Isolation, structure, and stability of a dodecanethiolate-protected Pd1Au24 cluster

A dodecanethiolate-protected Pd1Au24(SC12H25)(18) cluster, which is a mono-Pd-doped cluster of the well understood magic gold cluster Au-25(SR)(18), was isolated in high purity using solvent fractionation and high-performance liquid chromatography (HPLC) after the preparation of dodecanethiolate-protected palladium-gold bimetal clusters. The cluster thus isolated was identified as the neutral [Pd1Au24(SC12H25)(18)](0) from the retention time in reverse phase columns and by elemental analyses. The LDI mass spectrum of [Pd1Au24(SC12H25)(18)](0) indicates that [Pd1Au24(SC12H25)(18)](0) adopts a similar framework structure to Au-25(SR)(18), in which an icosahedral Au-13 core is protected by six [-S-Au-S-Au-S-] oligomers. The optical absorption spectrum of [Pd1Au24(SC12H25)(18)](0) exhibits peaks at similar to 690 and similar to 620 nm, which is consistent with calculated results on [Pd-1@Au-24(SC1H3)(18)](0) in which the central gold atom of Au-25(SC1H3)(18) is replaced with Pd. These results strongly indicate that the isolated [Pd1Au24(SC12H25)(18)](0) has a core-shell [Pd-1@Au-24(SC12H25)(18)](0) structure in which the central Pd atom is surrounded by a frame of Au-24(SC12H25)(18). Experiments on the stability of the cluster showed that Pd-1@Au-24(SC12H25)(18) is more stable against degradation in solution and laser dissociation than Au-25(SC12H25)(18). These results indicate that the doping of a central atom is a powerful method to increase the stability beyond the Au-25(SR)(18) cluster.