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

Theoretical Studies of Structural Design and Stability of Double-layered Sandwich-like Tetrapyrrolic Uranium Complexes

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PcU~ⅥPc(Pc=酞菁)为基础,设计双层三明治型PzU^mPzU^mPz(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.

To explore the interaction between tetrapyrrolic ligand and low-valent uranium ion,double-layered Sandwich-like complexes PzU-mPzU-mPz（ labeled as U2-mPz3; m = Ⅲ and Ⅳ,Pz = porphyrazine） were designed according to the single-layered Pc UⅥPc（ 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 U2-mPz3 have 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（ 5 f）-character high-lying occupied orbitals, in accordance with U-Ⅵ5 f-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.