Photoelectron velocity-map imaging signature of structural evolution of silver-doped lead Zintl anions

A set of silver-doped lead Zintl anions, Ag@Pb(n) (-) (n = 5-12), have been studied using photoelectron velocity-map imaging spectroscopy and quantum chemical calculation. The structures of Ag@Pb(n) (-) (n = 7-9, 11) built upon a square pyramid base, hitherto not considered, were assigned. Overall agreement between the experimental and calculated photoelectron spectra as well as vertical detachment energies allows for structural evolution to be established. The silver atom prefers to stay outside in the n ≤ 6 clusters and intends to be encapsulated by the lead atoms in n > 6. A stable endohedral cage with bicapped square antiprism structure is formed at n = 10, the endohedral structure of which persists for the larger clusters. Especially, these Ag@Pb(n) (-) anions have been found to undergo a transition between square pyramid and pentagonal pyramid molecular structures at n = 11.