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

Abstract

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, <b>[Au</b>_<b>25</b><b>(SC</b>_<b>2</b><b>Ph)</b>_<b>17</b><b>(Por)</b>_<b>1</b><b>]^-</b> and <b>[Au</b>_<b>25</b><b>(SC</b>_<b>2</b><b>Ph)</b>_<b>16</b><b>(Por)</b>_<b>2</b><b>]^-</b> (<b>SC</b>_<b>2</b><b>Ph</b> = 2-phenylethanethiolate), obtained by ligand exchange of <b>[Au₂₅(SC₂Ph)₁₈]^-</b> with one or two porphyrinthiolate (<b>Por</b>) ligands as mixtures of regioisomers. The ratio of two regioisomers in <b>[Au</b>_<b>25</b><b>(SC</b>_<b>2</b><b>Ph)</b>_<b>17</b><b>(Por)</b>_<b>1</b><b>]</b>^- 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.