ALKANETHIOLATE GOLD CLUSTER MOLECULES WITH CORE DIAMETERS FROM 1.5 TO5.2 NM - CORE AND MONOLAYER PROPERTIES AS A FUNCTION OF CORE SIZE

The mean size of the gold (Au) core in the synthesis of dodecanethiola te-stabilized Au cluster compounds can be finely adjusted by choice of the Au:dodecanethiolate ratio and the temperature and rate at which t he reduction is conducted. The Au clusters have been examined with a l arge number of independent analytical tools, producing a remarkably co nsistent picture of these materials. Average cluster and core dimensio ns, as ascertained by H-1 NMR line broadening, high-resolution transmi ssion electron microscopy, small-angle X-ray scattering, and thermogra vimetric analysis, vary between diameters of 1.5 and 5.2 nm (similar t o 110-4800 Au atoms/core). The electronic properties of the Au core we re examined by UV/vis and X-ray photoelectron spectroscopy; the core a ppears to remain largely metallic in nature even at the smallest core sizes examined. The alkanethiolate monolayer stabilizing the Au core r anges with core size from similar to 53 to nearly 520 ligands/core, an d was probed by Fourier transform infrared spectroscopy, differential scanning calorimetry, contact-angle measurements, and thermal desorpti on mass spectrometry. The dodecanethiolate monolayer on small and larg e core clusters exhibits discernable differences; the line dividing '' 3-dimensional'' monolayers and those resembling self-assembled monolay ers on flat Au (2-dimensional monolayers) occurs at clusters with simi lar to 4.4 nm core diameters.