¹H NMR study on quadridentate O₂N₂ schiff base complexes of iron(III): Bis(imidazole) complexes of the type [Fe^III(schiff base)(imidazole)₂]⁺

Abstract

High resolution (500 MHz) ¹H NMR study has been carried out complexes of the type [Fe^III(salen)(HIm)₂]X and [Fe^III(salophen)(HIm)₂]X, where salen = N,N'ethylenebis-( salicylideneaminato)anion, salophen = N, N'-<em>o</em>-phenylenebis-(salicylideneaminato)anion, HIm = imidazole, and X = Cl^-, ClO^- or BPh. A large isotropic protein shift (IPS) of about 80 ppm is observed for the salicylaldimine proton resonances. Temperature variation of IPS indicates that while the tetraphenylborate complexes are pure high-spin, the perchlorate complexes exhibit spin-equlibrium in solution. The paramagnetic shifts in these systems are mainly of contact type. The phenolate proton resonances in these complexes compare well with the proton resonances of tyrosine, coordinated to iron(III) in pink uteroferrin.