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.

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)(H(2)O)](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. DeltaH(Cm(III)) is 11.7 kJ mol(-1) more negative than DeltaH(Eu(III)), whereas the entropy difference is negligible. This is in good agreement with t-Bu-C2-BTBP's selectivity in liquid-liquid extraction.