N-Heterocyclic carbene derivatives to modify gold superatom characteristics. Tailorable electronic and optical properties of [Au11(PPh3)7LCl2]+ as a cluster from relativistic DFT

Abstract

Atomically precise gold superatoms are useful building blocks whose properties can be tuned by the proper choice of ligands in the protecting ligand layer. Herein, different N-heterocyclic carbene (NHC) derivatives of the prototypical [Au₁₁(PPh₃)₈Cl₂]⁺ cluster were evaluated by the replacement of a single ligand, which led to isoelectronic [Au₁₁(PPh₃)₇(NHC)Cl₂]⁺ species, enabling further understanding of the possible changes in the resulting cluster properties. Our results reveal the great variation in the HOMO–LUMO gap and optical features when going from strong to weak σ-donor NHC ligands. The Au₁₁ core retains similar features throughout the series, and the lowest unoccupied orbital (LUMO) is further stabilized, indicating greater π*–NHC character for the weaker σ-donor ligands, which favors directional core–ligand optical charge transfer to a single ligand. The ligand-tailored behavior of the [Au₁₁(PPh₃)₇LCl₂]⁺ cluster underlies its tunable characteristics, indicating its potential use in novel devices as building blocks of nanostructured materials, which favors further versatility and applications of superatomic clusters.