A Nuclear Magnetic Resonance Study on Ligand Exchange Reactions in La(III), Nd(III), and U(VI) Nitrato Complexes with n-Octyl(phenyl)-N, N-Diisobutylcarbamoylmethylphosphine Oxide in Non-aqueous Solvents
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The exchange reactions of n-Octyl(phenyl)-N, N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in La(III), Nd(III), and U(VI) nitrate complexes with CMPO (La(III)-, Nd(III)-, and U(VI)-CMPO complexes) have been studied in CD<SUB>3</SUB>COCD<SUB>3</SUB> by means of <SUP>31</SUP>P NMR method. The number of CMPO coordinated to the first coordination sphere of La(III) ion was directly determined to be 3 by the area integrations of <SUP>31</SUP>P NMR signals of free and coordinated CMPO molecules. The same coordination number of 3 was also obtained for the U(VI)-CMPO complex. The coordination number was not determined for the Nd(III)-CMPO complex, because of its paramagnetic behavior. The exchange rate constants of CMPO in La(III)- and U(VI)-CMPO complexes were obtained by the two-site exchange model. Paramagnetic line broadening was observed in the Nd(III)-CMPO complex and the rate constant for the exchange of CMPO was determined by the line-broadening method. The exchange rates of CMPO in La(III)- and Nd(III)-CMPO complexes depend on the free CMPO concentration ([CMPO]), while that in U(VI)-CMPO complex is independent of [CMPO]. The dissociative (D) and dissociative interchange (Id) mechanisms were proposed for the exchange reactions in the La(III)- and Nd(III)-CMPO complexes, and dissociative (D) or Id mechanism was proposed for the U(VI)-CMPO complex. The dissociative rate constants (s<SUP>-1</SUP>) at 25°C and activation parameters ΔH<SUP>≠</SUP>(kJ•mol<SUP>-1</SUP>) and ΔS<SUP>≠</SUP>(J•K<SUP>-1</SUP>•mol<SUP>-1</SUP>) are 4.76×103, 28.7±0.1, -78.4±0.2 for La(III)-CMPO complex, 4.72×10<SUP>3</SUP>, 42.6±0.4, -31.7±1.3 for Nd(III)-CMPO complex, and 3.20×10<SUP>3</SUP>, 46.9±0.6, -20.5±2.2 for U(VI)-CMPO complex, respectively.
- Journal of Nuclear Science and Technology
Journal of Nuclear Science and Technology 32(11), 1146-1153, 1995-11-25
Atomic Energy Society of Japan