Isomer-Selective Conversion of Au Clusters by Au(I) Thiolate Insertion.

Isomer-selective conversion is a challenging goal in the rational design of Au clusters. Herein, we demonstrate the isomer-selective conversion of Au18(ScC6)14 (ScC6 = cyclohexanethiolate) into Au24(SR)x(ScC6)20-x in high yields by reactions with gold(I) thiolate (AuSR) complexes. Electrospray ionization mass spectrometry indicated that even numbers of AuSR units are inserted into Au18(SR)x(ScC6)14-x to generate Au24(SR)x(ScC6)20-x through intermediates Au20(SR)x(ScC6)16-x or Au22(SR)x(ScC6)18-x. These results suggest that the number of constituent atoms in surface Au(I)SR oligomers only increases, while the number of electrons in an Au core is maintained. UV-vis analysis revealed the generation of one of two Au24(SR)x(ScC6)20-x isomers in the reactions of Au18(ScC6)14 with AuSR complexes, in contrast to the formation of both isomers by reactions with thiols. When the structures of Au18(SR)14 are compared with those of the Au24(SR)20 isomers, the partial structure in the Au cores is preserved in the isomer-selective conversion with AuSR complexes, regardless of the structures of the thiolate moiety.

Control over Ligand-Exchange Positions of Thiolate-Protected Gold Nanoclusters Using Steric Repulsion of Protecting Ligands.

Organic ligands on gold nanoclusters play important roles in regulating the structures of gold cores. However, the impact of the number and positions of the protecting ligands on gold-core structures remains unclear. We isolated thiolate-protected Au25 cluster anions, [Au25(SC2Ph)17(Por)1]- and [Au25(SC2Ph)16(Por)2]- (SC2Ph = 2-phenylethanethiolate), obtained by ligand exchange of [Au25(SC2Ph)18]- with one or two porphyrinthiolate (Por) ligands as mixtures of regioisomers. The ratio of two regioisomers in [Au25(SC2Ph)17(Por)1]- as measured by 1H NMR spectroscopy revealed that the selectivity could be controlled by the steric hindrance of the incoming thiols. Extended X-ray absorption fine structure studies of a series of porphyrin-coordinated gold nanoclusters clarified that the Au13 icosahedral core in the Au25 cluster was distorted through steric repulsion between porphyrin thiolates and phenylethanethiolates. This paper reveals interesting insights into the importance of the steric structures of protecting ligands for control over core structures in gold nanoclusters.