Functional Uranyl Coordination Polymer Compounds: Synthesis, Structure And Property Characterization

Since the report of MOF-5 by Yaghi et. al., metal-organic frameworks (MOFs) that involve metal ion centers and organic linkers attracted considerable attention. By simply varying the metal ion and/or organic ligands, a variety of MOF materials with unique structural features have been prepared, greatly enriching the structural chemistry of coordination compounds. MOF materials also exhibit interesting physicochemical properties and may find applications in the fields of gas sorption and storage, catalysis, enantiomeric discrimination, optics, magnetics and electrics.However, The exploration of MOFs containing 5f actinide metals, particularly uranium, has not received as much attention as d-block transition metals or even 4f lanthanide elements. Investigations on uranium containing MOFs and coordination polymers (CPs) are of particular importance to the crystal engineering and structural chemistry of MOFs. In addition, uranium containing MOFs and CPs bear the potential for optical, magnetic, fluorescent, electronic and nuclear waste repository applications. Four of uranyl-organic CPs are prepared under different hydrothermal/solvothermal conditions. The preparation, single-crystal structural analysis, photoluminescent and photocatalytic properties of these uranyl-organic materials are elucidated in the following four chapters.In the introduction, a brief history of coordination polymers is highlighted, with emphases on the synthesis, structures and properties of uranyl coordination polymers. In Chapter 2, four uranyl coordination compounds, UOUO₂(NDC)[(CH₃)₂SO]₂ (1), [UO₂(NDC)(CH₂OH)₂] (2), UO₂(NDC)₂Ni(4,4-bipydine)(H₂O)₃ (3)and UO₂(NDC)₂Co(4,4-bipydine)(H₂O)₃ (4), are synthesized in association with 1,4-naphthalene dicarboxylate molecules. 1 and 2 are featured by their one-dimensional (1-D) chain structures. The 1-D chains of 1 are constructed from seven-coordinated uranyl monomers through the linkage of NDC molecules and the DMSO molecules to complete the coordination spheres of uranium atoms. Interestingly, the uranyl centers are linked together by NDC ligands to form a centipede-like chain structure. In the structure of 2, the eight-coordinated uranyl hexagonal bipyramid are linked by NDC ligands and glycol molecules, resulting in a zigzag chain. One prominent feature of 2 is the coexistence of both cis and trans glycol molecules within the same cell unit. The voids generated between the zigzag chains are occupied by non-coordinating trans-glycol solvent molecules which form hydrogen bonding interactions with the oxygen atoms of the coordinating glycol molecules. 3 and 4 are mix-metal uranyl CPs with the similar structure characteristic. In the structure of 3, two independent kinds of chain are inter-linked by the NDC ligands to generate 2-D layered structure: One kind is uranyl-NDC chain and the other kind is the nickel-bipydine chain. The apertures within the layers packed into channels.In Chapter 3, the photocatalytic activities of the as-synthesized uranyl coordination compounds have been investigated. The results show that 1 and 2 exhibit high efficiency in degradation of rhodamine B under the irradiation of UV or visible light, whereas the two mix-metal coordination compounds show no photocatalytic activities under the identified condition. The as-synthesized uranyl photocatalysts can be used repeatedly and continuously.In Chapter 4, a brief conclusion and outlook have been given.