Overall structure of Au 12 Ag 60 (S- c -C 6 H 11 ) 31 Br 9 (Dppp) 6 : achieving a stronger assembly of icosahedral M 13 units.

Precise atomically assembled nanoclusters provide a great platform to elucidate the evolution of the assembly of building blocks. Herein, a large icosahedral (M)-based silver-gold alloy nanocluster [AuAg(S--CH)Br(Dppp)]Br (dppp = 1,3-bis(diphenylphosphino)propane) is reported. Structurally, AuAg consists of an AuAg kernel, which is viewed as the interpenetration of ten twisted complete icosahedrons (M) and two missing icosahedrons (M), and this is surrounded by a complex metal-organic shell. Benefiting from the extra doping of eight to twelve Au atoms, the octameric assembly was increased to a twelve-mer assembly. The time-dependent density functional theory (TDDFT) method with a Tamm-Dancoff approximation (TDA) was performed to investigate the difference in the optical properties of AuAg and AuAg. The results indicate that the difference in the amount of Au atoms results in different optical properties. Furthermore, transient absorption spectroscopy (TA) was also performed, revealing that a twelve-mer assembly greatly enhances the excited-state lifetime. The [AuAg(S--CH)Br(Dppp)]Br alloy nanocluster has provided a breakthrough in the number of icosahedral M assemblies, , achieving a twelve-mer assembly, helping to elucidate the fusion growth of M-based assembled nanoclusters as well as their geometric/electronic structure correlations, which will promote further research on the assembly of M nano-building blocks, especially on their optical properties.