Valence‐Delocalized and Valence‐Trapped FeIIFeIII Complexes: Drastic Influence of the Ligands

The two macrocyclic ligands H2L1 and H2L2 are not very different, but their FeIIFeIII complexes are remarkably so. [L1Fe2(μ-OAc)2](ClO4) is valence-delocalized on the Mössbauer time scale over the range 1.8–364 K, whereas [L2Fe2(μ-OAc)(OAc)(H2O)](ClO4)·2H2O is valence-trapped even at room temperature. The difference in properties of these complexes is also reflected in their electronic spectra, in their electrochemical and magnetic behavior, and in their structures.