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Synthetic bayleyite, Mg2[UO2(CO3)3]·18H2O: Thermochemistry, crystallography and crystal structure

Synthetischer Bayleyit, Mg2[UO2(CO3)3]·18H2O: Thermochemie, Kristallographie und Kristallstruktur

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Summary

Thermochemistry, morphology, optical properties and crystal structure of synthetic bayleyite, Mg2[UO2(CO3)3]·18H2O, monoclinic, have been studied. Incongruent melting at 55°, three steps of dehydration and two steps of decarboxylation have been found by thermochemic investigations. Morphology: Prisms along [001] with {100}, {110}, {210}, {001}, {401}, {021}, {211}, {111} and\(\{ \bar 311\} \) as the most important forms. Optical data:n α=1.453,n β=1.498,n γ=1.499, 2V x =16°,Y=b,X c=11°. Crystal structure: Space groupP21/a,a=26.560(3),b=15.256(2),c=6.505(1) Å, β=92.90(1)°,Z=4,R=0.029 for 5126 independent reflections measured with MoK α-radiation. The structure is built up from isolated Mg(H2O)6 octahedra, UO2(CO3)3 units and lattice water molecules, all held together by hydrogen bonds only.

Zuseammenfasung

Thermochemie, Morphologie, optische Eigenschaften und Kristallstruktur von Bayleyit, Mg2[UO2(CO3)3]·18H2O, monoklin, wurden anhand künstlich hergestellter Kristalle untersucht. Durch thermochemische Untersuchung wurden inkongruentes Schmelzen bei 55°, eine dreistufige Wasserabgabe sowie eine zweistufige CO2-Abgabe festgestellt. Morphologie: parallel zu [001] gestreckte Prismen mit {100}, {110}, {210}, {001}, {401}, {021}, {211}, {111}, und {311} als wichtigste Formen. Optische Daten:n α=1.453,n β=1.498,n γ=1.499, 2V x =16°,Y=b,X c=11°. Kristallstruktur: RaumgruppeP21/a,a=26.560(3),b=15.256(2),c=6.505(1) Å, β=92.90(1)°,Z=4;R=0.029 für 5126 unabhängige, mit MoK α-Strahlung gemessene Reflexe. Die Struktur enthält isolierte Mg(H2O)6-Oktaeder, UO2(CO3)3-Gruppen und “freie” Wassermoleküle, die ausschließlich durch Wasserstoffbrücken miteinander verknüpft sind.

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  1. H. Mayer &  K. Mereiter

    Present address: Institut für Mineralogie und Kristallographie und Strukturchemie, Technische Universität Wien, Getreidemarkt 9, A-1060, Wien, Austria

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    1. H. Mayer
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    Mayer, H., Mereiter, K. Synthetic bayleyite, Mg2[UO2(CO3)3]·18H2O: Thermochemistry, crystallography and crystal structure. TMPM Tschermaks Petr. Mitt. 35, 133–146 (1986). https://doi.org/10.1007/BF01140845

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