The Synthesis, Structural, and Spectroscopic Characterization of Uranium(IV) Perrhenate Complexes

We report the synthesis, structural, and spectroscopic characterization of a series of uranium(IV)−perrhenato
complexes. Three isostructural complexes with general formula [U(ReO4)4(L)4] (where L = tri-n-butylphosphine
oxide/TBPO (2), triethyl phosphate/TEP (3), or tri-iso-butyl phosphate/TiBP (4)), have been synthesized, both through
the photoreduction of ethanolic {UO2}2+ solutions and also via a novel UIV starting material, U(ReO4)4·5H2O (1).
Compound 1 has also been used in the preparation of [U(ReO4)4(TPPO)3(CH3CN)]·2CH3CN (5) and [U(ReO4)(DPPMO2)3(OH)][ReO4]2·2CH3CN (6), where TPPO represents triphenylphosphine oxide and DPPMO2 represents
bis(diphenylphosphino)methane dioxide. All six complexes have been spectroscopically characterized using NMR,
UV−vis−NIR, and IR techniques, with 2, 3, 5, and 6 also fully structurally characterized. The U atoms in compounds
2-6 all exhibit eight-coordinate geometry with up to four perrhenate groups in addition to three (DPPMO2 and
TPPO) or four (TEP, TiBP, TBPO) coordinated organic ligands. In the case of compounds 5 and 6, the coordination
of eight ligands to the UIV center is completed by the binding of a solvent molecule (CH3CN) and OH-, respectively.
Solid-state physical analysis (elemental and thermogravimetric) and infrared spectroscopy are in agreement with
the structural studies. The crystallographic data suggest that the strength of the UIV−O-donor ligand bonds decreases
across the series R3PO > [ReO4]-> (RO)3PO. Solution-state IR and 31P NMR spectroscopy appear to be in agreement
with these solid-state results.

本研究报道了一系列四价铀-高铼酸根配合物的合成、结构表征与光谱表征。我们通过乙醇相双氧铀（{UO₂}²⁺）溶液的光还原法，以及以新型四价铀起始原料五水合四高铼酸铀(IV)（U(ReO₄)₄·5H₂O，化合物1）为原料，成功合成了3种通式为[U(ReO₄)₄(L)₄]的同构配合物，其中L分别为三正丁基氧化膦（tri-n-butylphosphine oxide, TBPO，化合物2）、磷酸三乙酯（triethyl phosphate, TEP，化合物3）与磷酸三异丁酯（tri-iso-butyl phosphate, TiBP，化合物4）。化合物1还被用于制备[U(ReO₄)₄(TPPO)₃(CH₃CN)]·2CH₃CN（化合物5）与[U(ReO₄)(DPPMO₂)₃(OH)][ReO₄]₂·2CH₃CN（化合物6），其中三苯基氧化膦（triphenylphosphine oxide, TPPO）与双(二苯基膦基)甲烷二氧化物（bis(diphenylphosphino)methane dioxide, DPPMO₂）分别为对应配体的全称。所有6种配合物均通过核磁共振（NMR）、紫外-可见-近红外（UV−vis−NIR）及红外（IR）光谱技术完成了光谱表征，其中化合物2、3、5和6还实现了完整的晶体结构解析。化合物2~6中的铀原子均呈现八配位几何构型：除结合3~4个高铼酸根基团外，还配位了3个（针对DPPMO₂与TPPO配体）或4个（针对TEP、TiBP与TBPO配体）有机配体。对于化合物5和6，其铀(IV)中心的八配位环境分别由乙腈（CH₃CN）溶剂分子与羟基（OH⁻）配位得以完成。固态物理分析（元素分析与热重分析）及红外光谱结果与结构解析结果一致。晶体学数据显示，四价铀-氧供体配体键的强度遵循如下顺序：R₃PO > [ReO₄]⁻ > (RO)₃PO。溶液相红外光谱与³¹P核磁共振光谱结果与上述固态研究结论相符。