Solvation energy of metallocenes pilot ions: Beyond the Born approximation

Determination of the single-ion transfer energies demands for some extrathermodynamic assumption on the solvation energy of the pilot ion. Here, the factors affecting solvation energies of the metallocenes pilot ions are explored. The dielectric response energies for these ions in several organic solvents obey the predictions of the local continuum electrostatics. The dielectric response of water reveals to be anomalously large due to the effect of dipoles' correlation caused by hydrogen bonds. The effect of this nonlocal response has been estimated from the data on redox potentials in aqueous-organic solvents as equal to similar to 0.09-0.10 eV. The second reason for deviation of solvation energy from the simple picture of continuum electrostatics lies in the preferable orientation of water molecules with H atoms towards the neutral solute creating a positive intraphase potential. The determination of this potential based on experimental data has been done. Its value for ferrocene in water is estimated as similar to+0.1 V. This figure is in accordance with the value which one could expect from the MD simulations in the framework of the polarizable force field model. The list of the single-ion transfer energies based on the improved ferrocene-ferricenium standard is given. (c) 2008 Elsevier Ltd. All rights reserved.