The Golden Pathway to Thiolate-Stabilized Nanoparticles: Following the Formation of Gold(I) Thiolate from Gold(III) Chloride

Abstract

Pathways for the formation of gold thiolate complexes from gold­(III) chloride precursors AuCl₄^– and AuCl₃ 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