Isolable, water-soluble gold clusters protected by monolayers of tiopronin (tiopronin−MPCs) or coenzyme
A (CoA−MPCs) were synthesized by a procedure of comparable simplicity to the Brust synthesis for
alkanethiolate monolayer-protected gold clusters. High-resolution transmission electron microscopy shows
that, like their alkanethiolate−MPC counterparts, the average core diameters of tiopronin−MPCs can be
systematically controlled by varying the tiopronin:Au mole ratio employed in the reaction. The UV−vis
spectra of tiopronin−MPCs exhibit pH and core size dependency of the surface plasmon band position and
intensity, respectively. Thermogravimetric analysis of the tiopronin−MPCs gave average numbers of
tiopronin ligands per cluster; for example, tiopronin−MPCs with an average core size of 1.8 nm (∼Au201)
are protected with an average of 85 tiopronin ligands. 1H NMR reveals a size-dependent evolution of
spectral features interpreted as reflecting differences in attachment sites (terrace, defects) and/or restriction
in ligand mobility. Infrared spectroscopy reveals strong hydrogen bonding in the monolayer and provides
evidence for intercluster association, and acid/base titrations produce pK
A values similar to the free ligand
in the presence of a charge-screening supporting electrolyte, but higher in its absence. The same analytical
methods were also applied to CoA-MPCs.
Alloy particles 1 can exhibit electronic, 2-4 optical, 5-10 and catalytic properties 11,12 that are distinct from those of the corresponding mono-metal particles, 13-17 prompting numerous preparations of multi-metal nanoparticles, including those that can be considered core/shell bimetallic, partially segregated alloy, and pure alloy. 1-12 These earlier alloy particles typically required specialized equipment or handling procedures, posed difficulties in isolation and analysis, and could not be redissolved in airstable forms.This paper describes a simple synthesis of nanometer-sized monolayer-protected alloy clusters (MPACs) that are the first examples of stable, large, alloy molecules that can be isolated in solvent-free forms and redissolved without change. The stable alkanethiolate monolayer is the key to preventing metal core aggregation. The MPAC core compositions can be systematically varied in regards to ratios and numbers of groups 10 (Pt, Pd) and 11 (Cu, Ag, Au) metals, creating a pathway to studying the S0002-7863(98)01454-1 CCC: $15.00
This paper describes the synthesis, characterization, reactivity, and electrochemistry of monolayer-protected clusters (MPCs) of palladium that are passivated by monolayers of hexanethiolate or
dodecanethiolate ligands. The synthetic product is sensitive to the thiol:Pd ratio used in the reaction
mixture: a 1:1 ratio or smaller ratio produces metallic Pd(0) clusters that are similar to analogously
prepared Au MPCs, but much more ligand-rich, whereas ≥2:1 ratios yield a very different material that
is either extremely small Pd(0) clusters or a form of Pd(II) alkanethiolate complex. The monolayers of the
metallic Pd(0) MPCs that are synthesized using small thiol:Pd ratios can be modified by ligand place-exchange and coupling reactions. The electrochemistry of the Pd core and of electroactive labels attached
to the alkanethiolate ligands was studied. Quantized double-layer core charging is seen but less clearly
than with Au MPCs. The Pd nanoparticles were examined using NMR, FTIR, UV−vis, TEM, TGA, and
elemental analysis.
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.
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