Dawson结构钼砷杂多酸(盐)的合成与性质研究

The Syntheses and Characterization of Dawson Structure Molybdoarsenic Acid and Salts

采用酸化-回流-乙醚萃取法合成了二十种Dawson结构钼砷杂多酸及其盐,元素分析确定了它们的组成,其通式为M_xAs_2Mo_(18)O_(62)·H_2O,酸碱及电导滴定确定了碱度,系统地研究了它们的红外光谱、紫外光谱、极谱、循环伏安、热重-差热分析等性质,给出了杂多阴离子As_2Mo_(18)O_(62)^(6-)在水溶液中的氧化还原机理,讨论并指认了紫外吸收为e→e~*和e→b_2的荷移跃迂谱带。考察了抗衡离子M^(n+)对主要红外振动光谱、热分解温度及其分解产物的影响。

Twenty molybdoarsenic acid and salts M_aAs_2Mo_(18)O_(62)·nH_2O(M=NH_4^+, Li^+, Na^+, K^+, Cs^+, Ca^(2+), Mg^(2+), Sr^(2+), Co^(2+), Ni^(2+), Cu^(2+), Zn^(2+), Cd^(2+), Al^(3+), La^(3+), Ce^(3+), Pr^(3+), Nd^(3+), Sm^(3+), Gd^(3+)) with Dawson structure, were synthesized and characterized by IR and UV spectroscopy, polarography, cyclic voltammetry and thermogravimetry. Hexa-basicity were established by means of conductive and acid-base titrations. The reduction mechanism of the heteropolyanion As_2Mo_(18)O_(62)^(6+) in aqueous solution was suggested. The UV bands of the compounds were assigned as e→e~* and e→b_2 transition according to the energy levels of molecular orbitals of MOL_5 type compounds with C_(40) symmetry. The effects of the countercations M^(n+) on the IR spectra, thermal decomposition temperature and decomposition products were also discussed.