During the past decade isoindoline-based ligands became the subject of growing interest due to their modular set-up.

The spectroscopic characterisation of the (μ-1,2-peroxido)diiron(III) species formed transiently upon reaction of [Fe(II)(NN)₃]²⁺ complexes with H₂O₂ by UV/vis absorption and resonance Raman spectroscopy is reported. The intermediacy of such species in the disproportionation of H₂O₂ is demonstrated.