STUDIES ON REDOX PROPERTIES OF HETEROPOLY ACIDS (SALTS) AND THEIR DERIVATIVES WITH KEGGIN AND DAWSON STRUCTURES

We have systematically studied redox properties of two series of several dozen heteropoly acids （salts） and their derivatives with vanadium and rare-earth elements with Keggin and Dawson structures, e. g. LnHSiMo12, SiMo12-nVn, M1.5PMo12, PMo12-nVn, PW(12-nVn, Ln(PMo11)2, Sm(XMo11)2 and P2Mo18-nVn, etc., and obtained their sequence of oxidation. It was found that there is a linear relationship between the reduction potentials of heteropoly anions and the derivatives of heteropoly anions with rare-earth elements with Keggin structure and nq2 （n and q are the principal quantum number and charge of the central ion respectively）. On the basis of the electrostatic model the regularity of oxidation and reduction was rationalized.