Dioxygenase Models. Crystal Structures of the 2,4-Pentanedionato, Phenanthrenesemiquinone, and Catecholato Complexes of N,N′-Ethylenebis(salicylideneaminato)iron(III)

The X-ray structures of three complexes of [Fe(salen)]+ with bidentate ligands have been determined. Fe(salen)acac crystallizes in the orthorhombic space group P212121 (a = 8.568 (6) Å, b = 13.754 (5) ‘, c = 18.330 (7) Å, α = β = γ = 90.0); Fe(salen)PSQ, a chelated semiquinone complex, crystallizes in the monoclinic space group PI (a = 9.997 (2) Å, b = 10.164 (2) Å, c = 13.368 (2) Å, α = 94.41 (2), β = 105.67 (2), 7 = 105.67 (2)); K[Fe(salen)cat], a chelated catecholate complex, crystallizes in the tetragonal space group P42/mbc (a = 23.187 (9) Å, b = 23.180 (6) Å, c = 26.937 (7) Å, α = β = γ = 90.0). In all three structures, the presence of the bidentate ligand forces the salen ligand to adopt the nonplanar cis-β configuration; all complexes exhibit distorted octahedral geometry, with the oxygen atoms of the bidentate ligand and an oxygen and a nitrogen atom from the salen defining the best equatorial plane. The remaining two ligating atoms are bent away from the bidentate ligand. The structural parameters obtained are in agreement with those found for similar complexes. Fe(salen)PSQ and K[Fe(salen)cat] represent structures modeling proposed species in the reaction mechanism of the catechol dioxygenases.