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Synthesis and Optical Properties of a Dithiolate/Phosphine-Protected Au<sub>28</sub> Nanocluster
While
monothiols and simple phosphines are commonly exploited for
size-controlled synthesis of atomically precise gold nanoclusters
(NCs), dithiols or dithiol-phosphine combinations are seldom applied.
Herein, we used a dithiol (benzene-1,3-dithiol, BDT) and a phosphine
(triphenylphosphine, TPP) together as ligands and synthesized an atomically
precise gold NC with the formula [Au<sub>28</sub>(BDT)<sub>4</sub>(TPP)<sub>9</sub>]<sup>2+</sup>. This NC exhibited multiple absorption
features and a charge of +2, which are distinctly different from the
reported all-thiolated [Au<sub>28</sub>(SR)<sub>20</sub>]<sup>0</sup> NC (SR: monothiolate). The composition of [Au<sub>28</sub>(BDT)<sub>4</sub>(TPP)<sub>9</sub>]<sup>2+</sup> NC was deduced from high-resolution
electrospray ionization mass spectrometry (ESI MS) and it was further
corroborated by thermogravimetric analysis (TGA). Differential pulse
voltammetry (DPV) revealed a HOMO–LUMO gap of 1.27 eV, which
is in good agreement with the energy gap of 1.3 eV obtained from its
UV–vis spectrum. The successful synthesis of atomically precise,
dithiol-protected Au<sub>28</sub> NC would stimulate theoretical and
experimental research into bidentate ligands as a new path for expanding
the library of different metal NCs, which have so far been dominated
by monodentate thiols