Hydrothermal transformations of hydrated cerium(IV) fluoride in NaOH or HF media. The first crystal structure in the cerium tetrafluoride hydrate familyстатья
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Аннотация:In order to synthesize new nanocrystalline compounds of cerium fluorides, the transformations of hydrated cerium(IV) fluoride with the composition CeF4⋅H2O under mild hydrothermal conditions were studied, in aqueous alkaline (1 M NaOH) or acidic (1 M HF) media. In alkaline medium, at 130 °С and 220 °C, hydrated cerium(IV) fluoride hydrolyses to form CeO2, while in 1 M hydrofluoric acid at 130 °C, a mixture of crystalline Ce3F10⋅3H2O and CeF3 is formed. Hydrothermal treatment of cerium(IV) fluoride hydrate in 1 M HF at 220 °C yielded a new cerium(IV) fluoride hydrate (CeF4)3.H2O (Ce3F12.H2O). The new compound was studied by chemical analysis, powder and single crystal X-ray diffraction, scanning electron microscopy, 19F{1H} and 1H NMR, IR- and Raman spectroscopy. The noncentrosymmetric crystal structure of Ce3F12.H2O was found to be monoclinic (sp. gr. Cm, Z = 4) being isomorphic to uranium or neptunium tetrafluoride hydrates (U3F12.H2O or Np3F12.H2O). The structure of this compound exhibits a three-dimensional network of corner- and edge-shared [CeF9], [CeF7(OH2)], [CeF8(OH2)] and [CeF8] polyhedra. The influence of the cerium(IV) cations coordination sphere composition on the relative lengths of Ce-O bonds and F…Hsingle bondO hydrogen bonds discussed. The temperature behavior of the Ce3F12.H2O powder up to 500 °C was studied by thermogravimetry and differential scanning calorimetry.