Geometric and Electronic Structure of Au25(SPhX)18- (X = H, F, Cl, Br, CH3, and OCH3)

Using density functional theory calculations, the geometric structure of Au-25(SPh)(18)(-) is found to have S-6 symmetry. The electronic structure of this particle is affected by a splitting of the superatom P-z orbital from the set of P-x and P-y orbitals: this leads to a double peak similar to the characteristic double peak of Au-25(SCH2CH2Ph)(18)(-) and related compounds. Para substituents shift the HOMO and LUMO orbital energies, but the HOMO-LUMO gap remains constant. The shifts correspond with Hammett substituent constants, with the exception of OCH3. Calculated optical absorption spectra are mostly unaffected by ligand substitution, although slight (0.1 eV) changes are evident in ligand-based transitions.