Jennifer G Abigail, Varathan Elumalai
Department of Chemistry, SRM Institute of Science and Technology, Kattankulathur 603 203, Tamil Nadu, India.
Phys Chem Chem Phys. 2024 Sep 18;26(36):23739-23753. doi: 10.1039/d4cp01539h.
A recently synthesised novel macrocycle composed of four quinoline units called TEtraquinoline (TEQ) (, 2023, (4), 2609-2618) was reported to exhibit transition metal complexation ability. Meanwhile, there is a growing interest in different binding motifs for radioactive and toxic actinides. In this study, we modelled high-valent actinyl (AnO), An = U, Np, Pu; = 1, 2, 3 complexes of TEQ and studied their geometric and electronic properties using scalar relativistic density functional theory (SR-DFT). The calculated results showed that the equatorial An-N and axial AnO bonds were polar bonds with a high degree of covalence, the former being longer than the latter. Natural bond orbital (NBO) analysis of the An-N bond orders decreased from complexes of uranyl to plutonyl and from complexes of heptavalent to pentavalent actinyls. This was due to the localization of the 5f orbital in the heavier actinyl and the high charge on An. The charge analysis showed a ligand-to-metal charge transfer (LMCT) on complexation. It was interesting to observe metal-to-ligand spin delocalization only in the [AnOL] complexes, where the spin density on An was observed to increase on complexation. Based on the assigned oxidation states, it was observed that the heptavalent neptunyl cation retained its formal high oxidation state on complexation with TEQ. The energetics associated with the formation reaction of all the actinyl-TEQ complexes suggest spontaneity at lower temperatures (, lower than 298.15 K). The energy decomposition analysis (EDA) indicates that the electrostatic energy contributions were predominant in the [AnOL] complexes, while covalent (orbital) energy contributions were higher in the [AnOL] and [AnOL] complexes. The extended transition state-natural orbitals for chemical valence (ETS-NOCV) analysis confirmed the prominent covalent character in [AnOL] over [AnOL] and [AnOL]and the back donation of charges from An to N that stabilizes TEQ.
据报道，一种最近合成的由四个喹啉单元组成的新型大环化合物，称为四喹啉（TEQ）（《化学学报》，2023年，第4期，2609 - 2618页）具有过渡金属络合能力。与此同时，人们对放射性和有毒锕系元素的不同结合基序的兴趣与日俱增。在本研究中，我们对高价锕酰（AnO，An = U、Np、Pu； = 1、2、3）与TEQ形成的络合物进行了建模，并使用标量相对论密度泛函理论（SR - DFT）研究了它们的几何和电子性质。计算结果表明，赤道面的An - N键和轴向的AnO键是具有高度共价性的极性键，前者比后者长。对An - N键级的自然键轨道（NBO）分析表明，从铀酰络合物到钚酰络合物，以及从七价锕酰络合物到五价锕酰络合物，键级逐渐降低。这是由于较重的锕酰中5f轨道的局域化以及An上的高电荷所致。电荷分析表明，络合过程中存在配体到金属的电荷转移（LMCT）。有趣的是，仅在[AnOL]络合物中观察到了金属到配体的自旋离域，其中观察到络合时An上的自旋密度增加。基于指定的氧化态，观察到七价镎酰阳离子与TEQ络合时保持其形式上的高氧化态。所有锕酰 - TEQ络合物形成反应的能量学表明，在较低温度（低于298.15 K）下反应具有自发性。能量分解分析（EDA）表明，静电能贡献在[AnOL]络合物中占主导，而共价（轨道）能贡献在[AnOL]和[AnOL]络合物中更高。扩展过渡态 - 化学价自然轨道（ETS - NOCV）分析证实，[AnOL]中比[AnOL]和[AnOL]具有更显著的共价特征，以及从An到N的电荷回授使TEQ稳定。
