Beyond the Metal Core: Platinum Incorporation Reshapes Redox Levels and Ligand Shells in Au 25 Thiolate Clusters

Abstract Platinum incorporation into atomically precise Au25 thiolate clusters is known to strongly affect their electronic structure, but experimental studies of these systems are often complicated by the simultaneous formation of Au25 and Au24Pt species. Here, we examine butanethiolate- and hexanethiolate-protected Au25/Au24Pt cluster mixtures obtained by a Brust–Schiffrin-type synthesis, without applying oxidative purification conditions that caused substantial degradation of the platinum-containing products. The overall Au/Pt composition of the products was quantified by ICP-MS, while TEM and DLS were used to characterize their particle-size distributions. The Au/Pt ratios indicate that platinum incorporation competes with the formation of larger platinum-rich nanoparticles and reveal differences in product distribution between the butanethiolate- and hexanethiolate-protected systems. UV-Vis and square-wave voltammetry measurements reveal reproducible differences between the platinum-containing mixtures and the corresponding Au25 reference systems, while FT-IR spectroscopy shows ligand-dependent changes in the vibrational signatures of the alkylthiolate shell. DFT calculations reproduce the stronger core distortion expected for Au24Pt relative to Au25 and provide a qualitative framework for interpreting the experimental trends. Rather than assigning intrinsic properties to isolated Au24Pt clusters, the present work shows how platinum incorporation manifests itself in experimentally accessible Au25/Au24Pt mixtures. The results further show that these effects differ between the butanethiolate- and hexanethiolate-protected systems.