Probing the relative stability of thiolate- and dithiolate-protected Au monolayer-protected clusters.

Dithiolate ligands based on (+/-)-alpha-lipoic acid derivatives have been investigated as ligands for both Au monolayer-protected clusters (MPCs) and mixed alkanethiol/dithiolate Au MPCs. The oxidative and thermal stability of the MPCs were investigated by a combination of UV-vis spectroscopy, TEM, and (1)H NMR experiments. Results show that the dithiolate-protected MPCs are much more prone to oxidation by oxygen under ambient conditions than their alkanethiolate-protected MPC analogues; in addition, the Au core of the dithiolate-protected Au MPCs could be etched by KCN at much faster rates than both alkanethiolate-protected and mixed monolayer MPCs. These results suggest that strategies to increase ligand-metal interactions by incorporating more thiolate linkers into the ligand must also take into account the packing efficiency and/or stability of such ligands on the metal surface, which can make them much more prone to oxidation under ambient conditions.