Charge-transfer phase transition and ferromagnetism of iron mixed-valence complexes (n-CnH2n+1)4N[FeIIFe III(dto)3] (n = 3-6; dto = C2O 2S2)

Miho Itoi, Yuuki Ono, Norimichi Kojima, Kenichi Kato, Keiichi Osaka, Masaki Takata

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)

Abstract

The iron mixed-valence complex, (n-C3H7) 4N[FeIIFeIII(dto)3] (dto = dithiooxalato) shows a charge-transfer (CT) phase transition at TCT = 122.4 K. In the vicinity of TCT, the spin state changes from Fe II (S = 2) - FeIII (S = 1/2) (high-temperature phase: HTP) to FeII (S = 0) - FeIII (S = 5/2) (low-temperature phase: LTP) accompanied by a charge transfer between FeII and Fe III. This complex also undergoes a ferromagnetic transition at 7 K in the LTP. In order to investigate the mechanism of the CT phase transition and the ferromagnetism, we have systematically synthesized (n-CnH 2n+1)4N[FeIIFeIII-(dto) 3] (n = 3-6), and have investigated their physical properties by magnetic susceptibility, powder X-ray diffraction measurements, and ESR spectroscopy. The compounds (n-CnH2n+1) 4N[FeIIFeIII(dto)3] (n = 3-6) display ferromagnetic phase transitions at 7 K, 7 K (& 13 K), 19.5 K, and 22 K, respectively. For n = 3 and 4, the CT phase transitions take place at T CT ≈ 120 K and TCT ≈ 140 K, respectively. For n = 5 and 6, on the other hand, the CT phase transition does not occur, and the spin configuration of FeII (S = 2) and FeIII (S = 1/2) corresponding to the HTP for n = 3 and 4 is stable between 2 K and 300 K. The cation size of (n-CnH2n+1)4N+ (n = 3-6) acts as an effective internal pressure which induces the CT phase transition and the ferromagnetic ordering in the [FeIIFeIII(dto) 3]- layer. We also discuss the mechanism of the CT phase transition and the ferromagnetism induced by the charge-transfer interaction between FeII and FeIII.

Original languageEnglish
Pages (from-to)1198-1207
Number of pages10
JournalEuropean Journal of Inorganic Chemistry
Issue number6
DOIs
Publication statusPublished - 2006 Mar 20
Externally publishedYes

Keywords

  • Charge transfer
  • Iron
  • Magnetic properties
  • Mixed-valence compounds

ASJC Scopus subject areas

  • Inorganic Chemistry

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