The Assembly Mechanism Of Lanthanide And Actinide Complexes And The Insight Into Their Applications

Nuclear energy considering as an efficient and sustainable energy plays an important role in the world’s energy system,showing obvious economic advantages and development potential.How to realize the green and efficient mining of mineral resources,improve the reprocessing process of spent fuel,and rapidly enrich radionuclide from the environmental system are the keys to ensuring the sustainable development of nuclear energy.The coordination chemistry of lanthanide and actinide elements runs through the entire nuclear energy chemistry.Whether it is the separation of lanthanide and actinide elements during spent fuel reprocessing and mineral mining or the migration of actinides in the environmental system,it is based on the idea of coordination between the metal and the ligands to form specific complexes.Therefore,it is of a great significant theoretical basis for solving the problems of nuclear fuel cycle and environmental pollution to explore the structure and property relationship between lanthanides or actinides metal and ligand under different reaction conditions in the atomic,molecular and electronic level.Furthermore,they feature rich coordination methods and intriguing physiochemical properties,and it could form functional complexes with various structures,which can be utilized to develop potential functional materials in diverse fields including catalysis,ion adsorption,fluorescence,and single-molecule magnetism.This dissertation focuses on the assembly mechanism of lanthanide and actinide elements complexes,Choosing uranium（IV and VI）and lanthanides（III）as main research targets,and a series of lanthanides and actinides complexes with novel structures are synthesized by selecting the ligands of fluorides,sulfate ions,and TPTZ molecules,and tuning the reaction conditions including adjusting the counterions and pH values via the hydrothermal or solvothermal method.This research systematically studies the assembly mechanism of the complexes and their potential applications in ion-exchange,photocatalysis,and photoluminescence.The research results are as follows:（1）The exploration of a series of lanthanide and actinide elements bearing single-molecule coordination polymers via solvothermal reactions yielded fourteen new rare-earth single-molecule complexes with three distinct phases,Ln（TPTZ）（NO₃）₃CH₃CN（LnTPTZ-1,Ln=Pr and Nd）,[Ln（TPTZ）（NO₃）₃（H₂O）]·CH₃CN（LnTPTZ-2,Ln=Pr–Er）and[Ln（TPTZ）（NO₃）₃（H₂O）]·2CH₃CN（LnTPTZ-3,Ln=Tm–Lu）,as well as a uranyl coordination polymer UO₂（TPTZ）（NO₃）₂（UTPTZ）and a thorium coordination polymer Th（TPTZ）（NO₃）₄（CH₃OH）·CH₃OH（ThTPTZ）,and the structural evolution and tunable photoluminescence of f-element bearing coordination polymers were systematically explored.All of the structures exhibited single-molecule zero-dimensional topologies due to the selfassembly of f-element cations with2,4,6-tri-α-pyridyl-1,3,5-triazine（TPTZ）,a tridentate semiaperture ligand featuring three ortho-N atoms on its pyridine and triazine rings.Due to the effect of lanthanide contraction,the structural evolution of the lanthanide complexes,including a decrease in the unit cell dimensions and Ln–O/N bond lengths across the isomorphic structures,and more dramatically,transitions in the overall topology,was observed.In addition,a rather unusually bent O_yl≡U≡O_yl unit with a highly distorted hexagonal bipyramid coordination environment was identified in UTPTZ due to steric and electronic repulsions between the uranyl cation and the bulky equatorial TPTZ ligand.ThTPTZ has larger coordination numbers and longer Ln–O/N bond length than UTPTZ complex.The homoleptic structures of EuTPTZ-2 and TbTPTZ-2 allowed the fine-tuning of the molar ratio Eu/Tb in a single Eu_xTb_1-xTPTZ-2 complex,concomitantly giving rise to versatile photoluminescent colours in such materials.Explicitly,it exhibited multicolour photoluminescence ranging from green to yellow to red under the excitation of UV light,and an excellent linear relationship between chromacity coordinates and colour tunability could be obtained.（2）We describe the targeted isolation,through the choice of alkali-metal ions,of a family of tetravalent uranium sulfates complexes,showing the influence of the overall topology and the U^IV nuclearity upon the inclusion of such counter-cations.Analyses of the structures of U^IV oxo/hydroxo sulfate oligomeric species isolated from consistent synthetic conditions reveal that incorporation of Na⁺and Rb⁺promotes the crystallization of 0D discrete clusters with a hexanuclear[U₆O₄（OH）₄（H₂O）₄]¹²⁺core,whereas the larger Cs⁺ion allows for isolation of a 2D layered oligomer with a less condensed trinuclear[U₃（μ₃-O）]¹⁰⁺center.Interestingly,trends in nuclearity appear to positively correlate with the hydration enthalpies of alkali-metal cations,such that the alkali-metal cations with larger hydration enthalpies correspond to more hydrated complexes with cluster cores.Moreover,nucleation reduction from oxo/hydroxo bridged hexameric or trimeric U^IV cores found in KU^IVSO₄-2,RbU^IVSO₄-2,and CsU^IVSO₄-2 to monomeric and dimeric U^IV centers in KU^IVSO₄-1,RbU^IVSO₄-1,and CsU^IVSO₄-1 with the increasing acidity represents a nice illustration that the hydrolysis and nucleation occur for U^IV ions at low acidity condition in the aqueous medium.These findings expand the prevalent view that counterions play an innocent role in molecular complexes synthesis,affecting not only the overall packing but also the oligomerization of U^IV ions,and they also afford new insights into the mechanism of nucleation of U^IV.（3）A series of tetra-alkyl ammonium counterions were selected to explore their role in regulating the structure of layered uranyl complexes and the selective adsorption and photocatalytic degradation of organic dyes by the uranyl complexes.The results indicated that the cationic tetra-alkyl ammonium ions show selective complexation to hexavalent uranium ion under the same reaction conditions in the reaction between ThF₄ and UF₄.Therefore,six anionic uranium oxyfluorides with various dimensionalities,including a 3D framework（MeUF）,four 2D lamellar structures（EtUF-1,PrUF,BuUF-1,and BuUF-2）,and a 1D chained topology（EtUF-2）,have been rationally constructed by employing tetra-alkyl ammonium ions as structure-directing agents.The lamellar structures with tuned layer distances of uranium oxyfluorides suggest their potential application in the selective adsorption.Specifically,the absorption experiment demonstrates that BuUF-2 can efficiently capture 94.5%methylene blue（MB⁺）within 24 h from the solution.Based on the steric exclusion effect and anion framework properties,BuUF-2 can achieve selective adsorption of cationic MB⁺with specific sizes.Such size-and charge-dependent selectivity toward organic dyes have been documented for MOFs but is rare for 2D lamellar materials.Furthermore,the removal of MB⁺can be largely accelerated under UV radiation due to the photocatalytic activities of EtUF-1,EtUF-2,PrUF,and BuUF-2.By combining the tunable interlayer distance of the lamellar uranium oxyfluorides with the photooxygenation properties of uranyl ions in this work,a bifunctional platform for highly selective ion-exchange and photocatalytic degradation over organic dyes has been developed.