A TRLFS study on the complexation of Cm(iii) and Eu(iii) with 4-t-butyl-6,6′-bis-(5,6-diethyl-1,2,4-triazin-3-yl)-2,2′-bipyridine in a water/2-propanol mixture

Abstract

The complexation of Cm(III) and Eu(III) with 4-t-butyl-6,6′-bis-(5,6-diethyl-1,2,4-triazin-3-yl)-2,2′-bipyridine (t-Bu-C2-BTBP) in water/2-propanol solution is studied. With increasing ligand concentration, 1 : 2 complexes [M(t-Bu-C2-BTBP)₂(H₂O)]³⁺ form from the solvated metal ions. The stability constants are log K_Cm(III) = 11.1 and log K_Eu(III) = 9.0. For both Cm(III) and Eu(III), the complexation reaction is both enthalpy and entropy driven. ΔH_Cm(III) is 11.7 kJ mol⁻¹ more negative than ΔH_Eu(III), whereas the entropy difference is negligible. This is in good agreement with t-Bu-C2-BTBP's selectivity in liquid–liquid extraction.