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 [Au-25(PH3)(10)(SCH3)(5)Cl-2](2+). The cluster has a unique geometric structure consisting of two icosahedral Au-13 clusters bridged by methanethiolates sharing a vertex gold atom and terminated by chlorine atoms. This structure is very close to the biicosahedral gold cluster [Au-25(PPh3)(10)(SC2H5)(5)Cl-2](2+) reported in a recent experiment. We further demonstrate that a vertex-sharing triicosahedral gold cluster [Au-37(PH3)(10)(SCH3)(10)Cl-2](+) is also achieved through bridging with the methanethiolates. A comparison between the absorption spectra of the biand 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 Au-13 cluster.