Magneto-Structural Analysis of Iron(III) Keggin Polyoxometalates

A computational study and magnetic susceptibility measurements of three homonuclear Fe(III) Keggin structures are herein presented: the [FeO₄@Fe₁₂F₂₄(μ–OCH₃)₁₂]^5– anion (1), the [Bi₆{FeO₄@Fe₁₂O₁₂(OH)₁₂}(μ-O₂CCCl₃)₁₂]⁺ cation (2) and its polymorph [Bi₆{FeO₄@Fe₁₂O₁₂(OH)₁₀(H₂O)₂}(μ-O₂CCF₃)₁₀]³⁺ (3). These results are contrasted with the exchange interactions present in the previously characterized [Fe₆(OH)₃Ge₂W₁₈O₆₈(OH)₆]^11– and [H₁₂As₄Fe₈W₃₀O₁₂₀(H₂O)₂]^4– anions. The computational analysis shows that the most significant antiferromagnetic spin coupling takes place at the junction between each of the {Fe₃O₆(OH)₃}/{Fe₃F₆(OCH₃)₃} framework motifs, a possibility that had been previously discarded in the literature on the basis of the Fe–Fe distances. For all the examined iron(III) Keggin structures, it is found that the magnitude of the magnetic couplings within each structural subunit follows the same trend.