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 [FeO 4 @Fe 12 F 24 (μ–OCH 3 ) 12 ] 5– anion ( 1 ), the [Bi 6 {FeO 4 @Fe 12 O 12 (OH) 12 }(μ-O 2 CCCl 3 ) 12 ] + cation ( 2 ) and its polymorph [Bi 6 {FeO 4 @Fe 12 O 12 (OH) 10 (H 2 O) 2 }(μ-O 2 CCF 3 ) 10 ] 3+ ( 3 ). These results are contrasted with the exchange interactions present in the previously characterized [Fe 6 (OH) 3 Ge 2 W 18 O 68 (OH) 6 ] 11– and [H 12 As 4 Fe 8 W 30 O 120 (H 2 O) 2 ] 4– anions. The computational analysis shows that the most significant antiferromagnetic spin coupling takes place at the junction between each of the {Fe 3 O 6 (OH) 3 }/{Fe 3 F 6 (OCH 3 ) 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.