ABSTRACT
A bidentate chiral dithiol (diBINAS) is utilised to bridge Au25 nanoclusters to form oligomers. Separation by size allows the isolation of fractions that are stable thanks to the bidentate nature of the linker. The structure of the products is elucidated by small-angle X-ray scattering and calculated using density functional theory. Additional structural details are studied by diffusion-ordered nuclear magnetic resonance spectroscopy, transmission electron microscopy and matrix-assisted laser desorption/ionization time of flight mass spectrometry. Significant changes in the optical properties are analysed by UV/Vis and fluorescence spectroscopies, with the latter demonstrating a strong emission enhancement. Furthermore, the emergent chiral characteristics are studied by circular dichroism. Due to the geometry constraints of the nanocluster assemblies, diBINAS can be regarded as a templating molecule, taking a step towards the directed self-assembly of metal clusters.
ABSTRACT
The ligand exchange reaction between racemic Au(38)(2-PET)(24) (2-PET = 2-phenylethylthiolate) clusters and enantiopure 1,1'-binaphthyl-2,2'-dithiol (BINAS) was monitored in situ using a chiral high-performance liquid chromatography approach. In the first exchange step, a clear preference of R-BINAS for the left-handed enantiomer of Au(38)(2-PET)(24) is observed (about 4 times faster than reaction with the right-handed enantiomer). The second exchange step is much slower than the first step. BINAS substitution deactivates the cluster for further exchange, which is attributed to (stereo)electronic effects. The results constitute the first example of a ligand exchange reaction in a thiolate-protected gold cluster with directed enrichment of a defined species in the product mixture. This may open new possibilities for the design of nanomaterials with tailored properties.
