Dialkyl sulfides: Novel passivating agents for gold nanoparticles

Gold nanoparticles passivated with symmetrical and unsymmetrical dialkyl sulfides (H21C10SC10H21 and H37C18SC10H21) have been synthesized via the borohydride reduction of HAuCl4 and characterized by H-1 NMR, FTIR, UV-vis, Auger Electron, XPS spectroscopies, and TEM. Under equivalent conditions of formation, the size and polydispersity of the gold cores obtained was greater for dialkyl sulfide ligands (d(C10SC10) = 5.3 +/- 0.8 nm; d(C18SC10) = 6.3 +/- 1.1 nm) than alkanethiol ligands (d(C10H22SH) = 2.2 +/- 0.1 nm). Edge-edge interparticle spacing of 2-D arrays of the nanoparticles is found to be dependent on the length of the longest alkyl chain passivating the nanoparticles and is independent of the asymmetry of the alkyl chains in the dialkyl sulfide.