Antiferromagnetic coupling interaction

The visible spectra of oxyHr and metIh N3 are dominated by ligand-to-metal charge transfer bands from the hydroperoxide or azide anions, but otherwise they are similar to those of the synthetic complexes (Rgure 2) (38). The d-d transitions observed at 700 and KXX) nm are more intense than usually observed for high-spin iron(llI) complexes, probably due to the strong antiferromagnetic coupling interaction (38,40). 

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