Proton and Electron Transfer Mechanisms in the Formation of Neutral and Charged Quinhydrone-like Complexes: a Multi-layered Computational Study

The redox and proton transfer processes involving the several dimers arising from quinones are studied by quantum mechanical methods using second order perturbation theory (MP2) and a medium size basis set optimized for reproducing dispersion interactions. Furthermore, bulk solvent effects are taken into account by the polarizable continuum solvent (PCM) approach possibly integrated by two explicit water molecules for an improved description of the cybotactic region. Our results indicate that several neutral and anionic dimers are kept together mainly by strong hydrogen bonds, but dispersion forces introduce additional non-negligible effects. The computed energy paths indicate that a proton transfer process should accompany the two-electron reduction of quinhydrone and that two dimers in the reduced form can be simultaneously present in solution, in agreement with available experimental data.