Nanomolecular Metallurgy: Transformation from Au144(SCH2CH2Ph)60 to Au279(SPh‑tBu)84

Transformation brought about by ligand exchange is one of the effective methods for the synthesis of gold-thiolate nanomolecules (AuNMs). In this method, the AuNMs are treated with an excess exogenous thiol at an elevated temperature. It has been found that the ligand exchange is often accompanied by conversion of the metal core from a larger size to a smaller size, depending on the type of exogenous capping ligand employed. In this work, we present the transformation of a smaller-size AuNM (133 Au atoms) to a larger-size AuNM (279 Au atoms). Here, we observe that the Au144(SCH2CH2Ph)60 AuNM in the presence of 4-tert-butylbenzenethiol under refluxing conditions first transforms to Au133(SPh-tBu)52, and then with the transformation reaction proceeding to form larger-sized AuNMs, Au191(SPh-tBu)66 and Au279(SPh-tBu)84. The reaction progress was monitored with matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and UV–vis spectroscopy, and the intermediates and AuNMs were identified with electrospray ionization (ESI) MS. In conjunction with the above experiments, theoretical explorations using density functional theory calculations have been carried out, probing the energetics and thermodynamic stabilities underlying the observed size-changing transformations. It also elucidates the systematic size-dependent trends in the electronic structure of the original 144-gold-atoms-capped AuNM and the transformation products, including analysis of formation of superatom shells through the use of the core-cluster-shell model.