Eight-Electron Silver and Mixed Gold/Silver Nanoclusters Stabilized by Selenium Donor Ligands.

The first atomically and structurally precise silver-nanoclusters stabilized by Se-donor ligands, [Ag20 {Se2 P(O(i) Pr)2 }12 ] (3) and [Ag21 {Se2 P(OEt)2 }12 ](+) (4), were isolated by ligand replacement reaction of [Ag20 {S2 P(O(i) Pr)2 }12 ] (1) and [Ag21 {S2 P(O(i) Pr)2 }12 ](+) (2), respectively. Furthermore, doping reactions of 4 with Au(PPh3 )Cl resulted in the formation of [AuAg20 {Se2 P(OEt)2 }12 ](+) (5). Structures of 3, 4, and 5 were determined by single-crystal X-ray diffraction. The anatomy of cluster 3 with an Ag20 core having C3 symmetry is very similar to that of its dithiophosphate analogue 1. Clusters 4 and 5 exhibit an Ag21 and Au@Ag20 core of Oh symmetry composed of eight silver capping atoms in a cubic arrangement and encapsulating an Ag13 and Au@Ag12 centered icosahedron, respectively. Both ligand exchange and heteroatom doping result in significant changes in optical and emissive properties for chalcogen-passivated silver nanoparticles, which have been theoretically confirmed as 8-electron superatoms.