Heteroatom-Doping Increases Cluster Nuclearity: From an [Ag₂₀ ] to an [Au₃ Ag₁₈ ] Core

A templated galvanic exchange performed on [Ag₂₀ {Se₂ P(OiPr)₂ }₁₂ ] of C₃ symmetry with three equiv Au^I yields a mixture of [Au_1+x Ag_20-x {Se₂ P(OiPr)₂ }₁₂ ]⁺ (x=0-2) from which [Au@Ag₂₀ {Se₂ P(OiPr)₂ }₁₂ ]⁺ and [Au@Au₂ Ag₁₈ {Se₂ P(OiPr)₂ }₁₂ ]⁺ are successfully characterized to have T and C₁ symmetry, respectively. Crystal structural analyses combined with DFT calculations on the model compounds explicitly demonstrate that the central Ag⁰ of Ag₂₀ being oxidized by Au^I migrates to the protecting atomic shell as a new capping Ag^I , and both second and third Au dopants prefer occupying non-adjacent icosahedron vertices. The differences in symmetry, T and C₁ , are manifested in the spatial orientation of their protecting atomic shell composed of eight capping Ag atoms as well as re-construction upon the replacement of Ag atoms on the vertices of AuAg₁₂ icosahedral core with second and third Au dopants. As a result, a unique pathway for substitutional-doped clusters with increased nuclearity is proposed.