Assembly of Tetrahedral Units in the Atomic-Resolved Structural Evolution of Gold Nanostructures

Abstract

Materials achieve complexity from simple building blocks, yet directly capturing the atomic pathways of their dynamic assembly has remained a long-standing challenge. Here, we employ atomically precise gold nanoclusters as a model system to resolve a tetrahedral assembly toward [Au25(SR)18]− (SR = thiolate). In this pathway, tetrabutylammonium acts as a supramolecular director, selectively stabilizing metastable intermediates and steering Au(I)–SR reduction along a dominant trajectory. High-throughput robotic synthesis combined with tandem in situ spectroscopy uncovers a growth sequence: Au(I)–SR → [Au15(SR)13]0 → [Au20(SR)16]0 → [Au22(SR)16]0 → [Au23(SR)16]− → [Au25(SR)18]−. The cluster core grows through the stepwise incorporation of Au4 tetrahedral units from one to four corner-sharing tetrahedrons, culminating in a spontaneous rearrangement into a symmetric Au13. These results reveal atomic-level evidence that discrete Au4 units direct cluster growth and fuse into higher-order building blocks, resolving a long-sought question in nanomaterial formation and establishing smart, data-driven synthesis as a powerful paradigm for decoding complex reaction networks.