Octanuclear iron(III) complexes supported by Kemp’s tricarboxylate ligands

Abstract

Reactions of FeCl 2·4H 2O and diimino ligand (L) with H 3kta ( cis, cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid) in the presence of [ n Bu 4N][OH] afforded a series of octanuclear iron(III) complexes formulated as [Fe 8O 5(kta) 2(Hkta) 4(L) 2] (L = bpy ( 1), 5,5′-Me 2bpy ( 2), 4,4′-Me 2bpy ( 3), phen ( 4), 4-Mephen ( 5), 4,7-Me 2phen ( 6), and 3,4,7,8-Me 4phen ( 7)). The structure of 4 was determined by X-ray crystallography to consist of a planar {Fe 8(μ 4-O)(μ 3-O) 4} 14+ core supported by two kta 3− tricarboxylates, where the inner four Fe III ions form a {Fe 4O 5} square plane, of which apex μ-oxo atoms are further connected to the outer four Fe III ions. The peripheral part of the Fe 8 core is bridged by four Hkta 2− ligands and chelated by two phen ligands. 57Fe Mössbauer spectra of 2 at 290 K and 77 K indicated the presence of high-spin octahedral Fe(III) ions, and the temperature dependent dc magnetic susceptibility data for 1, 2, and 4 showed strong antiferromagnetic exchange in the {Fe 8O 5} moiety.