Constructing gold-thiolate oligomers and polymers on Au(111) based on the linear S-Au-S geometry

Although neat gold-thiolate oligomers and polymers made of linear S-Au-S bonds have been well-known, observation of RS-Au-SR linear complexes (RS- being an alkylthiolate group) on Au(111) has been reported only recently. On the basis of the unique geometry and bonding of the RS-Au-SR complex on Au(111), we construct simple geometric models of Au-SR oligomers and polymers on Au(111) by fusing linear S-Au-S units matched to the underlying Au(111) surface lattice. We then optimize these models by density functional theory. The hexagonal geometry of the Au(111) lattice determines three possible angles (60°, 120°, and 180°) for connecting two linear S-Au-S units, which lead to isomerism of the Au-SR oligomers and polymer on Au(111). Here we explore open dimers, trimers, and tetramers and cyclic trimers, tetramers, and hexamers of the Au-SR oligomers on Au(111). We also examine four isomers of the Au-SR polymer on Au(111). We find that the 120° Au-S-Au angle is preferred in constructing both oligomeric and polymeric isomers. The two polymeric isomers with 120° Au-S-Au angles are found to be energetically competitive with a previous model proposed for the Au-SR polymer on Au(111). We also discuss potential ways to create Au-SR oligomers on Au(111).