Ion Mobility Spectrometry Characterization of the Intermediate Hydrogen-Containing Gold Cluster Au₇(PPh₃)₇H₅²

We employ ion mobility spectrometry and density functional theory to determine the structure of Au₇(PPh₃)₇H₅²⁺ (PPh₃ = triphenylphosphine), which was recently identified by high mass resolution mass spectrometry. Experimental ion-neutral collision cross sections represent the momentum transfer between the ionic clusters and gas molecules averaged over the relative thermal velocities of the colliding pair, thereby providing structural insights. Theoretical calculations indicate the geometry of Au₇(PPh₃)₇H₅²⁺ is similar to Au₇(PPh₃)₇⁺, with three hydrogen atoms bridging two gold atoms and two hydrogen atoms forming single Au-H bonds. Collision-induced dissociation products observed during IMS experiments reveal that smaller hydrogen-containing clusters may be produced through fragmentation of Au₇(PPh₃)₇H₅²⁺. Our findings indicate that hydrogen-containing species like Au₇(PPh₃)₇H₅²⁺ act as intermediates in the formation of larger phosphine ligated gold clusters. These results advance the understanding and ability to control the mechanisms of size-selective cluster formation, which is necessary for scalable synthesis of clusters with tailored properties.