Intermediate-Spin Iron(III) Complexes Having a Redox-Noninnocent Macrocyclic Tetraamido Ligand

Takahiko Kojima, Fumiya Ogishima, Takahisa Nishibu, Hiroaki Kotani, Tomoya Ishizuka, Toshihiro Okajima, Shunsuke Nozawa, Yoshihito Shiota, Kazunari Yoshizawa, Hiroyoshi Ohtsu, Masaki Kawano, Takuya Shiga, Hiroki Oshio

Research output: Contribution to journalReview article

3 Citations (Scopus)

Abstract

An iron(III) complex having a dibenzotetraethyltetraamido macrocyclic ligand (DTTM 4- ), (NEt 4 ) 2 [Fe III (DTTM)Cl] (1), was synthesized and characterized by crystallographic, spectroscopic, and electrochemical methods. Complex 1 has a square-pyramidal structure in the S = 3 / 2 spin state. The complex exhibited two reversible redox waves at +0.36 and +0.68 V (vs SCE) in the cyclic voltammogram measured in CH 2 Cl 2 at room temperature. The stepwise oxidation of 1 using chemical oxidants allowed us to observe clear and distinct spectral changes with distinct isosbestic points for each step, in which oxidation occurred at the phenylenediamido moiety rather than the iron center. One-electron oxidation of 1 by 1 equiv of [Ru III (bpy) 3 ](ClO 4 ) 3 (bpy = 2,2′-bipyridine) in CH 2 Cl 2 afforded square-pyramidal (NEt 4 )[Fe(DTTM)Cl] (2), which was in the S = 1 spin state involving a ligand radical and showed a slightly distorted square-pyramidal structure. Complex 2 showed an intervalence charge-transfer band at 900 nm, which was assigned on the basis of time-dependent density functional theory calculations, to indicate that the complex is in a class IIA mixed-valence ligand-radical regime with H ab = 884 cm -1 . Two-electron oxidation of 1 by 2 equiv of [(4-Br-Ph) 3 N ·+ ](SbCl 6 ) in CH 2 Cl 2 afforded two-electron-oxidized species of 1, [Fe(DTTM)Cl] (3), which was in the S = 1 / 2 spin state; complex 3 exhibited a distorted square-pyramidal structure. X-ray absorption near-edge structure spectra of 1-3 were measured in both CH 3 CN solutions and BN pellets to observe comparable rising-edge energies for the three complexes, and Mössbauer spectra of 1-3 showed almost identical isomer shifts and quadruple splitting parameters, indicating that the iron centers of the three complexes are intact to be in the intermediate-spin iron(III) state. Thus, in complexes 2 and 3, it is evident that antiferromagnetic coupling is operating between the unpaired electron(s) of the ligand radical(s) and those of the iron(III) center.

Original languageEnglish
Pages (from-to)9683-9695
Number of pages13
JournalInorganic Chemistry
Volume57
Issue number16
DOIs
Publication statusPublished - Aug 20 2018

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Iron
Ligands
iron
ligands
methylidyne
Oxidation
oxidation
Electrons
electrons
Oxidation-Reduction
X ray absorption
Oxidants
pellets
Isomers
Density functional theory
Charge transfer
isomers
charge transfer
density functional theory
valence

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

Kojima, T., Ogishima, F., Nishibu, T., Kotani, H., Ishizuka, T., Okajima, T., ... Oshio, H. (2018). Intermediate-Spin Iron(III) Complexes Having a Redox-Noninnocent Macrocyclic Tetraamido Ligand. Inorganic Chemistry, 57(16), 9683-9695. https://doi.org/10.1021/acs.inorgchem.8b00037

Intermediate-Spin Iron(III) Complexes Having a Redox-Noninnocent Macrocyclic Tetraamido Ligand. / Kojima, Takahiko; Ogishima, Fumiya; Nishibu, Takahisa; Kotani, Hiroaki; Ishizuka, Tomoya; Okajima, Toshihiro; Nozawa, Shunsuke; Shiota, Yoshihito; Yoshizawa, Kazunari; Ohtsu, Hiroyoshi; Kawano, Masaki; Shiga, Takuya; Oshio, Hiroki.

In: Inorganic Chemistry, Vol. 57, No. 16, 20.08.2018, p. 9683-9695.

Research output: Contribution to journalReview article

Kojima, T, Ogishima, F, Nishibu, T, Kotani, H, Ishizuka, T, Okajima, T, Nozawa, S, Shiota, Y, Yoshizawa, K, Ohtsu, H, Kawano, M, Shiga, T & Oshio, H 2018, 'Intermediate-Spin Iron(III) Complexes Having a Redox-Noninnocent Macrocyclic Tetraamido Ligand', Inorganic Chemistry, vol. 57, no. 16, pp. 9683-9695. https://doi.org/10.1021/acs.inorgchem.8b00037
Kojima T, Ogishima F, Nishibu T, Kotani H, Ishizuka T, Okajima T et al. Intermediate-Spin Iron(III) Complexes Having a Redox-Noninnocent Macrocyclic Tetraamido Ligand. Inorganic Chemistry. 2018 Aug 20;57(16):9683-9695. https://doi.org/10.1021/acs.inorgchem.8b00037
Kojima, Takahiko ; Ogishima, Fumiya ; Nishibu, Takahisa ; Kotani, Hiroaki ; Ishizuka, Tomoya ; Okajima, Toshihiro ; Nozawa, Shunsuke ; Shiota, Yoshihito ; Yoshizawa, Kazunari ; Ohtsu, Hiroyoshi ; Kawano, Masaki ; Shiga, Takuya ; Oshio, Hiroki. / Intermediate-Spin Iron(III) Complexes Having a Redox-Noninnocent Macrocyclic Tetraamido Ligand. In: Inorganic Chemistry. 2018 ; Vol. 57, No. 16. pp. 9683-9695.
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abstract = "An iron(III) complex having a dibenzotetraethyltetraamido macrocyclic ligand (DTTM 4- ), (NEt 4 ) 2 [Fe III (DTTM)Cl] (1), was synthesized and characterized by crystallographic, spectroscopic, and electrochemical methods. Complex 1 has a square-pyramidal structure in the S = 3 / 2 spin state. The complex exhibited two reversible redox waves at +0.36 and +0.68 V (vs SCE) in the cyclic voltammogram measured in CH 2 Cl 2 at room temperature. The stepwise oxidation of 1 using chemical oxidants allowed us to observe clear and distinct spectral changes with distinct isosbestic points for each step, in which oxidation occurred at the phenylenediamido moiety rather than the iron center. One-electron oxidation of 1 by 1 equiv of [Ru III (bpy) 3 ](ClO 4 ) 3 (bpy = 2,2′-bipyridine) in CH 2 Cl 2 afforded square-pyramidal (NEt 4 )[Fe(DTTM)Cl] (2), which was in the S = 1 spin state involving a ligand radical and showed a slightly distorted square-pyramidal structure. Complex 2 showed an intervalence charge-transfer band at 900 nm, which was assigned on the basis of time-dependent density functional theory calculations, to indicate that the complex is in a class IIA mixed-valence ligand-radical regime with H ab = 884 cm -1 . Two-electron oxidation of 1 by 2 equiv of [(4-Br-Ph) 3 N ·+ ](SbCl 6 ) in CH 2 Cl 2 afforded two-electron-oxidized species of 1, [Fe(DTTM)Cl] (3), which was in the S = 1 / 2 spin state; complex 3 exhibited a distorted square-pyramidal structure. X-ray absorption near-edge structure spectra of 1-3 were measured in both CH 3 CN solutions and BN pellets to observe comparable rising-edge energies for the three complexes, and M{\"o}ssbauer spectra of 1-3 showed almost identical isomer shifts and quadruple splitting parameters, indicating that the iron centers of the three complexes are intact to be in the intermediate-spin iron(III) state. Thus, in complexes 2 and 3, it is evident that antiferromagnetic coupling is operating between the unpaired electron(s) of the ligand radical(s) and those of the iron(III) center.",
author = "Takahiko Kojima and Fumiya Ogishima and Takahisa Nishibu and Hiroaki Kotani and Tomoya Ishizuka and Toshihiro Okajima and Shunsuke Nozawa and Yoshihito Shiota and Kazunari Yoshizawa and Hiroyoshi Ohtsu and Masaki Kawano and Takuya Shiga and Hiroki Oshio",
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T1 - Intermediate-Spin Iron(III) Complexes Having a Redox-Noninnocent Macrocyclic Tetraamido Ligand

AU - Kojima, Takahiko

AU - Ogishima, Fumiya

AU - Nishibu, Takahisa

AU - Kotani, Hiroaki

AU - Ishizuka, Tomoya

AU - Okajima, Toshihiro

AU - Nozawa, Shunsuke

AU - Shiota, Yoshihito

AU - Yoshizawa, Kazunari

AU - Ohtsu, Hiroyoshi

AU - Kawano, Masaki

AU - Shiga, Takuya

AU - Oshio, Hiroki

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N2 - An iron(III) complex having a dibenzotetraethyltetraamido macrocyclic ligand (DTTM 4- ), (NEt 4 ) 2 [Fe III (DTTM)Cl] (1), was synthesized and characterized by crystallographic, spectroscopic, and electrochemical methods. Complex 1 has a square-pyramidal structure in the S = 3 / 2 spin state. The complex exhibited two reversible redox waves at +0.36 and +0.68 V (vs SCE) in the cyclic voltammogram measured in CH 2 Cl 2 at room temperature. The stepwise oxidation of 1 using chemical oxidants allowed us to observe clear and distinct spectral changes with distinct isosbestic points for each step, in which oxidation occurred at the phenylenediamido moiety rather than the iron center. One-electron oxidation of 1 by 1 equiv of [Ru III (bpy) 3 ](ClO 4 ) 3 (bpy = 2,2′-bipyridine) in CH 2 Cl 2 afforded square-pyramidal (NEt 4 )[Fe(DTTM)Cl] (2), which was in the S = 1 spin state involving a ligand radical and showed a slightly distorted square-pyramidal structure. Complex 2 showed an intervalence charge-transfer band at 900 nm, which was assigned on the basis of time-dependent density functional theory calculations, to indicate that the complex is in a class IIA mixed-valence ligand-radical regime with H ab = 884 cm -1 . Two-electron oxidation of 1 by 2 equiv of [(4-Br-Ph) 3 N ·+ ](SbCl 6 ) in CH 2 Cl 2 afforded two-electron-oxidized species of 1, [Fe(DTTM)Cl] (3), which was in the S = 1 / 2 spin state; complex 3 exhibited a distorted square-pyramidal structure. X-ray absorption near-edge structure spectra of 1-3 were measured in both CH 3 CN solutions and BN pellets to observe comparable rising-edge energies for the three complexes, and Mössbauer spectra of 1-3 showed almost identical isomer shifts and quadruple splitting parameters, indicating that the iron centers of the three complexes are intact to be in the intermediate-spin iron(III) state. Thus, in complexes 2 and 3, it is evident that antiferromagnetic coupling is operating between the unpaired electron(s) of the ligand radical(s) and those of the iron(III) center.

AB - An iron(III) complex having a dibenzotetraethyltetraamido macrocyclic ligand (DTTM 4- ), (NEt 4 ) 2 [Fe III (DTTM)Cl] (1), was synthesized and characterized by crystallographic, spectroscopic, and electrochemical methods. Complex 1 has a square-pyramidal structure in the S = 3 / 2 spin state. The complex exhibited two reversible redox waves at +0.36 and +0.68 V (vs SCE) in the cyclic voltammogram measured in CH 2 Cl 2 at room temperature. The stepwise oxidation of 1 using chemical oxidants allowed us to observe clear and distinct spectral changes with distinct isosbestic points for each step, in which oxidation occurred at the phenylenediamido moiety rather than the iron center. One-electron oxidation of 1 by 1 equiv of [Ru III (bpy) 3 ](ClO 4 ) 3 (bpy = 2,2′-bipyridine) in CH 2 Cl 2 afforded square-pyramidal (NEt 4 )[Fe(DTTM)Cl] (2), which was in the S = 1 spin state involving a ligand radical and showed a slightly distorted square-pyramidal structure. Complex 2 showed an intervalence charge-transfer band at 900 nm, which was assigned on the basis of time-dependent density functional theory calculations, to indicate that the complex is in a class IIA mixed-valence ligand-radical regime with H ab = 884 cm -1 . Two-electron oxidation of 1 by 2 equiv of [(4-Br-Ph) 3 N ·+ ](SbCl 6 ) in CH 2 Cl 2 afforded two-electron-oxidized species of 1, [Fe(DTTM)Cl] (3), which was in the S = 1 / 2 spin state; complex 3 exhibited a distorted square-pyramidal structure. X-ray absorption near-edge structure spectra of 1-3 were measured in both CH 3 CN solutions and BN pellets to observe comparable rising-edge energies for the three complexes, and Mössbauer spectra of 1-3 showed almost identical isomer shifts and quadruple splitting parameters, indicating that the iron centers of the three complexes are intact to be in the intermediate-spin iron(III) state. Thus, in complexes 2 and 3, it is evident that antiferromagnetic coupling is operating between the unpaired electron(s) of the ligand radical(s) and those of the iron(III) center.

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