An Au25(SR)18 Cluster with a Face-Centered Cubic Core
T. Omoda, S. Takano, S. Yamazoe, K. Koyasu, Y. Negishi, T. Tsukuda
J. Phys. Chem. C Accepted.
A representative thiolate (RS)-protected gold cluster, Au25(SR)18, shows a fingerprint-like characteristic spectral profile regardless of the R-groups, reflecting the common motif of the structural backbone made of Au and S: an icosahedral Au13 core fully protected by six staple units of Au2(SR)3. On the other hand, we reported in 2006 that an Au25(SPG)18 cluster (PGSH = N-(2-mercaptopropionyl)glycine) exhibited an optical absorption spectrum significantly different from that of the conventional Au25(SR)18, suggesting the formation of a non-icosahedral Au core. Here, we investigated the structure of Au25(SPG)18 by UV-Vis spectroscopy, extended X-ray absorption fine structure analysis and density functional theory calculations. Spectroscopic results indicated that Au25(SPG)18 has a face-centered cubic (FCC) Au core. We proposed a model structure formulated as Au15(SPG)4[Au2(SPG)3]2[Au3(SPG)4]2 in which an Au15(SPG)4 core with an FCC motif is protected by two types of staples with different lengths, Au2(SPG)3 and Au3(SPG)4. The formation of an FCC-based Au core is attributed to bulkiness around the α-carbon of the PGS ligand.