Kloditz Roger, Radoske Thomas, Schmidt Moritz, Heine Thomas, Stumpf Thorsten, Patzschke Michael
Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstraße 400, 01328 Dresden, Germany.
Faculty of Chemistry and Food Chemistry, Theoretical Chemistry, Technische Universität Dresden, Bergstraße 66c, 01069 Dresden, Germany.
Inorg Chem. 2021 Feb 15;60(4):2514-2525. doi: 10.1021/acs.inorgchem.0c03424. Epub 2021 Feb 3.
Key questions for the study of chemical bonding in actinide compounds are the degree of covalency that can be realized in the bonds to different donor atoms and the relative participation of 5f and 6d orbitals. A manifold of theoretical approaches is available to address these questions, but hitherto no comprehensive assessments are available. Here, we present an in-depth analysis of the metal-ligand bond in a series of actinide metal-organic compounds of the [M(salen)] type (M = Ce, Th, Pa, U, Np, Pu) with the Schiff base ,'-bis(salicylidene)ethylenediamine (salen). All compounds except the Pa complex (only included in the calculations) have been synthesized and characterized experimentally. The experimental data are then used as a basis to quantify the covalency of bonds to both N- and O-donor atoms using simple electron-density differences and the quantum theory of atoms in molecules (QTAIM) with interacting quantum atoms. In addition, the orbital origin of any covalent contributions was studied via natural population analysis (NPA). The results clearly show that the bond to the hard, charged O-donor atoms of salen is consistently not only stronger but also more covalent than bonds to the softer N-donor atoms. On the other hand, in a comparison of the metals, Th shows the most ionic bond character even compared to its 4f analogue Ce. A maximum of the covalency is found for Pa or Np by their absolute and relative covalent bond energies, respectively. This trend also correlates with a significant f- and d-orbital occupation for Pa and Np. These results underline that only a comprehensive computational approach is capable of fully characterizing the covalency in actinide complexes.
研究锕系元素化合物中化学键的关键问题是与不同供体原子形成的键中可实现的共价程度以及5f和6d轨道的相对参与情况。有多种理论方法可用于解决这些问题，但迄今为止尚无全面的评估。在此，我们对一系列[M(salen)]型（M = Ce、Th、Pa、U、Np、Pu）锕系金属有机化合物与席夫碱N,N'-双（水杨基亚甲基）乙二胺（salen）之间的金属-配体键进行了深入分析。除Pa配合物（仅包含在计算中）外，所有化合物均已合成并通过实验进行了表征。然后，以实验数据为基础，使用简单的电子密度差和分子中原子的量子理论（QTAIM）及相互作用量子原子来量化与N和O供体原子形成的键的共价程度。此外，通过自然布居分析（NPA）研究了任何共价贡献的轨道起源。结果清楚地表明，与salen中硬的、带电荷的O供体原子形成的键不仅始终更强，而且比与较软的N供体原子形成的键更具共价性。另一方面，在对金属的比较中，Th表现出最离子性的键特征，即使与其4f同系物Ce相比也是如此。分别通过其绝对和相对共价键能发现Pa或Np的共价性最大。这种趋势也与Pa和Np显著的f和d轨道占据相关。这些结果强调，只有全面的计算方法才能充分表征锕系元素配合物中的共价性。
