Sadhu Biswajit, Dolg Michael, Kulkarni Mukund S
Health Physics Division, Health Safety and Environment Group, Bhabha Atomic Research Centre, Mumbai, India.
Institute for Theoretical Chemistry, Greinstr. 4, University of Cologne, Cologne, Germany.
J Comput Chem. 2020 Jun 5;41(15):1427-1435. doi: 10.1002/jcc.26186. Epub 2020 Mar 3.
A relativistic density functional theory (DFT) study is reported which aims to understand the complexation chemistry of An ions (An = Th, U, Np, and Pu) with a potential decorporation agent, 5-LIO(Me-3,2-HOPO). The calculations show that the periodic change of the metal binding free energy has an excellent correlation with the ionic radii and such change of ionic radii also leads to the structural modulation of actinide-ligand complexes. The calculated structural and binding parameters agree well with the available experimental data. Atomic charges derived from quantum theory of atoms in molecules (QTAIM) and natural bond order (NBO) analysis shows the major role of ligand-to-metal charge transfer in the stability of the complexes. Energy decomposition analysis, QTAIM, and electron localization function (ELF) predict that the actinide-ligand bond is dominantly ionic, but the contribution of orbital interaction is considerable and increases from Th to Pu . A decomposition of orbital contributions applying the extended transition state-natural orbital chemical valence method points out the significant π-donation from the oxygen donor centers to the electron-poor actinide ion. Molecular orbital analysis suggests an increasing trend of orbital mixing in the context of 5f orbital participation across the tetravalent An series (Th-Pu). However, the corresponding overlap integral is found to be smaller than in the case of 6d orbital participation. An analysis of the results from the aforementioned electronic structure methods indicates that such orbital participation possibly arises due to the energy matching of ligand and metal orbitals and carries the signature of near-degeneracy driven covalency.
本文报道了一项相对论密度泛函理论(DFT)研究,旨在了解锕系元素离子(An = 钍、铀、镎和钚)与一种潜在的促排剂5-LIO(Me-3,2-HOPO)的络合化学。计算结果表明,金属结合自由能的周期性变化与离子半径具有良好的相关性,这种离子半径的变化也导致了锕系元素-配体配合物的结构调制。计算得到的结构和结合参数与现有的实验数据吻合良好。基于分子中的原子量子理论(QTAIM)和自然键序(NBO)分析得到的原子电荷表明,配体到金属的电荷转移在配合物稳定性中起主要作用。能量分解分析、QTAIM和电子定域函数(ELF)预测,锕系元素-配体键主要是离子键,但轨道相互作用的贡献相当大,并且从钍到钚逐渐增加。应用扩展过渡态-自然轨道化学价方法对轨道贡献进行分解指出,氧供体中心向贫电子锕系离子有显著的π-给予。分子轨道分析表明,在四价锕系元素系列(钍-钚)中,5f轨道参与的情况下轨道混合呈增加趋势。然而,发现相应的重叠积分比6d轨道参与的情况要小。对上述电子结构方法结果的分析表明,这种轨道参与可能是由于配体和金属轨道的能量匹配引起的,并带有近简并驱动共价性的特征。