Regioselective S/O substitutions in heteropolyoxothioanions: 31P NMR study and X-ray crystal structure of the half-substituted anion [(HPO4)4Mo6S3O9(OH)3]5−

The self-condensation of [Mo2O2S2]2+ in aqueous solution in the presence of phosphate ions as assembling groups leads at pH 5.5 and 50°C to the hexanuclear [(HPO4)4Mo6S6O6(OH)3]5− anion. When the synthesis solution is heated for 17 h at 70°C, three sulfur atoms are successively removed to give the half-substituted [(HPO4)4Mo6S3O9(OH)3]5− anion. 31P NMR experiments, together with the X-ray crystal structure of the final product, show that the S/O substitution is regioselective, only the sulfur atoms located on the opposite side to the phosphate groups being replaced.