Isolation, structure, and stability of a dodecanethiolate-protected Pd1Au24cluster

Abstract

A dodecanethiolate-protected Pd₁Au₂₄(SC₁₂H₂₅)₁₈ cluster, which is a mono-Pd-doped cluster of the well understood magic gold cluster Au₂₅(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 Au₂₅(SR)₁₈, in which an icosahedral Au₁₃ core is protected by six [–S–Au–S–Au–S–] oligomers. The optical absorption spectrum of [Pd₁Au₂₄(SC₁₂H₂₅)₁₈]⁰ exhibits peaks at ∼690 and ∼620 nm, which is consistent with calculated results on [Pd₁@Au₂₄(SC₁H₃)₁₈]⁰ in which the central gold atom of Au₂₅(SC₁H₃)₁₈ is replaced with Pd. These results strongly indicate that the isolated [Pd₁Au₂₄(SC₁₂H₂₅)₁₈]⁰ has a core–shell [Pd₁@Au₂₄(SC₁₂H₂₅)₁₈]⁰ structure in which the central Pd atom is surrounded by a frame of Au₂₄(SC₁₂H₂₅)₁₈. Experiments on the stability of the cluster showed that Pd₁@Au₂₄(SC₁₂H₂₅)₁₈ is more stable against degradation in solution and laser dissociation than Au₂₅(SC₁₂H₂₅)₁₈. These results indicate that the doping of a central atom is a powerful method to increase the stability beyond the Au₂₅(SR)₁₈ cluster.