Novel One-Phase Synthesis of Thiol-Functionalized Gold, Palladium, and Iridium Nanoparticles Using Superhydride

A new, facile, general one-phase synthesis for thiol-functionalized gold, palladium, and iridium nanoparticles, using tetrahydrofuran (THF) as the solvent and lithium triethylborohydride (Superhydride) as the reducing agent, is presented. For octadecanethiol-functionalized gold (Au/ODT) nanoparticles, HRTEM of drop-cast particle-films revealed the formation of spherical particles of d = 4 ± 0.3 nm average size. Electron diffraction shows fcc packing arrangement, similar to that of bulk gold. The crystalline gold cores are surrounded with closely packed n-alkyl chains mainly in an all-trans conformation, adopting orthorhombic packing as confirmed by FTIR spectroscopy. Particles are arranged in a discrete solidlike assembly with a correlation length of ∼5 nm, as the interparticle distance (center-to-center) and a constant edge-to-edge distance of 1 nm as shown by FFT analysis. Using the same synthetic procedure gold nanoparticles functionalized with 11-hydroxyundecane-1-thiol and with 4‘-bromo-4-mercaptobiphenyl were prepared. TEM images of drop-cast Pd/ODT and Ir/ODT nanoparticles show an average size of 2.25 nm for the former, while for the latter the distribution is broader with the majority of particles between 2.25 and 4.25 nm. Both nanoparticles are crystalline with fcc packing. FTIR spectroscopy reveals that octadecyl chains are close-packed in all-trans conformation, and that there is presumably one chain in unit cell.