Extraction and complexation of americium(III) and europium(III) by a N-donor ligand of 3,5-bis(2-pyridyl)pyrazole

Abstract The synthesis, Eu3+ complexation, and selective solvent extraction of trivalent americium (Am3+) over trivalent europium (Eu3+) in nitric acid solution by N-donor ligand of 3,5-bis(2-pyridyl)pyrazole (BisPypzH) were described. By using tert-butyl benzene as diluent, BisPypzH ligand in combination with 2-bromohexanoic acid demonstrated the extraction selectivity for Am3+ over trivalent lanthanides (Ln3+) with the separation factor (SFAm/Ln) value ranging from 14.3 to 59.4. Slope analysis showed the formation of 1:1 and 1:2 metal/ligand extracted species corresponding to the BisPypzH concentration below and above 0.025 mol/L, respectively, which was also confirmed by electrospray ionization mass spectrometry (ESI-MS) and dynamic light scattering (DLS) analyses. The extraction conformed to a cation-exchange model. Additionally, the 1:1 and 1:2 metal/ligand complexes were also observed in methanol solution and in solid state, severally, by means of UV–vis spectroscopy, luminescence spectroscopy and ESI-MS. Furthermore, the analyses of Fourier transform infrared spectra (FTIR), Raman spectra, and time-resolved laser-induced fluorescence spectra (TRLFS) indicated the presence of three bidentate NO3− and the absence of H2O molecules in the inner coordination sphere of the central Eu cation in the complex. Meanwhile, the stability constant for BisPypzH-Eu complex was also given.