Horizontal Expansion of Biicosahedral M13-Based Nanoclusters: Resolving Decades-Long Questions

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For metal nanoclusters with the “cluster of clusters” intramolecular evolution pattern, most efforts have been made towards the vertical superposition of icosahedral nanobuilding blocks (e.g., from mono-icosahedral Au13 to bi-icosahedral Au25 and tri-icosahedral Au37), while the horizontal expansion of these rod-shaped multi-icosahedral aggregates was largely neglected. We herein report the horizontal expansion of the biicosahedral M25 cluster framework, yielding an Au19Ag12(S-Adm)6(DPPM)6Cl7 nanocluster that contains an Au13Ag12 kernel and six Au1(DPPM)1(S-Adm)1 peripheral wings. The structural determination of Au19Ag12(S-Adm)6(DPPM)6Cl7 resolved a decades-long question for rod-shaped multi-icosahedral aggregates: how to load bidentate phosphine and bulky thiol ligands onto the nanocluster framework? The structural comparison between Au19Ag12(S-Adm)6(DPPM)6Cl7 and previously reported Au13Ag12(PPh3)10Cl8 or Au13Ag12(SR)5(PPh3)10Cl2 rationalized the unique packing of Au1(DPPM)1(S-Adm)1 motif structures on the surface of the former nanocluster. Overall, this work presents the horizontal expansion of rod-shaped multi-icosahedral nanoclusters, which provides new insights into the preparation of novel icosahedron-based aggregates with both vertically and horizontally growing extensions.