Nikitenko S I, Cannes C, Le Naour C, Moisy P, Trubert D
Institute of Physical Chemistry, Russian Academy of Science, Leninskii Pr. 31, 117915 Moscow, Russia.
Inorg Chem. 2005 Dec 12;44(25):9497-505. doi: 10.1021/ic051065b.
The behavior of U(IV) octahedral complexes [cation]2[UCl6], where the [cation]+ is [BuMeIm]+ and [MeBu3N]+, is studied using UV/visible spectroscopy, cyclic staircase voltammetry, and rotating disk electrode voltammetry in hydrophobic room-temperature ionic liquids (RTILs) [BuMeIm][Tf2N] and [MeBu3N][Tf2N], where BuMeIm+ and MeBu3N+ are 1-butyl-3-methylimidazolium and tri-n-butylmethylammonium cations, respectively, and Tf2N- is the bis(trifluoromethylsulfonyl)imide anion. The absorption spectra of [cation]2[UCl6] complexes in the RTIL solutions are similar to the diffuse solid-state reflectance spectra of the corresponding solid species, indicating that the octahedral complex UCl6(2-) is the predominant chemical form of U(IV) in Tf2N--based hydrophobic ionic liquids. Hexachloro complexes of U(IV) are stable to hydrolysis in the studied RTILs. Voltammograms of UCl(6)2- at the glassy carbon electrode in both RTILs and at the potential range of -2.5 to +1.0 V versus Ag/Ag(I) reveal the following electrochemical couples: UCl6-/UCl6(2-) (quasi-reversible system), UCl(6)2-/UCl6(3-) (quasi-reversible system), and UCl(6)2-/UCl6(Tf2N)x-3+x (irreversible reduction). The voltammetric half-wave potential, Ep/2, of the U(V)/U(IV) couple in [BuMeIm][Tf2N] is positively shifted by 80 mV compared with that in [MeBu3N][Tf2N]. The positive shift in the Ep/2 value for the quasi-reversible U(IV)/U(III) couple is much greater (250 mV) in [BuMeIm][Tf2N]. Presumably, the potential shift is due to the specific interaction of BuMeIm+ with the uranium-hexachloro complex in ionic liquid. Scanning the negative potential to -3.5 V in [MeBu3N][Tf2N] solutions of UCl6(2-) reveals the presence of an irreversible cathodic process at the peak potential equal to -3.12 V (at 100 mV/s and 60 degrees C), which could be attributed to the reduction of U(III) to U(0).
使用紫外/可见光谱、循环阶梯伏安法和旋转圆盘电极伏安法，在疏水性室温离子液体（RTILs）[BuMeIm][Tf2N]和[MeBu3N][Tf2N]中研究了八面体配合物[阳离子]2[UCl6]（其中[阳离子]+为[BuMeIm]+和[MeBu3N]+）的行为，其中BuMeIm+和MeBu3N+分别是1-丁基-3-甲基咪唑鎓和三正丁基甲基铵阳离子，而Tf2N-是双（三氟甲基磺酰）亚胺阴离子。RTIL溶液中[阳离子]2[UCl6]配合物的吸收光谱与相应固体物质的漫反射固态光谱相似，表明八面体配合物UCl6(2-)是基于Tf2N-的疏水性离子液体中U(IV)的主要化学形式。在研究的RTILs中，U(IV)的六氯配合物对水解稳定。在两种RTILs中的玻碳电极上以及相对于Ag/Ag(I)在-2.5至+1.0 V的电位范围内，UCl(6)2-的伏安图显示出以下电化学偶：UCl6-/UCl6(2-)（准可逆体系）、UCl(6)2-/UCl6(3-)（准可逆体系）和UCl(6)2-/UCl6(Tf2N)x-3+x（不可逆还原）。与[MeBu3N][Tf2N]相比，[BuMeIm][Tf2N]中U(V)/U(IV)偶的伏安半波电位Ep/2正向偏移80 mV。在[BuMeIm][Tf2N]中，准可逆U(IV)/U(III)偶的Ep/2值的正向偏移更大（250 mV）。据推测，电位偏移是由于BuMeIm+与离子液体中的铀六氯配合物之间的特定相互作用。在UCl6(2-)的[MeBu3N][Tf2N]溶液中将负电位扫描至-3.5 V，发现在峰电位等于-3.12 V（在100 mV/s和60℃下）存在不可逆的阴极过程，这可能归因于U(III)还原为U(0)。
