Application of Lever’s <i>E</i><sub>L</sub> Parameter Scale toward Fe(II)/Fe(III) versus Pc(2-)/Pc(1-) Oxidation Process Crossover Point in Axially Coordinated Iron(II) Phthalocyanine Complexes
Victor N. Nemykin, Dustin E. Nevonen, W. Ryan Osterloh, Laura S. Ferch, Laurel A. Harrison, Benjamin S. Marx, Karl M. Kadish
Abstract
The electronic structures and, particularly, the nature of the HOMO in a series of PcFeL2, PcFeL′L″, and [PcFeX2]2– complexes (Pc = phthalocyaninato(2-) ligand; L = NH3, n-BuNH2, imidazole (Im), pyridine (Py), PMe3, PBu3, t-BuNC, P(OBu)3, and DMSO; L′ = CO; L″ = NH3 or n-BuNH2; X = NCO–, NCS–, CN–, imidazolate (Im–), or 1,2,4-triazolate(Tz–)) were probed by electrochemical, spectroelectrochemical, and chemical oxidation as well as theoretical (density functional theory, DFT) studies. In general, energies of the metal-centered occupied orbitals in various six-coordinate iron phthalocyanine complexes correlate well with Lever Electrochemical Parameter EL and intercross the phthalocyanine-centered a1u orbital in several compounds with moderate-to-strong π-accepting axial ligands. In these cases, an oxidation of the phthalocyanine macrocycle (Pc(2-)/Pc(1-)) rather than the central metal ion (Fe(II)/Fe(III)) was theoretically predicted and experimentally confirmed.