Cis-trans conversion of the CH₃S-Au-SCH₃ complex on Au(111)

The RS-Au-SR complex (RS- being an alkylthiolate group) has been determined to be an important structural motif at the interface of self-assembled monolayers (SAMs) of thiolate on gold. We investigate the conversion between two stable configurations (cis and trans) of the CH₃S-Au-SCH₃ complex on Au(111) by applying density functional theory. We show that this cis-trans conversion has a barrier of only 0.5 eV, indicating that the two geometrical isomers can easily interchange on Au(111) to facilitate packing of the CH₃S-Au-SCH₃ complexes on Au(111). We further examine how this conversion connects two stable structural models recently predicted for the well known c(4 × 2) superstructure of SAMs on Au(111).