We report the structures, stability and catalysis properties of two Ag21 nanoclusters, namely [Ag21 (H2 BTCA)3 (O2 PPh2 )6 ]SbF6 (1) and [Ag21 (C≡CC6 H3 -3,5-R2 )6 (O2 PPh2 )10 ]SbF6 (2) (H4 BTCA=p-tert-butylthiacalix[4]arene, R=OMe). Both Ag21 structures possess an identical icosahedral kernel that is surrounded by eight peripheral Ag atoms. Single-crystal structural analysis and ESI-MS revealed that 1 is an 8-electron cluster and 2 has four free electrons. Theoretical results show that the P-symmetry orbitals are found as HOMO-1 and HOMO states in 1, and the frontier unoccupied molecular orbitals (LUMO, LUMO+1 and LUMO+2) show D-character, indicating 1 is a superatomic cluster with an electronically closed shell 1S2 1P6 , while 2 has an incomplete shell configuration 1S2 1P2 . These two Ag21 clusters show superior stability under ambient conditions, and 1 is robust even at 90 °C in toluene and under oxidative conditions (30 % H2 O2 ). Significantly, 2 exhibits much higher activity than 1 as catalyst in the reduction of 4-nitrophenol. This work demonstrates that ligands can influence the electronic structures of silver clusters, and further affect their stability and catalytic performance.
Keywords: Catalytic Properties; Icosahedral Kernel; Phosphinate Ligands; Silver Nanoclusters; Thermal Stability.
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