Evaluation of Electron Donation as a Mechanism for the Stabilisation of Chalcogenate-Protected Gold Nanoclusters.

Models based on Au(111) face have been extensively used to describe self-assembled monolayers, as well nanoparticles and nanoclusters. However, for very small clusters (<2 nm), the chemisorption of ligands leads to surface reconstruction, making necessary the use of a more reliable model that is able to simulate the main electronic and geometrical features of these small systems. In this work, a simple model to describe the geometries and the metal-ligand bonding in chalcogenate-protected gold nanoclusters is proposed. Three different models with Aun+ and [XCH3 ]- (n=10, 15, 19, 22 and X=S, Se, Te) are used in this work. The obtained structures are in close agreement not only with the available crystallographic data, but also with much more expensive computational procedures, confirming that the proposed models are robust enough to describe the metal-ligand bonding. The results reveal that the Au-X distances are dependent on both the nature of the chalcogen and the coordination mode. The shortest Au-X distances are observed in the face-centred cubic mode, indicating that the central gold atom seems to play a role in determining the adsorption strength. The proposed models show unambiguously chalcogen→cluster σ-donation, as supported by energy decomposition analysis coupled with the natural orbitals for chemical valence and natural bond orbital analyses. In all cases, the metal-ligand interactions are characterised as being more covalent than electrostatic.