Spectroscopic Manifestations and Implications for Catalysis of Quasi-d10 Configurations in Formal Gold(III) Complexes

Several gold +I and +III complexes are investigated computationally and spectroscopically, focusing on the d-configuration and physical oxidation state of the metal center. Density functional theory calculations reveal the non-negligible electron-sharing covalent character of the metal-to-ligand sigma-bonding framework. The bonding of gold(III) is shown to be isoelectronic to the formal Cu-III complex [Cu(CF3)(4)](1-), in which the metal center tries to populate its formally unoccupied 3d(x2-y2) orbital via sigma-bonding, leading to a reduced d(10) Cu-I description. However, Au L-3-edge X-ray absorption spectroscopy reveals excitation into the d-orbital of the Au-III species is still possible, showing that a genuine d(10) configuration is not achieved. We also find an increased electron-sharing nature of the sigma-bonds in the Au-I species, relative to their Ag-I and Cu-I analogues, due to the low-lying 6s orbital. We propose that gold +I and +III complexes form similar bonds with substrates, owing primarily to participation of the 5d(x2-y2) or 6s orbital, respectively, in bonding, indicating why Au-I and Au-III complexes often have similar reactivity.

Automated summary

This study investigates different valence states complexes of gold and focuses on the d-configuration and oxidation state of the metal center. It reveals that the bonding of gold(III) is similar to that of copper(III), and the genuine d(10) configuration is not achieved. The sigma bonds in Au(I) species have an increased electron-sharing nature compared to Ag(I) and Cu(I) due to the low-lying 6s orbital. These findings explain why Au(I) and Au(III) complexes often exhibit similar reactivity.