Molecular Magnets Containing Wheel Motifs

An overview of some compounds with structures that can be regarded as derived from an {Fe7(μ3-OR)6(μ-OR)6} motif is presented. Many of these compounds act as single-molecule magnets. In addition, the results of a comprehensive study on the single-crystal structures, magnetism, and spin structures for five new iron compounds with structural components related to this are given. This serves to illustrate the methodology that can be used to unravel the complicated magnetic behavior of such systems. Thus, the alkoxo- and phenoxo-bridged multinuclear iron complexes, [FeII7(Hbmsae)6(OMe)6]Cl2·6H2O (6), [FeIIFeIII6(bmsae)6(μ3-OMe)6]Cl2·23H2O (7), [NaFeIII6(bmsae)6(μ3-OMe)6]Cl·30H2O (8), [FeIII3(bmsae)3Cl2(MeOH)(OMe)]·MeOH·Et2O (9), and [FeIII2(Hbmsae)2(OMe)2Cl2][Fe3(bmsae)3(OMe)Cl2(MeOH)]2·1.5MeOH (10), were prepared by the reactions of iron sources with Schiff base ligands (H2bmsae = 5-bromo-3-methoxysalicylideneaminoethanol). Heptanuclear complexes of 6 and 7 have wheel structures in which six iron(II) and six iron(III) ions locate on the rim with the central iron(II) ions, respectively, while 8 also has a wheel structure with a diamagnetic sodium ion in the center. 9 is a trinuclear ferric complex with an incomplete cubic structure. In 10, di- and trinuclear complexes exist in the crystal, where the trinuclear complex has an incomplete cubic structure similar to that of 9. Magnetic susceptibility measurements revealed that 6 has an S = 10 spin ground state, while the antiferromagnetic interactions dominate in 7−10.