Regulating interaction with surface ligands on Au25 nanoclusters by multivariate metal-organic framework hosts for boosting catalysis

While atomically precise metal nanoclusters (NCs) with unique structures and reactivity are very promising in catalysis, the spatial resistance caused by the surface ligands and structural instability significantly poses great challenges. In this work, Au25(Cys)18 NCs are encapsulated in multivariate metal-organic frameworks (MOFs) to afford Au25@M-MOF-74 (M = Zn, Ni, Co, Mg). By the MOF confinement, the Au25 NCs showcase much enhanced activity and stability in the intramolecular cascade reaction of 2-nitrobenzonitrile. Notably, the interaction between the metal nodes in M-MOF-74 and Au25(Cys)18 is able to suppress the free vibration of the surface ligands on the Au25 NCs and thereby improve the accessibility of Au sites; meanwhile, the stronger interactions lead to higher electron density and core expansion within Au25(Cys)18. As a result, the activity exhibits the trend of Au25@Ni-MOF-74 > Au25@Co-MOF-74 > Au25@Zn-MOF-74 > Au25@Mg-MOF-74, highlighting the crucial roles of microenvironment modulation around the Au25 NCs by interaction between the surface ligands and MOF hosts.