Roy Chowdhury Sabyasachi, Rehberg Naomi, Vlaisavljevich Bess
Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States.
Department of Chemistry, University of South Dakota, Vermillion, South Dakota 57069, United States.
Inorg Chem. 2025 Mar 31;64(12):5866-5877. doi: 10.1021/acs.inorgchem.4c03924. Epub 2025 Mar 21.
The chemical bonding of actinide ions with arene and borohydride ligands is explored via quantum chemical methods to understand how the transuranium elements interact with soft-donor ligands. Specifically, the complexes (An = U, Np, and Pu) and their reduced congeners are studied. Density functional theory (DFT) shows that the metal-ligand interactions in the neutral complexes are governed by electrostatic interactions. Both DFT and complete active space (CASSCF) results show that as one moves from U to Pu, the 5f-orbitals are stabilized leading to a poorer energy match with the ligand orbitals. This contributes to progressively weaker metal-arene and metal-borohydride interactions across the series due to a decrease in energy-driven covalency. A reduction in orbital contributions to bonding is obtained for the transuranium-arene interactions as well. Upon reduction, the arene is reduced, forming a δ-bond. This causes the An-arene distances to contract by 0.1-0.2 Å compared to the neutral complexes. The ground state is assigned as the intermediate-spin state where the arene radical is antiferromagnetically coupled to the metal-centered f-electrons in Np and Pu. On the other hand, the ferromagnetically and antiferromagnetically coupled states are close in energy in the uranium complex, but do not mix when spin-orbit coupling is included using a state-interaction approach (SO-CASPT2). The population of the CASSCF δ*-antibonding natural orbital increases from U to Pu consistent with the increased An-arene distances, weaker interactions, and decreasing covalency across the series. Although the An-B distance increases by ca. 0.06 Å upon reduction, both the neutral and reduced species involve an An(III)-borohydride bond and as such are qualitatively similar. The Np complexes can be assigned to have slightly weaker bonding than the uranium analogs but are overall "uranium-like". The Pu complexes are predicted to have less covalent contributions to bonding in both the Pu-arene and Pu-borohydride interactions; however, the Pu-arene interaction is predicted to be particularly weak.
通过量子化学方法探索锕系离子与芳烃和硼氢化物配体的化学键合，以了解超铀元素如何与软供体配体相互作用。具体而言，研究了 配合物（An = U、Np 和 Pu）及其还原同系物。密度泛函理论（DFT）表明，中性配合物中的金属-配体相互作用受静电相互作用支配。DFT 和完全活性空间（CASSCF）结果均表明，从 U 到 Pu，5f 轨道稳定，导致与配体轨道的能量匹配变差。由于能量驱动的共价性降低，这导致该系列中金属-芳烃和金属-硼氢化物相互作用逐渐减弱。超铀-芳烃相互作用对键合的轨道贡献也有所减少。还原后，芳烃被还原，形成一个δ键。这使得与中性配合物相比，An-芳烃距离缩短了 0.1 - 0.2 Å。基态被指定为中间自旋态，其中芳烃自由基与 Np 和 Pu 中以金属为中心的 f 电子反铁磁耦合。另一方面，铁磁耦合态和反铁磁耦合态在铀配合物中的能量相近，但在使用态相互作用方法（SO-CASPT2）包含自旋-轨道耦合时不会混合。CASSCF δ*反键自然轨道的占据数从 U 到 Pu 增加，这与该系列中 An-芳烃距离增加、相互作用减弱和共价性降低一致。尽管还原后 An-B 距离增加了约 0.06 Å，但中性和还原物种均涉及 An(III)-硼氢化物键，因此在定性上相似。Np 配合物的键合预计比铀类似物略弱，但总体上“类似铀”。预计 Pu 配合物在 Pu-芳烃和 Pu-硼氢化物相互作用中对键合的共价贡献较小；然而，预计 Pu-芳烃相互作用特别弱。
