Methanolysis and Phenolysis Routes to Fe₆, Fe₈, and Fe₁₀ Complexes and Their Magnetic Properties: A New Type of Fe₈ Ferric Wheel

Alcoholysis of preformed tetranuclear and hexanuclear iron(III) clusters has been employed for the synthesis of four higher-nuclearity clusters. Treatment of [Fe4O2(O2CMe)7(bpy)2](ClO4) with phenol affords the hexanuclear cluster [Fe6O3(O2CMe)9(OPh)2(bpy)2](ClO4) (1). Reaction of [Fe6O2(OH)2(O2CR)10(hep)2] (R = But or Ph) with PhOH affords the new “ferric wheel” complexes [Fe8(OH)4(OPh)8(O2CR)12] [R = But (2) or Ph (3)]. Complexes 2 and 3 exhibit the same structure, which is an unprecedented type for Fe(III). In contrast, treatment of [Fe6O2(OH)2(O2CBut)10(hep)2] with MeOH leads to the formation of [Fe10(OMe)20(O2CBut)10] (4), which exhibits the more common type of ferric wheel seen in analogous complexes with other carboxylate groups. Solid-state variable-temperature magnetic susceptibility measurements indicate spin-singlet ground states for complexes 2 and 4. The recently developed semiempirical method ZILSH was used to estimate the pairwise exchange parameters (JAB) and the average spin couplings ŜA·ŜB between the Fe(III) centers, providing a clear depiction of the overall magnetic behavior of the molecules. All exchange interactions between adjacent Fe(III) atoms are antiferromagnetic.