The Brust synthesis of thiolate-protected gold clusters has been modified to produce identifiable proportions of a hexanethiolate-protected Au225 core nanoparticle that display quantized double layer charging voltammetry consistent with a Au225 core dimension. Transmission electron microscopy (TEM) and thermogravimetric results indicate an average nanoparticle formula of Au225[(S(CH2)5CH3)]75. A simulated pulse voltammogram that accounts for the TEM nanoparticle dispersity matches reasonably well with that of the polydisperse synthetic sample containing the Au225 component. In confirmation of the size determination, an HPLC analysis using ratiometric absorbance and electrochemical detectors gives a core radius of 1.0 nm for the Au225 nanoparticle.

The synthesis and compositional analysis of four different gold clusters with protecting monolayers comprised solely of ferrocene hexanethiolate ligands is described. The gold nanoparticles have average core diameters of 1.4, 1.6, 2.0, and 2.2 nm with estimated average atom counts of 55, 140, 225, and 314 Au atoms and average monolayer coverages of 37, 39, 43, and 58 ferrocenated ligands, respectively. The data show unequivocally that the number of ferrocene hexanethiolate ligands bound to each core size is constrained by the steric requirements of the ferrocene head group; the ligand numbers are significantly smaller than those for hexanethiolate ligands bonded to analogous-sized Au cores. Voltammetry of dilute solutions of these nanoparticles shows a large ferrocene oxidation wave and, at more negative potentials, smaller one-electron waves for the quantized double-layer charging of the Au cores. Together, the ferrocenes and core of the ferrocenated Au314 nanoparticle deliver 60 electrons at the ferrocene oxidation potential, which amounts to a very large volume charge capacity, 7x10(9) C/m3, for an undiluted nanoparticle sample.

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