Mercaptoammonium-Monolayer-Protected, Water-Soluble Gold, Silver, and Palladium Clusters

Abstract

This paper describes gold, silver, and palladium nanoparticles coated with monolayers of trimethyl(mercaptoundecyl)ammonium ligands. The monolayer-protected clusters (MPCs) are synthesized in aqueous medium and are water soluble. In dry films, their highly charged surfaces inhibit the interdigitation of monolayer chains known (transmission electron microscopy) in dry films of alkanethiolate-coated nanoparticles. UV−vis spectra exhibit surface plasmon bands for Au and Ag MPCs at the expected wavelengths but none for Pd clusters. Thermogravimetric and transmission electron microscopy results suggest that Au and Ag nanoparticles readily aggregate through ionic association of the terminal ammonium groups but without metallic core fusion between particles. Two-component multilayers of MPCs can be affixed to surfaces by alternating exposure to anionic, mixed-monolayer hexanethiolate−mercaptoundecanoic acid MPCs and cationic Au ammonium-MPCs.