Expanding the chemical versatility of colloidal nanocrystals capped with molecular metal chalcogenide ligands

We developed different strategies toward the synthesis of colloidal nanocrystals stabilized with molecular metal chalcogenide complexes (MCCs). Negatively charged MCCs, such as SnS₄^4-, Sn ₂S₆^4-, SnTe₄^4-, AsS ₃^3-, MoS₄^2-, can quantitatively replace the organic ligands at the nanocrystal surface and stabilize nanocrystal solutions in different polar media. We showed that all-inorganic nanocrystals composed of metals, semiconductors, or magnetic materials and capped with various MCC ligands can be synthesized using convenient and inexpensive chemicals and environmentally benign solvents such as water, formamide, or dimethylsulfoxide. The development of mild synthetic routes was found to be crucial for the design of highly luminescent all-inorganic nanocrystals, such as CdSe/ZnS and PbS capped with Sn₂S₆^4- MCCs, respectively. We also prepared conductive and luminescent layer-by-layer assemblies from inorganically capped colloidal nanocrystals and polyelectrolytes. In close-packed films of 5-nm Au nanocrystals stabilized with Na₂Sn₂S₆ we observed very high electrical conductivities (>1000 S cm^-1).