Effect of total charge on the electronic structure of thiolate-protected X@Ag12 superatoms (X = Ag, Au)

Electronic structures of chemically synthesized silver-based clusters [XAg16(TBBT)(12)](3-) (X = Ag or Au; TBBT = 4-tert-butylbenzenethiolate) having an icosahedral X@Ag-12 superatomic core were studied by gas-phase photoelectron spectroscopy and density functional theory calculations. The electron binding energy of the highest occupied molecular orbital (HOMO) with a 1P superatomic nature was determined to be 0.23 and 0.29 eV for X = Ag or Au, respectively. Resonant tunnelling electron emission through the repulsive Coulomb barrier (RCB) was observed. From the kinetic energy of the tunnelling electrons, it was estimated that the lowest unoccupied molecular orbital (LUMO) was supported at 1.51 and 1.62 eV above the vacuum level by the RCB for X = Ag or Au, respectively. The HOMO of [XAg16(TBBT)(12)](3-) (X = Ag or Au) was destabilized by 3.74 and 3.71 eV, respectively, compared with those of [XAg24(DMBT)(18)](-) (DMBT = 2,4-dimethylbenzenethiolate) having the icosahedral X@Ag-12 core due to the larger negative charge imparted by the ligand layers.

Automated summary

The electronic structures of chemically synthesized silver-based clusters with icosahedral X@Ag-12 core were studied using gas-phase photoelectron spectroscopy and density functional theory calculations. The HOMO binding energy and LUMO energy relative to the vacuum level were determined for X = Ag or Au. The destabilization of HOMO in [XAg16(TBBT)(12)](3-) compared to [XAg24(DMBT)(18)](-) was attributed to the larger negative charge from the ligand layers.