Iron(iii) and titanium(iv) oxoalkoxide chemistry: synthetic, structural, magnetochemical and spectroscopic studies of [Ti3(μ3-OPri)2(μ-OPri)3(OPri)6][FeCl4] and [Fe5(μ5-O)(μ-OPri)8Cl5]

Abstract

Two synthetic routes were employed for the preparation of iron(III) haloalkoxides in the presence of titanium(IV). Three crystalline products (A, B and C) were isolated and characterised by chemical and physical techniques including X-ray diffractometry, Mössbauer and EPR spectroscopies and variable-temperature magnetic susceptibility measurements. Products B and C are common to both synthetic routes. Product A is a mononuclear iron(II) complex, trans-[FeCl₂(HOPrⁱ)₄], probably produced by the oxidation of propan-2-ol by FeCl₃ in the reaction medium. B is the ionic, mixed-metal [Ti₃(μ₃-OPrⁱ)₂(μ-OPrⁱ)₃(OPrⁱ)₆][FeCl₄], while C is a high-yield oxo-haloalkoxide, [Fe₅(μ₅-O)(μ-OPrⁱ)₈Cl₅]. Magnetic moment measurements in [²H₈]-tetrahydrofuran solution from 323 to 173 K indicate that C contains antiferromagnetically coupled iron(III) centres with intermediate (S = 3/2) spin configuration. C is polymorphic in the solid state, crystallising in the monoclinic or the tetragonal systems as non- and mono-solvate species, respectively. The highly (Lewis) acidic character of iron(III), together with its oxophilic character, probably determined the formation of B and C instead of the targeted mixed-metal [Fe^IIICl_{(2 − x)}{Ti₂(OPrⁱ)_(9 + x)}], x = 0 or 1. The possibility of formation of heteronuclear alkoxides containing both iron(III) and titanium(IV) is re-assessed in the light of the results obtained in this work.