双层三明治四聚吡咯铀配合物的结构设计和稳定性理论计算

摘要

To explore the interaction between tetrapyrrolic ligand and low-valent uranium ion,double-layered Sandwich-like complexes PzUmPzUmPz(labeled as Um2Pz3; m=Ⅲ and Ⅳ, Pz=porphyrazine)were designed according to the single-layered PcUⅥPc(Pc=phthalocyanine)that was experimentally synthesized. Relativistic density functional theory(RDFT)was used to examine structures,stability and chemical bonding. It is shown that complexes Um2Pz3have the quintet ground state. Steric configurations are found to have a little effect on isomeric stability,while electron-spin states play more important role. Topological analyses of electron density suggest weakly polarized covalent character for U—N bonds. Tetravalent diuranium complex possesses four U(5f)-character high-lying occupied orbitals, in accordance with UⅥ5f-electron number counting. Differently,some electron transfer from uranium to ligand(Pz)is unraveled for the trivalent complex,leading to more ligand contribution to frontier molecular orbitals.%为探索四聚吡咯配体和低价铀离子相互作用,以实验合成单层三明治结构配合物PcUⅥPc(Pc=酞菁)为基础,设计双层三明治型PzUmPzUmPz(m=Ⅲ,Ⅳ,Pz=氮杂卟啉),采用相对论密度泛函理论考察了其几何结构、异构体相对稳定性以及成键和轨道性质.得到se(staggered-eclipsed)和es(eclipsed-staggered)2种类型稳定空间异构体,并进一步优化其所有可能的电子自旋态异构体.计算结果表明,这些低价铀配合物均具有五重态基态.分子中的原子量子理论(quantum theory of atoms in molecule, QTAIM)在U—N键临界点处的电子/能量密度拓扑分析显示U—N键为弱极性共价键.四价配合物拥有4个U(5f)性质高能占据轨道,与2个U4+的5f单电子数相一致;而三价配合物有很大配体参与作用.2个铀原子和中间Pz配体质心近似成线性,这与配合物具有稳定的σ(U—U)成键轨道密切相关.