Doping effect on the structure and properties of eight-electron silver nanoclusters

Abstract

The bimetallic M20 and M21 compounds, {[Cu3Ag17{S2P(OiPr)2}12]0.5 [Cu4Ag16{S2P(OiPr)2}12]0.5} ({[1a]0.5[1b]0.5}) and [Cu4Ag17{S2P(OiPr)2}12](PF6) (2), have been structurally characterized, in which the Cu(I) ions are randomly distributed on the eight outer positions capping the eight-electron [Ag13]5+ core. DFT calculations show that the statistical disorder results from the nearly neutral preference of copper to occupy any of the eight outer positions. Surprisingly, the UV-Vis absorption spectra of the M20 and M21 bimetallic nanoclusters display an almost identical absorption profile as that of their homometallic [Ag20{S2P(OiPr)2}12] and [Ag21{S2P(OiPr)2}12]+ relatives. This is rationalized by TD-DFT calculations, which show that the frontier orbitals of such eight-electron alloys are largely independent from the nature of the capping metal ions. A blue-shifted absorption is observed upon replacing by Au the central Ag atom in 2, forming the trimetallic compound [Cu4AuAg16{S2P(OiPr)2}12](PF6) (3).