On the structure of Au11(SR)9 and Au13(SR)11 clusters

Thiolated gold clusters are constituted by building blocks (Au-4, Au-6, Au-12 and so on) and protected by staple motifs (-S-Au-S-Au-S- horizontal ellipsis ). In this study, we propose the structure of Au-11(SR)(9) and Au-13(SR)(11) clusters that are in the synthesis route of the ubiquitous Au-15(SR)(13) cluster. Our DFT-D calculations support one triangular Au-3 unit as the smallest one comprising the structure of the Au-11(SR)(9) cluster, while it competes with the Au-4 unit found in the Au-13(SR)(11) cluster. The ligand effects on the electronic, optical and chiroptical properties were studied by considering H, CH3, phenyl and adamantyl as protecting ligands. In the case of the Au-11(SR)(9) cluster, its Au-3 inner core is protected by one dimer motif and one [Au-6(SR)(6)] cyclomer when H and CH3 were considered as ligands, and the preference for Au-3 over Au-4 inner core was calculated to be 0.042 (H), 0.190 (CH3), and 0.117 eV (adamantyl). In contrast, the preference for one Au-4 core increased when using phenyl ligands (0.23 eV energy difference) and dimer and pentamer motifs. Moreover, the Au-13(SR)(11) cluster (R = CH3) has one Au-4 inner core and is protected by the combination of cyclomer, monomer and dimer motifs, and the isomer containing one Au-3 inner core and protected by one tetramer and one [Au-6(SR)(6)] cyclomer is 0.170 eV less stable. This implies that the Au-3 unit is important in these small sizes and that the energetic preference depends on the used ligand types. Moreover, we discuss the IR/Raman, optical absorption (UV-vis), and circular dichroism (CD) spectra of our predicted new structures.

Automated summary

This study focuses on the structures of Au-11(SR)(9) and Au-13(SR)(11) thiolated gold clusters, highlighting the importance of the Au-3 unit in small clusters and the impact of different ligand types on cluster stability and properties. The results shed light on ligand effects on electronic, optical, and chiroptical properties, providing insights into the energetic preferences in these small-sized clusters. Additionally, discussions on IR/Raman, UV-vis, and CD spectra of the predicted new structures were carried out.