Compounds of the [PMo12O40]3− anion with surfactant cations forming nanoperiodic structures

Phosphomolybdic acid forms compounds with surfactant cations in acid aqueous media (pH 1.0–2.5) to give compounds A₃[PMo₁₂O₄₀] or Etn₃[PMo₁₂O₄₀]₂·nEtnCl₂ (n=0−3) with various nanoperiodicity depending on the surfactant and synthesis conditions. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 3, 184–190, May–June, 1998.     

Catalysis by heteropolyacids—VIII. Immobilization of keggin-type heteropolyacids on poly(4-vinylpyridine)

Anchoring of a Keggin-type heteropolyacid (HPA) to a polymeric support and the effect of heterogenization on the HPA catalysis of the oxidation of a primary diol have been studied. A coloured HPA such as H₆[Co(II)W₁₂O₄₀] (blue green), H₄[SiMo₁₂O₄₀] (yellow) or H₃[PMo₁₂O₄₀] (yellow), as the Keggin-type HPA and poly(4-vinylpyridine) as a polymeric support have been used. The anchoring of H₆[Co(II)W₁₂O₄₀] has led to a markedly increased stability of the oxidation catalyst.     

Hydrothermal syntheses, crystal structures, and properties of two polyoxometalates [Cd(2,2′-bpy)3]2[PMoVMoVI 11O40] and [H3PMo12O40]·3(4,4′-bpy)·4H2O

Two Keggin-type phosphododecamolybdate compounds [Cd(2,2′-bpy)₃]₂[PMo^VMo^VI ₁₁O₄₀] (1) and [H₃PMo₁₂O₄₀]·3(4,4′-bpy)·4H₂O (2) (bpy=bipyridine) were prepared by the hydrothermal method for the first time and characterized by elemental analyses, X-ray single-crystal diffraction, ESR spectra, and IR spectra, showing that compound 1 consists of a mixed valence Keggin polyanion [PMo^VMo^VI ₁₁O₄₀]⁴⁻ and two isolated coordinated cations [Cd(2,2′-bpy)₃]²⁺, while compound 2 is an intermolecular compound based on organic substrate 4,4′-bpy and heteropoly acid unit H₃PMo₁₂O₄₀. Furthermore, both the compounds show strong photoluminescence properties in the solid state at room temperature. The catalytic activities of the two compounds were also determined by the oxidation of benzaldehyde to benzoic acid using H₂O₂ as oxidant in a liquid–solid triphase system.     

Effect of adding H2SO4 and NaCl TO palladium-containing catalysts on the results of methane oxidation at 220°C

A study has been made of the interaction of methane at 220°C with silica gel-supported complexes of palladium(II), Na_n H_9-n[PMo₆V₆O₄₀], H₉[PMo₆V₆O₄₀], H₃[PMo₁₂O₄₀], NaCl, and with added sulfuric acid. Competition between electrophilic and chloride pathways is examined. Additions of Na⁺ and Cl^– direct the reaction along the chloride pathway, leading to the formation of CH₃Cl. Without NaCl, the electrophilic mechanism is realized, the main product of which is CO₂.L. M. Litvinenko Institute of Physical-Organic Chemistry and Coal Tar Chemistry, National Academy of Sciences of the Ukraine, 70 R. Luxembourg Street, Donetsk 340114, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 2, pp. 92–96, March–April, 1996. Original article submitted June 30, 1995.     

Hydrothermal Synthesis and Crystal Structure of Two New α-Keggin Derivatives Decorated by Transition Metal Complexes

Two new neutral Keggin-polyoxometalate derivatives: [{Co(2,2′-bipy)₂(H₂O)}₂]–[PMo^VI₇Mo^V₅O₄₀(V^IVO)₂] (1) and [{Ni(phen)₂(H₂O)}₂](H₃O) [PMo^VI₁₀Mo^V₂O₄₀] · 4H₂O (2) have been synthesized under hydrothermal conditions and characterized by i.r., t.g. analysis, x.p.s. spectra and single-crystal X-ray diffraction. In the case of (1), the polyoxoanion cluster [PMo₁₂O₄₀]⁸⁻ is capped by two vanadium atoms via four bridging oxo groups on two opposite {Mo₄O₄} pits of the Keggin polyoxoanion. Two {Co (2,2′-bipy)₂(H₂O)} fragments are supported on the two vanadium atoms through two terminal oxygen atoms from two vanadium atoms. In (2), two {Ni(phen)₂(H₂O)}²⁺ moieties are linked to the molybdophosphate cluster [PMo₁₂O₄₀] core to form a neutral bimetallic cluster. Furthermore, through the linkages of π – π stacking interactions and hydrogen bond contacts, extended three-dimensional supramolecular networks in the solid of (1) and (2) were formed.     

Formation of nanoperiodic structures based on keggin and lacunar anions of phosphotungstic acid and cationic surfactants

Surface-active cations (A⁺) in an aqueous medium, at pH 1.0 with excess phosphotungstic acid, form compounds with the composition A₃[PW₁₂O₄₀]; but at pH 4.5, they form acid salts A_nH_7−n[PW₁₁O₃₉]·xH₂O that have a nanoperiodic structure. The structural parameters are greatly dependent on the nature of the surfactant and on the type of heteropolyion. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospect Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 4, pp. 250–256, July–August, 1998.     

Oxychlorination of methane to methyl chloride at 300°C in the system palladium(II) complexes-heteropolyacids-silica gel

The activity of systems, applied to silica gel from chloride solutions, in the oxychlorination of CH₄ to CH₃Cl at 300° Cincreases in the order H₃[PMo₁₂O₄₀]9[PMo₆V₆O_40]2(PdCl₂-H₉[PMo₆V₆O₄₀] (or H₃[PMo₁₂O₄₀]))<(PdCl₂-Na_nH_9–n[PMo₆V₆O₄₀]). Additions of NaCl (molar ratio of the components NaClSiO₂7100) lead to an increase in the yield of CH₃Cl. The mechanisms of CH₄ oxidation have been discussed which are electrophilic with the participation of Pd(II) complexes and involve chlorides with the participation of surface Cl atoms.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 1, pp. 29–33, January–February, 1995.     

A supramolecular complex based on poly-Keggin-anion chains: synthesis, structure characterization, and conductivity

Abstract  

A proton-conductive supramolecular complex, {[Cu(H₂O)₈][H(H₂O)₃](HINO)₄(PMo₁₂O₄₀)} _n , was constructed by a self-assembly of H⁺(H₂O)₃ clusters, [Cu(H₂O)₈]²⁺ clusters, [PMo₁₂O₄₀]³⁻ anions, and isonicotinic acid N-oxide (HINO). Single-crystal X-ray diffraction analysis at 293 K revealed that the complex presented the three-dimensional (3D) supramolecular framework built from non-covalent interactions. Interestingly, [PMo₁₂O₄₀]³⁻ anions self-assembled into poly-Keggin-anion chains in the supramolecular framework. Thermogravimetric analysis shows no weight loss in the temperature range of 20–100 °C, indicating that all water molecules in the unit structure are not easily lost below 100 °C. Surprisingly, the proton conductivity of the complex in the temperature range of 85–100 °C under 98% RH condition reached good proton conductivity of 10⁻³ S cm⁻¹. A possible mechanism of the proton conduction was proposed according to the experimental results.     

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

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

Detection of steroids with molybdovanadophosphoric acids on thin-layer chromatograms

Two vanadium analogues of phosphomolybdic acid, H₄[PMo₁₁VO₄₀] and H₄[PMo₁₀V₂O₄₀], have been studied for use as detection reagents for steroids on thin-layer plates. They were found to produce characteristic colors with steroids after spraying and heating at 105 °C.     

Synthesis, physical–chemical, and catalytic properties of mixed compositions Ag/H3PMo12O40/SiO2

Deposited catalysts composition H₃PMo₁₂O₄₀/SiO₂ and Ag/H₃PMo₁₂O₄₀/SiO₂ have been synthesized on the basis of fumed silica, including milling technique. Physical–chemical characteristics of prepared catalysts have been studied by means of XRD, DTA-TG, FTIR, UV–Vis spectroscopy, and adsorption of nitrogen. Catalysts possess meso- or meso-macroporous structure and contain deposited Keggin heteropolycompounds. Deposition of heteropolycompounds on support with high specific surface area results in increase of selectivity to epoxide in epoxidation reactions. The use of milling during catalyst synthesis leads to further growth of selectivity of epoxides formation.     

Activation-controlled outer-sphere electron transfer reactions: reduction of heteropoly 11-tungstovanadophosphate and heteropoly 10-tungstodivanado phosphate by thiourea in aqueous acid medium

The kinetics of reduction of heteropoly 11-tungstovanadophosphate, [PV^VW₁₁O₄₀]⁴⁻, (HPA1) and heteropoly 10-tungstodivanadophosphate, [PV^VV^VW₁₀O₄₀]⁵⁻, (HPA2) by thiourea has been investigated in HClO₄/phthalate/acetate buffer solutions spectrophotometrically at 25 °C in aqueous medium. The stoichiometry of the reaction is 1:1 in both cases. The HPAs are converted into the corresponding one-electron reduced heteropoly blues, namely, [PV^IVW₁₁O₄₀]⁵⁻ and [PV^IVV^VW₁₀O₄₀]⁶⁻, and thiourea is oxidised to formamidine disulphide. The reaction shows first-order dependence in both [HPA] and [thiourea] at constant pH. The rate–pH profile shows the participation of both the neutral and deprotonated forms of thiourea in the reaction. The reaction proceeds through an outer sphere electron transfer mechanism in which activation-controlled electron transfer is the rate-determining step. Self-exchange rate constants for the couples [PV^VW₁₁O₄₀]⁴⁻/[PV^IVW₁₁O₄₀]⁵⁻, [PV^VV^VW₁₀O₄₀]⁵⁻/[PV^IVV^VW₁₀O₄₀]⁶⁻ and H₂NCSNH₂/H₂NCS^·+NH₂ have been evaluated by Marcus theory.     

Correlation between reduction potential of vanadium-containing heteropolyacid (HPA) catalysts and their oxidation activity for cyclohexanol dehydrogenation

Vanadium-containing H_6+xP₂Mo_18−xV_xO₆₂ (x = 0, 1, 2 and 3) Wells-Dawson heteropolyacid (HPA) and H_3+xPMo_12−xV_xO₄₀ (x = 0, 1, 2 and 3) Keggin HPA catalysts were applied to the vapor-phase dehydrogenation of cyclohexanol. The catalytic oxidation activity showed a volcano-shaped curve with respect to vanadium substitution for both families of HPA catalysts. The Wells-Dawson HPA showed a better catalytic oxidation performance than the Keggin HPA at the same level of vanadium substitution.     

Transition metal substituted polyoxometalates supported on amine-functionalized silica

A series of transition metal substituted polyoxometalates (POM) have been anchored to propylamine-functionalized mesoporous silica (silicaNH₂). These include V, Co and Mn Keggin-type anions such as [PMo₁₀V₂O₄₀]⁵⁻ and [PMo₁₁VO₄₀]⁴⁻, or [SiW₁₁Co^II(H₂O)O₃₉]⁶⁻ and [SiW₁₁Mn^III(H₂O)O₃₉]⁵⁻, and sandwich-type anions, [(PW₉O₃₄)₂ Co ₄ ^II (H₂O)₂]¹⁰⁻ and [(PW₉O₃₄)₂Mn ₄ ^II (H₂O)₂]¹⁰⁻. Experiments at different initial pH_i of aqueous suspension of silica were performed for the Co and Mn substituted Keggin anions. The novel silicaNH₂-POM materials having between 12–17% (w/w) of polyoxometalate were characterized by elemental analysis, solid-state ²⁹Si, ¹³C and ³¹P n.m.r., diffuse reflectance spectroscopy, FTIR spectroscopy, thermal analyses, and BET surface area measurements. The elemental analyses and spectroscopic results pointed to the integrity of POM structures after immobilization on the silica support while the latter one showed a slight decrease of BET surface area. Results of the visible diffuse reflectance spectroscopy for the Co-substituted Keggin anion revealed the coordination of cobalt centers in the cluster with the nitrogen atom of amine groups in modified silica at pH_i ≥ 5.5 or the electrostatic bonding between polyoxoanion and protonated C₃H₆NH ₃ ⁺ group at pH_i = 3.5. For the Co-substituted sandwich anion, external Co centres of the polyoxoanion have coordinated with the amine groups of modified silica under the experimental conditions used. ³¹P MAS n.m.r. showed a shifting of phosphorus atom resonances in H₅[PMo₁₀V₂O₄₀] and H₄[PMo₁₁VO₄₀] to a single resonance at ca. − 4.1 ppm (Δv _1/2 ~ 70 Hz) when these POM were immobilized on the functionalized silica under weak acidic conditions (pH 3), evidencing electrostatic interaction of POM clusters with the C₃H₆NH ₃ ⁺ groups.     

Synthesis, crystal structure and properties of a charge-transfer compound [(CH3)3CNH3]3[PMo12O40] · 2H2O

A charge-transfer compound [(CH₃)₃CNH₃]₃[PMo₁₂O₄₀] · 2H₂O was synthesized and characterized by IR, UV, ESR, diffusion reflectance electronic spectrum, cyclic voltammogram and X-ray crystallography. Oxygen atoms of the polyoxometalate anion, N atoms of organic substrates (CH₃)₃CNH₂ and O atoms of water molecules are involved in hydrogen bonding. The solid reflectance electronic spectra and IR data indicate the presence of interaction between the [PMo₁₂O₄₀]³⁻ and the organic substrates in the solid state. Photosensitivity to ultraviolet light was assessed for the compound, showing that charge-transfer resulted from oxidation of the organic substrates and the reduction of the heteropolyanion.     

Molybdovanadophosphoric Acid Catalyzed Oxidation of Hydrocarbons by H2O2 to Oxygenates

Heteropoly acids of the general formula H_3+x[PMo_12-xV_xO₄₀] (where x = 1,2,3) catalyzed the oxidation of aromatic hydrocarbons at 65°C with H₂O₂ to give oxygenated products. Among the catalysts, H₄[PMo₁₁VO₄₀] was found to be a more active catalyst and its activities have been reported in the oxidation of cyclohexane, methyl cyclohexane, naphthalene, 1-methyl naphthalene and biphenyl.     

Cobalt salts of decamolybdodicobaltic acid as precursors of the highly reactive type II CoMoS phase in hydrorefining catalysts

Catalysts have been synthesized using the Anderson polyoxometalates (POMs) (NH₄)₄[Ni(OH)₆Mo₆O₁₈] (NiMo₆POM), (NH₄)₆[Co₂Mo₁₀O₃₈H₄] · 7H₂O (Co₂Mo₁₀POM), and H₆[Co₂Mo₁₀O₃₈H₄] (Co₂Mo₁₀HPA) as the precursors and hydrogen peroxide as the solvent. The catalysts have been characterized by low-temperature nitrogen adsorption, XPS, and HRTEM. Their catalytic properties have been tested in thiophene hydrodesulfurization and in the hydrodesulfurization and hydrogenation of components of diesel oil. The active phase of the catalysts synthesized using the POMs is the type II CoMoS phase in which the mean plate length is 3.6–3.9 nm and the mean number of MoS₂ plate per plate packet is 1.8–2.0. Use of hydrogen peroxide provides an efficient means to reduce the proportion of Co²⁺ promoter atoms surrounded by oxygen in the case of an impregnating solution containing both an ammonium salt of a heteropoly acid and a Co²⁺ salt. In the catalysts synthesized using cobalt salts of Co₂Mo₁₀HPA, the support surface contains the multilayer type II CoMoS phase and cobalt sulfides. These catalyst show high catalytic properties in thiophene hydrogenolysis and diesel oil hydrorefining. Models are suggested for the catalysts synthesized using Anderson POMs.     

Interaction of platinum and molybdophosphoric heteropoly acid under conditions of catalyst preparation for benzene oxidation to phenol with an O2-H2 gas mixture

The transformations of platinum and a heteropoly acid (HPA) in binary systems prepared from H₂PtCl₆ or H₂PtCl₄ and H₃PMo₁₂O₄₀ were studied using IR and UV-VIS spectroscopy, elemental analysis, XPS, EXAFS, TPR, and HREM. The calcination of platinum chloride with the HPA to 450°C resulted in the formation of a platinum salt of the HPA along with decomposition products (mixture I). The reduction of calcined samples containing Pt: HPA = 1: 1 with hydrogen at 300°C (mixture II) followed by exposure to air resulted in the regeneration of the HPA structure. The resulting solid samples of Pt _1?n ⁰ Pt _n ^II Cl_mO_xH_y) (H_3+p PMo _12?p ^VI Mo _p ^V O₄₀) (III) contained platinum and molybdenum in both oxidized and reduced states. The following association species were isolated from mixtures I and II by dissolving in water: [Pt _n ^II PMo₁₂O₄₀] (I _s) (n = 0.3?0.8) and [Pt _n ⁰ PMo ₁₂ ^red O₄₀] (II _s) (n ≈ 1). Under exposure to air, the solutions of I _s were stable (pH ～2), whereas Pt^met was released from II _s. After the drying of I _s, the solid association species (Pt _n ^II Cl_mO_xH_y). (H₃PMo₁₂O₄₀), where n = 0.3?0.8, m = 0.2?1, and x = 3?0, (I _solid) were obtained. The I _solid/SiO₂ supported samples were prepared by impregnating SiO₂ with a solution of I _s and drying at 100°C. Platinum metal particles of size ～20 Å and a mixed-valence association species of platinum with the HPA were observed after the reduction of I _solid/SiO₂ with hydrogen at 100–250°C. These samples were active in the gas-phase oxidation of benzene to phenol at 180°C with the use of an O₂-H₂-N₂ mixture.     

Keggin类杂多化合物催化环氧化环戊烯的谱学研究

报道了一系列Keggin 类杂多化合物与H₂O₂ (30%)催化氧化环戊烯. 其中两缺位的 [γ-SiW₁₀(H₂O)₂O₃₄](Bu₄N)₄ 的催化活性最好, 环戊烯转化率为90%, 环戊烯环氧化物的选择性为98%. 反应前后的UV-vis, FT-IR分析表明, 反应后催化剂的结构保持, 没有发生降解. 在以磷为中心原子的磷系Keggin 杂多酸复合溴代十六烷基吡啶中, 钼钨混合型的催化活性优于钨磷酸(H₃PW₁₂O₄₀•mH₂O)和钼磷酸(H₃PMo₁₂O₄₀•mH₂O)的. 而在十一种钼钨混合型的含磷杂多化合物H₃PMo_12－nW_nO₄₀•mH₂O中, 当n＝6时的H₃PMo₆W₆O₄₀•mH₂O显示出了最好的活性. 我们采用UV-vis, FT-IR and ³¹P NMR 等谱学方法表征了新鲜的催化剂和处于反应状态下的催化剂. 发现在反应条件H₂O₂ (30%)的量是催化剂的50倍时, H₃PMo₆W₆O₄₀•mH₂O全部降解成数种含磷的物种, 这些含磷物种可能包含反应中最具催化活性的物种. 而在此条件时, 发现H₃PW₁₂O₄₀•mH₂O降解得很少, 只有一种磷钨氧物种生成, 但不是Venturello-Ishii催化体系中的活性物种{PO₄[WO(O₂)₂]₄}^3－.     

Spectral characteristics and redox behavior of the polynuclear managanese(III,IV) complex [Mn12O12(CH3COO)16(H2O)4] in liquid-phase oxidation of benzene

We have shown that benzene is oxidized to phenol by the polynuclear manganese complex [Mn₁₂O₁₂(CH₃COO)₁₆(H₂O)₄] in acetonitrile solution at room temperature and atmospheric pressure, with better than 80% selectivity. We have established that introduction of oxygen from the air into the reaction mixture as the reoxidant does not make it a catalytic process. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated fromTeoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 2, pp. 99–102, March–April, 1999.