Synthesis, structure and magnetic properties of a novel octairon(III) citrate complex

Abstract

A novel octairon(III) citrate complex, (Him)₉[Fe₈(μ₃-O)₂(μ₂-OH)₂(cit)₆(CH₃CO₂)₂(im)₂](ClO₄)·13H₂O has been obtained from DMF solution, by reacting ferric perchlorate, citric acid and imidazole in a 1 ∶ 1 ∶ 5 ratio. This compound crystallizes in the monoclinic space group P2₁/n with a = 15.271(1), b = 19.940(1), c = 44.197(1) Å, β = 91.965(1)°, V = 13450.2(9) ų and Z = 4. The complex consists of two equivalent tetranuclear units, which are not symmetrically related and are linked together by two of the six tetraionized citrate ligands. The iron(III) ions are antiferromagnetically coupled. Assumption of a four S = 5/2 spin system based on H = −2Σ_i < j J_ijS_iS_j leads to satisfactory agreement with the experimental magnetic behavior, with g = 2.0 and J₁₃ = J₂₃ = −32.1 cm⁻¹, J₁₂ = J₁₄ = −14.5 cm⁻¹, J₂₄ = J₃₄ = −11.1 cm⁻¹.