Elucidating the Doping Effect on the Electronic Structure of Thiolate-Protected Silver Superatoms by Photoelectron Spectroscopy

Gas- phase photoelectron spectroscopy (PES) was conducted on [XAg24(SPhMe2)(18)] (X=Ag, Au) and [YAg24(SPhMe2)(18)](2-) (Y=Pd, Pt), which have a formal superatomic core (X@Ag-12)(5+) or (Y@Ag-12)(4+) with icosahedral symmetry. PES results show that superatomic orbitals in the (Au@Ag-12)(5+) core remain unshifted with respect to those in the (Ag@Ag-12)(5+) core, whereas the orbitals in the (Y@Ag-12)(4+) (Y=Pd, Pt) core shift up in energy by about 1.4 eV. The remarkable doping effect of a single Yatom (Y=Pd, Pt) on the electronic structure of the chemically modified (Ag@Ag-12)(5+) superatom was reproduced by theoretical calculations on simplified model systems and was ascribed to 1) the weaker binding of valence electrons in Y@(Ag+)(12) compared to Ag+@(Ag+)(12) due to the reduction in formal charge of the core potential, and 2) the upward shift of the apparent vacuum level due to the presence of a repulsive Coulomb barrier between [YAg24(SPhMe2)(18)](-) and electron.