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, Joachim; Thiele, Axel; Palm, Rosemarie

doi:10.1515/znb-1981-0209

Cited by 35 publications

(24 citation statements)

References 11 publications

(11 reference statements)

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“…Kepert thus concluded that the α-Keggin structure, with four groups of M 3 O 13 triads (60° M−M−M angles), each connected to one another by corner-shared linkages, possessed the geometry most favorable for minimizing Coulombic repulsions. Baker and Figgis then proposed 1j (1970) that the β structure (Figure , β; confirmed by X-ray crystallography in 19732a) might be derived from 60° rotation of one M 3 O 13 triad about a 3-fold axis of the α anion. Additional isomersγ, δ, and εwere postulated to result from 60° rotations of the remaining triads (Figure , γ to ε).…”

Section: Introductionmentioning

confidence: 96%

“…β-Keggin anions are less common: their stabilities vary with both the nature of the heteroatom and the overall charge of the cluster. While β anions of the group V elements, β-[XW 12 O 40 ] 3- , X = P(V), As(V), are unknown, 4b, β isomers of the group IV elements, β-[XW 12 O 40 ] 4- , X = Si(IV), Ge(IV), possess substantial kinetic stabilities (in the order Si > Ge) 2b, as does β-metatungstate (β-[H 2 W 12 O 40 ] 6- ), 4i, a Keggin anion with X = 2H + . Notably however, β-dodecatungstate anions of the group III elements, β-[XW 12 O 40 ] 5- , X = B(III), Ga(III), have not been reported.…”

Section: Introductionmentioning

confidence: 99%

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Equilibria between α and β Isomers of Keggin Heteropolytungstates

et al. 1999

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Conventional wisdom maintains that β isomers of fully oxidized Keggin heteropolytungstates, [X n +WVI 12O40](8- n )- (X = main-group or transition-metal cation), are unstable with respect to α structures such that isomeric rearrangements all occur in the direction β → α. Contrary to this view, equilibria between α and β forms of the Keggin anion [AlIIIW12O40]5- (α- and β-1) have now been observed. Moreover, a trend in kinetic and thermodynamic stabilities of β isomers in the order X = Al(III) > Si(IV) > P(V) has been established, and the difference in energy between α and β isomers (α- and β-1) has been quantified for the first time. Mild acid condensation of WO4 2-, followed by addition of Al(III), gave [Al(AlOH2)W11O39]6- (2)three β-isomer derivatives, β1 (C s symmetry), β2 (C 1), and β3 (C s ), with the α derivative (C s ) a minor productin nearly quantitative yield by 27Al NMR spectroscopy. Acidification of the reaction mixture to pH 0 and refluxing cleanly converted 2 to H5[AlIIIW12O40] (1)mostly β-1 (yellow, C 3 v ), with α-1 (white, T d ) a minor product. Samples of each isomer were isolated by fractional crystallization and characterized by 27Al and 183W NMR, IR, and UV−vis spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction. The Al−O bond length in the T d AlO4 group at the center of α-1 (hydrated potassium salt of α-1; final R 1 = 3.42%) establishes a trend in X−O bond lengths in the [X n +O4](8- n )- groups of α-Keggin anions of 1.74(1), 1.64(2), and 1.53(1) Å, respectively, for X = Al(III), Si(IV), and P(V). Equilibria between isomers of 1 were observed by heating separate 0.1 M aqueous solutions of either pure α or β anions under identical conditions. The progress of the reaction was measured, and the relative concentrations of the α and β isomers present at equilibrium were determined by 27Al NMR spectroscopy. First-order rate constants for approach to equilibrium of α- and β-1 at 473 K were k 1( α → β ) = 7.68 × 10-7 s-1 and k - 1( β → α ) = 6.97 × 10-6 s-1. The equilibrium ratio of β-1 to α-1 (k 1/k - 1) was K eq(473 K, 0.1 M 1 ) = 0.11 ± 0.01. From ΔG = −RT ln K eq, α-1 is more stable than β-1 by 2.1 ± 0.5 kcal mol-1. Controlled hydrolysis of α-1 gave the monolacunary derivative α-Na9[AlW11O39] (α-3; C s ); hydrolysis of β-1 gave β2-3 (C 1) as the major product. Thermal equilibration of the lacunary Keggin heteropolytungstates could also be achieved: Independently heated solutions of either α-3 or β2-3 (0.13 M of either isomer in D2O at 333 K; natural pH values of ca. 7) both gave solutions containing α-3 (60%) and a single β-3 isomer of C s symmetry (40%). Using K eq = 1.5, the two isomers differ in energy by 0.3 kcal mol-1.

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Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Equilibria between α and β Isomers of Keggin Heteropolytungstates

et al. 1999

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“…In einer vorangehenden Arbeit [1] wurden die Strukturen und Schwingungsspektren eines a-und eines ß-Dodekawolframatosilicats beschrieben. Für diese Untersuchung waren Tetraalkylammoniumsalze ausgewählt worden, die in der Regel kristallwasserfrei anfallen und dadurch Schwingungsspektren besonders guter Qualität liefern.…”

Section: Introductionunclassified

“…Von Heteropolyanionen des Typs XMn039 z_ (X = Si, P; M = W, Mo) liegt bisher erst eine vollständige Strukturuntersuchung vor. Im kubisch kristallisierenden K8SiWn039 • 13H20 [2] .4508 (1) .1655 (2) .3685(1) 1 .2786 (1) .1656 (2) .3088(1) 1 .4028 (1) .1539 (2) .1730(1) 1 .2168 (1) .1538 (2) .1102(1) 1 .3410 (2) .3165 (4) .2465(2) 1 .5136 (1) .0 .2967(1) .5 .1580 (1) .0 .1753(1) .5…”

Section: Introductionunclassified

“….347 (1) .110 (2) .278(1) 1 .266 (2) .0 .184(2) .5 .393 (2) .0 .229(2) .5 .520 (2) .206 (3) .435(1) 1 .238 (2) .213 (3) .336(1) 1 .423 (1) .236 (3) .138 (3) 1 .165 (2) .036 (6) .047 (2) 1 .332 (4) .458 (9) .236 (3) 1 .599 (2) .0 .340(1) .5 .072 (2) .0 .154(2) .5 .449 (2) .0 .384(2) .5 .374 (1) .184 (3) .375(1) 1 .429 (2) .305 (3) .331(1) 1 .497 (1) .109 (3) .337(1) 1 .286 (3) .0 .327(3) .5 .284 (1) .304 (3) .279(1) 1 .201 (1) .114 (3) .233(1) 1 .402 (2) .0 .144(2) .5 .307 (2) .136 (4) .122(1) 1 .393 (2) .258 (4) .213(2) 1 .494 (1) .122 (3) .243(1) 1 .200 (2) .0 .080(2) .5 .253 (2) .265 (3) .167(1) 1 .153 (2) .110 (4) .125 (1) .0 .350(2) .5 .271 (2) .135 (3) .592(1) 1 .089 (2) .153 (3) ....…”

Section: Introductionmentioning

confidence: 99%

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Struktur und Schwingungsspektrum des α-Undekawolframatophosphats Na₂[N(CH₃)₄]₄HPW₁₁O₃₉ · 7H₂O / Structure and Vibrational Spectrum of the α-Undecatungstophosphate Na₂[N(CH₃)₄]₄HPW₁₁O₃₉ · 7H₂O

Fuchs

Thiele

Palm

1981

Zeitschrift Für Naturforschung B

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The crystal structure of the compound Na2[N(CH3)4]4HPW11O39 · 7H2O was solved by X-ray diffraction. It crystallizes in the space group C2/m with lattice parameters a= 23.895 Å, b = 11.417 Å, c = 28.930 Å, β= 126.0°.The distances between the tungsten atoms and the kind of bridging by oxygen atoms prove the α-isomer. The differences between the vibration spectra of α-undecatungsto-phosphate and α-dodecatungstophosphate are discussed

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Compared Behaviours of Dawson-Type Tungstodiarsenates and -diphosphates

Keita

Mbomekallé

Nadjo

et al. 2002

Eur. J. Inorg. Chem.

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The lacunary α 2 -[As 2 W 17 O 61 ] 10− derived from the Dawson molecule α-[As 2 W 18 O 62 ] 6− was used as a ligand for the following metal cations: Mn 2+ , Fe 3+ , Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ . The cyclic voltammograms of this lacunary precursor species, as well as those of the substituted complexes were run in a medium at pH = 3. A systematic comparison was carried out with the electrochemical characteristics of the corresponding complexes derived from α-[P 2 W 18 O 62 ] 6− , with the aim of highlighting the differences in their behaviour, which could be ascribed to the identity of the central atoms. The study was also extended to the Fe 3+ species of the α 1 series. The comparisons reveal that whatever the series, the first several

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

Cited by 35 publications

References 11 publications

Equilibria between α and β Isomers of Keggin Heteropolytungstates

Equilibria between α and β Isomers of Keggin Heteropolytungstates

Struktur und Schwingungsspektrum des α-Undekawolframatophosphats Na₂[N(CH₃)₄]₄HPW₁₁O₃₉ · 7H₂O / Structure and Vibrational Spectrum of the α-Undecatungstophosphate Na₂[N(CH₃)₄]₄HPW₁₁O₃₉ · 7H₂O

Compared Behaviours of Dawson-Type Tungstodiarsenates and -diphosphates

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

Cited by 35 publications

References 11 publications

Equilibria between α and β Isomers of Keggin Heteropolytungstates

Equilibria between α and β Isomers of Keggin Heteropolytungstates

Struktur und Schwingungsspektrum des α-Undekawolframatophosphats Na2[N(CH3)4]4HPW11O39 · 7H2O / Structure and Vibrational Spectrum of the α-Undecatungstophosphate Na2[N(CH3)4]4HPW11O39 · 7H2O

Compared Behaviours of Dawson-Type Tungstodiarsenates and -diphosphates

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Struktur und Schwingungsspektrum des α-Undekawolframatophosphats Na₂[N(CH₃)₄]₄HPW₁₁O₃₉ · 7H₂O / Structure and Vibrational Spectrum of the α-Undecatungstophosphate Na₂[N(CH₃)₄]₄HPW₁₁O₃₉ · 7H₂O