The Golden Pathway to Thiolate-Stabilized Nanoparticles:
Following the Formation of Gold(I) Thiolate from Gold(III) Chloride
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Abstract
Pathways for the formation of gold thiolate complexes from gold(III)
chloride precursors AuCl<sub>4</sub><sup>–</sup> and AuCl<sub>3</sub> are examined. This work demonstrates that two distinct reaction
pathways are possible; which pathway is accessible in a given reaction
may depend on factors such as the residue group R on the incoming
thiol. Density functional theory calculations using the BP86 functional
and a polarized triple-ζ basis set show that the pathway resulting
in gold(III) reduction is favored for R = methyl. A two-to-one ratio
of thiol or thiolate to gold can reduce Au(III) to Au(I), and a three-to-one
ratio can lead to polymeric Au(SR) species, which was first suggested
by Schaaff et al. <i>J. Phys. Chem. B</i>, <b>1997</b>, <i>101</i>, 7885 and later confirmed by Goulet and Lennox <i>J. Am. Chem. Soc.</i>, <b>2010</b>, <i>132</i>, 9582. Most transition states in the pathways examined here have
reasonable barrier heights around 0.3 eV; we find two barrier heights
that differ substantially from this which suggest the potential for
kinetic control in the first step of thiolate-protected gold nanoparticle
growth