Sulfur-bridged cubane-type molybdenum-gallium clusters [Mo3GaS4(H2O)(12)](5+) (2) and [Mo3GaS4(H2O)(12)](6+) (3) have been synthesized from [Mo3S4(H2O)(9)](4+) (1) and gallium metal and have been isolated as 2(pts)(5) . 14H(2)O (2.pts) and 3(pts)(6) . 17H(2)O (3.pts) (Hpts = p-toluenesulfonic acid), whose structures have been characterized by X-ray crystallography. Crystal data for 3.pts : orthorhombic, space group Pca2(1), a = 11.188(1) Angstrom, b = 30.936(4) Angstrom, c = 23.987(2) Angstrom, V = 8301(2) Angstrom(3), Z = 4, D-calcd = 1.628 g cm(-3), D-obsd = 1.63 g cm(-3), R (R(w)) = 5.8% (6.3%) for 6102 reflections (I > 3.0 sigma(I)). Crystal data for 2.pts : triclinic, space group , a = 16.406(4) Angstrom, b = 16.743(3) Angstrom, c = 13.173(4) Angstrom, alpha = 90.640, beta = 98.40(2)degrees, gamma = 89.32(2)degrees, V = 3579.2(14) Angstrom(3), Z = 2, D-calcd = 1.681 g cm(-3), D-obsd = 1.68 g cm(-3), R (R(w)) = 6.7% (10.1%) for 7612 reflections (I > 3.0 sigma(1)). The Mo-Ga distances (3.pts, 3.60[2] Angstrom; 2.pts, 3.52[2] Angstrom) are much longer than the corresponding Mo-Mo (3.pts, 2.679[7] Angstrom; 2.pts, 2.713[3] Angstrom) distances. At low H+ concentrations, such as 0.5 M HCl, 2 is stable, and at H+ concentration higher than 2 M HCl, 2 is oxidized by H+ to give 3 with evolution of hydrogen gas. Chloride ion plays an important role in the oxidation of 2. Electronic spectra of 3.pts and 2.pts are very similar. Peak positions and epsilon values (lambda max, nm (epsilon, M(-1) cm(-1))) : 3.pts, 762 (447), 550 (204); 2.pts, 760 (404), 548 (205). The cyclic voltammogram of 3 shows three reduction processes (the cathodic peak potentials, E(pc), are -0.83, -1.20, and -1.74 V, respectively), where the first and second processes are quasi-reversible (the anodic peak potentials, Epa, are -0.55 and -1.00 V, respectively). The reduction current of each process is close to 1:1:3.