O,N-Coordinated o-iminobenzoquinone and o-iminobenzosemiquinonato(1−) ligands in complexes of Ni(ii), Co(iii) and Fe(iii)

Abstract

Octahedral complexes of the type [M(tren)(L^IBQ)]ⁿ⁺ or [M(tren)(L^ISQ)]ⁿ⁺ (tren = tris(2-aminoethyl)amine; L^IBQ = o-iminobenzoquinone, (L^ISQ)¹⁻ = o-iminobenzosemiquinonate(1−) π radical, M = Ni, Co, Fe) have been prepared by the reaction of equimolar amounts of 2-anilino-4,6-di-tert-butylphenol, tris(2-aminoethyl)amine, M(CH₃CO₂)₂·4H₂O (M = Ni, Co) or FeCl₂·4H₂O in CH₃OH containing 2 equivalents of NEt₃ and air. The following complexes were isolated and characterized by X-ray crystallography: red–black [Ni^II(tren)(L^IBQ)](PF₆)₂ (1), green [Ni^II(tren)(L^ISQ)](ClO₄) (2), brown [Co^III(tren)(L^ISQ)](ClO₄)₂·0.5CH₃OH·0.5H₂O (3), [Fe^III(tren)(L^ISQ)](ClO₄)₂·0.5CH₃OH·0.5H₂O (4). Their electrochemistry has been studied and the oxidized and reduced species have been characterized by UV-vis, EPR and Mössbauer spectroscopy. Temperature-dependent magnetic susceptibility measurements (2–290 K) reveal that 1 possesses an S = 1, 2 an S = 3/2, 3 an S = ½, and 4 an S = 0 ground state. The metrical details of O,N-coordinated (L^AP-H)²⁻, (L^ISQ)¹⁻˙, and (L^IBQ)⁰ ligands are clearly established. (L^AP-H)²⁻ represents the aromatic dianion o-iminophenolate.