Isolation, structure, and stability of a dodecanethiolate-protected Pd(1)Au(24) cluster.

A dodecanethiolate-protected Pd(1)Au(24)(SC(12)H(25))(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 Pd(1)Au(24)(SC(12)H(25))(18) from the retention time in reverse phase columns and by elemental analyses. The LDI mass spectrum of Pd(1)Au(24)(SC(12)H(25))(18) indicates that Pd(1)Au(24)(SC(12)H(25))(18) 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 Pd(1)Au(24)(SC(12)H(25))(18) exhibits peaks at approximately 690 and approximately 620 nm, which is consistent with calculated results on Pd(1)@Au(24)(SC(1)H(3))(18) in which the central gold atom of Au(25)(SC(1)H(3))(18) is replaced with Pd. These results strongly indicate that the isolated Pd(1)Au(24)(SC(12)H(25))(18) has a core-shell Pd(1)@Au(24)(SC(12)H(25))(18) structure in which the central Pd atom is surrounded by a frame of Au(24)(SC(12)H(25))(18). Experiments on the stability of the cluster showed that Pd(1)@Au(24)(SC(12)H(25))(18) is more stable against degradation in solution and laser dissociation than Au(25)(SC(12)H(25))(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.