Szczepanik Dariusz W
Department of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian University Gronostajowa, 2 30-387 Kraków Poland
RSC Adv. 2023 Nov 22;13(48):34224-34229. doi: 10.1039/d3ra06603g. eCollection 2023 Nov 16.
Actinides have been known to form extremely weak homonuclear bonds with their d-type orbitals, and one should therefore expect the superposition of cyclic resonance forms containing such bonds to bring rather marginal aromatic stabilization to the system, if any. It is for this very reason that the discovery of the cyclically delocalized Th σ-bonding in the crystalline cluster isolated by Liddle and co-workers has sparked such vigorous discussion on the actual role of molecular aromaticity on the periphery of the periodic table. It has recently been argued that the tri-thorium ring at the heart of the cluster features considerable aromatic stabilization energy comparable to the heterocyclic π-aromatic rings such as thiophene. However, previous investigations involved highly ionized model clusters like ThCl or Th in which aromatic stabilization associated with the cyclic delocalization of charge is dramatically exaggerated. In this work we investigate the model tri-thorium clusters at different geometries and ionization states to show that cyclic delocalization of electrons in the isolated crystalline cluster may be associated with rather marginal σ-aromatic stabilization energy thus strongly suggesting its non-aromatic character.
已知锕系元素会通过其d型轨道形成极其微弱的同核键，因此可以预期，包含此类键的环状共振形式的叠加，即便能给体系带来芳香稳定作用，也会相当有限。正是出于这个原因，利德尔及其同事分离出的晶体簇中发现的环状离域钍σ键，引发了关于分子芳香性在元素周期表边缘实际作用的激烈讨论。最近有人认为，该簇核心的三钍环具有相当可观的芳香稳定能，可与噻吩等杂环π芳香环相媲美。然而，此前的研究涉及高度电离的模型簇，如ThCl或Th，其中与电荷环状离域相关的芳香稳定作用被大幅夸大。在这项工作中，我们研究了处于不同几何构型和电离态的三钍模型簇，以表明在分离出的晶体簇中电子的环状离域可能与相当有限的σ芳香稳定能相关，从而有力地表明其非芳香性。
