Simple 17O NMR method for studying electron self-exchange reaction between UO22+ and U4+ aqua ions in acidic solution

I. Bányai, Ildikó Farkas, Imre Tóth

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Abstract

17O NMR spectroscopy is proven to be suitable and convenient method for studying the electron exchange by following the decrease of 17O-enrichment in U17OO2+ ion in the presence of U4+ ion in aqueous solution. The reactions have been performed at room temperature using I=5 M ClO4- ionic medium in acidic solutions in order to determine the kinetics of electron exchange between the U4+ and UO22+ aqua ions. The rate equation is given as R=a[H+]-2+R', where R' is an acid independent parallel path. R' depends on the concentration of the uranium species according to the following empirical rate equation: R'=k1[UO2+]1/2[U4+]1/2+k2[UO2+]3/2[U4+]1/2. The mechanism of the inverse H+ concentration-dependent path is interpreted as equilibrium formation of reactive UO2+ species from UO22+ and U4+ aqua ions and its electron exchange with UO22+. The determined rate constant of this reaction path is in agreement with the rate constant of UO22+-UO2+, one electron exchange step calculated by Marcus theory, match the range given experimentally of it in an early study. Our value lies in the same order of magnitude as the recently calculated ones by quantum chemical methods. The acid independent part is attributed to the formation of less hydrolyzed U(V) species, i.e. UO3+, which loses enrichment mainly by electron exchange with UO22+ ions. One can also conclude that 17O NMR spectroscopy, or in general NMR spectroscopy with careful kinetic analysis, is a powerful tool for studying isotope exchange reactions without the use of sophisticated separation processes.

Original languageEnglish
JournalMagnetic Resonance in Chemistry
DOIs
Publication statusAccepted/In press - 2015

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Ion exchange
Nuclear magnetic resonance
Ions
Electrons
Nuclear magnetic resonance spectroscopy
Rate constants
Kinetics
Uranium
Acids
Isotopes
Temperature

Keywords

  • <sup>17</sup>O NMR
  • Electron exchange
  • Isotope exchange
  • Kinetic analysis
  • Mechanism
  • NMR
  • Uranyl aqua complexes

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)

Cite this

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title = "Simple 17O NMR method for studying electron self-exchange reaction between UO22+ and U4+ aqua ions in acidic solution",
abstract = "17O NMR spectroscopy is proven to be suitable and convenient method for studying the electron exchange by following the decrease of 17O-enrichment in U17OO2+ ion in the presence of U4+ ion in aqueous solution. The reactions have been performed at room temperature using I=5 M ClO4- ionic medium in acidic solutions in order to determine the kinetics of electron exchange between the U4+ and UO22+ aqua ions. The rate equation is given as R=a[H+]-2+R', where R' is an acid independent parallel path. R' depends on the concentration of the uranium species according to the following empirical rate equation: R'=k1[UO2+]1/2[U4+]1/2+k2[UO2+]3/2[U4+]1/2. The mechanism of the inverse H+ concentration-dependent path is interpreted as equilibrium formation of reactive UO2+ species from UO22+ and U4+ aqua ions and its electron exchange with UO22+. The determined rate constant of this reaction path is in agreement with the rate constant of UO22+-UO2+, one electron exchange step calculated by Marcus theory, match the range given experimentally of it in an early study. Our value lies in the same order of magnitude as the recently calculated ones by quantum chemical methods. The acid independent part is attributed to the formation of less hydrolyzed U(V) species, i.e. UO3+, which loses enrichment mainly by electron exchange with UO22+ ions. One can also conclude that 17O NMR spectroscopy, or in general NMR spectroscopy with careful kinetic analysis, is a powerful tool for studying isotope exchange reactions without the use of sophisticated separation processes.",
keywords = "<sup>17</sup>O NMR, Electron exchange, Isotope exchange, Kinetic analysis, Mechanism, NMR, Uranyl aqua complexes",
author = "I. B{\'a}nyai and Ildik{\'o} Farkas and Imre T{\'o}th",
year = "2015",
doi = "10.1002/mrc.4235",
language = "English",
journal = "Magnetic Resonance in Chemistry",
issn = "0749-1581",
publisher = "John Wiley and Sons Ltd",

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TY - JOUR

T1 - Simple 17O NMR method for studying electron self-exchange reaction between UO22+ and U4+ aqua ions in acidic solution

AU - Bányai, I.

AU - Farkas, Ildikó

AU - Tóth, Imre

PY - 2015

Y1 - 2015

N2 - 17O NMR spectroscopy is proven to be suitable and convenient method for studying the electron exchange by following the decrease of 17O-enrichment in U17OO2+ ion in the presence of U4+ ion in aqueous solution. The reactions have been performed at room temperature using I=5 M ClO4- ionic medium in acidic solutions in order to determine the kinetics of electron exchange between the U4+ and UO22+ aqua ions. The rate equation is given as R=a[H+]-2+R', where R' is an acid independent parallel path. R' depends on the concentration of the uranium species according to the following empirical rate equation: R'=k1[UO2+]1/2[U4+]1/2+k2[UO2+]3/2[U4+]1/2. The mechanism of the inverse H+ concentration-dependent path is interpreted as equilibrium formation of reactive UO2+ species from UO22+ and U4+ aqua ions and its electron exchange with UO22+. The determined rate constant of this reaction path is in agreement with the rate constant of UO22+-UO2+, one electron exchange step calculated by Marcus theory, match the range given experimentally of it in an early study. Our value lies in the same order of magnitude as the recently calculated ones by quantum chemical methods. The acid independent part is attributed to the formation of less hydrolyzed U(V) species, i.e. UO3+, which loses enrichment mainly by electron exchange with UO22+ ions. One can also conclude that 17O NMR spectroscopy, or in general NMR spectroscopy with careful kinetic analysis, is a powerful tool for studying isotope exchange reactions without the use of sophisticated separation processes.

AB - 17O NMR spectroscopy is proven to be suitable and convenient method for studying the electron exchange by following the decrease of 17O-enrichment in U17OO2+ ion in the presence of U4+ ion in aqueous solution. The reactions have been performed at room temperature using I=5 M ClO4- ionic medium in acidic solutions in order to determine the kinetics of electron exchange between the U4+ and UO22+ aqua ions. The rate equation is given as R=a[H+]-2+R', where R' is an acid independent parallel path. R' depends on the concentration of the uranium species according to the following empirical rate equation: R'=k1[UO2+]1/2[U4+]1/2+k2[UO2+]3/2[U4+]1/2. The mechanism of the inverse H+ concentration-dependent path is interpreted as equilibrium formation of reactive UO2+ species from UO22+ and U4+ aqua ions and its electron exchange with UO22+. The determined rate constant of this reaction path is in agreement with the rate constant of UO22+-UO2+, one electron exchange step calculated by Marcus theory, match the range given experimentally of it in an early study. Our value lies in the same order of magnitude as the recently calculated ones by quantum chemical methods. The acid independent part is attributed to the formation of less hydrolyzed U(V) species, i.e. UO3+, which loses enrichment mainly by electron exchange with UO22+ ions. One can also conclude that 17O NMR spectroscopy, or in general NMR spectroscopy with careful kinetic analysis, is a powerful tool for studying isotope exchange reactions without the use of sophisticated separation processes.

KW - <sup>17</sup>O NMR

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KW - Isotope exchange

KW - Kinetic analysis

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KW - NMR

KW - Uranyl aqua complexes

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