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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U~Ⅱ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[(U~Ⅱ)_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,[(U~Ⅱ)_2(L)]具有三重态基态,其电子组态为π~4σ~2δ~2;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2.33?、Mayer键级为3.89和对应的伸缩振动频率为259 cm~(–1),被指认为U—U弱四重键.这一结论与QTAIM(quantum theory of atoms in molecule)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[(U~m)_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-金属多重键.
After more than 30 years of hard work, uranium solution chemistry has achieved breakthroughs in recent years. Evans and Meyer successfully obtained two organometallic uranium (Ⅱ) complexes that can be characterized by X-ray crystal diffraction. In order to further expand U (U ~ Ⅱ) _2 (L)] (L is an eight-tooth nitrogen donor oligomeric pyrrole macrocyclic tetravalent anion), and the relativistic theory of relativity Density functional theory is used to optimize the possible electronic spin-isomer structures and computationally relevant properties. The results show that [(U ~ Ⅱ) _2 (L)] has a triplet ground state with an electronic configuration of π ~ 4σ ~ 2δ ~ 2; U (5f) atomic orbitals have an important contribution to high occupied molecular orbitals. The U-U bond length is 2.33 μm, the Mayer bond order is 3.89 and the corresponding stretching vibration frequency is 259 cm -1. Which means that it is the weak quadruple bond of U-U. This conclusion is consistent with the results of topological analysis of the electron / energy density at the critical point of U-U bond of quantum theory of atoms in molecule. The comparison of the U-U distance with the increase of the uranium oxidation state shows that the bond-level increases with the increase of the uranium oxidation state (U ~ m) _2 (L)] ~ (n + Smaller, stretching vibration frequency (? SU) increases with the conventional expected value. Combined with the molecular orbital and QTAIM parameter analysis, it is found that the oxidation state of metal can regulate the energy level matching between ligand and metal orbit and change the ratio of metal- Metal multiple key.