Hydride- and halide-substituted Au₉(PH₃)₈³⁺ nanoclusters: similar absorption spectra disguise distinct geometries and electronic structures

Ligands dramatically affect the electronic structure of gold nanoclusters (NCs) and provide a useful handle to tune the properties required for nanomaterials that have high performance for important functions like catalysis. Recently, questions have arisen about the nature of the interactions of hydride and halide ligands with Au NCs: hydride and halide ligands have similar effects on the absorption spectra of Au₉ NCs, which suggested that the interactions of the two classes of ligands with the Au core may be similar. Here, we elucidate the interactions of halide and hydride ligands with phosphine-protected gold clusters via theoretical investigations. The computed absorption spectra using time-dependent density functional theory are in reasonable agreement with the experimental spectra, confirming that the computational methods are capturing the ligand-metal interactions accurately. Despite the similarities in the absorption spectra, the hydride and halide ligands have distinct geometric and electronic effects. The hydride ligand behaves as a metal dopant and contributes its two electrons to the number of superatomic electrons, while the halides act as electron-withdrawing ligands and do not change the number of superatomic electrons. Clarifying the binding modes of these ligands will aid in future efforts to use ligand derivatization as a powerful tool to rationally design Au NCs for use in functional materials.