The Molecular and Electronic Structure of Symmetrically and Asymmetrically Coordinated, Non-Heme Iron Complexes Containing [FeIII(μ-N)FeIV]4+ (S=3/2) and [FeIV(μ-N)FeIV]5+ (S=0) Cores

Either an St=1/2 or an St=3/2 ground state is found for complexes containing the [Fe(μ-N)Fe]4+ core; the former contains two Fe3.5 ions with delocalized valencies (class III) and the latter contains formally an FeIV (S=1) and an FeIII (S=5/2) ion (class II) (see picture). In comparison, the electronic structures of the complexes containing the [FeIII(μ-O)FeIII]4+ and [FeIV(μ-N)FeIV]5+ cores with diamagnetic ground states are also investigated experimentally and theoretically. In all cases, the Fe–Nb bonds display a significant degree of covalency.