Can Dithiolate Ligands Report Electronic Communication in Transuranium Complexes?

The actinide elements and, in particular, the transuranic elements are some of the least studied elements on the periodic table. As a consequence, there is not currently a consensus on the impact of covalency in actinide complexes. Dithiolene/dithiolate ligands provided a revolution in understanding the bonding in transition metals through the geometric differences the ligands exhibit when interacting with electron-deficient or -abundant metal centers. To test if dithiolene/dithiolate ligands can be utilized to provide an analogous understanding of transuranic element bonding, density functional theory calculations have been performed on U, Np, and Pu complexes of the formula Cp2AnS2C2H2. These calculations show that the dithiolate maintains its non-innocent redox-active nature when bonding with actinides. In stark contrast with the transition metals, the direction of electron donation is reversed; in the actinide series, the direction of electron flow in high-fold cases is from the metal center to the ligand. This suggests that the communication is between the π* system of the ligand interacting with the f orbitals of the metal center.锕系元素（actinide elements），尤其是超铀元素（transuranic elements），是元素周期表中研究程度最低的元素类群之一。因此，目前学界对于锕系配合物中共价键（covalency）的作用尚未达成共识。二硫烯/二硫代配体（dithiolene/dithiolate ligands）通过与缺电子或富电子金属中心结合时展现出的几何结构差异，为人们理解过渡金属（transition metals）的成键机制带来了革命性突破。为验证二硫烯/二硫代配体能否用于实现对超铀元素成键方式的类似阐释，研究人员针对化学式为Cp₂AnS₂C₂H₂的铀（U）、镎（Np）及钚（Pu）配合物开展了密度泛函理论（density functional theory, DFT）计算。计算结果表明，二硫代配体与锕系元素成键时，仍保留其非无辜配体（non-innocent ligand）的氧化还原活性特性。与过渡金属形成鲜明反差的是，电子供体的方向发生了逆转：在锕系元素序列中，高配位数情形下的电子流动方向为从金属中心流向配体。这表明配体的π*轨道体系与金属中心的f轨道之间存在相互作用。