Thermodynamic, Spectroscopic, and Computational Studies of f-Element Complexation by N-Hydroxyethyl-diethylenetriamine-N,N′,N″,N″-tetraacetic Acid

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• 作者：Travis S. GrimesColt R. Heathman ; Santa Jansone-Popova ; Vyacheslav S. Bryantsev ; Sriram Goverapet SrinivasanMasahiko Nakase ; Peter R. Zalupski
• 刊名：Inorganic Chemistry
• 出版年：2017
• 出版时间：February 6, 2017
• 年：2017
• 卷：56
• 期：3
• 页码：1722-1733
• 全文大小：603K
• ISSN：1520-510X

文摘

Potentiometric and spectroscopic techniques were combined with DFT calculations to probe the coordination environment and determine thermodynamic features of trivalent f-element complexation by N-hydroxyethyl-diethylenetriamine-N,N′,N″,N″-tetraacetic acid, HEDTTA. Ligand protonation constants and lanthanide stability constants were determined using potentiometry. Five protonation constants were accessible in I = 2.0 M (H⁺/Na⁺)ClO₄. UV–vis spectroscopy was used to determine stability constants for Nd³⁺ and Am³⁺ complexation with HEDTTA. Luminescence spectroscopy indicates two water molecules in the inner coordination sphere of the Eu/HEDTTA complex, suggesting HEDTTA is heptadentate. Luminescence data was supported by DFT calculations, which demonstrate that substitution of the acetate pendant arm by a N-hydroxyethyl group weakens the metal–nitrogen bond. This bond elongation is reflected in HEDTTA’s ability to differentiate trivalent actinides from trivalent lanthanides. The trans-lanthanide Ln/HEDTTA complex stability trend is analogous to Ln/DTPA complexation; however, the loss of one chelate ring resulting from structural substitution weakens the complexation by ∼3 orders of magnitude. Successful separation of trivalent americium from trivalent lanthanides was demonstrated when HEDTTA was utilized as aqueous holdback complexant in a liquid–liquid system. Time-dependent extraction studies for HEDTTA were compared to diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA) and N-hydroxyethyl-ethylenediamine-N,N′,N′-triacetic acid (HEDTA). The results indicate substantially enhanced phase-transfer kinetic rates for mixtures containing HEDTTA.