Computational electrochemistry. Ab-initio calculation of solvent effect in the multiple electroreduction of polypyridinic compounds

The electrochemical multiple reduction of a series of polypyridinic compounds, yielding mono, di and trianionic species is theoretically studied. Calculated electron affinity values were used to obtain molecular-structure/reactivity relationships, the latter reflected by the experimental half-wave electroreduction potentials. Gas-phase electron affinity data vs. half-wave potentials produced satisfactory linear correlations, but separated for each successive electron transfer step (i.e. a linear relationship for the first electron transfer, yield of the monoanion, neatly separated from the one concerning the second electron transfer, yield of the dianionic species). The theoretical approach was pushed further, also including solvent effects. This was done by means of two methods based on the continuum solvation model: the Onsager cavity (SCRF) and the more sophisticated SM5.42R solvation models. In particular, the latter is able to group in a single correlation the potentials referring to the first, second and third electron transfer.