectroscopy, solid state magic-angle spinning (MAS) 11B and 31P NMR spectroscopy, and photoluminescence spectroscopy. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Analysis of structural transformations during the synthesis of a MoVTeNb mixed oxide catalyst

Abstract: This work presents a detailed investigation of the preparation routine for the multi-metal oxide Mo 1 V 0.30 Te 0.23 Nb 0.125 O x used as catalyst for the selective oxidation of propane to acrylic acid. In situ Raman spectroscopy on the initial aqueous polyoxometalate solution prepared from ammonium heptamolybdate, ammonium metavanadate and hexaoxotelluric acid reveals the coexistence of Anderson-type anions [TeM 6 O 24 ] n − , M = Mo, V; n ≥ 6 and protonated decavanadate species [H x V 10 O 28 ] (6− x )− . Raman analysis showed that the monomeric motif of the Anderson-type tellurate is preserved after addition of the Nb precursor and the subsequent spray-drying process. Calcination of the X-ray amorphous spray-dried material in air at 548 K seems to be the essential step, leading to a re-arrangement of the tellurate building blocks, generating nanocrystalline precursors of the phases finally established during treatment in helium at 873 K.

Polyoxometalate (W/Mo) compounds connected via lanthanide cations with a three-dimensional framework, H2{ [K (H2O )2 ]2 [Ln (H2O )5 ]2 (H2M12O42 )}·nH2O : Synthesis, structures, and magnetic properties

Abstract: A series of 10 novel polyoxometalate (W/Mo) compounds connected via a trivalent lanthanide cation bridge, H2{[K(H2O)2]2[Ln(H2O)5]2(H2M12O42)}·nH2O (Ln = La, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu; M = W or W/Mo) (1−10), were designed and synthesized on the basis of the abduction of Al3+ in aqueous solution. X-ray diffraction analyses reveal that the structures of complexes 1−10 are three-dimensional frameworks assembled from the arrangement of H2M12O4210- (named paradodecmetalate-B) and Ln(H2O)53+ with two planes, which are constructed via the unification of H2M12O4210- and Ln(H2O)53+, along the [100] and [001] directions. Magnetic measurements reveal the paramagnetic properties and a strong ferromagnetic coupling between the two nearest-neighboring lanthanide cations, Ln3+ (Ln = Dy, Er), within the circle for compounds 2 and 4−9.

Sensitization of photo-reduction of the polyoxometalate anions [S2M18O62]4− (M = Mo, W) in the visible spectral region by the [Ru(bpy)3]2+ cation

Abstract: Voltammetric, photo-physical and photo-electrochemical properties of the Dawson polyoxometalate anions α-[S2M18O62]4− (M = Mo, W) are presented, both in the presence and absence of a series of [RuIILn]+/2+ cations [Ln = (bpy)3, (bpy)2(Im)2, (bpy)2(dpq), (bpy)2(box) and (biq)2(box)]. Electrochemical processes for both the anion and RuII/III couples were detected in solutions of the salts [RuIILn]2[S2M18O62] in dimethylformamide (0.1 M Bu4NPF6) by both cyclic and hydrodynamic voltammetries. Responses were also detected when the solid salts were adhered to the surface of a glassy carbon electrode in contact with an electrolyte in which they are insoluble (CH3CN; 0.1M Bu4NPF6). Photolysis experiments were performed on solutions of the salts [R4N]4[S2M18O62] (R = n-butyl or n-hexyl) and [RuIILn]2[S2M18O62] at 355 and 420 nm in dimethylformamide and acetonitrile in the presence and absence of benzyl alcohol (10% v/v). When associated with [Ru(bpy)3]2+, the molybdate anion exhibited a large increase in the quantum yield for photo-reduction at 420 nm. The quantum yield for the tungstate analogue was lower but the experiments again provided clear evidence for sensitization of the photo-reduction reaction in the visible spectral region. The origin of this sensitization is ascribed to the new optical transition observed around 480 nm in static ion clusters {[Ru(bpy)3][S2M18O62]}2− and {[Ru(bpy)3]2[S2M18O62]} present in solution. Measurable photocurrents resulted from irradiation of solutions of the anions with white light in the presence of the electron donor dimethylformamide. Evidence is also presented for possible quencher–fluorophore interactions in the presence of certain [RuIILn]+ cations.

Synthesis and Characterization of Two Novel, Mono‐Lacunary Dawson Polyoxometalate‐Based, Water‐Soluble Organometallic Ruthenium(II) Complexes: Molecular Structure of [{(C6H6)Ru(H2O)}(α2‐P2W17O61)]8–

Abstract: The synthesis and structural characterization of a novel class of mono-lacunary Dawson polyoxometalate-(POM-)based, water-soluble organometallic complexes, which are expected to be effective homogeneous oxidation catalyst precursors in water, is described. The organometallic complexes K8[{(C6H6)Ru(H2O)}(α2-P2W17O61)]·12H2 O( 1) and K8[{(p-cymene)Ru(H2O)}(α2-P2W17O61)]·16H2 O( 2) were successfully prepared by direct reactions of the mono-lacunary Dawson POM K10[α2-P2W17O61]·19H2O with the organometallic precursors [(C6H6)RuCl2]2 and [(p-cymene)RuCl2]2, respectively, in aqueous media and characterized by complete elemental analysis, thermogravimetric and differential thermal analy