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

The reaction of iron(II) acetate with the tetradentate Schiff base like ligands H 2 L1 ((E,E)‐[{diethyl 2,2′‐[1,2‐phenylenebis‐(iminomethylidyne)]bis[3‐oxobutanato]}]) and H 2 L2 ([([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.