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Title: Rates of Ligand Exchange around the Bis-Oxalato Complex [NpO 2(C 2O 4) 2] 3- Measured by Using Multinuclear NMR Spectroscopy under Neutral to Semi-Alkaline Conditions [Rates of ligand exchange around the bis-oxalato complex NpO2(C2O4)23- measured using multinuclear NMR at neutral to semi-alkaline conditions]

Abstract

The kinetics of ligand exchange between the free oxalate ion, C 2O 4 2-, and the bis-oxalato Np V complex, [NpO 2(C 2O 4) 2] 3-, in aqueous solution are reported by using 13C and 17O NMR spectroscopy methods. Rates of exchange were measured in the pH regime of 6.5–9.0, at which speciation is shown to be suitably simple. Because the neptunium(V) complex is paramagnetic, the rates of ligand exchange were estimated by following the width of the 13C and 17O signals assigned to the free oxalate ion in solution and by applying the Swift–Connick method for measuring rates of exchange. A set of experiments were conducted in which pH and total oxalate concentration were varied, and the linear dependence of the rate on these parameters was demonstrated. Variable-temperature NMR spectroscopy was also performed to measure activation parameters of complexation. Finally, at pH<8.0, ΔH =16.9 ±4.9 kJ mol -1 and ΔS≠=-116.3 ±17.1kJ mol -1K -1, whereas at pH>8.0 there is almost no dependence on temperature, which is interpreted to indicate that hydrolysis is coupled to ligand exchange under these conditions.

Authors:
ORCiD logo [1];  [2];  [2]; ORCiD logo [1]
  1. Univ. of California, Davis, CA (United States). Dept. of Chemistry
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Energy Frontier Research Centers (EFRC) (United States). Materials Science of Actinides (MSA)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1466938
Alternate Identifier(s):
OSTI ID: 1423490
Report Number(s):
LLNL-JRNL-744744
Journal ID: ISSN 2192-6506; 899908
Grant/Contract Number:  
AC52-07NA27344; SC0001089
Resource Type:
Accepted Manuscript
Journal Name:
ChemPlusChem
Additional Journal Information:
Journal Volume: 83; Journal Issue: 7; Journal ID: ISSN 2192-6506
Publisher:
ChemPubSoc Europe
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; kinetics; ligand effects; neptunium; NMR spectroscopy; radiochemistry

Citation Formats

Pilgrim, Corey D., Mason, Harris E., Zavarin, Mavrik, and Casey, William H. Rates of Ligand Exchange around the Bis-Oxalato Complex [NpO2(C2O4)2]3- Measured by Using Multinuclear NMR Spectroscopy under Neutral to Semi-Alkaline Conditions [Rates of ligand exchange around the bis-oxalato complex NpO2(C2O4)23- measured using multinuclear NMR at neutral to semi-alkaline conditions]. United States: N. p., 2018. Web. doi:10.1002/cplu.201800025.
Pilgrim, Corey D., Mason, Harris E., Zavarin, Mavrik, & Casey, William H. Rates of Ligand Exchange around the Bis-Oxalato Complex [NpO2(C2O4)2]3- Measured by Using Multinuclear NMR Spectroscopy under Neutral to Semi-Alkaline Conditions [Rates of ligand exchange around the bis-oxalato complex NpO2(C2O4)23- measured using multinuclear NMR at neutral to semi-alkaline conditions]. United States. doi:10.1002/cplu.201800025.
Pilgrim, Corey D., Mason, Harris E., Zavarin, Mavrik, and Casey, William H. Fri . "Rates of Ligand Exchange around the Bis-Oxalato Complex [NpO2(C2O4)2]3- Measured by Using Multinuclear NMR Spectroscopy under Neutral to Semi-Alkaline Conditions [Rates of ligand exchange around the bis-oxalato complex NpO2(C2O4)23- measured using multinuclear NMR at neutral to semi-alkaline conditions]". United States. doi:10.1002/cplu.201800025. https://www.osti.gov/servlets/purl/1466938.
@article{osti_1466938,
title = {Rates of Ligand Exchange around the Bis-Oxalato Complex [NpO2(C2O4)2]3- Measured by Using Multinuclear NMR Spectroscopy under Neutral to Semi-Alkaline Conditions [Rates of ligand exchange around the bis-oxalato complex NpO2(C2O4)23- measured using multinuclear NMR at neutral to semi-alkaline conditions]},
author = {Pilgrim, Corey D. and Mason, Harris E. and Zavarin, Mavrik and Casey, William H.},
abstractNote = {The kinetics of ligand exchange between the free oxalate ion, C2O42-, and the bis-oxalato NpV complex, [NpO2(C2O4)2]3-, in aqueous solution are reported by using 13C and 17O NMR spectroscopy methods. Rates of exchange were measured in the pH regime of 6.5–9.0, at which speciation is shown to be suitably simple. Because the neptunium(V) complex is paramagnetic, the rates of ligand exchange were estimated by following the width of the 13C and 17O signals assigned to the free oxalate ion in solution and by applying the Swift–Connick method for measuring rates of exchange. A set of experiments were conducted in which pH and total oxalate concentration were varied, and the linear dependence of the rate on these parameters was demonstrated. Variable-temperature NMR spectroscopy was also performed to measure activation parameters of complexation. Finally, at pH<8.0, ΔH≠=16.9 ±4.9 kJ mol-1 and ΔS≠=-116.3 ±17.1kJ mol-1K-1, whereas at pH>8.0 there is almost no dependence on temperature, which is interpreted to indicate that hydrolysis is coupled to ligand exchange under these conditions.},
doi = {10.1002/cplu.201800025},
journal = {ChemPlusChem},
number = 7,
volume = 83,
place = {United States},
year = {2018},
month = {3}
}

Journal Article:
Free Publicly Available Full Text
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Figures / Tables:

Figure 1 Figure 1: A representative absorbance spectrum of the mixture of NpO2(C2O4)- and NpO2(C2O4)3- in aqueous solution, with no free NpO2+ seen.

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