Structure, optical properties, and catalytic applications of alkynyl-protected M4Rh2 (M = Ag/Au) nanoclusters with atomic precision: a comparative study

We report two atomically precise alloy nanoclusters of Ag4Rh2(C=CArF)(8)(PPh3)(2) and Au4Rh2(C=CArF)(8)(PPh3)(2) (Ar = 3,5-(CF3)(2)C6H3, abbreviated as Ag4Rh2 and Au4Rh2, respectively) co-protected by alkynyl and phosphine ligands. Both clusters have identical octahedral metal core configurations and can be termed superatoms with two free electrons. However, they possess different optical features, manifested by totally different absorbance peaks, and drastically different emission peaks, and also, Ag4Rh2 has a much higher fluorescence quantum yield (18.43%) than Au4Rh2 (4.98%). Moreover, Au4Rh2 exhibited markedly superior catalytic performance in the electrochemical hydrogen evolution reaction (HER), manifested by a much lower overpotential at 10 mA cm(-2) and better stability. Density functional theory (DFT) calculations revealed that the free energy change of Au4Rh2 for the adsorption of two H* (0.64 eV) is lower than that of Ag4Rh2 for the adsorption of one H* (-0.90 eV) after stripping a single alkynyl ligand from the cluster. In contrast, Ag4Rh2 demonstrated much stronger catalytic capability for catalyzing 4-nitrophenol reduction. The present study provides an exquisite example to understand the structure-property relationship of atomically precise alloy nanoclusters, and emphasizes the importance of fine-tuning of the physicochemical properties and catalytic performance of the metal nanoclusters through modulating the metal core and beyond.

Automated summary

We report two atomically precise alloy nanoclusters of Ag4Rh2 and Au4Rh2 co-protected by alkynyl and phosphine ligands, which have different optical features and catalytic performances. Ag4Rh2 has a much higher fluorescence quantum yield and Au4Rh2 exhibits superior catalytic performance in the electrochemical hydrogen evolution reaction. The study emphasizes the importance of fine-tuning the physicochemical properties and catalytic performance of metal nanoclusters through modulation of the metal core and beyond.