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.