Electronic structures and ligand effect on redox potential of iron and cobalt complexes: a computational insight

Density functional theory is applied to account the ligand effect on modification in the redox potential of coordination of three NN bidentate ligands (bpy/phen) to the metal ion (Fe2+/3+/Co2+/3+). Also, the role of the ligand framework for the stabilization of [M(bpy/phen)(3)](2+/3+) species is discussed in detail. In this work, we have found that the M2+ ions are more stabilized with the bpy ligands while the M3+ ions are more stable with the phen ligands. The electronic structure and geometrical study disclosed the electronic configurations of the metal ions in both the possible spin states of a species. Furthermore, the HOMO-LUMO analysis demonstrates that the M3+ ion coordinated species have more energy gap as compared to the M2+ ion coordinated species. Among all the species, HOMO-LUMO energy gap has been found highest (4.62 eV) in the [Fe(bpy)(3)](3+) whereas lowest (3.28 eV) in the [Co(phen)(3)](2+) species. Additionally, we have also found that the bpy coordinated species have relatively higher redox potential value as compared to phen ligated species. Here we have noticed a close relationship between the redox potential and the optimized structural parameters of the studied species. Also, all the computed structural parameters of the studied species are in good agreement with the experimental data.

Automated summary

Density functional theory is used to study the ligand effect on the redox potential of metal ion coordination with three NN bidentate ligands. The stability of the species [M(bpy/phen)(3)](2+/3+) is discussed, with M2+ ions found to be more stabilized with bpy ligands and M3+ ions more stable with phen ligands. The electronic structure and geometrical study reveal the electronic configurations of the metal ions in different spin states, and the HOMO-LUMO analysis shows that M3+ ion coordinated species have a larger energy gap compared to M2+ ion coordinated species. Additionally, the redox potential and optimized structural parameters of the species show a close relationship, and the computed structural parameters are in good agreement with experimental data.