Acidobasic behavior of the diphosphato dodecameric ring [(HPO4)2Mo12S12O12(OH)12(H2O)2]4−. Synthesis and characterization of the conjugated form [(HPO4)2Mo12S12O12(OH)14(H2O)2]6−

A novel diphosphato anionic ring, [(HPO4)2Mo12S12O12(OH)14(H2O)2]6− noted B-[P2Mo12]6− was characterized by single crystal-X ray diffraction. B-[P2Mo12]6− formally derives from the acidic parent [(HPO4)2Mo12S12O12(OH)12(H2O)2]4− (noted A-[P2Mo12]4−) by addition of two hydroxo groups in the cavity. The phosphate groups are hydrogen bonded to the inner hydroxo bridges. The H-bonding network within the cavity contributes to the elliptical conformations which differ in the acid and basic conjugated forms. The basic B-[P2Mo12]6− ring was characterized in solution by 31P NMR. The three-line spectrum indicates that a chemical equilibrium takes place for giving uncoordinated phosphate and a monophosphate ring, noted [PMo10]n−. IR characterizations are also given.