Modulating Iron Spin States with Radical Ligands: A Density Functional Theoretical Study

Abstract

AbstractThe ground state electronic structures of [FeIIIX(LISQ)2]0 where X is a halide (F−, Cl−, Br−, I−) or pseudo‐halide (N3−, NCS−) and (LISQ)1− is the o‐iminobenzosemiquinonato π‐radical ligand, have been calculated using DFT at the B3LYP* level of theory. The modified functional with 15% Hartree‐Fock exchange is required to successfully reproduce the spin ground state of the complex as either S=3/2 for X=F−, Cl− and NCS−, or S=1/2 for X=Br−, I− and N3−. The difference in ground state stems from an SFe=5/2→SFe=3/2 spin transition at the iron ion, prompted by the donor properties of the apical ligand. The computational methodology was validated through accurate calculation of the Mössbauer parameters. The redox chemistry of the o‐aminophenolate ligand was examined for the putative five‐membered electron transfer series for [FeIIIF(LISQ)2]z and [FeIIII(LISQ)2]z (z=2+1+, 0, 1−, 2−). The redox chemistry is entirely ligand‐centered with retention of the ferric ion, where only the strong ligand field provided by a fully reduced o‐anilinophenolate(2−) ligand in conjunction with a soft apical donor will support an intermediate‐spin Fe(III) central ion.