Gerber Evgeny, Krot Anna D, Chernyshev Vladimir V, Trigub Alexander L, Sobolev Nikita A, Averin Alexey, Maksimov Sergey, Svetogorov Roman, Nevolin Iurii M
A. N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS, 31 Leninsky Prospect, Moscow 119071, Russian Federation.
Department of Chemistry, M.V. Lomonosov Moscow State University, 1-3 Leninskie Gory, Moscow 119991, Russian Federation.
Inorg Chem. 2024 Jul 22;63(29):13402-13412. doi: 10.1021/acs.inorgchem.4c01292. Epub 2024 Jul 8.
The crystal structure of ammonium polyuranates has been investigated. Powder X-ray diffraction (PXRD) has been employed to define single-phase samples within a series of synthesized compounds, which are further characterized by elemental analysis to ascertain the stoichiometry, revealing compositions of and . Analysis using extended X-ray absorption fine structure and vibrational spectroscopy has elucidated that both and possess a local structure similar to the metaschoepite─layered U(VI) oxohydroxide UO·2HO, but with HO and NH groups in the interlayers. The structures of ammonium polyuranates are solved from PXRD data, revealing their relationship to the U(VI) oxohydroxide with the established composition of and for and , respectively. These structures maintain the arrangement of U-O polyhedra as pentagonal bipyramids. However, disparities in lattice parameters, space group, and layer topology from UO·2HO emphasize significant structural modifications resulting from the substitution of water by ammonium. Moreover, the anion topology of the has no analogues among uranium oxohydroxide minerals. Notably, ammonium polyuranates, when compared, have minimal alterations in lattice parameters regardless of the presence of ammonia within the structure. The revealed results contribute valuable insights into the UO-NH-HO system and hold potential applications in the field of nuclear power as ammonium polyuranates form during actinide precipitation in back-end of the nuclear fuel cycle and also serve as precursors in the fabrication of nuclear fuel.
已对多铀酸铵的晶体结构进行了研究。粉末X射线衍射（PXRD）已被用于在一系列合成化合物中确定单相样品，这些样品通过元素分析进一步表征以确定化学计量，揭示了其组成分别为[具体组成1]和[具体组成2]。使用扩展X射线吸收精细结构和振动光谱进行的分析表明，[具体物质1]和[具体物质2]都具有与变水铀矿（层状U(VI)羟基氧化物UO₂·2H₂O）相似的局部结构，但在层间有H₂O和NH₄基团。多铀酸铵的结构是根据PXRD数据解析出来的，分别揭示了它们与组成既定的U(VI)羟基氧化物的关系，对于[具体物质1]和[具体物质2]，其组成分别为[具体组成1]和[具体组成2]。这些结构保持了U-O多面体为五角双锥体的排列。然而，与UO₂·2H₂O相比，晶格参数、空间群和层拓扑结构的差异强调了由于铵取代水而导致的显著结构变化。此外，[具体物质1]的阴离子拓扑结构在铀羟基氧化物矿物中没有类似物。值得注意的是，相比之下，多铀酸铵的晶格参数变化极小，无论结构中是否存在氨。所揭示的结果为UO₂-NH₄-H₂O体系提供了有价值的见解，并在核电领域具有潜在应用，因为在核燃料循环后端的锕系元素沉淀过程中会形成多铀酸铵，并且它还可作为核燃料制造的前体。
