Structure And Redox Properties Of 5f System Complexes Of Schiff Base

5f-element complexes play an increasingly important role in the fields of power resource. Thermodynamically-stable and kinetically-inert hexavalenturanyl species(UO₂²⁺) are widely present in the natural water system and the nuclear fuel cycle. Comparatively, its pentavalent analogue(UO²⁺) is unstable and only experimentally synthesized in the laboratory. In the thesis, the all-electron relativistic density functional theory（DFT） was used to examine geometrical structure of complexes, electronic structure,infrared vibrational spectra, and energy of formation reaction. The influence of structural variation of complex on redox potential was addressed.To explore the effectof the fifth coordination in the equatorial plane of actinyl, we varied solvent molecule from vacant,thf to py.Other changes included actinide sorts（U, Np, Pu） and metal oxidation states（VI and V）. And thus, the resulting 18 complexes were investigated. It is shown that the inclusion and exclusion of solvent as the fifth donor have slight effect on geometrical parameters and An= O stretching vibrational frequencies, consistent with experimental findings that actinyl complexes feature 4⁶ equatorial donors. The calculated reduction potentials（E⁰） from VI to V follow the order of Np> Pu> U. Solvent polarity is found to significantly affectthe E⁰ values. One can note the calculated E⁰ is relatively small, which is caused by the weak interaction between Oendo and hydrogens of pyrrolides. The alkali metals such as A = Li, Na and K were attempted to replace the remaining hydrogens of porrolides in the second compartment of macrocyclic ligand. With the increase of their radii, alkali metals tend to escape from the mouth of the Pacman complex. E⁰ of alkali complexes was calculated to follows the sequence of Li>Na>K. Experimental studies have shown that uranyl oxo（=O） group can not be replaced by uranium imido（=NR）, but the contrary exchange does work. And thus, we designed a series of complexes [（thf）（OUE）（A₂L）]（E = O, NH, NMe and NPh; A = H and Li, labeled as UE-A）.The analyses of bond orders and wavefunction reveal the partial triple character for U=O_exo and U=N, but a modest one between single and double bonds that is assigned to U=O_endo of UE-Li as reflected by the bond order of 1.5. I t is found that both O= U= NH and O= U= O show symmetrical/asymmetrical stretching vibrational bands. The introduction of steric substituents like Me and Ph leads to two greatly separate peaks of U=O and U=N-C. The strong coupling of Me and Ph with U=N bonding blue-shift the U=N-C vibrations to the high-frequency region. When carefully selecting the A atom and the imidosubstituent, the Pacman-like complex UO-A would be easier to undergo the oxo exchange with the imido group, compared with regular pentagonal dipyrimid complex. This study is expected to provide theoretical support for experimental study of mixed oxo-imido complex.