中文摘要：

经三十余年努力，二价铀溶液化学于近年取得突破性进展，Evans和Meyer等成功获得两个可通过X-ray晶体衍射表征结构的有机金属铀（Ⅱ）配合物．为进一步拓展UⅡ配合物化学和探索可能存在的金属多重键，设计双核配合物[（UⅡ）2（L）]（L为八齿氮供体低聚吡咯大环四价阴离子），并使用相对论密度泛函理论优化其可能的电子自旋态异构体结构和计算相关性质．结果表明，[（UⅡ）2（L）]具有三重态基态，其电子组态为π4σ2δ2。；U（5f）原子轨道对高占据分子轨道有重要贡献；它的U-U键长为2133A、Mayer键级为3．89和对应的伸缩振动频率为259cm^-1，被指认为U-U弱四重键．这一结论与QTAIM（quantumtheoryofatomsinmolecule）的U-U键临界点处的电子／能量密度拓扑分析结果相一致．与不同氧化态铀同类物[（Um）2（L）]n＋（m=Ⅲ，n=2；m=IV,n=4）比较显示，随着铀氧化态增大，U-U距离增长、键级变小、伸缩振动频率变小，金属铀电子自旋密度与常规预期值的差值（△SU）增大；结合分子轨道和QTAIM参数分析，发现金属氧化态可以调控配体和金属轨道能级匹配程度和改变金属一金属多重键．

英文摘要：

Although attempts to synthesize divalent uranium molecules were begun three decades ago, molecular U（II） spe- cies isolable in solution have been not achieved until recent years. In 2013, Evans and co-workers synthesized the first U（II） complex, [U（Cp＇）3]·[K（2,2,2-cryptand）] （Cp＇=C5H4SiMe3） via flash reduction, that was suitable for X-ray crystal diffraction characterization. A year later, the group of Meyer obtained another divalent uranium complex, [U（（Ad,MeArO）3mes）]·[K（2,2,2-cryptand）] employing their particularly interesting tris（aryloxide） arene ligand. The 5fa6d1 and 5f4 ground states were assigned to these two complexes, respectively, by the jointed experimental/theoretical studies. It was demonstrated that the ligand significantly affect the nature of the ground state of divalent uranium complex by tuning the energetic separation of the 5f and 6d orbitals. Therefore, careful selection of ligand makes it possible to have access to ＋II oxidation state of uranium and prepare new UII complex. A flexible octadentate polypyrrollic Schiff-base macrocycle （H4L） has been developed to complex a variety of metals such as actinides, rare earth and transition metals that show a wide range of size and diverse oxidation states. Both mono- and bimetallic complexes featured with an intriguing ＂Pacman-like＂ struc- ture were obtained. For example, the reaction of H4L with a trivalent uranium precursor [（UⅢ）I3（THF）4] yielded a neutral [（UIV）（L）] complex, where the uranium ion was determined by the single crystal X-ray diffraction to be situated inside the ligand mouth and held by eight nitrogen atoms together. The ＋IV oxidation state was assigned to the uranium by presuming dihydrogen elimination. Considering the flexibility, tetravalent-anion nature as well as capability of accommodating bimetal- lic ions and stabilizing various oxidation states of uranium （e.g. III~VI complexes have been found so far） that the polypyr- rolic ligand has exhibited i