Synthesis and Structural Determination of Multidentate 2,3-Dithiol-Stabilized Au Clusters

Interface bond structure, in addition to the well-known size and shape quantum confinement effects, is another factor that affects the properties of nanomaterials that is less known and studied. Inspired by the thiol-bridging staple motif (RS-Au-SR, Jadzinsky; et al. Science 2007, 318, 430.) discovered from monothiol-stabilized gold nanoclusters, dithiol ligand 2,3-dimercaptopropanesulfonic (DMPS) acid has been employed to synthesize dithiol-protected Au clusters (DTCs). The structure and property of the Au DTCs are studied to probe two effects: the entropy gain of dithiol over monothiol ligand protection and the constraint to the formation of the thiol bridging surface bonding. The hydrodynamic sizes of Au DTCs were estimated by diffusion nuclear magnetic resonance (NMR). The size distribution, Au core plus ligands on solid support, was confirmed by atomic force microscope (AFM) imaging. Size-dependent optical properties were observed. Au-4 clusters at high purity, characterized by mass spectrometry and organic metal ratio confirmed by thermogravimetric analysis (TGA), display a characteristic absorbance band at 282 nm. The proton chemical environments as well as Au S bond information of the Au4 cluster were fully elucidated by C-13-H-1 heteronuclear single-quantum coherence (HSQC) in conjunction with other two-dimensional (2D) NMR techniques. The Au S bonding was further studied in thiol stretching by infrared and Au(4f) and S(2p) electrons by X-ray photoelectron spectroscopy (XPS). One possible structure of the Au-4 cluster has been proposed that needs further theoretical studies or single-crystal confirmation.