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1,3-Bis[3-(2-pyridyl)pyrazol-1-yl]propane (Bippp) and 1,2-bis[3-(2-pyridyl)pyrazyl-1-methyl]benzene (Dbnpp), the pyridylpyrazole based tetradentate ligands, were synthesized and characterized by MS, NMR, and FT-IR. The solvent extraction and complexation behaviors of Am(III) and Eu(III) with the ligands were investigated experimentally and theoretically. In the presence of 2-bromohexanoic acid, the two ligands can effectively extract Am(III) over Eu(III) and other rare earth(III) metals (RE(III)) in HNO3 solution with the separation factors (SFAm/RE) ranging from 15 to 60. Slope analyses showed that both Am(III) and Eu(III) were extracted as monosolvated species, which agrees well with the results observed from X-ray crystallography and MS analyses. The stability constants (log K) obtained from UV-vis titration for Eu(III) complexes with Bippp and Dbnpp are 4.75 ± 0.03 and 4.45 ± 0.04, respectively. Both UV-vis titration and solvent extraction studies indicated that Bippp had stronger affinity for Eu(III) than Dbnpp, which is confirmed by density functional theory (DFT) calculations. DFT calculations revealed that the AmL(NO3)3 (L = Bippp and Dbnpp) complexes are thermodynamically more stable in water than their Eu(III) analogues, which is caused by greater covalency of the Am-N than Eu-N bonds. Theoretical studies gave an insight into the nature of the M(III)-ligand bonding interactions.

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A novel water-soluble ligand of N,bisdiglycolamide (TEE-BisDGA) was synthesized and used as a masking agent for selective extraction of Am(III) over Eu(III) from HNO3 solution by Nhexaoctylnitrilotriacetamide (NTAamide(C8)) in kerosene. Influences of acidity, concentration of water-soluble ligands and extractant on the distribution ratios (D) and separation factors (SF) of Am(III) and Eu(III) were investigated. In the range of examined acidity from 0.001 to 0.2 mol/L, DAm and DEu decreased with the increase of HNO3 concentration. Using 0.1 mol/L NTAamide(C8) as an extractant, the maximum SFAm/Eu of 26 can be obtained in the presence of 0.01 mol/L TEE-BisDGA in aqueous phase with pH of 3.0, which was significantly higher than that case with no TEE-BisDGA. Job's method and mole ratio method were employed for extraction mechanism research. It has been shown that Am(III) and Eu(III) formed di-solvated species with TEE-BisDGA and mono-solvated species with NTAamide(C8), © 2017. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ respectively. Moreover, the stability constants logβ values were obtained from UV-vis adsorption spectroscopic titration for Nd(III) complexes with TEE-BisDGA and N,N,N',N'-tetraethyldiglycolamide (TEDGA), which indicated that TEDGA had a stronger complex ability than TEE-BisDGA.

To clarify the structure-property relationships of pyridylpyrazole ligands and provide guidance for the design of new and more efficient ligands for the selective extraction of actinides over lanthanides, a series of alkyl-substituted pyridylpyrazole ligands with different branched chains at different positions of the pyrazole ring were synthesized. Extraction experiments showed that the pyridylpyrazole ligands exhibited good selective extraction abilities for Am III ions, and the steric effects of the branched chain had a significant impact on the distribution ratios of Am III and Eu III ions as well as the separation factor. Moreover, both slope analyses and UV/Vis spectrometry titra- [a]