A Crystalline Tri-thorium Cluster with σ-Aromatic Metal-Metal Bonding.

From PubMed via Jisc Publications RouterHistory: received 2020-12-07, accepted 2021-08-06Publication status: aheadofprintMetal-metal bonding is a widely studied area of chemistry , and has become a mature field spanning numerous d transition metal and main group complexes . In contrast, actinide-actinide bonding is predicted to be weak , being currently restricted to spectroscopically-detected gas-phase U and Th , U H and U H in frozen matrices at 6-7 Kelvin (K) , or fullerene-encapsulated U . Conversely, attempts to prepare thorium-thorium bonds in frozen matrices produced only ThH (n = 1-4) . Thus, there are no isolable actinide-actinide bonds under normal conditions. Computational investigations have explored the likely nature of actinide-actinide bonding , concentrating on localised σ-, π-, and δ-bonding models paralleling d transition metal analogues, but predictions in relativistic regimes are challenging and have remained experimentally unverified. Here, we report thorium-thorium bonding in a crystalline cluster, prepared and isolated under normal experimental conditions. The cluster exhibits a diamagnetic, closed-shell singlet ground-state with a valence-delocalised three-centre-two-electron σ-aromatic bond that is counter to the focus of previous theoretical predictions. The experimental discovery of actinide σ-aromatic bonding adds to main group and d transition metal analogues, extending delocalised σ-aromatic bonding to the heaviest elements in the periodic table and to principal quantum number six, and constitutes a new approach to elaborating actinide-actinide bonding. [Abstract copyright: © 2021. The Author(s), under exclusive licence to Springer Nature Limited.