2,6-Bis(5,6-diisopropyl-1,2,4-triazin-3-yl)pyridine: a highly selective N-donor ligand studied by TRLFS, liquid–liquid extraction and molecular dynamics

The complexation of Cm(III) and Eu(III) with 2,6-bis(5,6-di-i-propyl-1,2,4-triazin-3-yl)-pyridine (Pr-i-BTP) is studied in methanol:water (1:1, vol) by time-resolved laser-induced fluorescence spectroscopy (TRLFS). With increasing ligand concentration [Cm(Pr-i-BTP)(3)](3+) and (Eu(Pr-i-BTP)(3)](3+) are formed, respectively. Stability constants of log) beta(3)'([Cm(Pr-i-BTP)(3)](3+)) = 16.3 +/- 0.3 and log beta(3)'([Eu(Pr-i-BTP)(3)](3+)) = 14.9 +/- 0.3 are determined. Thermodynamic data of the complexation reactions is obtained in a temperature range of 20-60 degrees C. The complexation of Pr-i-BTP with both metal ions is exothermic (Cm(III): Delta H-r(3)' = -(64.1 +/- 3.0) kJ mol(-1); Eu(III): Delta H-r(3)' = -(42.6 +/- 2.0) kJ mol(-1)). The reaction entropy for the formation of [Eu(Pr-i-BTP)(3)](3+) is higher compared to the Cm(III) complex (Cm(III): Delta S-r(3)' = (96.5 +/- 6.5) J mol(-1) K-1; Eu(III): Delta S-r(3)' = (136.0 +/- 15.2) J mol(-1) K-1). Different complexation entropies for the formation of [Cm(Pr-i-BTP)(3)] and [Cm(Pr-n-BTP)(3)] are explained by molecular dynamics simulations. Results from liquid-liquid extraction tests confirm the ligand's peculiar extraction kinetics observed in previous studies and link them to the thermodynamic data.