A Au55 nanocluster with the composition of [Au55 (p-MBT)24 (Ph3 P)6 ](SbF6 )3 (p-MBT=4-methylbenzenethiolate) is synthesized via direct reduction of gold-phosphine and gold-thiolate precursors. Single-crystal X-ray diffraction reveals that this Au55 nanocluster features a face-centered cubic (fcc) Au55 kernel, different from the well-known two-shell cuboctahedral arrangement in Au55 (Ph3 P)12 Cl6 . The Au55 cluster shows a wide optical absorption band with optical energy gap (Eg =1.28 eV). It is found that the exclusion of chloride is crucial for the formation of the title cluster, otherwise rod-like [Au25 (SR)5 (PPh3 )10 Cl2 ]2+ is obtained. The strategy to run synthetic reaction in the absence of halide leads to new members of phosphine/thiolate co-protected metal nanoclusters. The Au55 nanocluster exhibits high catalytic activity and selectivity for electrochemical reduction of CO2 to CO; the Faradaic efficiency (FE) reaches 94.1 % at -0.6 V vs. reversible hydrogen electrode (RHE).
Keywords: Au55; CO2 electroreduction; ligand-protected nanocluster; optical properties.
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