Chalcogenide-Stabilized Metal Nanoclusters: Synthesis, Characterizations, and Applications
This seminar focuses on the atomically precise gold NPs, or NCs. Au25(SR)18 was selected as a model NC to investigate their magnetic properties, with pentanethiol, hexanethiol and octanethiol used as bonding ligands. Both negatively charged and neutral NCs were synthesized, and 1H/13C NMR were used for detailed structural analysis, as well as surface bonding ligand environment analyses. The anion NC (diamagnetic) and neutral (paramagnetic) NCs are compared and by using the diamagnetic chemical shifts as references, paramagnetic Knight shifts can be calculated. These shifts measure the spin density along the carbon chain of the surface ligand. Temperature dependent NMR was used to study the spin density effect. Density functional theory calculations were used to predict the spin density on Au25(SC8H17)18 and compared with the Knight shifts observed from the experiments. New magnetic properties were observed from the Knight shifts plots.
Chalcogenide stabilized NCs, such as with selenolates and tellurolates, have been less investigated, especially their exchange reactions with thiolate. The reaction mechanism, specifically the site preferences and how the mixed ligand layer is distributed on the NCs surface in the exchange reaction, is much less understood. PhSeH and (PhTe)2 were used to exchange Au25(SC8H17)18 at different ratios. When the exchange ratio was low, a low exchange extent was observed. With the assistance of 13C, 77Se, and 125Te NMR, surface ligands’ chemical and electronic environments were able to be studied, as well as the exchange mechanism. A direct measurement of 77Se and 125Te NMR revealed the electronic environment of these anchoring atoms in the exchange reaction with Au25(SR)18. The metal alloy NC-Pt1Au24(SR)18 was also studied. After confirmation of the NC structure by MALDI-MS, 13C and 195Pt NMR were used to investigate the surface ligand and center doping metal atom. Based on these studies, a new structure is proposed for this metal alloy NC.