A TRLFS Study on the Complexation of CmIII and EuIII with 2,6-Bis(5,6dipropyl-1,2,4-triazin-3-yl)pyridine in Water/Methanol Mixture

The complexation of Cm-III and Eu-III with 2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine (nPr-BTP) in water/methanol solution is studied. 1:3 complexes [M(nPr-BTP)(3)](3+) form from the solvated metal ions upon addition of ligand. The conditional stability constants are log K-Cm(III) = 14.4 and log K-Eu(III) = 11.9. For both metal ions the complexation reaction is both enthalpy and entropy driven. Delta H-CmIII is 10.1 kJ/mol more negative than Delta H-EuIII, whereas the entropy difference is small. The difference in Delta G between the formation of the Cm-III and Eu-III complexes is in good agreement with nPr-BTP's selectivity in liquid-liquid extraction.