Institut de Physique Nucléaire, CNRS, Univ. Paris-Sud 11 , 91406 Orsay Cedex, France.
Inorg Chem. 2013 Oct 7;52(19):11218-27. doi: 10.1021/ic4014653. Epub 2013 Sep 10.
The redox properties of uranium(IV) hexachloro complex have been investigated with a glassy carbon electrode in four bis(trifluoromethylsulfonyl)imide (Tf2N(-)) based ionic liquids (ILs): the 1-butyl-3-methylimidazolium (BuMeIm), the 1-butyl-2,3-dimethylimidazolium (BuMe2Im), the N-butylmethylpyrrolidinium (BuMePyr), and the tributyl-methylammonium (MeBu3N). The cyclic voltammetric analysis has revealed two main redox systems: U(V)Cl6(-)/U(IV)Cl6(2-) around 0.2 V and U(IV)Cl6(2-)/U(III)Cl6(3-) around -2 V. The formation of U(V)Cl6(-), a non-dioxo uranium(V) species, can then be observed at the electrode in Tf2N based ILs. This work also provides evidence of a specific interaction between the uranium anionic species and the IL cations because the standard potentials of both redox couples depend on the IL. The interaction extent has been evaluated by comparison of the IL cation number associated with the uranium anionic complex. For that purpose, the standard potentials of both systems have been measured in the less interacting medium [MeBu3N][Tf2N] as a function of the BuMeIm, BuMe2Im, and BuMePyr concentration. Predominance diagrams for uranium hexachloro complexes, analogous to the Pourbaix diagram, have then been built in [MeBu3N][Tf2N] depending on the IL cations concentration. The exploitation of these diagrams leads to the conclusion that the interaction is function of the charge of the uranium hexachloro complex (U(V)Cl6(-) < U(IV)Cl6(2-) < U(III)Cl6(3-)) and the IL cation (BuMe2Im < BuMePyr < BuMeIm). The influence of the IL cation could be correlated to the size and the electropositivity of the IL cation. The association would occur by H-bonding and electrostatic interaction. Ab initio calculations were also carried out to evaluate the strength of the interaction between the anionic uranium(IV) chloro complex and the IL cations. The results show that BuMeIm interacts the most and MeBu3N the least with U(IV)Cl6(2-), and the magnitude of the interaction is comparable for BuMe2Im and BuMePyr.
铀(IV)六氯配合物的氧化还原性质已在四种双(三氟甲基磺酰基)亚胺 (Tf2N(-)) 基离子液体 (ILs) 中的玻璃碳电极上进行了研究：1-丁基-3-甲基咪唑鎓(BuMeIm)、1-丁基-2,3-二甲基咪唑鎓(BuMe2Im)、N-丁基甲基吡咯烷鎓(BuMePyr)和三丁基甲基铵(MeBu3N)。循环伏安分析揭示了两个主要的氧化还原体系：在 0.2 V 左右的 U(V)Cl6(-)/U(IV)Cl6(2-)和在-2 V 左右的 U(IV)Cl6(2-)/U(III)Cl6(3-)。然后可以在基于Tf2N的 ILs 中的电极上观察到非二氧铀(V)物种 U(V)Cl6(-)的形成。这项工作还提供了铀阴离子物种与 IL 阳离子之间存在特定相互作用的证据，因为这两个氧化还原对的标准电势都取决于 IL。通过比较与铀阴离子配合物相关联的 IL 阳离子数，可以评估相互作用的程度。为此，在作为非相互作用介质的[MeBu3N][Tf2N]中测量了这两个体系的标准电势，作为BuMeIm、BuMe2Im和BuMePyr浓度的函数。然后，根据 IL 阳离子浓度，在[MeBu3N][Tf2N]中构建了类似于 Pourbaix 图的铀六氯配合物优势图。这些图的利用得出的结论是，相互作用取决于铀六氯配合物的电荷(U(V)Cl6(-)<U(IV)Cl6(2-)<U(III)Cl6(3-))和 IL 阳离子(BuMe2Im<BuMePyr<BuMeIm)。IL 阳离子的影响可以与 IL 阳离子的大小和电正性相关联。这种缔合可能通过氢键和静电相互作用发生。还进行了从头算计算以评估阴离子铀(IV)氯配合物与 IL 阳离子之间相互作用的强度。结果表明，BuMeIm与 U(IV)Cl6(2-)的相互作用最强，MeBu3N的相互作用最弱，而BuMe2Im和BuMePyr的相互作用强度相当。
