Phosphorescent Metal Rotaxane-like Bimetallic Ag/Au Clusters

A series of Ag/Au clusters have been synthesized by reacting the π-acidic cyclic trinuclear Ag­(I) pyrazolate and its Au­(I) analogue with 3-substituted phenylacetylene. Single-crystal X-ray studies reveal that these 13-atom bimetallic clusters are anionic and isostructural, featuring a rotaxane-like architecture with a “rod-in-belt” fashion. Interestingly, the Ag/Au clusters exhibit high-energy phosphorescence tunable from blue to cyan through the modulation of the substituents on the phenylacetylene ligand. Albeit a small amount doping of Au, an over 23-fold boost in phosphorescence quantum yield is observed for these heterometallic clusters compared with their homometallic Ag­(I) analogue. Together with our previously reported Ag/Cu clusters capable of furnishing low-energy phosphorescence through the modulation of the Cu-doping amount, we have completed the luminescence puzzle of bimetallic Ag/M clusters with phosphorescence emissions that cover the entire visible-light region. Further computational studies suggest cooperative effects of electrostatic attraction and metal–metal interaction on the modulation of emission color and the stabilization of the rod-in-belt rotaxane structure.