Structural Studies Coupling X-ray Diffraction and High-Energy X-ray Scattering in the UO22+–HBraq System

The structural chemistry of uranium(VI) in concentrated aqueous hydrobromic acid solutions was investigated using both single crystal X-ray diffraction and synchrotron-based high-energy X-ray scattering (HEXS) to reveal the structure of the uranium(VI) complexes in solution prior to crystallization. The crystal structures of a series of uranyl tetrabromide salts are reported, including Cs2UO2Br4, Rb2UO2Br4·2H2O, K2UO2Br4·2H2O, and (NH4)2UO2Br4·2H2O, as well as a molecular dimer of uranium(VI), (UO2)2(OH)2Br2(H2O)4. Limited correspondence exists between the structures observed in the solid state and those in solution. Quantitative analysis of the HEXS data show an average U–Br coordination number of 1.9(2) in solution, in contrast to the U–Br coordination number of 4 in the solid salts.

本研究采用单晶X射线衍射（single crystal X-ray diffraction）与基于同步辐射的高能X射线散射（HEXS）两种实验手段，对浓氢溴酸水溶液中六价铀（uranium(VI)）的结构化学特性展开探究，以解析结晶前溶液内六价铀配合物的分子结构。本研究报道了一系列四溴合铀酰盐的晶体结构，包括Cs₂UO₂Br₄、Rb₂UO₂Br₄·2H₂O、K₂UO₂Br₄·2H₂O与(NH₄)₂UO₂Br₄·2H₂O，同时还解析了六价铀的分子二聚体(UO₂)₂(OH)₂Br₂(H₂O)₄的结构。固态下观测到的配合物结构与溶液中的对应结构仅存在有限的对应关系。对HEXS数据的定量分析显示，溶液中铀-溴的平均配位数为1.9(2)，而固态盐中铀-溴的配位数为4，二者形成鲜明对比。