Abstract: The redox properties of four series of more than one handred acids and salts of rare earth heteropoly compounds, such as LnHSiMo₁₂O₄₀, In (PMo₁₁ O₃₉)₂^11-, Ln (PW₁₁ O₃₉)₂^11-, Ln (AsW₁₁ O₃₉)₂^11-, Ln(GeW₁₁O₃₉)₂^13-, Ln(BW₁₁O₃₉)₂^15-, Ln(GaW₁₁O₃₉)₂^16-, Ln(P₂Mo₁₇O₆₁)₂^17-, Ln (As₂W₁₇O₆₁)₂^17-, Ln₂P₂Mo₁₈O₆₂and Ln₂HP₂Mo₁₇VO₆₂(Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, etc. ) which have Keggin, Daw-son and their derivative structures, were studied by means of potentiometric titration, polarography and cy-clovoltammetry. The mechanisms of the redox reactions were supposed-and the orders of redox ability of the heteropoly compounds were concluded. The periodic changes in reduction potentials of Ln(PMo₁₁O₃₉)₂^11-and Ln(P₂Mo₁₇O₆₁)₂^17- with Ln atomic numbers, and the correlation between E_1/2 of Ln(XMo₁₁O₃₉)₂^n-(X =P, Ge, Si) and nq²(n is the main quantum number of the central atoms and q is their charges) were found.

Key words: Redox, Rare earth, Heteropolyanions