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

Abstract

The complexation of Cm(III) and Eu(III) with 2,6-bis(5,6-di-i-propyl-1,2,4-triazin-3-yl)-pyridine (ⁱPr-BTP) is studied in methanol : water (1 : 1, vol) by time-resolved laser-induced fluorescence spectroscopy (TRLFS). With increasing ligand concentration [Cm(ⁱPr-BTP)₃]³⁺ and [Eu(ⁱPr-BTP)₃]³⁺ are formed, respectively. Stability constants of log β₃′([Cm(ⁱPr-BTP)₃]³⁺) = 16.3 ± 0.3 and log β₃′([Eu(ⁱPr-BTP)₃]³⁺) = 14.9 ± 0.3 are determined. Thermodynamic data of the complexation reactions is obtained in a temperature range of 20–60 °C. The complexation of ⁱPr-BTP with both metal ions is exothermic (Cm(III): Δ_rH₃′ = −(64.1 ± 3.0) kJ mol⁻¹; Eu(III): Δ_rH₃′ = −(42.6 ± 2.0) kJ mol⁻¹). The reaction entropy for the formation of [Eu(ⁱPr-BTP)₃]³⁺ is higher compared to the Cm(III) complex (Cm(III): Δ_rS₃′ = (96.5 ± 6.5) J mol⁻¹ K⁻¹; Eu(III): Δ_rS₃′ = (136.0 ± 15.2) J mol⁻¹ K⁻¹). Different complexation entropies for the formation of [Cm(ⁱPr-BTP)₃] and [Cm(ⁿPr-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.