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]

Pilgrim, Corey D.; Mason, Harris E.; Zavarin, Mavrik; Casey, William H.

doi:10.1002/cplu.201800025

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]

Journal Article · 02 March 2018 · ChemPlusChem

DOI: https://doi.org/10.1002/cplu.201800025 · OSTI ID:1466938

^[1]; Mason, Harris E. ^[2]; Zavarin, Mavrik ^[2];

^[1]

Univ. of California, Davis, CA (United States). Dept. of Chemistry
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

The kinetics of ligand exchange between the free oxalate ion, C₂O₄^2-, and the bis-oxalato Np^V 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.

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Research Organization:: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Energy Frontier Research Centers (EFRC) (United States). Materials Science of Actinides (MSA)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Biological and Environmental Research (BER)

Grant/Contract Number:: AC52-07NA27344; SC0001089

OSTI ID:: 1466938

Alternate ID(s):: OSTI ID: 1423490

Report Number(s):: LLNL-JRNL-744744; 899908

Journal Information:: ChemPlusChem, Vol. 83, Issue 7; ISSN 2192-6506

Publisher:: ChemPubSoc EuropeCopyright Statement

Country of Publication:: United States

Language:: English

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