Reduction of a equimolar amount of (NH4)(2)WS4 and Na-2[Mo2O2S2(cys)(2)].4H(2)O with NaBH4 gives a mixture of sulfur-bridged clusters, chromatographic separation of which gives novel incomplete cubane-type molybdenum-tungsten mixed-metal clusters [MoW2S4(H2O)(9)](4+) and [Mo2WS4(H2O)(9)](4+). From the aqua clusters solid samples [MoW2S4(H2O)9](CH3C6H4SO3)(4).9H2O (MoW(2)aq) and [Mo2WS4(H2O)9] (CH3C6H4SO3)(4).9H2O (Mo(2)Waq) were isolated, and the derivatives Na-2[MoW2S4(Hnta)(3)].5H(2)O (MoW(2)nta), and Na-2[Mo2WS4(Hnta)(3)].5H(2)O (Mo-2-Wnta) were obtained (H(3)nta = nitrilotriacetic acid). Crystal structures of the four clusters were determined. Compound MoW(2)aq crystallized in the triclinic space group P ($) over bar 1 with a 15.303(3) Angstrom, b = 16.682(6) Angstrom, c = 12.055(3) Angstrom, alpha = 96.02(3)degrees, beta = 108.58(2)degrees, gamma = 102.16(2)degrees, V = 2802.1(15) Angstrom(3), Z = 2, R = 4.77%. Compound Mo(2)Waq crystallized in the triclinic space group P ($) over bar 1 with a = 15.327(5) Angstrom, b = 16.704(5) Angstrom, c = 12.057(5) Angstrom, alpha = 95.64(3)degrees beta = 108.82(3)degrees, gamma = 102.41(2)degrees, V = 2806.2(18) Angstrom(3), Z = 2, R = 5.98%. Compound MoW(2)nta crystallized m the monoclinic space group P2(1)/a with a = 21.754(5) Angstrom, b = 12.733(5) Angstrom, c = 13.374(5) Angstrom, beta = 101.95(3)degrees, V = 3624.4(21) Angstrom(3), Z = 4, R = 3.90%. Compound Mo(2)Wnta crystallized in the monoclinic space group P2(1)/a with a = 21.741(5) Angstrom, b = 12.714(5) Angstrom, c = 13.384(6) Angstrom, beta = 102.10(3), V = 3617.3(24) Angstrom(3), Z = 4, R = 4.74%. Molybdenum and tungsten atoms in the four crystals are statistically disordered. Peak positions of the two big bands in each infrared spectrum of the four aqua clusters, [Mo3S4(H2O)9](CH3C6H4SO3)(4).9H(2)O (Mo(3)aq), Mo(2)Waq, MoW(2)aq, and [W3S4(H2O)(9)](CN3C6H4SO3)(4).9H(2)O (W(3)aq), in the 550-400-cm(-1) region shift to lower wavenumbers when the molybdenum atom is replaced by tungsten.