Insights into the PhCC/Au Interface

The phenylethynyl group (PhC C-) has attracted attention recently as a new way to passivate gold surfaces, but -little is known of the interfacial structure and bonding. Here we employ density functional theory to investigate the organogold interfaces between PhC C- and the flat An(III) surface as well as between PhC C- and a model gold nanoduster (Au-20). Although isolated prefers the three-coordinate hollow site on the perfect Au(111) surface, formation of the PhCC-Au-adatom -CCPh motif becomes energetically preferred when the Au adatom is present, resembling the RS-Au-SR motif on Au(111). However, distinct from the thiolate/Au interface, the PhC C-Au-adatom-C CPh staple motif features pi-bonding of the C C bond to the Substrate Au atom in addition to the sigma-bonding of the terminal carbon to the gold adatom (or the staple gold atom). Geometry optimization and simulated annealing further show that this new type of staple motif is also the preferred bonding mode of the PhC C- groups on the Au-20 cluster. The novel PhC CAu-C CPh motif with pi-bonding to the Au substrate is expected to be a key feature of the PhC C/Au interface for gold clusters, nanopartides, and surfaces. This insight will help structural elucidation and chemical understanding of both self-assembled monolayers of PhC C- groups on gold surfaces and PhC C- protected gold nanosystems.