Synthesis and Magnetic Properties of New Octahedral Iron(II) Complexes^†

The reaction of iron(II) acetate with the tetradentate Schiff base like ligands H₂L1 ((E,E)-[{diethyl 2,2′-[1,2-phenylenebis-(iminomethylidyne)]bis[3-oxobutanato]}]) and H₂L2 ([([3,3′]-[1,2-phenylenebis(iminomethylidyne)]bis(2,4-pentane-dionato)(2-)-N,N′,O2,O2′]) in the presence of 1-meim (1-methylimidazole) or 2-meim (2-methylimidazole) leads to the formation of pentacoordinated or octahedral complexes depending on the used reaction conditions. Two pentacoordinated and four octahedral iron(II) complexes of the composition [FeL1(1-meim)₂] (1), [FeL2(1-meim)] (2), [FeL2(1-meim)₂] (3), [FeL2(1-meim)₂](DMF) (3(DMF)), [FeL1(2-meim)](MeOH)_0.5 (4) and [FeL1(2-meim)₂] (5) were isolated and structurally characterized. For the 2-meim complexes a hydrogen bond network between the imidazole N-H hydrogen and the carbonyl oxygen of the equatorial ligand is formed, while for the 1-meim derivatives only weak van der Waals interactions are observed. Magnetic measurements were performed on all samples. As expected, the pentacoordinated complexes remain in the high-spin state in the whole temperature range investigated. For the octahedral complexes, 1 and 5 are pure high-spin complexes while for 3 and 3(DMF) spin transition behaviour is observed.