Ionic association of Ce(IV)-decatungstate in the context of heteroatom reduction

The kinetics of single electron heteroatom reduction in Ce(IV)-decatungstate anion is demonstrated to be strongly dependent on the nature of the supporting electrolyte cation. DC polarography reveals an increase of both reduction rate at a positively charged mercury electrode and a limiting diffusion current in the Li+…Cs+ sequence. Both effects look anomalous in the framework of traditional concepts of electrode kinetics. To clarify the nature of these observations, ionic association of Ce(IV)-decatungstate with various alkali metal cations was addressed experimentally by means of the potentiometric technique. Finally, our self-consistent interpretation of various cation nature effects rests on a difference in the number of bound cations and their location around the polyanion. The ionic association is modeled by using the results of DFT calculations of the CeW10 anion, non-local electrostatics and an extended version of the Bjerrum model.