Keggin cluster formation by hydrothermal reaction of tungsten trioxide with methyl substituted ammonium : The crystal structure of two novel compounds, [NH2(CH3)2]6H2W12O40.∼4H2O and [N(CH3)4]6H2W12O40.2H2O

doi:10.1006/JSSC.1996.0155

Paper

Keggin cluster formation by hydrothermal reaction of tungsten trioxide with methyl substituted ammonium : The crystal structure of two novel compounds, [NH2(CH3)2]6H2W12O40.∼4H2O and [N(CH3)4]6H2W12O40.2H2O

Published Apr 1, 1996 · P. Zavalij, Jingdong Guo, M. Whittingham

Journal of Solid State Chemistry

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Abstract

Abstract Tungsten(VI) oxides can be formed by mild hydrothermal reactions, with the exact crystalline structure being determined by the cations in solution. The impact on the reaction between tungstic acid and ammonium ions as the hydrogen atoms are systematically substituted by methyl groups is investigated. Ammonium and methylammonium (MA) cations form the pyrochlore structure type (NH4)xWO3+x/2·nH2O (A) and (MA)xWO3+x/2·nH2O (B). Ammonium may also form the hexagonal bronze tunnel structure. Using dimethylammonium (DMA), trimethylammonium (TrMA), and tetramethylammonium (TMA) leads to the formation of well crystallized Keggin structures: DMA6[H2W12O40] ·nH2O (C), DMA6[H2W12O40] · ∼4H2O (D), TrMA6[H2W12O40] (E), TrMA6[H2W12O40] · ∼2H2O (F), TMA6[H2W12O40] · 2H2O (G), and in some cases hexagonal tungsten bronzes. Characterization was done using powder and single crystal X-ray analysis, as well as IR and TGA methods. The pyrochlore structures have been refined by the Rietveld method. The powder patterns were indexed to the orthorhombic system (space groupPnma,a= 21.886(4),b= 21.469(4),c= 13.232(3) A) forEand monoclinic system (P21/n,a= 19.273(4),b= 12.017(2),c= 12.253(2) A, β = 90.70(1)°) in the case ofF. The crystal structures ofDandGwere determined by single crystal X-ray analysis. Blue crystals ofDare orthorhombic, space groupPnma,a= 22.446(3),b= 19.810(3),c= 12.854(2) A,Vcell= 5716 A3,Z= 4,dclc= 3.72 g/cm3(MoKα radiation, 2θmax.= 55°,R= 0.077 for 2076 reflections). Dark blue crystals ofGare orthorhombic, space groupPnma,a= 21.90(1),b= 21.507(7),c= 13.27(1) A,Vcell= 6250 A3,Z= 4,dclc= 3.54 g/cm3(MoKα radiation, 2θmax.= 55°,R= 0.052 for 4488 reflections). Both structures consist of a hexagonal close packed arrangement of the almost spherical Keggin anions [H2W12O40]−6. They are not isostructural because of a different orientation of the tungsten clusters.

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Hydrothermal reactions with methyl substituted ammonium can produce novel Keggin structures, forming tungsten(VI) oxides with unique crystalline structures.

PopulationOlder adults (50-71 years)

Sample size24

MethodsObservational

OutcomesBody Mass Index projections

ResultsSocial networks mitigate obesity in older groups.

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Keggin cluster formation by hydrothermal reaction of tungsten trioxide with methyl substituted ammonium : The crystal structure of two novel compounds, [NH2(CH3)2]6H2W12O40.∼4H2O and [N(CH3)4]6H2W12O40.2H2O

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