In the aqueous chemistry of molybdenum(IV) and tungsten(IV), trinuclear, incomplete cubane-like, oxo and sulfido clusters of the type [M3E4](4+) (M = MO, W; E = O, S) play a central role. We here describe how formato complexes of all these cluster cores can be prepared in high yields by crystallization from methanol-water or ethanol-water mixtures, Since potassium and ammonium formate ape very soluble in these alcohol-water mixtures, high formate concentrations could be accomplished in the solutions from which the corresponding salts of cluster formato complexes crystallized. The [Mo3O4](4+) compounds could be synthesized without: requiring the use of noncomplexing acids in the process. Some [M3E4](4+) compounds were characterized by single-crystal structure determinations. [NH4](3.20)[K](0.08)[H3O][Mo3O4(HCO2)(8)][HCO2].H2O was triclinic, space group P1 (No. 2) with a = 11.011(2) Angstrom, b 13.310(2) Angstrom, c = 9.993(1) Angstrom, alpha = 106.817(7)degrees, beta = 91.651(9)degrees, gamma = 88.340(9)degrees, and two formula units per cell. [K](6)[W3S4(HCO2)(9)][HCO2].2.27H(2)O.0.73CH(3)OH was monoclinic, space group C2/m (No. 12) with a = 19.605(6) Angstrom, b = 14.458(7) Angstrom, c = 13.627(5) Angstrom,beta = 118.94(2)degrees, and four formula units per cell, Generally, the nine coordination sites of [M3E4](4+) were, occupied either by a mixture of monodentate and mu(2)-bridging formato ligands or by monodentate formato ligands only. By dissolution in noncomplexing strong acid, all the formato complexes immediately hydrolyzed to form [M3E4(H2O)(9)](4+) aqua complexes. This allows, for example, high concentrations of [Mo3S4(H2O)(9)](4+) in CF3SO3H to be obtained and chese solutions to be used for the synthesis of bimetallic clusters containing the cubane-like motif MO3M'S-4.