The synthesis and electrochemical and spectroscopic characterization of biicosahedral Au-25 clusters with a composition of [Au-25(PPh3)(10)(thiolate)(5)Cl-2](2+) are described. The biicosahedral Au-25 clusters protected with various types of thiol ligands including alkanethiols, 2-phenylethanethiol, 11-mercaptoundecanoic acid, and 11-mercapto-1-undecanol were synthesized in high yields using a onestep, one-phase procedure in which Au(PPh3)Cl is reduced with tert-butylamine-borane in the presence of the thiol ligand in a 3:1 v/v chloroform/ethanol solution. All blicosahedral Au-25 clusters prepared exhibit characteristic optical absorption and photoluminescence properties. The emission energy is found to be substantially smaller than the optical absorption energy gap of 1.82 eV, indicating a subgap energy luminescence. The electrochemical HOMO-LUMO gap (similar to 1.54 eV) of the clusters is also substantially smaller than the optical absorption energy gap but rather similar to the emission energy. These electrochemical and optical properties of the blicosahedral Au-25 clusters are distinctly different from those of the Au-25(thiolate)(18) clusters.