Polymerization of Anions: The Hydrolysis of Sodium Tungstate and of Sodium Chromate<sup>1</sup>

Freedman, Meyer L.

doi:10.1021/ja01542a013

Cited by 27 publications

(8 citation statements)

References 5 publications

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“…Freedman studied the condensation of aqueous Na 2 CrO 4 and Na 2 WO 4 into polyoxoanions in the presence of other anions like sulfate or nitrate and obtained clear evidence for the formation of a sulfatochromate complex ion. [35] This complex was, however, too unstable to allow characteriza-tion. In the case of tungstate, the condensation reactions were also influenced by the presence of sulfate, [35] although its effect was less pronounced.…”

Section: Resultsmentioning

confidence: 99%

“…[35] This complex was, however, too unstable to allow characteriza-tion. In the case of tungstate, the condensation reactions were also influenced by the presence of sulfate, [35] although its effect was less pronounced. The existence of cis-dioxosulfatotungsten(VI) species was later demonstrated by Raman spectroscopy upon dissolution of WO 3 in K 2 S 2 O 7 / K 2 SO 4 melts.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Chromate‐Mediated One‐Step Quantitative Transformation of PW₁₂ into P₂W₂₀ Polyoxometalates

et al. 2012

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Polyoxometalates have been at the frontiers of science since the discovery of Keggin-type polyoxometalates (POMs) about a century ago. Today these polyoxometalates are still of major scientific interest, not only due to their wide range of applications [1][2][3][4][5][6][7][8][9][10][11][12] in analytical chemistry, in life sciences, as homo-and heterogeneous catalysts, as essential building blocks for the design of photoactive complexes, and hybrid organic/inorganic materials, but also from purely synthetic chemistry and structural points of view. [13,14] A review of patent applications [2] and commercial realizations reveals the popularity of Keggin-type POMs, H 8-x XM 12 O 40 3-[with X = Si 4+ or P 5+ , x = 4 (Si) or 5 (P), M = Mo 6+ or W 6+ ] and their salts due to their wellestablished fundamental chemistry, [15] easy synthesis and commercial availability. Polyoxometalate science and technology gains further momentum each time a new type of POM becomes easily accessible. In this work it has been demonstrated that the presence of potassium chromate enables the quantitative conversion of H 3 PW 12 O 40 crystals into K 13 [KP 2 W 20 O 72 ]·24H 2 O in alkaline aqueous medium. This new convenient room-temperature synthesis procedure makes K 13 [KP 2 W 20 O 72 ]·24H 2 O crystals readily accessible [a

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Chromate‐Mediated One‐Step Quantitative Transformation of PW₁₂ into P₂W₂₀ Polyoxometalates

et al. 2012

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“…In fact, the TiO 2 surface is known to be readily covered with hydroxyl groups in a water-rich environment, as TiO 2 has both Lewis acidic and basic centers which allow its surface to be easily hydroxylated by dissociative and molecular water adsorption . The pH of 9.54 for the Na 2 WO 4 ·2H 2 O solution falls within the pH range 9.15–10.5 reported in the literature for molar solutions prepared from Na 2 WO 4 ·2H 2 O and purified water . The alkalinity of the WO 4 2– solution may be due to the presence of excess alkali (i.e., NaOH) in commercial Na 2 WO 4 ·2H 2 O or to the hydrolysis and polymerization of Na 2 WO 4 …”

Section: Results and Discussionmentioning

confidence: 59%

Preparation of Activated Carbon-SnO₂, TiO₂, and WO₃ Catalysts. Study by FT-IR Spectroscopy

Barroso-Bogeat

Alexandre-Franco

Fernández-González

et al. 2016

Ind. Eng. Chem. Res.

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The chemical changes produced in the surface of activated carbon as a result of the process of preparation of activated carbon−metal oxide catalysts from SnCl 2 , TiO 2 , and Na 2 WO 4 in water at pH 1.37 for SnCl 2 , 5.84 for TiO 2 , and 9.54 for Na 2 WO 4 are studied. The samples were first prepared by the wet impregnation method in two successive steps of soaking at 80 °C for 5 h and oven-drying at 120 °C for 24 h. Then, they were analyzed by elemental analysis, FT-IR spectroscopy, and measurement of pH of the point of zero charge (pH pzc ). The process yield was 149 wt % with SnCl 2 , 103 wt % with TiO 2 , and 106 wt % with Na 2 WO 4 . The impregnation of the carbon with the catalyst precursors in water entails the oxidation of chromene and pyrone type structures with formation of carboxylic acid groups. pH pzc is 10.50, activated carbon; <1.60, SnCl 2 ; 9.35, TiO 2 ; and 7.90, Na 2 WO 4 . The changes originating in the surface chemistry of AC with influence on the acid−base character are stronger by the order SnCl 2 ≫ Na 2 WO 4 > TiO 2 .

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“…The ion can grow rapidly at either end (actually: at several sites since the chain may branch [35, 36a]) in a variety of linear orientations, also with the addition of dimetalate or higher units [35, 36a, 58, 60]. A "limiting trimetalate ion" was claimed to be more stable than the linear polymers [58,60]. However, it was then shown that the ring-like ("closed") polymers built according to this principle should be the most stable ones and that, for statistical reasons, the smallest rings should be the most favorable, namely tetrameric "rings" existing in two isomeric forms, planar (see Fig.…”

Section: The Mechanistic Basis Of the Modelmentioning

confidence: 99%

A bond model for polyoxometalate ions composed of MO6 octahedra (MOk polyhedra with k>4)

Tytko¹

Structure and Bonding

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The literature relating to the bonding in polyoxometalate ions is reviewed. The author's opinions are presented and expanded to give a bond model for polyoxometalate ions of the early transition elements (groups V and VI) composed of MO 6 octahedra (MOk polyhedra with k > 4). This bond model concerns in particular the bond valence (bond lengths) and charge distribution in the polyoxometalate ions and the factors modifying them. It is based on the following commonly used concepts and principles as applied to polyoxometalate ions: -Lewis's octet rule, extended to the decet and dodecet rule for M v and MVI; -prc-drc M----O double bond and the coordinate bond (dative bond); -the resonance concept; -the resonance bond number (or the bond valence concept and the valence sum rule); -polydentate ligands and the chelate effect; -the larger space requirements of unshared electron pairs (cf. the VSEPR model); -the model of multicenter prc-drc multiple bonds for certain #-oxo bridges between metal atoms; -Bronsted's acid/base concept and acid/base equilibria; -Pauling's rules for the acid/base strength of (monomeric) oxoacids/oxoanions; -the law of mass action (Le Chatelier's principle), and others. The result is a set of resonance structures for polyoxometalate species in which three types of resonance can be distinguished. These, in turn, explain: -the cohesion of the strongly distorted tetrahedral M04 building units in the structures by formation of MO 6 octahedra and hence the enhanced stability of the polyoxometalate ions; -the distribution of the formal ionic charge over (nearly) all types of oxygen atoms, but preferably the terminal ones; -the occurrence of positively charged oxygen atoms, caused by charge separation processes; -the enhanced basicity of polyoxometalate ions; and further features. A "meshing effect" defines the increase of the bond valence in inner (bridging) M-O bonds and hence the stabilization of the structures due to extension of the coordination spheres of MO4 tetrahedra. Thus, the bond lengths of the different structure types are governed by a maximization of the bond valence of the inner, bridging (or minimization of the bond valence of the outer, terminal, in contrast to frequent statements in the literature) M-O bonds. The limits of the maximization of the inner bond valences of the polyoxometalate ions are determined -by minimum stoichiometric requirements for corresponding resonance formulae (inevitability of charge on bridging oxygen atoms); -by the necessity to fulfill simultaneously the geometrical relationships of the M-O bond lengths (as defined by their interdependence in the M-O frameworks) and the valence

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Polymerization of Anions: The Hydrolysis of Sodium Tungstate and of Sodium Chromate¹

Cited by 27 publications

References 5 publications

Chromate‐Mediated One‐Step Quantitative Transformation of PW₁₂ into P₂W₂₀ Polyoxometalates

Chromate‐Mediated One‐Step Quantitative Transformation of PW₁₂ into P₂W₂₀ Polyoxometalates

Preparation of Activated Carbon-SnO₂, TiO₂, and WO₃ Catalysts. Study by FT-IR Spectroscopy

A bond model for polyoxometalate ions composed of MO6 octahedra (MOk polyhedra with k>4)

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Polymerization of Anions: The Hydrolysis of Sodium Tungstate and of Sodium Chromate1

Cited by 27 publications

References 5 publications

Chromate‐Mediated One‐Step Quantitative Transformation of PW12 into P2W20 Polyoxometalates

Chromate‐Mediated One‐Step Quantitative Transformation of PW12 into P2W20 Polyoxometalates

Preparation of Activated Carbon-SnO2, TiO2, and WO3 Catalysts. Study by FT-IR Spectroscopy

A bond model for polyoxometalate ions composed of MO6 octahedra (MOk polyhedra with k>4)

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Polymerization of Anions: The Hydrolysis of Sodium Tungstate and of Sodium Chromate¹

Chromate‐Mediated One‐Step Quantitative Transformation of PW₁₂ into P₂W₂₀ Polyoxometalates

Chromate‐Mediated One‐Step Quantitative Transformation of PW₁₂ into P₂W₂₀ Polyoxometalates

Preparation of Activated Carbon-SnO₂, TiO₂, and WO₃ Catalysts. Study by FT-IR Spectroscopy