Chanel K. Yee, Abraham Ulman, Julia D. Ruiz, Atul N. Parikh, Henry White, and Miriam Rafailovich, Langmuir 19, (22), 9450-9458, 2003

We have studied the effects of relative mole ratios of the reactant precursors in the one-phase synthesis of alkaneselenoate- and alkanethiolate-functionalized gold nanoparticles. Specifically, we prepared a series of dodecaneselenoate (DDSe)- and dodecanethiolate (DDT)-functionalized gold nanoparticles using four different Se/Au and S/Au mole ratios in reactant mixtures at two different reaction temperatures employing three different solvents. In all cases, the synthesis relied on the reduction of H[AuCl4], in the presence of dodecanethiol (DDT) and didodecyl diselenide (DD2Se2) using lithium triethylborohydride (superhydride) as the reducing agent. Nanoparticle formation, structure, and bonding characteristics were investigated using a combination of transmission electron microscopy, UV absorption spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Passivation by alkyl selenide was more efficient and was characterized by greater chain density and stronger Au−Se bond strength when high ligand/substrate ratios were employed. Particle size was surprisingly uniform in all cases, independent of mole ratio. By contrast, particle size (2−5 nm) was found to increase with increasing mole ratios when the passivating ligand was alkanethiolate, whose chain grafting density increased with increasing mole ratio, fully coincided with the literature. These results can be reconciled in terms of a simple mechanistic scenario wherein the nanoparticle formation using alkanethiolate ligands proceeds via the formation of a “polymer-like” intermediate between the Au ions and the alkanethiolate ligands prior to reduction whereas such an intermediate is not formed when selenoate is used as the binding ligand.