Studies leading to the incorporation of Group 14 germanium into the in complete cuboidal clusters [M3E4(H2O)(9)](4+) (M = Mo, W; E = S, Se) have been carried out. From the clusters [Mo3E4(H2O)(9)](4+), corner-shared double cubes [Mo6GeE8(H2O)(18)] are obtained with GeO, by heating with Ge powder at 90 degreesC, or by heating with GeO2 in the presence of H3PO2 as reductant at 90 degreesC, illustrating the dominance of the double cubes. The yellow-green single cube [Mo3GeS4 (H2O)(12)](6+) is only obtained by controlled air oxidation of [Mo6GeS8(H2O)(18)](8+) over a period of similar to4 days followed by Dowex purification. In the case of the trinuclear clusters [W3E4(H2O)(9)](4+), the single cubes [W3GeE4(H2O)(12)](6+) are dominant and prepared by the reactions with GeO, or GeO2/H3PO2. Conversion of [W3GeE4(H2O)(12)](6+) to the corresponding double cubes is achieved by reductive addition with BH4- in the presence of a further equivalent Of [W3E4(H2O)(9)](4+). The crystal structures (pts(-) = p-toluene-sulfonate) of [Mo6GeS8(H2O)(18)](pts)(8)(.)28H(2)O, (1); [W6GeS8(H2O)(18)](pts)(8)(.)23H(2)O, (2); and [Mo6GeSe8(H2O)(18)](pts)(8)(.)8H(2)O, (3); have been determined, of which (2) is the first structure of a W-6 double cube. The M-M bond lengths of similar to2.7 A are consistent with metal-metal bonding, and the M-Ge of similar to3.5 A corresponds to nonbonding separations. Of the Group 13-15 corner-shared double cubes from [Mo3S4(H2O)(9)](4+), [Mo6GeS8(H2O)(18)](8+) is the least reactive with [Co(diPiC)(2)](-) as oxidant (0.077 M-1 s(-1)), and [Mo6SnS8(H2O)(18)](8+) is next (14.9 M-1 s(-1)). Both Ge and Sn (Group 14) have an even number of electrons, resulting in greater stability. In contrast, [W6GeS8(H2O)(18)](8+) is much more reactive (7.3 x 10(3) M-1 s(-1)), and also reacts more rapidly with O-2.