Alkyl Selenide- and Alkyl Thiolate-Functionalized Gold Nanoparticles:  Chain Packing and Bond Nature

Abstract

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.

Exchange Reactions between Alkanethiolates and Alkaneselenols on Au{111}

“…Packing densities of C12 and C12Se are similar, 26,72 so a thermodynamic drive toward increased coverage is absent. 57 The Se−Au bond is stronger than the S−Au bond; 73 we have shown that the Se− Au bond is more promiscuous in terms of binding sites. 26 Garrell and co-workers 38 showed a strong surface preference for benzeneselenolates over benzenethiolates, a phenomenon attributed to the higher acidity of the selenol group relative to the thiol.…”

Modification of biphenylselenolate monolayers by low‐energy electrons

“…In fact, there are experimental data showing that organoselenols bind stronger to coinage metals than organothiols. In particular, this is evidenced by displacement and competitive adsorption studies performed with biphenyl diselenide and biphenyl disulfide [46], detailed studies of alkaneselenol and alkanethiol SAMs using XPS [34], and synchrotron-based high-resolution XPS studies of the adsorbate induced shift of the substrate emission BE in different thiol-and selenolbased SAMs [35,36]. Theoretical calculations of the adsorption energy performed for the entire set of chalcogenates on coinage metals further support these results [75,76].…”

Gold surfaces and nanoparticles are protected by Au(0)–thiyl species and are destroyed when Au(I)–thiolates form

“…X-ray photoelectron spectroscopy (XPS) measurements indicate that gold surface atoms are essentially uncharged when stabilized by RS groups (29,(46)(47)(48)(49)(50). This result also applies even for pure sulfur monolayers (51) but not when anions bind (47).…”