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 characterised [Fe6(OH)3Ge2W18O68(OH)6]11- and [H12As4Fe8W30O120(H2O)2]4- anions. The computational analysis shows that the most significant anti-ferromagnetic 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 sub-unit follows the same trend.