Uranyl-halide complexation in N,N-dimethylformamide: halide coordination trend manifests hardness of [UO2]2+
Uranyl-halide complexation in N,N-dimethylformamide: halide coordination trend manifests hardness of [UO2]2+
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N,N-二甲基甲酰胺中卤化铀络合：卤化物配位趋势体现了 [UO2]2 的硬度
DOI：
10.1039/c3dt51191j
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发表时间：
2013
影响因子：
4
通讯作者：
Christoph Hennig
中科院分区：
文献类型：
--
作者：
Koichiro Takao;Shinobu Takao;Yasuhisa Ikeda;Gert Bernhard;Christoph Hennig
用紫外-可见吸收光谱和扩展X射线吸收精细结构（EXAFS）研究了[UO 2]2+与Cl-、Br-和I-在N，N-二甲基甲酰胺（DMF）中的络合作用，以明确区分[UO 2] 2+与卤化物的配位强度。在Cl−系统中，澄清了Cl−与DMF中[UO 2]2+的配位几乎定量进行。Cl−的配位数几乎定量地增加到4，即，极限络合物是[UO 2Cl 4]2−。[UO 2Clx]2−x（x = 1-4）的对数总稳定常数从紫外-可见滴定实验中估算为log β1 = 9.67，log β2 = 15.49，log β3 = 19.89，log β4 = 24.63。EXAFS结果很好地证明了[UO 2]2+在赤道平面上不仅有Cl−配位，而且有DMF溶剂化。研究了Br−和I−与[UO 2]2+在DMF中的相互作用。因此，Br−与[UO 2]2+的配位在第二步停止，即，只观察到[UO_2Br]~+和UO_2Br_2。EXAFS证实了每种物质的分子结构。[UO 2Brx]2−x（x = 1，2）的log βx值分别为3.45和5.42。log βx比[UO 2Clx]2−x小得多，表明Br−是[UO 2]2+比Cl−弱得多的配体。EXAFS实验表明，测试溶液中I−的存在不会改变[UO 2]2+周围的任何配位结构。因此，I−在DMF中不会形成任何稳定的[UO 2]2+络合物。因此，[UO_2]~（2+）卤代配合物在DMF中的稳定性与卤化物的硬度顺序完全一致。
Complexation of [UO2]2+ with Cl−, Br−, and I− in N,N-dimethylformamide (DMF) was studied by UV-vis absorption spectroscopy and extended X-ray absorption fine structure (EXAFS) to clearly differentiate halide coordination strengths to [UO2]2+. In the Cl− system, it was clarified that the Cl− coordination to [UO2]2+ in DMF proceeds almost quantitatively. The coordination number of Cl− almost quantitatively increases up to 4, i.e., the limiting complex is [UO2Cl4]2−. Logarithmic gross stability constants of [UO2Clx]2−x (x = 1–4) were evaluated as log β1 = 9.67, log β2 = 15.49, log β3 = 19.89, and log β4 = 24.63 from UV-vis titration experiments. The EXAFS results well demonstrated not only the Cl− coordination, but also the DMF solvation in the equatorial plane of [UO2]2+. The interaction of Br− and I− with [UO2]2+ in DMF was also investigated. As a result, the Br− coordination to [UO2]2+ stops at the second step, i.e., only [UO2Br]+ and UO2Br2 were observed. The molecular structure of each occurring species was confirmed by EXAFS. The evaluated log βx values of [UO2Brx]2−x (x = 1, 2) are 3.45 and 5.42, respectively. The much smaller log βx than those of [UO2Clx]2−x indicates that Br− is a much weaker ligand to [UO2]2+ than Cl−. The EXAFS experiments revealed that the presence of I− in the test solution does not modify any coordination structure around [UO2]2+. Thus, I− does not form any stable [UO2]2+ complexes in DMF. Consequently, the stability of the halido complexes of [UO2]2+ in DMF is exactly in line with the hardness order of halides.