Falaise Clément, Volkringer Christophe, Hennig Christoph, Loiseau Thierry
Unité de Catalyse et Chimie du Solide (UCCS) - UMR CNRS 8181, Université de Lille, USTL-ENSCL, Bat C7, BP 90108, 59652 Villeneuve d'Ascq (France).
Institut Universitaire de France (IUF), 1, rue Descartes, 75231 Paris (France).
Chemistry. 2015 Nov 9;21(46):16654-64. doi: 10.1002/chem.201502207. Epub 2015 Sep 29.
The ex-situ qualitative study of the kinetic formation of the poly-oxo cluster U38 , has been investigated after the solvothermal reaction. The resulting products have been characterized by means of powder XRD and scanning electron microscopy (SEM) for the solid phase and UV/Vis, X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and NMR spectroscopies for the supernatant liquid phase. The analysis of the different synthesis batches, stopped at different reaction times, revealed the formation of spherical crystallites of UO2 from t=3 h, after the formation of unknown solid phases at an early stage. The crystallization of U38 occurred from t=4 h at the expense of UO2 , and is completed after t=8 h. Starting from pure uranium(IV) species in solution (t=0-1 h), oxidation reactions are observed with a U(IV) /U(VI) ratio of 70:30 for t=1-3 h. Then, the ratio is inversed with a U(IV) /U(VI) ratio of 25/75, when the precipitation of UO2 occurs. Thorough SEM observations of the U38 crystallites showed that the UO2 aggregates are embedded within. This may indicate that UO2 acts as reservoir of uranium(IV), for the formation of U38 , stabilized by benzoate and THF ligands. During the early stages of the U38 crystallization, a transient crystallized phase appeared at t=4 h. Its crystal structure revealed a new dodecanuclear moiety (U12 ), based on the inner hexanuclear core of {U6 O8 } type, decorated by three additional pairs of dinuclear U2 units. The U12 motif is stabilized by benzoate, oxalates, and glycolate ligands.
在溶剂热反应后，对多氧簇U38的动力学形成进行了非原位定性研究。通过粉末X射线衍射（XRD）和扫描电子显微镜（SEM）对所得产物的固相进行了表征，通过紫外可见光谱（UV/Vis）、X射线吸收近边结构（XANES）、扩展X射线吸收精细结构（EXAFS）以及核磁共振光谱（NMR）对上清液相进行了表征。对在不同反应时间停止的不同合成批次的分析表明，在早期形成未知固相后，从t = 3小时开始形成UO2球形微晶。U38的结晶从t = 4小时开始，以UO2为代价，并在t = 8小时后完成。从溶液中的纯铀（IV）物种开始（t = 0 - 1小时），在t = 1 - 3小时观察到氧化反应，U（IV）/U（VI）比例为70:30。然后，当UO2沉淀发生时，该比例反转，U（IV）/U（VI）比例为25/75。对U38微晶的全面SEM观察表明，UO2聚集体嵌入其中。这可能表明UO2作为铀（IV）的储存库，用于形成由苯甲酸酯和四氢呋喃配体稳定的U38。在U38结晶的早期阶段，在t = 4小时出现了一个瞬态结晶相。其晶体结构揭示了一个新的十二核部分（U12），基于{U6O8}型的内部六核核心，由另外三对双核U2单元修饰。U12基序由苯甲酸酯、草酸盐和乙醇酸酯配体稳定。
