Facial and meridional geometrical isomers of tris(2-methylimidazol-4-yl- methylideneaminobenzyl)iron(II) with Δ- And Λ-configurations and their enantio-discriminative assembly via imidazole⋯chloride hydrogen bonding and spin cross-over properties

Daisuke Furushou, Tomotaka Hashibe, Takeshi Fujinami, Koshiro Nishi, Hiroaki Hagiwara, Naohide Matsumoto, Yukinari Sunatsuki, Masaaki Kojima, Seiichiro Iijima

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Abstract

A bidentate 2-methylimidazol-4-yl-methylideneaminobenzyl ligand (HL Me-Benz) reacts with Fe IICl 2·4H 2O and NaPF 6 at a 3:1:1 molar ratio to yield a tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II) chloride hexafluorophosphate solvate with the formula of [Fe II(HL Me-Benz) 3]Cl·PF 6·solvent. Meridional and facial geometrical isomers, i.e., mer-[Fe II (HL Me-Benz) 3]Cl·PF 6·1.5H 2O (1·PF 6·1.5H 2O) and fac-[Fe II(HL Me-Benz) 3]Cl·PF 6·EtOH·H 2O (2·PF 6· EtOH·H 2O), were selectively crystallized from methanol and ethanol solutions, respectively. fac-[Fe II(HL Me-Benz) 3]Cl·SbF 6·H 2O (2·SbF 6·H 2O) and fac-[Fe II(HL Me-Benz) 3]Cl·ClO 4·EtOH· H 2O (2·ClO 4·EtOH·H 2O) are synthesized in ethanol, using the corresponding anions. Each Fe II ion has an octahedral coordination geometry with N 6 donor atoms from three bidentate ligands. All three imidazole groups in both the fac- and mer-[Fe II(HL Me-Benz) 3] 2+ cations are hydrogen-bonded to neighboring three Cl - ions, and each Cl - ion is hydrogen-bonded to three imidazole groups of three neighboring complex cations; this results in the formation of hydrogen-bonded assembly structures. mer-Complex 1·PF 6·1.5H 2O forms a heterochiral two-dimensional (2D) network structure comprised of cyclic {mer-[Fe II(HL Me-Benz) 3] 2+⋯Cl -} 3 units with an ΔΔΛ or ΛΛΔ configuration; the PF 6 - ions occupy the spaces between the 2D layers. All the fac-complexes have isomorphous cubane-like tetrameric structures, i.e., {fac-[Fe II(HL Me-Benz) 3] 2+⋯ Cl -} 4. The tetranuclear structure comprises four homo-chiral fac-Δ- or fac-Λ-[Fe II(HL Me-Benz) 3] 2+ cations and four Cl - ions interconnected by twelve imidazole-chloride hydrogen bonds to form a chiral cubane supramolecule that encapsulates one counter anion. In the crystal lattice, the cubane-like tetramers with opposite chiralities are alternately arrayed. The temperature dependence of the magnetic susceptibilities and Mössbauer spectra reveal that the fac-complexes show incomplete spin crossover behavior, while the mer-complex shows a gradual spin crossover between high-spin (HS, S = 2) and low-spin (LS, S = 0) states.

Original languageEnglish
Pages (from-to)194-203
Number of pages10
JournalPolyhedron
Volume44
Issue number1
DOIs
Publication statusPublished - Aug 31 2012

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Keywords

  • Bidentate ligand
  • Geometrical isomer
  • Hydrogen bond
  • Iron(II) complex
  • Optical isomer
  • Spin crossover

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

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