Metal complex in solution: A theoretical investigation

Abstract

The chemical properties of the metal complex in solution are different from the ones in gas phase in terms of energy and a geometry. Many research fields such as biochemistry, catalyst and battery developments have interested in the metal complexes in solution. The quantum chemical study which is useful to understand these systems at the molecular level is strongly required. This thesis aims to suggest the protocols to evaluate the energy-related properties of the metal complexes such as reduction potential and hydration enthalpy. The redox potentials are the main concern of the battery field. Density functional theory (DFT) 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 (PCM) and the cavity creation energy is included for the accurate description of the spin state. 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, which has the same meaning to the reduction potentials in chemistry, our protocol performs well yielding the mean absolute error (MAE) of 0.112 V for the whole test set. The close correlation between the calculated and the experimental OCV are obtained. ...