Biicosahedral gold clusters [Au25(PPh3)10(SCnH2n+1)5Cl2]2+ (n=2-18):: A stepping stone to cluster-assembled materials

The chemical reaction between [Au-11(PPh3)(8)Cl-2](+) and n-alkanethiol CnH2n+1SH (n = 2, 8, 10, 12, 14, 16, and 18) serendipitously yielded stable Au-25 cluster compounds with the formula, [Au-25(PPh3)(10)(SCnH2n+1)(5)Cl-2](2+). Single-crystal X-ray structural analysis of [Au-25(PPh3)(10)(SC2H5)(5)Cl-2](SbF6)(2) revealed that the Au-25 core is constructed by bridging two icosahedral Au-13 clusters with thiolates sharing a vertex atom. Optical absorption spectroscopy showed that coupling between the Au-13 building blocks gives rise to new electronic levels in addition to those of the Au-13 constituents.