【摘要】 合成了一个系列具有Keggin结构的磷钼钨杂多酸H₃PMo_12-nW_nO₄₀（n=0,3,6,9,11,12）.用电子自旋共振（ESR）方法研究了这些杂多酸的还原性.结果表明,在还原态的杂多酸中,除了因失去桥氧产生的Mo⁵⁺信号A(其g_?^A=1.952,g_?^A=1.852)外,钨取代后产生另一Mo⁵⁺信号B,其g_?^B=1.923,g_?^B=1.877.该信号被认为是由于杂多酸中钼的端氧还原所致.由此提出钨的取代影响了杂多酸的氧化还原性,即桥氧的稳定性相对增强,端氧的稳定性相对减弱.更多还原

【Abstract】 A series of heteropoly acids with Keggin unit, H3PMO12-nWnO40(n = 0, 3, 6, 9, 11, 12), were prepared. Reduction of these acids in hydrogen was investigated by ESR, and two signals were observed. One ESR signal was assigned to the loss of bridging oxygen in Keggin unit with g⊥A = 1.952, g∥A =1.852. Another ESR signal with g⊥B=1.928, g∥B= 1.877, which only could be observed for the samples partially substituted by W, was probably resulted from the reduction of the terminal oxygen. It is suggested that the redox mechanism could be affected by the substitution of Ma by W in Keggin unit, and the bridging oxygen is relatively strengthened and terminal oxygen is weakened as the result of the substitution.更多还原