Crystal structures of tetravalent uranium fluorides obtained in the presence of hydrazine from uranyl source

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• 作者：Jakub Olchowka ; Christophe Volkringer ; Natacha Henry ; Thierry Loiseau
• 关键词：Uranium(IV) ; Fluoride ; Hydrazine ; Sodium ; Hydrothermal ; Structure
• 刊名：Journal of Fluorine Chemistry
• 出版年：March, 2014
• 年：2014
• 卷：159
• 期：Complete
• 页码：1-7
• 全文大小：3475 K

文摘

Four new tetravalent uranium fluorides have been obtained by using hydrothermal route from a hexavalent uranium precursor (UO₂(NO₃)₂路6H₂O or UO₂(SO₄)路4H₂O) in the presence of hydrazine and HF in water. The major phase is the hydrated uranium fluoride U₃F₁₂(H₂O) (1) and in some conditions, four other phases are formed in mixture with the latter. Both compounds 2 and 3 exhibit layered structures with intercalated hydrazinium cations. UF₅路H₃N-NH₂ (2) consists of double uranium fluoride sheets with nine-fold coordinated uranium (UF₉, tricapped trigonal prism). It is related to the anionic archetype [UF₅]^{鈭?/sup>路X+ or [U₂F₁₀]2鈭?/sup>路Y2+ (depending of the charge of the counter-cations) previously reported in literature. U₃F₄(SO₄)₆路2NH₄路H₃N-NH₃ (3) contains trinuclear 渭₃-fluoro-centered uranium (UO₆F₃, tricapped trigonal prism) core linked to each other via the sulfate groups in order to form infinite sheets intercalated by ammonium and diprotonated hydrazinium cationic species. It is a new type of uranium arrangement for tetravalent uranium sulfates. The phases NaU₂F₉ (4) and NaU₆F₂₅ (5) appeared when sodium sulfate is added to the reaction medium. Crystal structure of 4 can be viewed from the connection of double uranium fluorides layers of nine-fold coordinated uranium (UF₉) centers, similar to that observed in the compound 2. Due to the small size of sodium cation, the resulting [UF₅]鈭?/sup> sheets are connected to each other via the remaining non-bonded fluoride anions in order to form a three-dimensional network with channels encapsulating the alkali atoms. The structure of NaU₆F₂₅ (5) corresponds to the stacking of double layers of 6-membered ring sub-net of UF₉ units, resulting in the formation of elongated cavities in which sodium atoms are located.}