Molecular binding at gold transport interfaces. IV. Thiol chemisorption

Area of Science:

• Surface Science
• Computational Chemistry
• Materials Science

Background:

• Alkene thiol/coinage metal interfaces form well-ordered self-assembled monolayers.
• The energetics and binding pathways (thiol radical, thiol, thiolate) are complex and debated.
• Previous studies offer differing experimental and theoretical accounts.

Purpose of the Study:

• To investigate the energetics of different thiol binding pathways to gold clusters using computational methods.
• To determine the preferred binding configuration and stability of thiolates, thiol radicals, and thiols on gold surfaces.
• To explore the structural implications of thiol binding, specifically S-H bond retention.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• A four-atom gold cluster model was used to simulate interactions.
• Calculations focused on alkane, alkene, and alkyne thiolates interacting with the gold cluster.

Main Results:

• Thiolate addition to the gold cluster was found to be strongly exoergic (highly favorable).
• Thiol radical binding was approximately half as favorable as thiolate addition.
• Thiol binding was only slightly favorable, with a tendency for S-H bond cleavage.
• The S-H bond can remain intact upon thiol attachment, leading to increased sulfur coordination.

Conclusions:

• Thiolate formation is the most energetically favorable pathway for thiol adsorption on gold clusters.
• The binding energetics vary significantly depending on the thiol's oxidation state (thiolate, radical, or intact thiol).
• The possibility of S-H bond preservation offers alternative binding modes and influences surface structure.