Asymmetrically Dibridged Diiron(III) Complexes with Aminebis(phenoxide)-Based Ligands for a Magnetostructural Study

The ligands [N,N-bis(3,5-di-tert-butyl-2-hydroxybenzyl)aminoacetic acid] (H3L1), [N, N-bis(2-hydroxy-3,5-dimethylbenzyl)aminoacetic acid] (H3L2), [N, N-bis(2-hydroxy-3,5-dimethylbenzyl)-N-(2-pyridylmethyl)amine] (H2L3) and [methylamino-N,N-bis(6-tert-butyl-4-methyl-2-methylenephenol)] (H2L4) were used to investigate their coordination properties toward Fe-III. The ligand H3L1 yields mononuclear iron(III) complexes, complexes 1-3, whereas the asymmetrically di-bridged diiron(III) complexes 4-8 were isolated with the ligands H3L2, H2L3 and H2L4. The complexes 1-8 have been structurally, magnetochemically (2-290 K) and spectroscopically investigated. Presumably as an effect of the sterically demanding tert-butyl groups, only mononuclear Fe-III complexes 1-3 were isolated with H3L1, whereas H3L2 bearing the less bulky methyl groups results in the diferric(III) complex 4. Complexes 4-8, containing two d(5) high-spin ferric centres, possess a diamagnetic S-t = 0 ground state that is attained through intramolecular antiferromagnetic coupling between the two paramagnetic centres. We have focused our investigation largely on the magnetostructural correlation of the asymmetrically dibridged (hydroxo, methoxo, acetate) diferric(III) complexes 4-8 and compared these to similar compounds reported in the literature. The spin-exchange ability of the groups such as -OH, -OMe, -OR and -OPh is also compared.