Site-specific doping of silver atoms into a Au₂₅ nanocluster as directed by ligand binding preferences

For the first time site-specific doping of silver into a spherical Au₂₅ nanocluster has been achieved in [Au₁₉Ag₆(MeOPhS)₁₇(PPh₃)₆] (BF₄)₂ (Au₁₉Ag₆) through a dual-ligand coordination strategy. Single crystal X-ray structural analysis shows that the cluster has a distorted centered icosahedral Au@Au₆Ag₆ core of D ₃ symmetry, in contrast to the I _h Au@Au₁₂ kernel in the well-known [Au₂₅(SR)₁₈]^- (R = CH₂CH₂Ph). An interesting feature is the coexistence of [Au₂(SPhOMe)₃] dimeric staples and [P-Au-SPhOMe] semi-staples in the title cluster, due to the incorporation of PPh₃. The observation of only one double-charged peak in ESI-TOF-MS confirms the ordered doping of silver atoms. Au₁₉Ag₆ is a 6e system showing a distinct absorption spectrum from [Au₂₅(SR)₁₈]^-, that is, the HOMO-LUMO transition of Au₁₉Ag₆ is optically forbidden due to the P character of the superatomic frontier orbitals.