Coordination Recognition And Assembly Of Uranyl Clusters By Pseudorotaxane Ligands Based On Neutral O-Donor Ligands

With the rapid development of nuclear power,a lot of spent fuel has been produced and needed to be disposed of.Closed cycle of nuclear fuel is the only choice to realize the sustainable development of nuclear energy.In addition,some nuclides in spent fuel play important roles in medicine,agriculture,and industrial measurement.The study of valence state,species information and coordination behaviors of lanthanides,actinides and fission products will provide meanningful information for the entire nuclear fuel cycle process.A new type of O donor neutral organic ligand（N-O）was employed to investigate the hydrolysis and coordination behavior of uranyl ions.A series of uranyl-organic coordination polymers were obtained by using this neutral ligand,in addition pseudorotaxane ligands are constructed by this ligand and macrocyclic molecules（cucurbituril macrocycle and crown ether macrocycle）.Hydrolyzed uranyl species were identified and immobilized using pseudorotaxane ligands.The coordination behavior between uranyl cations and N-O ligands/pseudorotaxane ligands in these uranyl-organic coordination polymers was studied.The relationship between the topological structures and the corresponding synthesis conditions,the properties and applications of these materials were investigated.The specific research contents are as follows:（1）A novel neutral N-O organic ligand（4,4’-bipyridine N,N’-dioxygenated ligand,DPO）was designed and synthesized.The DPO and some ligands were employed to coordinate with uranyl ions,under different the conditions（solvothermal/volatilization method,aqueous phase/organic solvent）,and as a result 10 coordination polymers were obtained.The assembly mechanism of these ten compounds were discussed in terms of factors affecting the assembly process（solvent,temperature,different source of uranyl cations,and auxiliary ligands）.In order to gain a deeper understanding of the bonding properties between uranyl ions and coordinating oxygen atoms,the structures of U-DPO complexes were theoretically analyzed in detail through theoretical calculations.（2）DPO was combined with cucurbit[7]uril（CB[7]）to form a new pseudorotaxane ligand（DPO@CB[7]）for the investigation of the hydrolysis of uranyl cation.The molecular dimension of DPO guest used here matches well with the size of the cavity of macrocyclic CB[7],which helps to enhance coordination synergy of DPO@CB[7]pseudorotaxane and facilitate more flexibility in coordination modes towards uranyl species.The inclusion behavior between the host and guest ligand was investigated.The coordination recognition and crystallographic separation of mononuclear,dinuclear,trinuclear,and tetranuclear oligouranyl species at different pH conditions were achieved using DPO@CB[7]ligand（URC1～4）.DPO@CB[7]ligands adapt to different uranyl hydrolyzates by adjusting the positions of DPO in the CB[7]macrocyclic cavity and the coordination mode of DPO@CB[7]ligand with uranyl centers.DPO@CB[7]ligand shows good structural adaptability to the geometry and coordination requirements of uranyl centers via the mechanical interlocking structure formed by weak interaction between DPO and CB[7]in DPO@CB[7]ligand.（3）On the basis of the coordination and assembly between DPO@CB[7]ligands and uranyl,DPO ligand was extended to obtain viologen derivatives ligand 1,1’-bis（4-carboxybenzene）-4,4’-bipyridinedichloro（（H₂bcbp）Cl₂）.The pseudorotaxane ligand（（H₂bcbp）Cl₂@CB[7]）was assembled with CB[7]and（H₂bcbp）Cl₂,and then coordinated with uranyl ions at different pH conditions.Three uranyl-rotaxane coordination polymers UVDRC1～UVDRC3 were obtained.UVDRC1～UVDRC3 exhibited the properties of photochromic with X-ray irradiation and thermochromic.The electrochemical behavior on UVDRC1～UVDRC3,（H₂bcbp）Cl₂ and（H₂bcbp）Cl₂@CB[7]were studied.UVDRC3 with a two-dimensional network structure has a lot of hydrogen bonds between the layers due to the CB[7]macrocycle.Ultrasonic stripping and ion-exchange intercalation stripping was employed for the destruction of these weak interactions to prepare nanosheet materials.（4）A new pyridinium N-O ligand was obtained by extending the structure of the DPO ligand.In this work,a crown ether macrocycle was introduced into the construction of actinide polyrotaxanes for the first time:UCER-1 was obtained by the direct solvent evaporation method,while UCER-2 was obtained by the step-by-step solvothermal method.The in situ assembly of host-guest is crucial for the successful construction of actinide polyrotaxane compounds,and this pre-assembly process is greatly affected by the synthesis conditions.The coordination situation of different coordination atoms（especially bromine）with uranyl was analyzed in detail.The crown ether macrocycle was further modified,sulfonated by concentrated sulfuric acid,and assembled with guest molecules to form supramolecular rotaxane structures.In the research of this paper,we design and synthesize a new type of neutral DPO ligand,and the coordination behavior of DPO ligand with uranyl ions is investigated in detail.Moreover,pseudorotaxane ligands were obtained via the supramolecular assembly between the CB[7]macrocycle and the N-O ligands.The coordination identification of uranyl hydrolyzate was performed,and the mononuclear,dinuclear,trinuclear,and tetranuclear uranyl clusters were successfully identified by crystallization with the pseudorotaxane ligands under different pH.The DPO ligand was further extended in size:increasing the benzene rings as（H₂bcbp）Cl₂（rigid extension）,increasing the alkyl chain as pyridinium N-O ligand（flexible extension）.Crown ethers（Sulfonated crown ethers）were employed to construct new pseudorotaxane ligands,thus to rich the variety of the macrocycle.The coordination behavior of neutral N-O ligands and pseudorotaxane ligands（N-O ligand and CB[7]or DB24C8）with uranyl ions and the effect of assembly conditions on the coordination behavior were investigated.Moreover,the formation mechanism,structural properties and potential applications of uranyl-organic coordination polymers were preliminarily studied and discussed.