Preparation, Structure, and Reactivity of Ge-Containing Heterometallic Cube Derivatives of [M₃E₄(H₂O)₉]⁴⁺ (M = Mo, W; E = S, Se)

Studies leading to the incorporation of Group 14 germanium into the incomplete 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 °C, or by heating with GeO2 in the presence of H3PO2 as reductant at 90 °C, 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 ∼4 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)8·28H2O, (1); [W6GeS8(H2O)18](pts)8·23H2O, (2); and [Mo6GeSe8(H2O)18](pts)8·8H2O, (3); have been determined, of which (2) is the first structure of a W6 double cube. The M−M bond lengths of ∼2.7 Å are consistent with metal−metal bonding, and the M−Ge of ∼3.5 Å 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 × 103 M-1 s-1), and also reacts more rapidly with O2.