Sulfur-Bridged Cubane-Type Molybdenum−Gallium Clusters with Mo₃GaS₄ⁿ⁺ (n = 5, 6) Cores. X-ray Structures of [Mo₃GaS₄(H₂O)₁₂](CH₃C₆H₄SO₃)₅·14H₂O and [Mo₃GaS₄(H₂O)₁₂](CH₃C₆H₄SO₃)₆·17H₂O

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)₅·14H₂O (2·pts) and 3(pts)₆·17H₂O (3·pts) (Hpts = p-toluenesulfonic acid), whose structures have been characterized by X-ray crystallography. Crystal data for 3·pts:  orthorhombic, space group Pca2₁, a = 11.188(1) Å, b = 30.936(4) Å, c = 23.987(2) Å, V = 8301(2) ų, 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 > 3.0σ(I)). Crystal data for 2·pts:  triclinic, space group P1̄, a = 16.406(4) Å, b = 16.743(3) Å, c = 13.173(4) Å, α = 90.64°, β = 98.40(2)°, γ = 89.32(2)°, V = 3579.2(14) ų, 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 > 3.0σ(I)). The Mo−Ga distances (3·pts, 3.60[2] Å; 2·pts, 3.52[2] Å) are much longer than the corresponding Mo−Mo (3·pts, 2.679[7] Å; 2·pts, 2.713[3] Å) 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 ε values (λ_max, nm (ε, 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, E_pa, are −0.55 and −1.00 V, respectively). The reduction current of each process is close to 1:1:3.