Mercaptoammonium-monolayer-protected, water-soluble gold, silver, and palladium clusters

This paper describes gold, silver, and palladium nanoparticles coated with monolayers of trimethyl(mercaptoundecyl)ammonium ligands. The monolayer-pro tected clusters (MPCs) are synthesized in aqueous medium and are water solu ble. In dry films, their highly charged surfaces inhibit the interdigitatio n of monolayer chains known (transmission electron microscopy) in dry films of alkanethiolate-coated nanoparticles. UV-vis spectra exhibit surface pla smon bands for Au and Ag MPCs at the expected wavelengths but none for Pd c lusters. Thermogravimetric and transmission electron microscopy results sug gest that Au and Ag nanoparticles readily aggregate through ionic associati on 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 - mercapto undecanoic acid MPCs and cationic Au ammonium-MPCs.