Bonding in a Crystalline Tri-Thorium Cluster: Not σ-Aromatic But Still Unique

Abstract

Very recently, Boronski et al. reported the first thorium–thorium bond in a crystalline cluster prepared under normal experimental conditions. By using a range of experimental techniques and computational models, the authors found that the isolated actinide cluster contains at its heart two paired electrons delocalized over the tri-thorium ring. The recorded Raman spectrum allegedly confirmed the existence of a σ-aromatic three-center two-electron bond. In the following we demonstrate that the experimentally observed broad inelastic scattering bands between 60 and 135 cm−1, originally assigned by the authors to thorium-thorium vibrations, represent the combination of Th−Cl stretching and Th−Cl−Th bending modes, and they establish the existence of an unprecedented multicenter charge-shift bonding (ThCl2)3 rather than the σ-aromatic bonding Th3. In the light of the presented findings, the latter remains experimentally unproven and computationally questionable.