Seven-coordinate iron(II) complexes of sulfur-based N3S2-macrocyclic ligands: synthesis,properties, and crystal structure

The reaction of pyridine-2,6-dicarbaldehyde or 2,6-diacetylpyridine with 1,2-bis(o-aminophenylthio)ethane (1) in acetonitrile in the presence of stoichiometric amounts of iron(II) perchlorate gave the complexes [(pyN₃S₂)Fe^II(ClO₄)₂] (4) and [(pyN₃Me₂S₂)Fe^II(ClO₄)₂] (5) of the 15-membered N₃S₂ macrocyclic ligands, pyN₃S₂ ?=?{6,7-dihydro-15,19-nitrilobenzo(e,p)(1,4,7,15)dithiadiazacyclo-heptadecine-N,N′,N″,S,S′} and pyN₃Me₂S₂?=?{6,7-dihydro-16,18-dimethyl-15,19-nitrilobenzo(e,p)(1,4,7,15)dithiadiazacyclo-heptadecine-N,N′,N″,S,S′}, respectively. Physical measurements led to the conclusion that these complexes contained seven-coordinate iron(II) and a single-crystal X-ray examination of 4 confirmed this. Coordination of the Fe(II) center in 4 is best described as distorted pentagonal-bipyramidal with the three nitrogen atoms and two sulfur donors of the macrocycle defining the pentagonal plane and the perchlorate ions occupying axial positions. Room temperature (293?K) magnetic moments of 4 and 5 (μ _eff?=?4.9 and 4.7 B.M., respectively) are close to the value predicted for high-spin d⁶ systems.