六聚吡咯大环与铀/超铀酰基离子相互作用:成键、热力学和光谱性质

采用全电子相对论密度泛函理论探索多种六聚吡咯大环锕酰基配合物(nAn;n=1~3;An=U,Np and Pu)的电子结构本质、成键规律和化学反应特性。结构优化发现大环配体空穴大小与锕酰离子尺寸相当时,配合物锕酰基采用性对规则的六角双锥结构,而当空穴尺寸相对大时,配合物则采取扭曲结构以降低体系能量。当配体相同时,随着铀、镎、钚变化,An=O伸缩振动频率逐渐变小,这与优化的键长和键级变化规律相一致。QTAIM(quantum theory of atoms in molecule)拓扑分析显示An-N为弱共价单键特征,具有较大离子性成分。依据不同铀源,得到与大环配体的反应自由能均小于146 kJ·mol~(-1),与实验合成配合物的反应能计算数值相当。对含铀配合物电子吸收光谱计算显示,低能(近红外和可见光区)的吸收带具有全部或较大的配体→金属电荷转移性质贡献。

Interaction Behavior Between Hexa-dentate Polypyrrolic Macrocycles and Actinyl Species: Bonding, Thermodynamic and Spectroscopic Properties

A relativistic density functional theory (DFT) was used to systematically examine a series of uranyl and transuranyl complexes of N-donor macrocyclic ligands,(AnO₂)(Ln)]^2-(labeled as nAn; n=1~3; An=U, Np and Pu). Further comparison was made with(UO₂)(L⁰)]^2-(A) that was experimentally synthesized. Cavities of L¹ and L² macrocycles are found to match well with actinyl ions, but the one of L³ is a lot larger. Consequently, the L³ complexes have to adopt distorted geometry to energetically stabilize systems. Infrared vibrational spectra presented that the An=O stretching frequencies decrease in going from U, Np to Pu. This agrees with the trend of optimized bond lengths of An=O and bond orders. Topological analyses of quantum theory of atoms in molecule (QTAIM) indicate that the An-N bonds have largely ionic character. Depending on different actinyl source, free energies reacting with various macrocyclic ligands were calculated around 146.4 kJ·mol^-1, comparable to the calculated values of A. Time-dependent DFT calculations on four uranyl complexes well reproduced absorption spectra of experimentally reported analogue. The absorption bands in the near-IR and visible region have large contribution from ligand-to-metal charge transfer (LMCT), which is responsible for changes of solution color in the process of macrocyclic ligand sensing uranyl species.