Synthesis and Characterization of (μ‐Hydroxo)bis(μ‐acetato)diiron(II) and (μ‐Oxo)bis(μ‐acetato)diiron(III) 1,4,7‐Trimethyl‐1,4,7‐triazacyclononane Complexes as Models for Binuclear Iron Centers in Biology; Properties of the Mixed Valence Diiron(II,III) Species.