The Coordination Chemistry of FeCl 3 and FeCl 2 to Bis[2‐(2,3‐dihydroxyphenyl)‐6‐pyridylmethyl](2‐pyridylmethyl)amine: Access to a Diiron( III ) Compound with an Unusual Pentagonal‐Bipyramidal/Square‐Pyramidal Environment

Coordination of FeCl 3 to the title ligand yields a mononuclear iron( III ) complex 1 , which was characterized by spectroscopic techniques and X‐ray diffraction. The ligand is (κ 3 ‐N ) tridentate and the metal, which lies in a pseudo‐octahedral environment, is bound to a phenolate group from the catechol substituent. The dichloroiron( II ) complex 2 was easily obtained by metalation of the ligand with FeCl 2 and characterized by various spectroscopic techniques. In their cyclic voltammograms both 1 and 2 display the same reversible Fe II/ Fe III wave at E 1/2 =10 mV (vs. SCE). Reduction of compound 1 with Zn/Hg yields 2′ , which displays identical properties to 2 . Taken together, these findings indicate that in spite of the different oxidation state of the metal in 2 , no major geometrical/structural change is observed at the metal center with respect to 1 . The reaction of 2 with dioxygen in the absence of organic substrates proceeds extremely rapidly and yields compound 3 , which is a diiron( III ) derivative whose X‐ray crystal structure is also reported. The possibility of a radical‐based mechanism is discussed. Compound 3 displays an unusual geometry: one iron( III ) center is seven‐coordinate, whereas the other lies in a square‐pyramidal environment. The two iron atoms are bridged by the catecholato substituents. To the best of our knowledge, 3 is the first example of a seven‐coordinate iron( III ) derivative with tris(2‐pyridylmethyl)amine ligands.