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

The bimetallic M(20) and M(21) compounds, {[Cu(3)Ag(17){S(2)P(O(i)Pr)(2)}(12)](0.5) [Cu(4)Ag(16){S(2)P(O(i)Pr)(2)}(12)](0.5)} ({[1a](0.5)[1b](0.5)}) and [Cu(4)Ag(17){S(2)P(O(i)Pr)(2)}(12)](PF(6)) (2), have been structurally characterized, in which the Cu(I) ions are randomly distributed on the eight outer positions capping the eight-electron [Ag(13)](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 M(20) and M(21) bimetallic nanoclusters display an almost identical absorption profile as that of their homometallic [Ag(20){S(2)P(O(i)Pr)(2)}(12)] and [Ag(21){S(2)P(O(i)Pr)(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 [Cu(4)AuAg(16){S(2)P(O(i)Pr)(2)}(12)](PF(6)) (3).