Anion photoelectron spectroscopy and quantum chemical calculations of bimetallic niobium–aluminum clusters NbAln−/0 (n = 3–12): identification of a half-encapsulated symmetric structure for NbAl12−

Abstract

Bimetallic niobium-doped aluminum clusters, NbAl_n^−/0 (n = 3–12), are investigated through a synergetic combination of size-selected anion photoelectron spectroscopy and theoretical calculations. It is found that the dominant structures of NbAl_n⁻ anions with n = 3–8 can be described by gradually adding Al atoms to the NbAl₃⁻ core. Starting from n = 9, the lowest-energy geometric structures of NbAl_9–12⁻ transform into bilayer structures. In particular, NbAl₁₂⁻ has a C_3v symmetric structure, which can be viewed as a NbAl₆ regular hexagon over a bowl-shaped Al₆ structure. More detailed analyses indicate that NbAl₉ and NbAl₁₂⁻ possess unusual stability, which may be attributed to their closed-shell electron configurations with superatomic features.