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

Abstract

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.

Keywords:

• Iron(II) complexes
• Seven-coordinate
• Macrocyclic ligands
• Pentagonal-bipyramidal

Acknowledgments

The authors gratefully acknowledge financial support from the Deutsche Forschungsgemeinschaft and the Kafrelsheikh University (Egypt).