Interactions between thiol molecular linkers and the Au₁₃ nanoparticle

The structure and binding of thiol molecular linkers to gold surfaces and nanoparticles is central to the understanding of the electronic properties of self-assembled monolayers and, of relevance to recent studies, to nanoscale assemblages consisting of molecular wires and metal nanoparticles. The study of mono-molecular electron transport generally requires consideration of bonding with irregular metallic contacts or poorly defined surfaces such as break junctions, electromigration generated gaps, and scanning probe microscopy tips. These structures can locally bear a closer resemblance to atomic clusters, as compared to neat metallic surfaces. It has also emerged that the prediction and understanding of the electronic transport properties for molecular wires and nanoscale assemblies requires detailed knowledge of thiolate-gold cluster interactions. Recent debate has focused on the nature of the thiolate bonding to surfaces, and the effect of disordering and distortion in gold cluster structures on thiolate bonding. We apply density functional theory methods to study the interactions of two thiols-methanethiol and benzenethiol-with Au₁₃, a gold "magic" number cluster. Our study emphasizes the effects of thiolate bonding on the electronic structure of the linker molecule and gold cluster. We find significant local distortion of the gold cluster upon bonding to a thiol group, resulting in modifications to the electronic structure of the complex. Consideration of a finite gold cluster avoids many of the issues related to thiolate bonding on gold surfaces, and allows us to assess the impact of bonding to gold nanoparticles in terms of electronic structure. We discuss our findings in relation to electron transport properties in self-assembled systems.