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Showing papers on "Polyoxometalate published in 2001"


Journal ArticleDOI
TL;DR: In this paper, a series of polyoxometalate/H2O2 systems were evaluated for dibenzothiophene oxidation using toluene solutions of the model compounds.
Abstract: Dibenzothiophene, 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene are typical thiophenic sulfur compounds that exist in diesel fuels Using toluene solutions of the model compounds, experiments were carried out to compare the reactivity of the different dibenzothiophenes in oxidation reactions, a key step for oxidative desulfurizations A series of polyoxometalate/H2O2 systems were evaluated for dibenzothiophene oxidation The H2O2 solutions of phosphotungstic acid and its salt were very active catalyst systems for the model compound oxidation, while their molybdenum counterpart systems were much less active The H2O2 solutions of silicotungstic and silicomolybdic compounds were the least active catalyst systems for the reaction Oxidation reactivities decreased in the order of dibenzothiophene>4-methyldibenzothiophene>4,6-dimethyldibenzothiophene, the same reactivity trend that exists in HDS However, the oxidation of the dibenzothiophenes was achieved under mild reaction conditions and it was easy to increase reaction temperature or reaction time to achieve high oxidation conversions, even for the least reactive 4,6-dimethyldibenzothiophene Apparent activation energies of dibenzothiophene, 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene oxidation were 538, 560, and 587 kJ/mol, respectively These activation energies indicated a decrease in reactivity of dibenzothiophenes as methyl substitutes increased at the 4 and 6 positions on dibenzothiophene rings Interestingly, in a formic acid/H2O2 system, the oxidation reactivity of the dibenzothiophenes showed the reverse trend, suggesting that steric hindrance might play a role when bulky polyoxoperoxo species, which likely form in a hydrogen peroxide solution, act as catalysts

390 citations


Journal ArticleDOI
08 Nov 2001-Nature
TL;DR: This system facilitates a two-step O2-based process for the selective delignification of wood (lignocellulose) fibres by directly monitoring the central Al atom, and shows that equilibration reactions typical of polyoxometalate anions keep the pH of the system near 7 during both process steps.
Abstract: Although many enzymes can readily and selectively use oxygen in water-the most familiar and attractive of all oxidants and solvents, respectively-the design of synthetic catalysts for selective water-based oxidation processes utilizing molecular oxygen remains a daunting task. Particularly problematic is the fact that oxidation of substrates by O2 involves radical chemistry, which is intrinsically non-selective and difficult to control. In addition, metallo-organic catalysts are inherently susceptible to degradation by oxygen-based radicals, while their transition-metal-ion active sites often react with water to give insoluble, and thus inactive, oxides or hydroxides. Furthermore, pH control is often required to avoid acid or base degradation of organic substrates or products. Unlike metallo-organic catalysts, polyoxometalate anions are oxidatively stable and are reversible oxidants for use with O2 (refs 8,9,10). Here we show how thermodynamically controlled self-assembly of an equilibrated ensemble of polyoxometalates, with the heteropolytungstate anion [AIVVW11O40]6- as its main component, imparts both stability in water and internal pH-management. Designed to operate at near-neutral pH, this system facilitates a two-step O2-based process for the selective delignification of wood (lignocellulose) fibres. By directly monitoring the central Al atom, we show that equilibration reactions typical of polyoxometalate anions keep the pH of the system near 7 during both process steps.

170 citations


Journal ArticleDOI
TL;DR: An analysis of deltaG for electron transfer from the conduction band of TiO2 to POMs in this study shows that the electron transfer takes place even when it is endothermic.
Abstract: The present study reports the investigation of polyoxometalate catalyzed electron transfer from the conduction band of photoexcited TiO2 to molecular oxygen. The oxidation of 1,2-dichlorobenzene (DCB) was used as an index reaction for evaluating the photocatalyst systems TiO2−PW12O403-, TiO2−SiW12O40,4- and TiO2−W10O324- in oxygenated aqueous solution. Addition of these polyoxometalate (POM) anions to TiO2 suspensions resulted in significant rate enhancement for DCB oxidation. Photodegradation kinetics exhibited [POM] dependence, experiencing different maximum (k = 0.0318 min-1, 0.0108 min-1, and 0.0066 min-1) for each POM at different [POM] (0.1 mM PW12O403-, 0.07 mM SiW12O40,4- and 1 mM W10O32,4- respectively). The probability that the difference in the adsorption affinity of POMs on TiO2 surface could account for the observed ranking of photodegradation rates was ruled out by adsorption isotherm experiments that revealed similar binding constants for each POM (467 M-1, 459 M-1, and 417 M-1 for PW12O403...

169 citations


Journal ArticleDOI
TL;DR: Both the amine surface groups and the cobalt centers in the clusters were found to be necessary to prevent cluster loss during washing or reaction processes and catalytic activities of the supported TMSP clusters were tested by the epoxidation of cyclo hexene to cyclohexene oxide in the presence of isobutyraldehyde.
Abstract: Transition-metal-substituted polyoxometalates (TMSP) of the type [MII(H2O)PW11O39]5- (M = Co, Zn) and [SiW9O37(CoII(H2O))3]10- have been chemically anchored to modified macroporous (400 nm pores), mesoporous (2.8 nm pores), and amorphous silica surfaces. The materials were characterized by solid-state 31P MAS NMR, UV-vis, FT-IR spectroscopy, and N2 adsorption experiments to verify cluster attachment and the structure of the TMSP on the support. On the basis of the spectroscopic evidence, clusters were attached datively to the surface, and the integrity of the [CoPW11] cluster was maintained for nonaqueous impregnation with TBA5[CoPW11]; partial degradation of the cluster occurred when it was impregnated from aqueous solution using the K5[CoPW11] salt. Both the amine surface groups and the cobalt centers in the clusters were found to be necessary to prevent cluster loss during washing or reaction processes. The catalytic activities of the supported TMSP clusters were tested by the epoxidation of cyclohexene to cyclohexene oxide in the presence of isobutyraldehyde. The percent conversion of the substrate and the amount of product formed per unit time were similar for [CoPW11] clusters on each of the three silica supports, but slightly lower than for purely homogeneous reactions. [SiW9Co3] clusters with three available cobalt centers exhibited higher catalytic activity with nearly identical performance on a silica support or in homogeneous solution.

164 citations


Journal ArticleDOI
TL;DR: The mechanism of aerobic oxidation of aromatic and alkyl aromatic compounds using anthracene and xanthene as a model compound was investigated using a phosphovanadomolybdate polyoxometalate, H(5)PV(2)Mo(10)O(40), as catalyst under mild, liquid- phase conditions to prove that a Mars-van Krevelen mechanism is possible also in liquid-phase, homogeneous oxidation reactions.
Abstract: The mechanism of aerobic oxidation of aromatic and alkyl aromatic compounds using anthracene and xanthene, respectively, as a model compound was investigated using a phosphovanadomolybdate polyoxometalate, H5PV2Mo10O40, as catalyst under mild, liquid-phase conditions. The polyoxometalate is a soluble analogue of insoluble mixed-metal oxides often used for high-temperature gas-phase heterogeneous oxidation which proceed by a Mars−van Krevelen mechanism. The general purpose of the present investigation was to prove that a Mars−van Krevelen mechanism is possible also in liquid-phase, homogeneous oxidation reactions. First, the oxygen transfer from H5PV2Mo10O40 to the hydrocarbons was studied using various techniques to show that commonly observed liquid-phase oxidation mechanisms, autoxidation, and oxidative nucleophilic substitution were not occurring in this case. Techniques used included (a) use of 18O-labeled molecular oxygen, polyoxometalate, and water; (b) carrying out reactions under anaerobic conditi...

159 citations


Journal ArticleDOI
TL;DR: In this paper, 3D ordered macroporous (3DOM) materials functionalized with highly dispersed polyoxometalate clusters have been prepared via direct synthesis, and the products were characterized by IR, solid-state 29Si and 13C NMR, scanning electron microscopy (SEM) and X-ray energy-dispersive spectroscopy, and chemical analysis.
Abstract: Three-dimensionally ordered macroporous (3DOM) silica materials functionalized with highly dispersed polyoxometalate clusters have been prepared via direct synthesis. Lacunary γ-decatungstosilicate clusters were incorporated into the wall structures of macroporous silica by reaction of the clusters in acidic solution with tetraethoxysilane, with or without addition of the polyfunctional linking group 1,2-bis(triethoxysilyl)ethane, followed by condensation around polystyrene colloidal crystals. Removal of the polystyrene template by extraction with a tetrahydrofuran/acetone solution produced the porous hybrid materials. The products were characterized by IR, solid-state 29Si and 13C NMR, scanning electron microscopy (SEM), transmission electron microscopy, X-ray energy-dispersive spectroscopy, and chemical analysis. The polyoxometalate clusters remained intact in the hybrid structures and were nearly molecularly dispersed throughout the walls of the 3DOM materials. High incorporation levels of cluster were...

148 citations


Journal ArticleDOI
TL;DR: The effect of cation size on the rate and energy of electron transfer to [(M(+))(acceptor)] ion pairs is addressed by assigning key physicochemical properties (reactivity, relative energy, structure, and size) to an isoelectronic series of well-defined M(+)-acceptor pairs.
Abstract: The effect of cation size on the rate and energy of electron transfer to [(M+)(acceptor)] ion pairs is addressed by assigning key physicochemical properties (reactivity, relative energy, structure, and size) to an isoelectronic series of well-defined M+−acceptor pairs, M+ = Li+, Na+, K+. A 1e- acceptor anion, α-SiVVW11O405- (1, a polyoxometalate of the Keggin structural class), was used in the 2e- oxidation of an organic electron donor, 3,3‘,5,5‘-tetra-tert-butylbiphenyl-4,4‘-diol (BPH2), to 3,3‘,5,5‘-tetra-tert-butyldiphenoquinone (DPQ) in acetate-buffered 2:3 (v/v) H2O/t-BuOH at 60 °C (2 equiv of 1 are reduced by 1e- each to 1red, α-SiVIVW11O406-). Before an attempt was made to address the role of cation size, the mechanism and conditions necessary for kinetically well behaved electron transfer from BPH2 to 1 were rigorously established by using GC−MS, 1H, 7Li, and 51V NMR, and UV−vis spectroscopy. At constant [Li+] and [H+], the reaction rate is first order in [BPH2] and in [1] and zeroth order in [1re...

141 citations



Journal ArticleDOI
TL;DR: The increased solubility in organic media opens the door to new polyoxometalate-polymer hybrid materials.
Abstract: Increased hydrophobicity of well-defined polyoxometalate clusters is possible through complexation with cationic surfactants in a one-pot reaction. The clusters, of toroid and spherical shape and colloidal dimensions, then organized into ordered, supramolecular assemblies, as shown schematically, are similar to classical liquid crystals. The increased solubility in organic media opens the door to new polyoxometalate-polymer hybrid materials.

113 citations


Journal ArticleDOI
TL;DR: The Mo≡N bond is conjugated with the organic segment in the novel molecular organic-inorganic hybrid materials obtained by Pd-catalyzed coupling of an iodo-functionalized hexamolybdate anion and an alkyne.
Abstract: The Mo≡N bond is conjugated with the organic segment in the novel molecular organic-inorganic hybrid materials that have been obtained by Pd-catalyzed coupling of an iodo-functionalized hexamolybdate anion and an alkyne (see scheme; Ar=4-methylphenyl,3-5-di(tert-butyl)phenyl). The interaction between the polyoxometalate cluster and the organic conjugated system is particularly apparent from the strong red-shifted absorption in the UV/Vis spectrum.

108 citations



Journal ArticleDOI
TL;DR: The structure of the sodium salt of 2 (Na2), determined by single-crystal X-ray diffraction analysis (a = 13.4413 A, b = 21.2590 A, c = 25.5207 A, α = 80.475 A, β = 85.555 A, γ = 89.563 A, triclinic, P1, R1 = 5.42%, based on 43097 independent reflections), consists of a defect Fe2Cu central unit sandwiched between two different trivacant Wells−Dawson
Abstract: Reaction of the diferric sandwich-type polyoxometalate (NaOH2)2FeIII2(P2W15O56)216- (1) with excess aqueous Cu(II) or Co(II) yields a new type of d-electron-metal substituted polyoxometalate, [TMIIFeIII2(P2W15O56) (P2TMII2W13O52)]16-, TM = Cu (2), Co (3), respectively. The structure of the sodium salt of 2 (Na2), determined by single-crystal X-ray diffraction analysis (a = 13.4413(9) A, b = 21.2590(15) A, c = 25.5207(18) A, α = 80.475(2)°, β = 85.555(2)°, γ = 89.563(2)°, triclinic, P1, R1 = 5.42%, based on 43097 independent reflections), consists of a defect Fe2Cu central unit sandwiched between two different trivacant Wells−Dawson-type units, P2W15 and P2Cu2W13, where the latter unit has two octahedral Cu(II) ions substituted for two adjacent belt W(VI) atoms. The CuO5OH2 octahedron in the central unit shows pronounced Jahn−Teller distortion. A low-resolution X-ray structure of Na3 is included in the Supporting Information. UV−visible, infrared, 31P NMR, cyclic voltammetric, and elemental analysis data ...

Journal ArticleDOI
TL;DR: The synthesis and characterization of (Bu4N)4[S2W18O62].1.0.27H2O are reported, it is suggested that this process actually comprises two one-electron transfer processes, occurring at different potentials, with associated proton-transfer reactions.
Abstract: The synthesis and characterization of (Bu4N)4[S2W18O62]·1.23MeCN·0.27H2O are reported. It crystallizes in the monoclinic space group C2/c with a = 22.389(6) A, b = 22.104(3) A, c = 25.505(5) A, β = 95.690(15)°, V = 12560(5) A3, and Z = 4. The anion exists as the γ* isomer, the second example of this isomer type to be characterized structurally. The equivalent molybdenum salt occurs as the α isomer. γ*-[S2W18O62]4- in MeCN solution displayed four electrochemically reversible one-electron redox processes at E1/2 values of −0.24, −0.62, −1.18, and −1.57 V versus the Fc+/Fc couple. Upon addition of acid in MeCN/H2O (95/5 v/v), the two most cathodic processes converted to an overall two-electron process at −0.71 V. The total data suggested that this process actually comprises two one-electron transfer processes, occurring at different potentials, with associated proton-transfer reactions. The interpretation is supported by simulation of the effect of acid titration upon the cyclic voltammetry. While multiple p...

Journal ArticleDOI
TL;DR: New organic derivatives of "inverse-Keggin" polyoxometalate (POM) clusters, [Mo(12)O(46)(AsR)(4)](4-) (R = C(6)H(4)-4-COOH), have been synthesized and hydrogen-bonding ability of the solvent affects the connectivity of the POM clusters through interactions with the organic group and the inorganic core.
Abstract: New organic derivatives of “inverse-Keggin” polyoxometalate (POM) clusters, [Mo12O46(AsR)4]4- (R = C6H4-4-COOH, C6H3-4-OH-3-NO2, C6H4-4-OH), have been synthesized. Structures of the corresponding sodium or iron salts were elucidated by single-crystal X-ray diffraction and shown to be 3D structures connected through hydrogen bonds and/or O−Na−O linkages. Parameters which influence the final solid-state architecture, such as the crystallizing solvent, organic moiety, and counterions, have been examined. The hydrogen-bonding ability of the solvent affects the connectivity of the POM clusters through interactions with the organic group and the inorganic core. The organic groups influence the structure through hydrogen bonds to other organic groups, to neighboring clusters, and/or to solvent molecules. Hydrogen bonding between the organic groups and the solvent appears to inhibit some possible connectivity patterns, such as the hydrogen-bonded dimerization of carboxylic acid groups. Na+ ions were found directl...

Journal ArticleDOI
TL;DR: In this paper, the same compound was doped with Sb3+ ions, in an amount corresponding to 0.23 Sb atom per Keggin unit, which significantly modified the reactivity of the POM-based catalyst in the title reaction with respect to the undoped catalyst.

Journal ArticleDOI
Yihang Guo1, Danfeng Li1, Changwen Hu1, Yong-Hui Wang1, Enbo Wang1 
TL;DR: In this article, the photocatalytic activities of the intercalates were studied by the degradation reaction of an aqueous organochlorine pesticide, hexachlorocyclohexane (HCH).


Journal ArticleDOI
TL;DR: In this paper, the authors reviewed the research progress in the layered double hydroxides intercalated with metal coordinate ions or oxometalates in the last ten years and forecasted the prospects of the field.
Abstract: Research progresses in the layered double hydroxides [M (1- )/2+ M 3+ (OH)2] x+ A n/n− ·mH2O intercalated with metal coordinate ions or oxometalates in the last ten years are reviewed. These layered double hydroxides are mainly intercalated with polyoxometalate (POM) ions, a LiAl-LDH photochemical assembly containing TiO2 and CH3(CH2)12COO− anions, together with Zn(TPPC) (porphyrin derivate) and macrocyclic ligand-containing porphyrin derivate anions. Emphasis is put on the synthesis methods for intercalation of the anions into the interlayer regions, the characterization techniques and structures for the layered compounds and the newest research progress in the fields such as catalysis. The review also forecasts the prospects of the field.

Journal ArticleDOI
Li-Juan Zhang1, Yun-Shan Zhou1, Zhi Yu1, Guo-Su Fang1, Xiao-Zeng You1 
TL;DR: In this article, two new poloxometalate-based organic/inorganic hybrid compounds, 4(2,2′-DPA)·pseudo-α-H 4 SiMo 12 O 40 4 ·4DMF·2H 2 O (1 ) and 4( 2, 2′)-DPA ·pseudo-, have been synthesized and characterized.

Journal ArticleDOI
TL;DR: In this article, the first example of a urea-heteropoly acid species was synthesized and characterized by IR, 13C NMR and X-ray diffraction, which was called [H3PMo12O40][CO(NH2)2]3·5H2O.

DissertationDOI
20 Mar 2001
TL;DR: In this article, the influence of V and/or W promoters on the structures of mixed MoVW oxides and their catalytic properties are investigated by XRD, TEM, SEM, in situ Raman spectroscopy and TPRS.
Abstract: The preparation (aqueous chemistry and the thermal activation of polyoxometalates) and the structures of promoted molybdenum oxide catalysts are investigated under the condition of selective propene oxidation by in situ Raman spectroscopy. The influences of V and/or Wpromoters on the structures of mixed MoVW oxides and their catalytic properties are investigated by XRD, TEM, SEM, in situ Raman spectroscopy and TPRS. V addition causes high propene conversions and the formation of an oxide with Mo5O14 structure is observed. Minor amounts of W in the molybdenum oxides matrix inhibit structural reorganisation processes which is explained by preferred octahedral coordination of the redox stable W. The combined XRD, TEM and Raman spectroscopic identification of the oxide of Mo5O14 structure points to its relevant role for the selective propene oxidation. A resonance Raman effect is proven to be operative in oxygen defective molybdenum oxides. For an excitation wavelength of 632 nm (1.96 eV), the observed Raman cross section varies as a function of the degree of reduction of five different MoO3 x samples. A model of the electronic transitions in MoO3 x based on crystal field theory explains the electronic transitions observed by DR-UV/VIS spectroscopy. The observed resonant Raman scattering is coupled to the IVCT transition at about 2 eV arising from oxygen vacancies present in the materials. Due to the local nature of the absorption process, the developed model is valid for intermediate oxides too. Resonant Raman scattering was proven for Mo4O11 and MoO2 too. Hence, the experimentally observed Raman intensity bears information about the degree of reduction of the molybdenum oxide. In situ Raman spectroscopy of MoO3 x catalysts during propene partial oxidation indicates that the propene conversions and the selectivities are a function of the degree of reduction of the catalyst. It is attempted to control the spatial elemental distribution within the polyoxometalate catalyst precursor by the formation of molecularly defined species in solution by addition of acetate, oxalate or tartrate. Due to the low stability of the acetate complexes, the addition of acetate only leads to minor amounts of monomeric species beside mixed and pure polyoxometalates. The formation of stable monomeric oxometalate oxalate and tartrate complexes is observed, which are expected to lead to the formation of a catalyst precursor with a homogeneous elemental distribution.

Patent
27 Jul 2001
TL;DR: An electrolyte comprising a cationic species disposed in a polyoxometalate network is defined in this article, where a bridge ligand is used to connect the two bridges.
Abstract: An electrolyte comprising a cationic species disposed in a polyoxometalate network. A composition comprising cationic species and polyoxometalate anionic species, wherein the polyoxometalate anionic species are coupled through a network of bridge ligands. An apparatus comprising a first electrode and a second electrode; a current collector coupled to one of the first and the second electrode; and an electrolyte disposed between the first electrode and the second electrode, the electrolyte comprising a cationic species disposed in a polyoxometalate network.

Journal ArticleDOI
TL;DR: In this paper, a charge transfer complex between the heteropolymolybdate anion, GeMo12O4−40 and the organic cation, protonated 7-methyl-quinoline has been synthesized and characterized.
Abstract: A charge-transfer complex, [C10H10N]4GeMo12O40 · 6DMF, between the heteropolymolybdate anion, GeMo12O4− 40 and the organic cation, protonated 7-methyl-quinoline has been synthesized and characterized. Light yellow crystals of the title compound as a DMF solvate of formula [C10H10N]4GeMo12O40 · 6DMF were crystallized from DMF by diffusing acetone vapor into the solution. Spectroscopic data support the presence of a significant electronic interaction between the electron-rich aromatic organic cations and the inorganic anion in the solid state. The complex is strongly photosensitive under irradiation with sunlight, resulting in charge-transfer by oxidation of the 7-methyl-quinoline and reduction of the polyoxometalate. The variable temperature ESR spectra indicate thermal electron delocalization occurs among the Mo atoms in the title compound.

Journal ArticleDOI
TL;DR: The simple salt CuCl2·2H2O, and the new Cu-substituted polyoxometalate (POM), Na7[CuCoW11O39]·5H 2O 1 are highly efficient catalysts for the oxidation of ascorbic acid by peroxynitrite as mentioned in this paper.

Journal ArticleDOI
TL;DR: The electron spin resonance (ESR) spectra of cluster polyoxometalate systems are investigated in this paper, where the initial samples are colored under exposure to ultraviolet (UV) irradiation (photochromic effect) and thermal annealing.
Abstract: The electron-spin resonance (ESR) spectra of cluster polyoxometalate systems—a finely dispersed powder of the (NH4)6[Mo7O24]-citrie acid complex, molybdic acid, and molybdenum(VI) oxide—are investigated. The initial samples are colored under exposure to ultraviolet (UV) irradiation (photochromic effect) and thermal annealing. The ESR signal (g ⊥ = 1.94, g ‖ = 1.92) which is observed for the (NH4)6[Mo7O24]-citric acid photocolored samples corresponds to an electron of the molybdenum atom. This is in agreement with the data derived from the electronic spectrum. In addition, the (NH4)6[Mo7O24]-citric acid colored system exhibits an ESR signal (g=2.02) which corresponds to a hole at the organic ligand. This confirms the previously advanced model of intramolecular electron transfer under UV irradiation. The thermally colored molybdic acid has a similar ESR spectrum (g=1.88, 1.92, 1.93, and 1.98). For the other samples, the ESR signal is not observed. It is demonstrated that an unpaired electron of molybdenum atoms is substantially delocalized over all metal atoms in the cluster.

Book ChapterDOI
26 Mar 2001
TL;DR: A new environmentally friendly technology for wood pulp delignification, based on the use of polyoxometalates (POMs) and oxygen, is being developed as mentioned in this paper.
Abstract: A new environmentally friendly technology for wood pulp delignification, based on the use of polyoxometalates (POMs) and oxygen, is being developed. Polyoxometalate solutions that selectively oxidize lignin under anaerobic conditions can be reoxidized by oxygen and also catalyze the aerobic mineralization ofthe lignin fragments to CO2 and H2O, making possible the closed-mill manufacture of paper. Model studies on the oxidation of various lignin-like soluble compounds with POMs suggest that single-electron oxidation of phenolic substructures occurs first, followed by the hydrolysis of cationicintermediates. Detailed physico-chemical studies of the solutions of the alkali-metal salts of POMs show a correlation between the reduction potentials of POMs and the rate of oxidation of a phenolic lignin model that is ascribed to ion pairing between alkali-metal cations and POM anions.

Journal ArticleDOI
TL;DR: Salts of the heteropolytungstates [PW11 M(H2O)O39]5-, M=Cu, Co, Mn, with the following complex cations were prepared: [Cu(LL)2(H 2O)]2+, [Cu[LL)3]2+, LL= 1,10-phenantroline (phen), 2,2′-bipyridine (...
Abstract: Salts of the heteropolytungstates [PW11 M(H2O)O39]5-, M=Cu, Co, Mn, with the following complex cations were prepared: [Cu(LL)2(H2O)]2+, [Cu(LL)3]2+, LL= 1,10-phenantroline (phen), 2,2′-bipyridine (...

Hu, Chang-wen, Li, Danfeng, Guo, Yi-hang, Wang, En-bo 
01 Jan 2001
TL;DR: In this article, a review of layered double hydroxides intercalated with metal coordinate ions or oxometalates in the last ten years is presented, focusing on the synthesis methods for intercalation of the anions into the interlayer regions, characterization techniques and structures for the layered compounds and the newest research progress in the fields such as catalysis.
Abstract: Research progresses in the layered double hydroxides [M2+(1-x)M3+x(OH)2]x+An-x/n.mH2O intercalatedwith metal coordinate ions or oxometalates in the last ten years are reviewed. These layered double hydroxides are mainly intercalated with polyoxometalate (POM) ions, a LiAl-LDH photochemical assembly containing TiO2 and CH3(CH2)12COO- anions, together with Zn(TPPC) (porphy-rin derivate) and macrocyclic ligand-containing porphyrin derivate anions. Emphasis is put on the synthesis methods for intercalation of the anions into the interlayer regions, the characterization techniques and structures for the layeredcompounds and the newest research progress in the fields such as catalysis. The review also forecasts the prospects of the field.

Book ChapterDOI
01 Jan 2001
TL;DR: The vibrational spectra of the polyoxometalate anion (the primary structure) and from the water of crystallisation and hydrated protons (the secondary structure) of heteropoly acids are reviewed in this article.
Abstract: The vibrational spectra of the heteropoly acids can be conveniently regarded as composed of contributions from the polyoxometalate anion (the primary structure) and from the water of crystallisation and hydrated protons (the secondary structure). Following a brief general survey of vibrational spectra of hydrogen-bonded systems, the spectra of water and hydrated protons in crystalline solids are reviewed. The vibrational spectra of the primary structure of heteropoly acids (the Keggin anion) are described and the observed spectra of the secondary structures of highly hydrated, hexahydrated and dehydrated heteropoly acids are discussed in relation to the spectra expected for protons in different environments.

Book ChapterDOI
01 Jan 2001
TL;DR: In this article, the potential of non-aqueous reductive aggregation for rational polyoxometalate assembly has been demonstrated by the synthesis of [PV2Mo12O42]3− from [PMo12O40] 3− and [VOCl3(dme).
Abstract: Heteronuclear hexametalates [XM′ M5O18]n−(M = Mo, W),including the first examples of Zr and Hf derivatives, have been prepared by hydrolytic aggregation in non-aqueous media, enabling the reactivity of alkoxide surface groups (X = OMe, Opri) to be investigated. Organoimido derivatives result from reactions between [Mo6O19]2−and organic isocyanates or aromatic amines at elevated temperatures. In studies of vanadate systems we have achieved the quantitative conversion of [H3V10O28]3− to [V13O34]3− under ambient conditions and the synthesis of a range of new vanadophosphonates. The potential of non-aqueous reductive aggregation for rational polyoxometalate assembly has been demonstrated by the synthesis of [PV2Mo12O42]3− from [PMo12O40]3− and [VOCl3(dme)]. In the first examples of controlled polyoxometalate halogenation, the hexabromo species [PW9O28Br6]3− has been obtained from [NaPW11O39]6− and [PW9O34]9− by treatment with C2O2Br2 or SOBr2. The structure of this anion features a fully brominated face which provides opportunities for further derivatisation.