Biicosahedral Gold Clusters Au25(PPh3)10(SCnH2n+1)5Cl22+ (n = 2−18):  A Stepping Stone to Cluster-Assembled Materials

The chemical reaction between Au11(PPh3)8Cl2+ and n-alkanethiol CnH2n+1SH (n = 2, 8, 10, 12, 14, 16, and 18) serendipitously yielded stable Au25 cluster compounds with the formula, Au25(PPh3)10(SCnH2n+1)5Cl22+. Single-crystal X-ray structural analysis of Au25(PPh3)10(SC2H5)5Cl2(SbF6)2 revealed that the Au25 core is constructed by bridging two icosahedral Au13 clusters with thiolates sharing a vertex atom. Optical absorption spectroscopy showed that coupling between the Au13 building blocks gives rise to new electronic levels in addition to those of the Au13 constituents.