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

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 [Au 25 (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 → [Au 15 (SR) 13 ] 0 → [Au 20 (SR) 16 ] 0 → [Au 22 (SR) 16 ] 0 → [Au 23 (SR) 16 ] − → [Au 25 (SR) 18 ] − . The cluster core grows through the stepwise incorporation of Au 4 tetrahedral units from one to four corner-sharing tetrahedrons, culminating in a spontaneous rearrangement into a symmetric Au 13 . These results reveal atomic-level evidence that discrete Au 4 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.