Theoretical insights into the formation of thiolate-protected nanoparticles from gold (III) chloride

Reaction pathways for the formation of thiolate-gold nanoparticles are investigated by density functional theory (DFT) and a new mechanism upon solvent polarity and tetraalkylammonium is obtained. In solvents with high polarities, Au(I)SR_n polymers can be formed as the precursor of metal ions prior to the addition of a reducing agent; while a product of Cl…AuCl(HSR) is identified as the precursor in solvents with low polarities, such as toluene and chloroform. In addition, tetraalkylammonium also has an obvious effect on the reactions when it is used as a phase transfer agent in the two-phase synthesis. These findings offer a systematic analysis on the pathways to thiolate-stabilized nanoparticles and give a favorable explanation by comparison with those in an experimental system.