Chelating and/or templating role of oxalates with {M2S2O2}2+ building units M = Mo, W.: Examples of [Mo2S2O2(C2O4)2(H2O)2]2-, [M4S4O4(C2O4)5]6- M = Mo, W and [Mo8S8O8(OH)8(C2O4)]2-

The hydrolysis of the cyclic K-2.6(NMe4)(0.4)I-3[Mo12S12O12(OH)(12)(H2O)(6)] . 30H(2)O resulted in the {Mo2S2O2(H2O)(6)} soluble building unit. The reaction with oxalate clearly depends on the pH value of the reaction mixture more than on the stoichiometry in oxalate. About pH = 1.5, compound 1 was obtained at room temperature and isolated as red cubic crystals. X-ray diffractions determinations showed that NaCs3[Mo2S2O2(C2O4)(2)(H2O)(2)] . 6H(2)O (1) is arranged in the solid state in a three-dimensional way, cations and anions being linked to each other. In this reaction oxalate anions reacted as only chelating groups. In less acidic medium, about pH = 4, the soluble precursor {Mo2S2O2(H2O)(6)} condenses in the presence of oxalate to give the tetranuclear compound [H3N(CH2)(3)NH3](3)[Mo4S4O4(C2O4)(5)] . 4H(2)O (2) in which the oxalate groups act both as chelating and templating agents. Above pH = 5, the nuclearity continues to increase and K-2[Mo8S8O8(OH)(8)(C2O4)] (3) was isolated showing that the oxalate group acts here as only a templating agent. The homologue of 2 with tungsten K-6[W4S4O4(C2O4)(5)] . 2DMF (4) was isolated from reactions carried out in DMF instead of water. Compound 4 has been fully characterized by X-ray diffraction methods.