Ligand Engineering toward the Trade-Off between Stability and Activity in Cluster Catalysis

We report the structures, stability and catalysis properties of two Ag-21 nanoclusters, namely [Ag-2(1)-(H(2)BTCA)(3)(O2PPh2)(6)]SbF6 (1) and [Ag-21(C (math)CC6H3-3,5-R-2)(6)(O2PPh2)(10)]SbF6 (2) (H(4)BECA=p-tert-butylthiacalix-[4]arene, R= OMe). Both Ag-21 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 1S(2)1P(2), while 2 has an incomplete shell configuration 1S(2)1P(2). These two Ag-21 clusters show superior stability under ambient conditions, and 1 is robust even at 90 degrees C in toluene and under oxidative conditions (30% H2O2). 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.

Automated summary

We report the structures, stability, and catalytic properties of two Ag-21 nanoclusters with different electronic structures and an identical icosahedral kernel. These clusters exhibit superior stability under ambient conditions and one of them shows higher activity as a catalyst in a reduction reaction.