National Security Sciences Directorate, Oak Ridge National Laboratory, 1 Bethel Valley Rd, Oak Ridge, Tennessee, USA.
Dalton Trans. 2019 Sep 17;48(36):13685-13698. doi: 10.1039/c9dt02835h.
Hydrated uranyl fluoride, [(UO2F2)(H2O)]7·4H2O, is not stable at elevated water vapor pressure, undergoing a complete loss of fluorine to form a uranyl hydroxide hydrate. Powder X-ray diffraction data of the resultant uranyl hydroxide species is presented for the first time, along with Raman and infrared (IR) spectra. The new uranyl hydroxide species is structurally similar to the layered uranyl hydroxide hydrate minerals schoepite and metaschoepite, but has a significantly expanded interlayer spacing (c = 15.12 vs. 14.73 Å), suggesting that additional H2O molecules may be present between the uranyl layers. Comparison of the Raman and IR spectra of this new uranyl hydroxide hydrate and synthetic metaschoepite ([(UO2)4O(OH)6]·5H2O) suggests that the equatorial environment of the uranyl ion may differ and that H2O molecules in the new species participate in stronger hydrogen bonds. In addition, the interlayer spacing of both this new uranyl hydroxide species and synthetic metaschoepite is shown to be sensitive to the environmental humidity, contracting and re-expanding with desiccation and rehydration. Structural distinction between the new uranyl hydroxide species and synthetic metaschoepite is confirmed by a comparison of the thermal behavior; unlike metaschoepite, the new hydrate does not form α-UO2(OH)2 upon dehydration.
水合二氟化铀，[(UO2F2)(H2O)]7·4H2O，在较高的水蒸气压力下不稳定，会完全失去氟形成氢氧化铀水合物。首次呈现了由此产生的氢氧化铀物种的粉末 X 射线衍射数据，以及拉曼和红外（IR）光谱。这种新的氢氧化铀物种在结构上与层状氢氧化铀水合物矿物羟硅铍石和羟硅铍石相似，但层间间距显著扩大（c = 15.12 对 14.73 Å），表明在铀层之间可能存在额外的 H2O 分子。比较这种新的氢氧化铀水合物和合成羟硅铍石（[(UO2)4O(OH)6]·5H2O）的拉曼和 IR 光谱表明，铀离子的赤道环境可能不同，并且新物种中的 H2O 分子参与了更强的氢键。此外，新的氢氧化铀物种和合成羟硅铍石的层间间距都对环境湿度敏感，干燥和再水合时会收缩和再膨胀。新的氢氧化铀物种和合成羟硅铍石之间的结构区别通过比较热行为得到证实；与羟硅铍石不同，新的水合物在脱水时不会形成 α-UO2(OH)2。
