Ligand-exchange Synthesis Of Selenophenolate-Capped Gold Nanoclusters

Gold nanoparticles has been studied for more than150years of history. The gold in nano scale has different optical and other physicochemical properties with the bulk gold. Such nanoclusters provide a new class of nanomaterial that holds potential in catalysis, bioassays, biolabelling, and sensing. The kinetically controlled synthetic method of gold nanoclusters has been rapidly developed when Brust opened up the Bottom up method for the synthesis of gold nanoclusters in1994. Many monodispersed gold nanoclusters with precise atoms have been obtained. Since then people have tried to replace S with Se, synthesized Se-cappd gold nanoclusters. On the basis of predecessors’research work of S-capped gold nanoclusters, we found a ligand-exchange method for synthesis of selenophenolate-protected monodispersed gold nanoclusters. The main work of this paper is as follows:1We synthesized selenophenolate-capped25-gold-atom nanoclusters via a ligand-exchange approach. In this method, phenylethanethiolate (PhCH2CH2S-) capped Au25nanoclusters are utilized as the starting material, which is subject to ligand-exchange with selenophenol (PhSeH). The as-obtained cluster product is confirmed to be selenophenolate-protected Au25nanoclusters through characterization by electrospray ionization (ESI) and matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), thermogravimetric analysis (TGA), elemental analysis (EA), UV-Vis and1H/13C NMR spectroscopies. The ligand-exchange synthesis of Au25(SePh)18nanoclusters demonstrates that the core size of gold nanoclusters is retained in the thiolate-to-selenolate exchange process and that the18surface thiolate ligands can be completely exchanged by selenophenolate, rather than giving rise to a mixed ligand shell on the cluster. The two types of Au25L18(L=thiolate or selenolate) nanoclusters also show some differences in stability and optical properties.2This work reports the first synthesis of selenophenolate-protected Au18(SePh)14nanoclusters. This cluster exhibits distinct differences from its thiolate analogue in terms of optical absorption properties. The Au18(SePh)14nanoclusters were obtained via a controlled reaction of Au25(SCH2CH2Ph)18with selenophenol. Electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) revealed the crude product to contain predominantly Au18(SePh)14nanoclusters, and side products include Au15(SePh)13,Au19(SePh)15and Au2o(SePh)16. High-performance liquid chromatography (HPLC) was employed to isolate Au18(SePh)14nanoclusters. The results of thermogravimetric analysis (TGA), elemental analysis (EA), and1H/13C NMR spectroscopy confirmed the cluster composition. To the best of our knowledge, this is the first report of selenolate-protected Au18nanoclusters. Future theoretical and X-ray crystallographic work will reveal the geometric structure and the nature of selenolate-gold bonding in the nanocluster.