Complexation of Th(IV) and various lanthanides(III) by glycolic acid; potentiometric, 13C-NMR and EXAFS studies
Complexation of Th(IV) and various lanthanides(III) by glycolic acid; potentiometric, 13C-NMR and EXAFS studies
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乙醇酸络合Th(IV)和各种镧系元素(III)；
DOI：
10.1039/b204717a
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
I. Grenthe
中科院分区：
文献类型：
--
作者：
T. Toraishi;I. Farkas;Z. Szabó;I. Grenthe
乙醇酸HOCH 2CO 2 −作用下四价钍和各种三价镧系元素的络合物形成
用电位法、~（13）C-NMR谱和EXAFS研究了A-。利用电位数据推导了反应pMn+（aq）的化学计量比和平衡常数。
+
rA−
MpH−qArnp − q − r
+
qH+，25 ℃，在Na+恒定浓度等于3.00 M的离子介质中。单核配合物Th（HOCH 2CO 2 −）n; n
= 1-4，在−log[H+]范围2.5-4.5内确定。使用实验数据的最小二乘分析获得的这些络合物的平衡常数与先前公布的信息一致;这些测试溶液还包含双核三元络合物Th 2 H −2Ar，r
= 2、4和6。在高浓度和恒定浓度的乙醇酸盐，0.50，0.75和1.0 M，分别在pH范围5-10的复合物的形成进行了研究。在这些条件下，除了双核物质外，还形成了四核配合物M4 H − qA 8，其中Th（IV）和Ln（III）体系的q分别在6到13和6到8之间变化。13 C NMR光谱显示，在pH 4.5时，配位和游离的乙醇酸酯快速交换，而在较高pH时，配位配体的CH 2和CO2−区域有两个独立的窄峰，表明两个相同分布的位点之间的交换缓慢。对于Th（IV）和Ln（III），峰积分对应于每个金属的两个键合配体。EXAFS数据被用来推断四核钍配合物的键距。这些数据与NMR数据一起表明，四核配合物具有立方烷样核心“M4（OCH 2CO 2）4”，其上配位有另外的乙醇酸酯、羟基乙酸酯和氢氧化物配体。α-羟基羧酸盐的新结构和成键特征的鉴定，特别是在较高pH下，可用于探索不同氧化态的锕系元素之间的新分离方案，也可用于镧系元素（III）和锕系元素（III）离子之间的族分离。
The complex formation of tetravalent thorium and various trivalent lanthanides by glycolate HOCH2CO2−
A−, has been investigated by potentiometry, 13C-NMR spectroscopy and EXAFS. The potentiometric data were used to deduce the stoichiometry and equilibrium constants for the reactions pMn+(aq)
+
rA−
⇄ MpH−qArnp − q − r
+
qH+ at 25 °C, in an ionic medium with a constant concentration of Na+ equal to 3.00 M. Mononuclear complexes Th(HOCH2CO2−)n; n
= 1–4, were identified in the −log[H+] range 2.5–4.5. The equilibrium constants of these complexes obtained using a least-squares analysis of the experimental data agree well with previously published information; these test solutions also contain dinuclear ternary complexes Th2H−2Ar, r
= 2, 4 and 6. The complex formation in the pH range 5–10 was studied at high and constant concentrations of glycolate, 0.50, 0.75 and 1.0 M, respectively. Under these conditions, in addition to the dinuclear species, also tetranuclear complexes M4H−qA8 are formed, where q varies from 6 to 13 and 6 to 8 for the Th(IV) and Ln(III) systems, respectively. 13C NMR spectra show that coordinated and free glycolate are in fast exchange at pH 4.5, while at higher pH there are two separate narrow peaks both in the CH2 and CO2− regions for the coordinated ligand, indicating slow exchange between two equally populated sites. The peak integrals correspond to two bonded ligands per metal for both Th(IV) and Ln(III). EXAFS data were used to deduce bond distances within the tetranuclear Th complexes. These data together with the NMR-data indicate that the tetranuclear complexes have a cubane-like core “M4(OCH2CO2)4” to which additional glycolate, oxyacetate and hydroxide ligands are coordinated. The identification of new structure and bonding characteristics of α-hydroxycarboxylates, in particular at higher pH, may be used to explore new separation schemes between actinides in different oxidation states, but also for group separations between lanthanide(III) and actinide(III) ions.