Oligomeric Gold Clusters with Vertex-Sharing Bi- and Triicosahedral Structures

We present density functional studies of the geometric and electronic structures of a gold cluster compound [Au25(PH3)10(SCH3)5Cl2]2+. The cluster has a unique geometric structure consisting of two icosahedral Au13 clusters bridged by methanethiolates sharing a vertex gold atom and terminated by chlorine atoms. This structure is very close to the biicosahedral gold cluster [Au25(PPh3)10(SC2H5)5Cl2]2+ reported in a recent experiment. We further demonstrate that a vertex-sharing triicosahedral gold cluster [Au37(PH3)10(SCH3)10Cl2]+ is also achieved through bridging with the methanethiolates. A comparison between the absorption spectra of the bi- and triicosahedral clusters shows that the new electronic levels due to each oligomeric structure appear sequentially, whereas other electronic properties remain almost unchanged compared to the individual icosahedral Au13 cluster.