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

Abstract

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@Ag12 )5+ or (Y@Ag12 )4+ with icosahedral symmetry. PES results show that superatomic orbitals in the (Au@Ag12 )5+ core remain unshifted with respect to those in the (Ag@Ag12 )5+ core, whereas the orbitals in the (Y@Ag12 )4+ (Y = Pd, Pt) core shift up in energy by about 1.4 eV. The remarkable doping effect of a single Y atom (Y=Pd, Pt) on the electronic structure of the chemically modified (Ag@Ag12 )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.