Study On The Coordination Chemistry Of Some Ligand Bearing N, O Donors With Lanthanides And Minor Actinides: Thermodynamics And Equilibrium Extraction

Separation of minor actinides from lanthanides is the research forcus for nuclear chemistry and radiochemistry. Coordination chemistry of minor actinides (Am, Cm, Np) is the basis of spent fuel reprocessing technology study and process design. In this dissertation, two new ligands bearing nitrogen and oxygen were synthesized. The coordination chemistry of the two new ligands with trivalent americium and lanthanides and the differences between them were compared with various methods, such as solvent extraction, speciation and thermodynamics studies of complex formation reactions in homogeneous system, and DFT calculation. Moreover, coordination thermodynamics of pentavalent neptunium, known as the "problem element" because of its weak complexation with ligands, with 1,10-phenanthroline-2,9-dicarboxylic acid (PhenDA) and 2,2’-bipyridine-6,6’-dicarboxylic acid (BiPDA) were compared. The two ligands with "soft-hard hybrid donors" (N, O) can obtain a reasonable actinide selectivity over lanthanides and complex strongly with metallic ions.Electronic property of the para-substituents affects the basicity of nitrogen in pyridine. The stability constants of the 1:3 complexes of some para-substituted-bipyridines with trivalent europium increase with the the electron donating capacity of substituents. Solvation effects reduce the differences of the stability constants between the Eu(Ⅲ) and Am(Ⅲ) complexes with such ligands.N-methylamidecalix[4]pyridine, a novel ligand synthesized in this work, forms 1:1 complex with lanthanides. The stability constants, becoming larger along the series, decrease with the solvation effects getting stronger. The solvent extraction experiments with chloroform as diluent show that the distribution ratios of 241Am and 152Eu are small values, while increasing with pH of aqueous phase. DFT calculation indicates that the solvation of species should be the main factor to the change of Gibbs free energy of the complexation between ligand and metal in water, which increased greatly if there were no methyl on the amide group.2,9-di(quinazolin-2-yl)-1,10-phenanthroline (BQPhen), another novel ligand, coordinates strongly with Ln(Ⅲ) and An(Ⅲ), forming 1:1 and 1:2 (M:L) complexes in DMF, a very strong solvating agent. The enthalpy values of the complexation reactions are small, indicating that entropy is the predominant attributor to the Gibbs free energy. However, for the complexation with Am(Ⅲ) and Eu(Ⅲ) on the same conditions, the difference of the Gibbs free energy between them comes from the enthalpy because of different bonding covalency of nitrogen with metal. Solvent extraction 241Am and 152Eu with BQPhen in nitrobenzene confirm the conclusions conducted from the complexation thermodynamics research. The separation factor 5F(Am/Eu)=11.5, which is consistent with the evaluation value with the stability constants of 1:2 complexes in DMF.Donor preorganization improves ligand’s coordination ability with metallic ions, because of not only "entropy favor" but also "enthalpy favor". For PhenDA, The stability constant of 1:1 complex with Np(V) is logβ=11.73±0.02 (t=25℃,I=0.1 M NaC104), which is much larger than that of EDDA (logβ=8.40±0.11) on the same conditions. For ligands with similar donor preorganization, such as PA (2-picolinic acid), DPA (dipicolinic acid), and PhenDA, the stability constant of 1:1 complex with Np(Ⅴ) increase donors, and the increased amplitude is larger for ligand with one more O-donor than which with one more N-donor.In summary, N-methylamidecalix[4]pyridine can be used to separate/remove An(Ⅲ) and Ln(Ⅲ) from waste water with high selectivity. BQPhen is a new potential extractant for An(Ⅲ) partition from Ln(Ⅲ) with high affiliate with An(Ⅲ) and subtle selectivity of Am(Ⅲ) over Ln(Ⅲ). For the complexation of Np(Ⅴ), ligand bearing N,O hybrid donors with good preorganization is very useful. The primary results are creative and very useful for the further research, such as designing and selecting new ligands, developing the actinide separation technology and materials with our own characters.