Abstract: The thermal decomposition behavior of metal-oxygen clusters with Dawson structure, Y_mH_nP₂M₁₈O₆₂•qH₂O, was systematically investigated using the X-ray power thermodiffractometry and FTIR at different temperatures, TG-DTA. The experimental results indicated that Dawson-type metal-oxygen clusters with anion,[P₂Mo₁₈O₆₂]^6-,and different counter cations,NH⁴⁺,Cu²⁺,K⁺,underwent an irreversible thermal rearrangement around 210 ℃,240 ℃,250 ℃, respectively to give the corresponding Keggin-type metal-oxygen clusters containing [PMo₁₂O₄₀]^3-as one of the products. For the metal-oxygen clusters containing tungsten, the pyrolysis procedure of potassium salt with [P₂W₁₈O₆₂]^6-anion is similar to that of metal-oxygen clusters with [P₂Mo₁₈O₆₂]^6-anion, whenas the NH⁴⁺, Cu²⁺salts of [P₂W₁₈O₆₂]^6-seem to decompose directly into WO₃ at 400 ℃, 450 ℃,respectively.These results testify that the thermal solid-state rearrangements of Dawson-type anions correlated with the thermal stability of the corresponding Keggin-type compounds. Furthermore, some proposals about the criterion and the adjudication of thermal decomposition temperature for metal-oxygen clusters with different thermal decomposition behavior are also given.

Key words: metal-oxygen clusters, thermal decomposition, Dawson structure, metal-oxygen clusters, thermal decomposition