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 gTensor 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 gtensor for LS FeIIIcomplexes, 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.