Carboxylate-Protected "Isostructural" Cu₂₀ Nanoclusters as a Model System: Carboxylate Effect on Controlling Catalysis

Several recent studies have demonstrated the great promise of ligand-protected atomically precise copper nanoclusters in driving various chemical transformation processes. The insights into key factors in controlling the catalytic performance of copper clusters at the molecular level are highly desirable but difficult to gain. Herein, we report the synthesis and comprehensive characterization of two novel Cu-20 nanoclusters, with the molecular formulae of Se@Cu-20(PhSe)(12)(PPh3)(2)(C6H5COO)(6) (Cu-20-1) and Se@Cu-20(PhSe)(12)(PPh3)(2)(CF3COO)(6) (Cu-20-2), which are proved to be great candidates in clarifying the structure and property relationship in catalysis. As revealed by single-crystal X-ray analysis, the two Cu-20 structures share an identical metal skeleton and similar ligand distributions with the only difference being in the carboxylate ligands on the surface: C6H5COO for Cu-20-1 while CF3COO for Cu-20-2. Surprisingly, such small distinctions in the structure cause a 16-fold catalytic activity leap in the catalytic reduction of 4-nitrophenol to 4-aminophenol. The electronic structures of the resulting clusters are distinct, which accounts for their distinct catalytic performances. This work not only provides a model system to highlight the importance of the carboxylate structures on controlling the catalysis of copper clusters but, more importantly, is also expected to simulate research attention on carboxylate engineering to modulate physicochemical properties of carboxylate-functionalized copper metal nanoclusters beyond catalysis.