Collision-Induced Fission of Oblate Gold Superatom in [Au 9 (PPh 3 ) 8 ] 3+ : Deformation-Mediated Mechanism.

Collision-induced dissociation (CID) patterns of the phosphine-protected Au-based clusters [PdAu 8 (PPh 3 ) 8 ] 2+ ( PdAu8 ) and [Au 9 (PPh 3 ) 8 ] 3+ ( Au9 ), featuring crown-shaped M@Au 8 (M = Pd, Au) cores, were investigated. For PdAu8 , ordinary sequential PPh 3 losses ( PdAu8 → [PdAu 8 (PPh 3 ) m ] 2+ + (8 - m )PPh 3 ( m = 7, 6, 5)) were observed. In contrast, Au9 underwent cluster-core fission ( Au9 → [Au 6 (PPh 3 ) 6 ] 2+ ( Au6 ) + [Au 3 (PPh 3 ) 2 ] + ( Au3 )) upon sufficiently high energy collision, associated with splitting the number of valence electrons in the superatomic orbitals from 6e ( Au9 ) into 4e ( Au6 ) and 2e ( Au3 ). Density functional theory calculations revealed oblate and prolate cores of Au9 and Au6 with semiclosed superatomic electron configurations of (1S) 2 (1P x ) 2 (1P y ) 2 and (1S) 2 (1P z ) 2 , respectively. This result indicated a significant deformation of the cluster-core motif during the CID process. We attribute the clear difference between PdAu8 and Au9 to the softer Au-Au bond in Au9 and propose that the collision-induced structural deformation plays a critical role in the fission.