Model for the outer-sphere association of heteropoly anions and the electroreduction kinetics of ensembles of ionic associates

The most probable positions of cations, successively added during a multist age association in electrolytes, are determined from positions of hydrated cations in crystals of sodium salts of heteropoly anions (HPA) with the And erson structure. For the structurally close HPA [Co-2(III)Mo10O38H4](6-), e quilibriums in solutions are analyzed at widely diverse concentrations c of the supporting electrolyte, using the Co-59 NMR technique. Stability const ants, calculated from these data with the Fuoss equation, lead to the model parameters (separations between centers of HPA and sodium cation) that are close to relevant separations in sodium salts of HPA, i.e., the model sati sfactorily describes bulk properties of associates. The current density j o f the HPA central ion reduction in solutions of sodium salts of [Co(III)Mo6 O24H6](3-) and [Mn(IV)W6O24](8-) is studied at a positively charged mercury electrode as a function of the concentration of the I,l-valence supporting electrolyte (CH3COONa + CH3COOH). The considerable differences of the deri vative of logj over logc in the sign and absolute value for HPA with charge s of -3 and -8 may be caused, along with some other factors, by different e ffective electrostatic interactions that are due to a nonuniform charge dis tribution in particles of the reagents. Models of the reaction layer are co nsidered, along with relevant approaches to a calculation of basic kinetic parameters.