Dodecatungstophosphoric acid hexahydrate, (H5O2+)3(PW12O403−). The true structure of Keggin's `pentahydrate' from single-crystal X-ray and neutron diffraction data

Brown, G.; Noe-Spirlet, M.-R.; Busing, W. R.; Levy, H. A.

doi:10.1107/s0567740877005330

Cited by 501 publications

(303 citation statements)

References 6 publications

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“…In contrast, H 3 PW, treated at 300° for 4 h, showed a crystalline pattern compatible with the cubic structure (space group Pn3m) with cell parameter a = 12.16 Å, which is related to a hexahydrate crystalline phase. 29 The most intense reflections for H 3 PW are 2θ at 10.4° (110), 25.4° (222) and 34.5° (332). The crystallites of hydrated H 3 PW showed domain sizes greater than 50 nm by calculation using Scherrer's equation of that reflections.…”

Section: Resultsmentioning

confidence: 99%

Acidity and Characterization of 12-Tungstophosphoric Acid Supported on Silica-Alumina

Mattos¹,

Carvalho²,

Freitas³

et al. 2016

Journal of the Brazilian Chemical Society

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This work deals with preparation and characterization of H 3 PW 12 O 40 (H 3 PW) supported on silica-alumina. Impregnation of H 3 PW (15, 20, 30 and 40 wt.%) on commercial silica-alumina support in acidic aqueous solution is effective for preparing this catalyst keeping its Keggin structure, according to different methods of characterization. The catalysts were tested in a model reaction of acetic acid with ethanol and 30 wt.% H 3 PW/SiO 2 -Al 2 O 3 had the highest activity under the conditions: catalyst calcination at 300 °C, temperature of 100 °C, acetic acid:ethanol molar ratio of 2:1 and catalyst:acetic acid mass ratio of 10 wt.%. The reaction yield was 79 and 100% selectivity for ethyl acetate over three reutilizations, for reaction time of 2 h. The calculated total acid site distribution was 0.299 mmol g -1 (97% of the theoretical probed by pyridine), and most of these (0.236 mmol g -1 ) were Brønsted weak-medium strength (pyridine desorption between 300 and 500 °C).

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Section: Resultsmentioning

confidence: 99%

Acidity and Characterization of 12-Tungstophosphoric Acid Supported on Silica-Alumina

Mattos¹,

Carvalho²,

Freitas³

et al. 2016

Journal of the Brazilian Chemical Society

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“…The parameter a i corresponds to the energy of the orbital i, t ij to the hopping integral of an electron between sites i and j, U i to the on-site effective electrostatic repulsion between two electrons on site i and V ij to the inter-site effective electrostatic repulsion between two electrons on site i and j. In idealized Keggin compound as well as in the real structure of the particular salt studied in this work [17] all the W ions are equivalent. Then, all the d xy -like orbitals of the W ions (the d orbital pointing between the equatorial O ions of the octahedron) considered in the model Hamiltonian are equivalent.…”

Section: Abstract In Frenchmentioning

confidence: 99%

Electron Delocalization and Electrostatic Repulsion at the Origin of the Strong Spin Coupling in Mixed‐Valence Keggin Polyoxometalates: Ab Initio Calculations of the One‐ and Two‐Electron Processes

Suaud

Gaita‐Ariño

Clemente‐Juan

et al. 2004

Chemistry A European J

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We present here a general theoretical procedure to treat the problem of electron delocalization and magnetic interactions in high-nuclearity mixed valence clusters based on polyoxometalates. The main interactions between the delocalized electrons of mixed-valence polyoxometalate anions are extracted from valence spectroscopy ab initio calculations on embedded fragments. Electron transfer, magnetic coupling and exchange transfer parameters between nearest and next-nearest-neighbor metal ions, as well as the value of the electrostatic repulsion between pairs of metal ions are determined. These parameters are introduced in a model Hamiltonian that considers the whole anion. It thus provides macroscopic properties that should be compared with the experimental data. This method is applied to a two-electron-reduced polyoxowolframate Keggin anion. The results demonstrate that the electron transfer processes, combined with the Coulombic repulsion between the "extra" electrons, induce a strong antiferromagnetic coupling between the two delocalized spins providing a definite explanation of the diamagnetic properties of these high nuclearity mixed-valence clusters.

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“…Es ist isomorph mit dem PW12O40 3 "", dessen Struktur von Keggin [4] 1934 aus Pulver-Röntgendiffrakto-grammen ermittelt wurde. Inzwischen liegen Ergebnisse mehrerer Strukturuntersuchungen an a-Silicowolframaten [5,6] und anderen Heteropolyverbindungen dieses Typs vor [7][8][9][10][11][12]. Über die Struktur des ß-Typs gab es längere Zeit nur Vermutungen.…”

Section: Introductionunclassified

Strukturen und Schwingungsspektren des Tetramethylammonium -a -dodekawolframatosilikats und des Tetrabutylammonium-β-dodekawolframatosilikats / Structures and Vibrational Spectra of Tetramethylammonium a-Dodecatungstosilicate and Tetrabutylammonium β-Dodecatungstosilicate

Fuchs

Thiele

Palm

1981

Zeitschrift Für Naturforschung B

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Abstract Dodecatungstosilicates free of crystal water were prepared for the first time by using tetraalkylammonium as cation. The crystal structure of the tetramethylammonium a-dodeeatungstosilicate [N(CH3)4]4SiW12O40 (1) and tetrabutylammonium) β-dodecatungstosilicate, [N(C4H9)4]4SiWi2040 (2) were solved by X-ray diffraction. (1) crystallizes tetragonal in the space group 14̅ with lattice parameters a = 14.642 Å; c= 12.706 Å; (2) orthorhombic, space group P212121 with a = 29.277 Å, b = 22.181 Å and c = 15.381 Å. The differences between the two isomeric heteropolyanions are discussed, especially the distances and angles between the tungsten atoms. Comparison of characteristic differences in the vibrational spectra permits the identification of the isomeric anions.

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Dodecatungstophosphoric acid hexahydrate, (H5O2+)3(PW12O403−). The true structure of Keggin's `pentahydrate' from single-crystal X-ray and neutron diffraction data

Cited by 501 publications

References 6 publications

Acidity and Characterization of 12-Tungstophosphoric Acid Supported on Silica-Alumina

Acidity and Characterization of 12-Tungstophosphoric Acid Supported on Silica-Alumina

Electron Delocalization and Electrostatic Repulsion at the Origin of the Strong Spin Coupling in Mixed‐Valence Keggin Polyoxometalates: Ab Initio Calculations of the One‐ and Two‐Electron Processes

Strukturen und Schwingungsspektren des Tetramethylammonium -a -dodekawolframatosilikats und des Tetrabutylammonium-β-dodekawolframatosilikats / Structures and Vibrational Spectra of Tetramethylammonium a-Dodecatungstosilicate and Tetrabutylammonium β-Dodecatungstosilicate

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