Complexation of Uranium(VI) with N-(2-Hydroxyethyl)ethylenediamine- N, N′, N′-triacetic Acid in Aqueous Solution: Thermodynamic Studies and Coordination Analyses

Xingliang Li; Zhicheng Zhang; Leigh R. Martin; Shunzhong Luo; Linfeng Rao

doi:10.1021/acs.inorgchem.8b00655

Complexation of Uranium(VI) with N-(2-Hydroxyethyl)ethylenediamine- N, N′, N′-triacetic Acid in Aqueous Solution: Thermodynamic Studies and Coordination Analyses

Xingliang Li, Zhicheng Zhang, Leigh R. Martin, Shunzhong Luo, Linfeng Rao

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Abstract

N-(2-Hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA, denoted as H₃L in this work, and the three dissociable protons represent those of the three carboxylic groups) is a strong chelating ligand and plays an important role in the treatment and disposal of nuclear wastes as well as separation sciences of f-elements. In this work, the complexation of HEDTA with U(VI) was studied thermodynamically and structurally in aqueous solutions. Potentiometry and microcalorimetry were used to measure the complexation constants (298-343 K) and enthalpies (298 K), respectively, at I = 1.0 mol·L^-1 NaClO₄. Thermodynamic studies identified three 1:1 U(VI)/HEDTA complexes with different degrees of deprotonation, namely, UO₂(HL)(aq), UO₂L^-, and UO₂(H_-1L)^2-, where H_-1 represents the deprotonation of the hydroxyl group. The results indicated that all three complexation reactions are endothermic and driven by entropy only. Coordination modes of the three complexes were investigated by NMR and extended X-ray absorption fine structure spectroscopies. In the UO₂(HL)(aq) complex, HEDTA holds a tridentate mode, and the coordination occurs to the end of the ethylenediamine backbone. Two oxygens of the two carboxylic groups and one nitrogen of the amine group participate in the coordination. In both UO₂L^- and UO₂(H_-1L)^2-, HEDTA holds a tetradentate mode and coordinates to U(VI) along the side of the ethylenediamine backbone. The difference is that in the UO₂(H_-1L)^2- complex, the alkoxide form of the HEDTA hydroxyl group directly binds to the U(VI) atom, forming a highly strong chelation.

Original language	English
Pages (from-to)	7684-7693
Number of pages	10
Journal	Inorganic Chemistry
Volume	57
Issue number	13
DOIs	https://doi.org/10.1021/acs.inorgchem.8b00655
State	Published - Jul 2 2018
Externally published	Yes

Funding

The experimental work was supported by the Fuel Cycle Research and Development (FCR&D) Thermodynamics and Kinetics Program, Office of Nuclear Energy, the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231 at Lawrence Berkeley National Laboratory (LBNL). Preparation of the manuscript was supported by the Director, Office of Science, Office of Basic Energy Sciences under U.S. DOE Contract No. DE-AC02-05CH11231 at LBNL. L.R.M. acknowledges the support from DOE NE FCR&D Thermodynamics and Kinetics program, under DOE Idaho Operations Office Contract No. DE-AC07-05ID14517. The EXAFS data were collected at Stanford Synchrotron Radiation Laboratory, which is a user facility operated for the U.S. DOE by Stanford Univ. The experimental work was supported by the Fuel Cycle Research and Development (FCR&D) Thermodynamics and Kinetics Program Office of Nuclear Energy, the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231 at Lawrence Berkeley National Laboratory (LBNL). Preparation of the manuscript was supported by the Director Office of Science, Office of Basic Energy Sciences under U.S. DOE Contract No. DE-AC02-05CH11231 at LBNL. L.R.M. acknowledges the support from DOE NE FCR&D Thermodynamics and Kinetics program, under DOE Idaho Operations Office Contract No. DE-AC07-05ID14517.

Funders	Funder number
DOE Idaho Operations Office
DOE NE FCR&D Thermodynamics and Kinetics program
Fuel Cycle Research and Development
Kinetics Program
Office of Basic Energy Sciences
U.S. Department of Energy	DE-AC02-05CH11231
Office of Science
Office of Nuclear Energy
Lawrence Berkeley National Laboratory

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title = "Complexation of Uranium(VI) with N-(2-Hydroxyethyl)ethylenediamine- N, N′, N′-triacetic Acid in Aqueous Solution: Thermodynamic Studies and Coordination Analyses",

abstract = "N-(2-Hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA, denoted as H3L in this work, and the three dissociable protons represent those of the three carboxylic groups) is a strong chelating ligand and plays an important role in the treatment and disposal of nuclear wastes as well as separation sciences of f-elements. In this work, the complexation of HEDTA with U(VI) was studied thermodynamically and structurally in aqueous solutions. Potentiometry and microcalorimetry were used to measure the complexation constants (298-343 K) and enthalpies (298 K), respectively, at I = 1.0 mol·L-1 NaClO4. Thermodynamic studies identified three 1:1 U(VI)/HEDTA complexes with different degrees of deprotonation, namely, UO2(HL)(aq), UO2L-, and UO2(H-1L)2-, where H-1 represents the deprotonation of the hydroxyl group. The results indicated that all three complexation reactions are endothermic and driven by entropy only. Coordination modes of the three complexes were investigated by NMR and extended X-ray absorption fine structure spectroscopies. In the UO2(HL)(aq) complex, HEDTA holds a tridentate mode, and the coordination occurs to the end of the ethylenediamine backbone. Two oxygens of the two carboxylic groups and one nitrogen of the amine group participate in the coordination. In both UO2L- and UO2(H-1L)2-, HEDTA holds a tetradentate mode and coordinates to U(VI) along the side of the ethylenediamine backbone. The difference is that in the UO2(H-1L)2- complex, the alkoxide form of the HEDTA hydroxyl group directly binds to the U(VI) atom, forming a highly strong chelation.",

author = "Xingliang Li and Zhicheng Zhang and Martin, {Leigh R.} and Shunzhong Luo and Linfeng Rao",

note = "Publisher Copyright: {\textcopyright} 2018 American Chemical Society.",

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doi = "10.1021/acs.inorgchem.8b00655",

language = "English",

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T1 - Complexation of Uranium(VI) with N-(2-Hydroxyethyl)ethylenediamine- N, N′, N′-triacetic Acid in Aqueous Solution

T2 - Thermodynamic Studies and Coordination Analyses

AU - Li, Xingliang

AU - Zhang, Zhicheng

AU - Martin, Leigh R.

AU - Luo, Shunzhong

AU - Rao, Linfeng

PY - 2018/7/2

Y1 - 2018/7/2

N2 - N-(2-Hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA, denoted as H3L in this work, and the three dissociable protons represent those of the three carboxylic groups) is a strong chelating ligand and plays an important role in the treatment and disposal of nuclear wastes as well as separation sciences of f-elements. In this work, the complexation of HEDTA with U(VI) was studied thermodynamically and structurally in aqueous solutions. Potentiometry and microcalorimetry were used to measure the complexation constants (298-343 K) and enthalpies (298 K), respectively, at I = 1.0 mol·L-1 NaClO4. Thermodynamic studies identified three 1:1 U(VI)/HEDTA complexes with different degrees of deprotonation, namely, UO2(HL)(aq), UO2L-, and UO2(H-1L)2-, where H-1 represents the deprotonation of the hydroxyl group. The results indicated that all three complexation reactions are endothermic and driven by entropy only. Coordination modes of the three complexes were investigated by NMR and extended X-ray absorption fine structure spectroscopies. In the UO2(HL)(aq) complex, HEDTA holds a tridentate mode, and the coordination occurs to the end of the ethylenediamine backbone. Two oxygens of the two carboxylic groups and one nitrogen of the amine group participate in the coordination. In both UO2L- and UO2(H-1L)2-, HEDTA holds a tetradentate mode and coordinates to U(VI) along the side of the ethylenediamine backbone. The difference is that in the UO2(H-1L)2- complex, the alkoxide form of the HEDTA hydroxyl group directly binds to the U(VI) atom, forming a highly strong chelation.

AB - N-(2-Hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA, denoted as H3L in this work, and the three dissociable protons represent those of the three carboxylic groups) is a strong chelating ligand and plays an important role in the treatment and disposal of nuclear wastes as well as separation sciences of f-elements. In this work, the complexation of HEDTA with U(VI) was studied thermodynamically and structurally in aqueous solutions. Potentiometry and microcalorimetry were used to measure the complexation constants (298-343 K) and enthalpies (298 K), respectively, at I = 1.0 mol·L-1 NaClO4. Thermodynamic studies identified three 1:1 U(VI)/HEDTA complexes with different degrees of deprotonation, namely, UO2(HL)(aq), UO2L-, and UO2(H-1L)2-, where H-1 represents the deprotonation of the hydroxyl group. The results indicated that all three complexation reactions are endothermic and driven by entropy only. Coordination modes of the three complexes were investigated by NMR and extended X-ray absorption fine structure spectroscopies. In the UO2(HL)(aq) complex, HEDTA holds a tridentate mode, and the coordination occurs to the end of the ethylenediamine backbone. Two oxygens of the two carboxylic groups and one nitrogen of the amine group participate in the coordination. In both UO2L- and UO2(H-1L)2-, HEDTA holds a tetradentate mode and coordinates to U(VI) along the side of the ethylenediamine backbone. The difference is that in the UO2(H-1L)2- complex, the alkoxide form of the HEDTA hydroxyl group directly binds to the U(VI) atom, forming a highly strong chelation.

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Complexation of Uranium(VI) with N-(2-Hydroxyethyl)ethylenediamine- N, N′, N′-triacetic Acid in Aqueous Solution: Thermodynamic Studies and Coordination Analyses

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