Structure and properties of H₈(PW₁₁TiO₃₉)₂O heteropoly acid

Heteropoly acid (HPA) H-8(PW11TiO39)(2)O center dot xH(2)O (I) is synthesized by three different ways and studied by chemical analysis, potentiometric titration, mass-spectrometry, IR, P-31, W-183, and O-17 NMR spectroscopy, thermogravimetry, and transmission electron microscopy. Anion I consists of two subparticles of the Keggin structure bridged by Ti-O-Ti. The dimeric anion exists in HPA aqueous solutions at [I] > 0.02 M. At pH > 0.6 it splits to a [PW11TiO40](5-) monomer stable up to pH similar to 6. When heated (150-400)A degrees C, I splits into H3PW12O40 and, apparently, H3PW10Ti2O38 without phase separation. Thermolysis products are soluble and when dissolved in water turn again into I. Complete decomposition of I to oxides occurs at similar to 450A degrees C.