Lucks Christian, Rossberg André, Tsushima Satoru, Foerstendorf Harald, Scheinost Andreas C, Bernhard Gert
Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf (HZDR) , P.O. Box 510119, 01314 Dresden, Germany.
Inorg Chem. 2012 Nov 19;51(22):12288-300. doi: 10.1021/ic301565p. Epub 2012 Oct 30.
We employed density functional theory (DFT) calculations, and ultraviolet-visible (UV-vis), extended X-ray absorption fine-structure (EXAFS), and attenuated total reflection Fourier-transform infrared (IR) spectroscopy analyzed with iterative transformation factor analysis (ITFA) to determine the structures and the pH-speciation of aqueous acetate (ac) and succinate (suc) U(VI) complexes. In the acetate system, all spectroscopies confirm the thermodynamically predicted pH-speciation by Ahrland (1951), with the hydrated uranyl ion and a 1:1, a 1:2 and a 1:3 U(VI)-ac complex. In the succinate system, we identified a new 1:3 U(VI)-suc complex, in addition to the previously known 1:1 and 1:2 U(VI)-suc complexes, and determined the pH-speciation for all complexes. The IR spectra show absorption bands of the antisymmetric stretching mode of the uranyl mojety (υ3(UO2)) at 949, 939, 924 cm(-1) and at 950, 938, 925 cm(-1) for the 1:1, 1:2 and 1:3 U(VI)-ac and U(VI)-suc complexes, respectively. IR absorption bands at 1535 and 1534 cm(-1) and at 1465 and 1462 cm(-1) are assigned to the antisymmetric υ3,as(COO) and symmetric υ3,s(COO) stretching mode of bidentately coordinated carboxylic groups in the U(VI)-ac and U(VI)-suc complexes. The assignment of the three IR bands (υ3(UO2), υ3,as(COO), υ3,s(COO)) and the stoichiometry of the complexes is supported by DFT calculations. The UV-vis spectra of the equivalent U(VI)-ac and U(VI)-suc complexes are similar suggesting common structural features. Consistent with IR spectroscopy and DFT calculations, EXAFS showed a bidentate coordination of the carboxylic groups to the equatorial plane of the uranyl moiety for all uranyl ligand complexes except for the newly detected 1:3 U(VI)-suc complex, where two carboxylic groups coordinate bidentately and one carboxylic group coordinates monodentately. All 1:1 and 1:2 complexes have a U-Owater distance of ∼2.36 Å, which is shorter than the U-Owater distance of ∼2.40 Å of the hydrated uranyl ion. For all complexes the U-Ocarboxyl distance of the bidentately coordinated carboxylic group is ∼2.47 Å, while the monodentately coordinated carboxylic group of the 1:3 U(VI)-suc complex has a U-Ocarboxyl distance of ∼2.36 Å, that is, similar to the short U-Owater distance in the 1:1 and 1:2 complexes.
我们采用密度泛函理论（DFT）计算，并运用迭代变换因子分析（ITFA）对紫外可见（UV-vis）光谱、扩展X射线吸收精细结构（EXAFS）光谱以及衰减全反射傅里叶变换红外（IR）光谱进行分析，以确定乙酸根（ac）和琥珀酸根（suc）的U(VI)水配合物的结构及pH形态。在乙酸根体系中，所有光谱均证实了Ahrland（1951）热力学预测的pH形态，即水合铀酰离子以及1:1、1:2和1:3的U(VI)-ac配合物。在琥珀酸根体系中，除了先前已知的1:1和1:2的U(VI)-suc配合物外，我们还鉴定出一种新的1:3的U(VI)-suc配合物，并确定了所有配合物的pH形态。IR光谱显示，对于1:1、1:2和1:3的U(VI)-ac和U(VI)-suc配合物，铀酰基团反对称伸缩模式（υ3(UO2)）的吸收带分别位于949、939、924 cm⁻¹以及950、938、925 cm⁻¹处。位于1535和1534 cm⁻¹以及1465和1462 cm⁻¹处的IR吸收带分别归属于U(VI)-ac和U(VI)-suc配合物中双齿配位羧基的反对称υ3,as(COO)和对称υ3,s(COO)伸缩模式。DFT计算支持了这三个IR谱带（υ3(UO2)、υ3,as(COO)、υ3,s(COO)）的归属以及配合物的化学计量比。等效的U(VI)-ac和U(VI)-suc配合物的UV-vis光谱相似，表明它们具有共同的结构特征。与IR光谱和DFT计算结果一致，EXAFS显示，除新检测到的1:3的U(VI)-suc配合物外，所有铀酰配体配合物中羧基均与铀酰基团的赤道平面呈双齿配位，在该配合物中，两个羧基呈双齿配位，一个羧基呈单齿配位。所有1:1和1:2配合物的U-O水距离约为2.36 Å，短于水合铀酰离子的U-O水距离（约2.40 Å）。对于所有配合物，双齿配位羧基的U-O羧基距离约为2.47 Å，而1:3的U(VI)-suc配合物中呈单齿配位的羧基的U-O羧基距离约为2.36 Å，即与1:1和1:2配合物中的短U-O水距离相似。
