Theoretical Prediction of S–H Bond Rupture in Methanethiol upon Interaction with Gold

Abstract

Organic thiols are known to react with gold surface to form self-assembled monolayers (SAMs), which can be used to produce materials with highly attractive properties. Although the structure of various SAMs is widely investigated, some aspects of their formation still represent a matter of debate. One of these aspects is the mechanism of S-H bond dissociation in thiols upon interaction with gold. This work presents a new suggestion for this mechanism on the basis of DFT study of methanethiol interaction with a single gold atom and a Au(20) cluster. The reaction path of dissociation is found to be qualitatively independent of the model employed. However, the highest activation barrier of S-H bond dissociation on the single gold atom (12.9 kcal/mol) is considerably lower than that on the Au(20) cluster (28.9 kcal/mol), which can be attributed to the higher extent of gold unsaturation. The energy barrier of S-H cleavage decreases by 4.6 kcal/mol in the presence of the second methanethiol molecule at the same adsorption site on the model gold atom. In the case of the Au(20) cluster we have observed the phenomenon of hydrogen transfer from one methanethiol molecule to another, which allows reducing the energy barrier of dissociation by 9.1 kcal/mol. This indicates the possibility of the "relay" hydrogen transfer to be the key step of the thiol adsorption observed for the SAMs systems.

Photoelectron velocity-map imaging spectroscopic and theoretical study on the reactivity of the gold atom toward CH3SH, CH3OH, and H2O

“…Previous theoretical investigations predicted that the RS-Au-SR staple motif were formed from the co-adsorption of two CH 3 SH molecules on metal atom. 20 − products simultaneously present in the Au − + CH 3 SH reaction (Fig. S1 of the supplementary material), 51 supporting this formation mechanism.…”

“…Experimentally, the loss of hydrogen has been observed upon the exposure of thiols to very large gold particles (∼4 nm, about Au 2000 size). 19 Theoretical investigations have suggested a most likely pathway of S-H bond rupture of the CH 3 SH molecule on the Au atom and Au 20 , 20 surfaces, 22 namely, the co-adsorption of two or three CH 3 SH molecules on the gold clusters induce the release of H 2 and the formation of the staple motif. Recent photoelectron spectroscopic and theoretical investigation reveals a covalent characteristic of the Au-S bond.…”

Density functional theory approach to gold-ligand interactions: Separating true effects from artifacts

“…A several-functional compilation for AuCO 30 provides binding energies from 1/3 (M06-2X 31 ) to 3/2 (PBE0) to over twofold overbinding by the favorites of the gold community: BP86, 32, 33 PBE, 34 and PW91. 35 A similar, albeit narrower, comparison for Au-methylthiol 36 shows twofold disparity between PW91 (PBE) and B3LYP. 37 Arguably, with such uncertainty on every rung of DFT, the structural and energetical predictions of ligand protected gold nanoparticles could vary from functional to functional.…”

“…The latter issue has been extensively discussed in the literature. 36,45,47,46,82 A less convoluted explanation takes into account that electrons tend to flow from a region of high chemical potential (low electronegativity) to a region of low chemical potential (high electronegativity). Both of these quantities are well defined within DFT.…”

Adsorption of small molecules on helical gold nanorods: A relativistic density functional study

“…[26,27] For both H 2 S and SO 2 adsorption on small gold clusters (which are planar), the sulfur atom is in the same plane and these molecules preferentially adsorb at a single low-coordination gold atom on the gold cluster. [28][29][30][31][32][33] Although impressive progress has been achieved in understanding the adsorption of small molecules on small gold clusters, computational studies for large gold clusters are generally lacking. A notable exception is the study of Gao et al [34] which examined the adsorption of CO on free subnanometer gold clusters (Au 16 -Au 18 , Au 20 , and Au 27 -Au 35 ).…”