The synthesis and characterization of the clusters Au-13[PPh3](4)[S(CH2)(11)CH3](2)Cl-2 (1) and Au-13[PPh3](4)[S(CH2)(11)-CH3](4) (2) are described. These mixed-ligand, sub-nanometer clusters, prepared via exchange of dodecanethiol onto phosphine-halide gold clusters, show enhanced stability relative to the parent. The characterization of these clusters features the precise determination of the number of gold atoms in the cluster cores using high-angle annular dark-field scanning transmission electron microscopy, allowing the assignment of 13 gold atoms (+/- 3 atoms) to the composition of both cluster molecules. Electrochemical and optical measurements reveal discrete molecular orbital levels and apparent energy gaps of 1.6-1.7 eV for the two cluster molecules. The electrochemical measurements further indicate that the Au-13[PPh3](4)[S(CH2)(11)CH3](2)Cl-2 cluster undergoes an overall two-electron reduction. The electrochemical and spectroscopic properties of the two Au-13 cluster molecules are compared with those of a secondary synthetic product, which proved to be larger Au thiolate-derivatized monolayer-protected clusters with an average core of Au-180. The latter shows behavior fully consistent with the adoption of metallic-like properties.