Joung-Won Park

A protocol to evaluate one electron redox potential for iron complexes

Density functional theory calculation has been performed to calculate the redox potential and the correct ground spin state of iron complexes in acetonitrile. Widely used B3LYP functional is applied with the spin state corrected basis sets. The newly developed protocol for the set of 21 iron complexes is to optimize the structure at the level of the B3LYP/6‐31G* and to calculate the single point electronic energy with the same functional and the modified basis sets s6‐31G* for the iron atom and 6‐31+G* for other ligand atoms. The solvation energy is considered through the polarized continuum model and the cavity creation energy is included for the accurate spin state description. Modifying the cavity size by employing the different scaling factor according to the mean absolute value of the natural population analysis charge (MA‐NPA) is introduced. The molecule with the large MA‐NPA requires the cavity size smaller than the less polar one. This protocol gives only 1 wrong ground spin state among the 18 iron complexes for which experimental data are known. For the open circuit voltage (OCV) calculation, our protocol performs well yielding the mean absolute error of 0.112 V for the test set. The close correlation between the calculated and the experimental OCV are obtained.

Prediction of the reduction potential of tris(2,2′-bipyridinyl)iron(III/II) derivatives

The reduction potentials of a tris(2,2′‐bipyridinyl)iron (III/II) and iron(III/II) couples complexed with 2,2′‐bipyridinyl derivatives in acetonitrile are predicted using density functional theory. The calculation protocol proposed by Kim et al. (Kim, J. Park, Y. S. Lee, J. Comput. Chem. 2013, 34, 2233) showing reliable performance for the reduction potential is used. The four kinds of the functional groups, a methoxy group, a methyl group, a chlorine atom, and a cyanide group, are substituted at the ligands to examine the electronic effect on the reduction potential. Electron donating/withdrawing effect is analyzed by comparing the reduction potential having different substituents at the same position. The influence of the geometrical strain on the reduction potential is investigated. The good correlation between the experimental results and the calculated results is obtained. Not only the general trend, but also the detailed phenomena are correctly reproduced. The maximum deviation from the experimental value is 0.083 V for the methyl substitution at the position 4. The mean absolute error for the seven couples is 0.047 V. The difference of the reduction potential between the chlorine atom substituted at the positions 4 and 5, 0.1 V, is well described. The difference between the CN and the Cl substitution of 0.318 and 0.228 V for the position 4 and 5 is correctly obtained as 0.325 and 0.213 V, respectively. The simple linear relation between the lowest unoccupied molecular orbital (LUMO) energy of the Fe(III) complexes in solution and the calculated reduction potentials is obtained with the R2 of 0.977.