Molecular binding at gold transport interfaces. IV. Thiol chemisorption

Alkene thiol/coinage metal molecular interfaces are relatively easy to make, and can result in well-ordered self-assembled monolayer films. The energetics of such formation is complex-differing experimental and theoretical accounts have focused on the nature of the binding, the energetics via different pathways (thiol radical, thiol or thiolate) and the geometry of binding. We report density functional theory calculations on a four atom gold cluster interacting with different (alkane, alkene, alkyne) thiolates. We find thiolate addition to be strongly exoergic, thiol radical to be roughly half as favorable, and thiol to be slightly favorable. We also find that the S-H bond can remain when the thiol attaches to the gold cluster, formally resulting in increased coordination on the sulfur atom. (C) 2004 American Institute of Physics.