Thermodynamics of Thorium(IV) complexes with N-methylethylenediamine-N,Nʹ,Nʹ-triacetate in aqueous solutions: Potentiometry and microcalorimetry

Nuclear Analysis Pub Date : 2023-09-01 DOI:10.1016/j.nucana.2023.100082

Zhuoxi Li , Yuyu Liang , Xiang Li , Wanjun Mu , Baihua Chen , Jun Tu , Lina Lv , Yanqiu Yang , Xingliang Li

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Abstract

The thermodynamic parameters of the complexes of Th with N-methylethylenediamine-N,Nʹ,Nʹ-triacetic acid (MEDTA; denoted as H₃L with three dissociable protons) were studied. Potentiometry and microcalorimetry were used to determine formation constants and enthalpies, respectively. Thermodynamic analysis revealed two successively formed complexes, namely, ThL⁺ and ThL₂²⁻ (L³⁻ denotes the totally deprotonated MEDTA). Results indicated that both complexation reactions were exothermic and driven by entropic force. The first stepwise reaction (Th⁴⁺ + L³⁻ = ThL⁺) was mainly driven by entropy with minimal effect on enthalpy change. The second stepwise reaction (ThL⁺ + L³⁻ = ThL₂²⁻) was more exothermic and showed less entropic change than the first stepwise reaction. The strong chelation of MEDTA would inhibit the hydrolysis of Th⁴⁺ and increase solubility.

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钍(IV)与N-甲基乙二胺-N,N′，N′-三乙酸盐配合物在水溶液中的热力学:电位法和微量热法

Th与N-甲基乙二胺-N,N,N -三乙酸(MEDTA)配合物的热力学参数;表示为含有三个可解离质子的H3L)。用电位法和微量热法分别测定了生成常数和焓。热力学分析表明，ThL+和ThL22−两个络合物依次形成(L3−表示完全去质子化的MEDTA)。结果表明，两种络合反应均为放热反应，均受熵的驱动。第一个分步反应(Th4+ + L3−= ThL+)主要由熵驱动，对焓变的影响很小。与第一步反应相比，第二步反应(ThL+ + L3−= ThL22−)放出热量更大，熵变更小。MEDTA的强螯合作用会抑制Th4+的水解，增加其溶解度。

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Nuclear Analysis

CiteScore

1.70

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