Preparation and Characterization of a Microcrystalline Non-Heme FeIII(OOH) Complex Powder: EPR Reinvestigation of FeIII(OOH) Complexes-Improvement of the Perturbation Equations for the g Tensor of Low-Spin FeIII

The first example of a microcrystalline powder of a synthetic low‐spin (LS) mononuclear FeIII(OOH) intermediate has been obtained by the precipitation of the [FeIII(L52)(OOH)]2+ complex at low temperature. The high purity of this thermally unstable powder is revealed by magnetic susceptibility measurements. EPR studies on this complex, in the solid state and also in frozen solution, are reported and reveal the coexistence of two related FeIII(OOH) species in both states. We also present a theoretical analysis of the g tensor for LS FeIII complexes, based on new perturbation equations. These simple equations provide distortion‐energy parameters that are in good agreement with those obtained by a full‐diagonalization calculation. Deep purple: A purple microcrystalline powder of a low‐spin FeIII(OOH) complex was obtained at low temperature and characterized (see graphic). The EPR properties were also analyzed and perturbation equations are presented. This powder is a promising step towards obtaining single crystals and an X‐ray structure for compounds of this type.