N-Heterocyclic carbene derivatives to modify gold superatom characteristics. Tailorable electronic and optical properties of [Au 11 (PPh 3 ) 7 LCl 2 ] + as a cluster from relativistic DFT.

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 [Au 11 (PPh 3 ) 8 Cl 2 ] + cluster were evaluated by the replacement of a single ligand, which led to isoelectronic [Au 11 (PPh 3 ) 7 (NHC)Cl 2 ] + 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 Au 11 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 [Au 11 (PPh 3 ) 7 LCl 2 ] + 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.