Toward Controlled Syntheses of Diphosphine-Protected Homochiral Gold Nanoclusters through Precursor Engineering.
basic_science · Level V
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- Also identified by DOI 10.1021/acsnano.1c04421.
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Abstract
Controllable syntheses of Au nanoclusters (NCs) with different nuclearities are of great significance due to the kernel-dependent physicochemical properties. Herein, two pairs of enantiomeric Au NCs [Au<sub>19</sub>(<i>R</i>/<i>S</i>-BINAP)<sub>4</sub>(PhC≡C)Cl<sub>4</sub>] (<b>SD/Au19</b>) and [Au<sub>11</sub>(<i>R</i>/<i>S</i>-BINAP)<sub>4</sub>(PhC≡C)<sub>2</sub>]·Cl (<b>SD/Au11</b>), both with <i>atropos</i> (rigid axial chirality) diphosphine BINAP (2,2'-bis(diphenylphosphino)-1,1'-binaphthalene) as the predominant organic ligands, were controllably synthesized through precursor engineering. The former was obtained by direct reduction of HAuCl<sub>4</sub>·4H<sub>2</sub>O, while the latter was obtained by reduction of [Au(SMe<sub>2</sub>)Cl] instead. Intriguingly, the kernel of <b>SD/Au19</b> contains an Au<sub>7</sub> pentagonal bipyramid capped by two boat-like Au<sub>6</sub> rings, which represents another type of Au<sub>19</sub> kernel, making <b>SD/Au19</b> a good candidate for comparative study with other Au<sub>19</sub> NCs to get more insight into the distinct structural evolution of phosphine-protected Au NCs. Despite the previous chiroptical studies on some other chiral undecagold NCs, the successful attainment of the X-ray crystal structures for <b>SD/Au11</b> not only provides a step forward toward better correlating the chiroptical activities with their structural details but also reveals that even the auxiliary protecting ligands also play a nontrivial role in tuning the geometrical structures of the metal NCs. The chiroptical activities of both <b>SD/Au19</b> and <b>SD/Au11</b> were found to originate from the chiral ligands and core distortions; the extended π-electron systems in the BINAP ligands have proved to positively contribute to the electronic absorptions and thus disturb the corresponding circular dichroism (CD) responses.