Theoretical Study On Coordination Chemistry Of Actinides Compounds

Nuclear fuel cycle involves numerous important physicochemical processes.A fundamental understanding of the bonding trends in actinide complexes is essential for design of robust extractant ligands used in the actinide-lanthanide separation and assessment of the environmental impact of complexation of radioactive actinide elements.With the rapid development of experimental techniques and theoretical methods,significant advances have been achieved in actinide chemistry,which provide critical knowledge in actinide science.Currently few systematic studies have been carried out on the bonding trends and oxidation states changes in actinide complexes.In this dissertation,several important actinide complexes have been studied by using quantum chemistry methods combined with modern bonding analysis methods to gain a deep understanding of the bonding trends.First,AnO2(18C6)1/2+(An=U-Cm)complexes were investigated by quantum chemistry in both vacuum and water solution environments to obtain their ground state structure,electronic structure,and chemical bonding of the complexes.The calculated structures are consistent with experimentally available data.We found that the bonding is mainly electronic interactions between actinyl ions AnO21/2+ and 18-crown-6(18C6)ligand,with slight covalent contributions.This An-OL bond is strongly polarized towards the O atom of 18C6.Furthermore,the interactions between AnO22+ions and 18C6 in AnO2(18C6)2+are stronger than that of AnO21+and 18C6 in AnO2(18C6)1+.In addition,the interactions between AnO21/2+and 18C6 show a turning point at An=Pu,showing relatively weak interactions after An=Pu.Secondly,we performed an exhaustive search on the potential energy surfaces(PES)of UAu7 and WAu7 clusters by density functional theory,and systematically studied the electronic structures and chemical bonding analyses of the ground state structures from the combination of the global optimal searching and structural optimizations.It was found that the ground state structures of the AnAu7(An=Th-Cm)clusters are wheel-like structures with D7h symmetry and the valence states for An are+3,from the results of the combination of the global optimal searching and structural optimizations.Due to the strong spin-orbit coupling(SOC)of the An atoms,the clusters become more stable.Through a series of chemical bonding analyses,we found that the bonding between An and the Au7 unit is mainly covalent,while the electronic interactions are weaker especially.There are two inflection points,at An=U and An=Am,for the interactions between An and the Au7 unit,while the interactions between An and the Au7 unit increasing between Th-U and decreasing between U-Am,finally forming an inverse increase at An=Cm.At the same time,the calculations on UCM7(CM=Cu,Ag and Au)clusters with different ligands were also performed.The results show that UCM7(CM=Cu,Ag and Au)clusters have a similar structure and the same bonding type.The bonding between U and CM7 unit is mainly covalent,while the electronic interactions are relatively weak.Moreover,the interactions between U and CM7 unit increase from Ag to Cu and then to Au.