Experimental Confirmation of a Topological Isomer of the Ubiquitous Au25(SR)18 Cluster in the Gas Phase.

High-resolution electrospray ionization ion mobility mass spectrometry has revealed a gas-phase isomer of the ubiquitous, extremely well-studied Au25(SR)18 cluster both in anionic and cationic form. The relative abundance of the isomeric structures can be controlled by in-source activation. The measured collision cross section of the new isomer agrees extremely well with a recent theoretical prediction (Matus, M. F.; et al. Chem. Commun. 2020, 56, 8087) corresponding to a Au25(SR)18- isomer that is energetically close and topologically connected to the known ground-state structure via a simple rotation of the gold core without breaking any Au-S bonds. The results imply that the structural dynamics leading to isomerization of thiolate-protected gold clusters may play an important role in their gas-phase reactions and that isomerization could be controlled by external stimuli.