Ligand-Dependent Interface Dynamics of Rod-like Au25 Nanoclusters in Acidic and Electrochemical Media

Abstract

Atomically precise gold nanoclusters have emerged as ideal model systems for studying structure–property relationships and revealing electrocatalytic reaction mechanisms. However, an atomic scale understanding of the dynamic stability and desorption behavior of surface ligands under operating conditions remains lacking. In this work, we systematically probed the ligand-dependent interface dynamics of three rod shaped Au25 model nanoclusters (N-heterocyclic carbenes (NHCs) stabilized [Au25(NHCs)10Br7]2+, phosphine/thiolated [Au25(PR)10(SR)5Cl2]2+ and phosphine/alkyne-ligated [Au25(PR)10(C≡CR)5Cl2]2+) under both acidic and electrochemical conditions. Under acidic conditions, the NHC protected cluster exhibited the highest structural stability, whereas the alkynyl protected cluster showed the most pronounced distortion of the metal core. The electrochemical environment exerted stronger destructive effect on the cluster structure than the acidic medium, as evidenced by severe distortion of the metal core and widespread weakening and elongation of metal–ligand bonds. With the exception of the NHC and thiolate ligands, all other ligand types were able to desorb within the electrochemical time scale. Bader charge analysis revealed that the kinetic barrier for ligand desorption depends strongly on the charge difference between the ligand and the most active charge carrier in its local microenvironment. In acidic media, this role is played by water molecules acting as proton carriers, while under electrochemical conditions, this role is assumed by the Au25 metal core serving as an electron reservoir. This study provides a quantitative theoretical framework for understanding the interfacial dynamic behavior of nanoclusters in reactive environments and offers important guidance for the rational design of highly stable cluster based electrocatalysts and assemblies.