The Pivotal Radical Intermediate [Au<sub>21</sub>(SR)<sub>15</sub>]<sup>+</sup> in the Ligand-Exchange-Induced Size-Reduction of [Au<sub>23</sub>(SR)<sub>16</sub>]<sup>-</sup> to Au<sub>16</sub>(SR)<sub>12</sub>.
basic_science · Level V
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- Also identified by DOI 10.1021/acsnano.3c12765.
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Abstract
The atomic precision of sub-nanometer-sized metal nanoclusters makes it possible to elucidate the kinetics of metal nanomaterials from the molecular level. Herein, the size reduction of an atomically precise [Au<sub>23</sub>(CHT)<sub>16</sub>]<sup>-</sup> (HCHT = cyclohexanethiol) cluster upon ligand exchange with HSAdm (1-adamantanethiol) has been reported. During the 16 h conversion of [Au<sub>23</sub>(CHT)<sub>16</sub>]<sup>-</sup> to Au<sub>16</sub>(SR)<sub>12</sub>, the neutral 6e Au<sub>21</sub>(SR)<sub>15</sub>, and its 1e-reduction state, i.e. the 5e, cationic radical, [Au<sub>21</sub>(SR)<sub>15</sub>]<sup>+</sup>, are active intermediates to account for the formation of thermodynamically stable Au<sub>16</sub> products. The combination of spectroscopic monitoring (with UV-vis and ESI-MS) and DFT calculations indicates the preferential size-reduction on the corner Au atoms on the core surface and the terminal Au atoms on longer Au<sub><i>n</i></sub>S<sub><i>n</i>+1</sub> staples. This study provides a reassessment on the electronic state of the Au<sub>21</sub> structure and highlights the single electron transfer processes in cluster systems and thus the importance of the EPR analysis on the mechanistic issues.