Highly Efficient Trivalent Americium/Europium Separation by Phenanthroline-Derived Bis(pyrazole) Ligands

The synthesis, Eu3+ complexation, and solvent extraction of Am3+ and Eu3+ from nitric acid solutions by tetradentate phenanthroline-derived bis­(pyrazole) (BPPhen) ligands were described. By using meta-nitrobenzotrifluoride as diluent, BPPhen ligands in combination with 2-bromohexanoic acid extracted Am3+ and Eu3+ with remarkably high efficiency, excellent selectivity, and fast extraction kinetics. Stripping posed no issues. The ligands also showed excellent hydrolytic stability and acid tolerance. 2-Bromohexanoic anion neutralized the charge and increased the lipophilicity of the extracted ion pair. The extraction conformed to a cation exchange model. Slope analysis demonstrated the extraction of 1:2 metal/ligand complexes. Analyses by electrospray ionization mass spectrometry, time-resolved laser-induced fluorescence spectroscopy, Raman, and Fourier transform infrared techniques indicated that the composition of the extracted species is [Eu­(nOct-BPPhen)2­(H2O)]3+. The formation of 1:2 complexes was also confirmed by UV–vis spectroscopic titration and microcalorimetric titration methods. Meanwhile, the stability constants (K) and the thermodynamic parameters (ΔH, ΔS, ΔG) for the complexation of Eu3+ with nOct-BPPhen were presented too.