Intermediate-Spin Iron(III) Complexes Having a Redox-Noninnocent Macrocyclic Tetraamido Ligand
- Takahiko Kojima*Takahiko Kojima*E-mail: [email protected]Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, JapanCREST, Japan Science and Technology Agency, 4 Chome-1-8, Kawaguchi, Honcho, Saitama 332-0012, JapanMore by Takahiko Kojima,
- Fumiya OgishimaFumiya OgishimaDepartment of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, JapanMore by Fumiya Ogishima,
- Takahisa NishibuTakahisa NishibuDepartment of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, JapanMore by Takahisa Nishibu,
- Hiroaki KotaniHiroaki KotaniDepartment of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, JapanMore by Hiroaki Kotani,
- Tomoya IshizukaTomoya IshizukaDepartment of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, JapanMore by Tomoya Ishizuka,
- Toshihiro OkajimaToshihiro OkajimaKyushu Synchrotron Light Research Center, 8-7 Yayoigaoka, Tosu, Saga 841-0005, JapanMore by Toshihiro Okajima,
- Shunsuke NozawaShunsuke NozawaPhoton Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801, JapanMore by Shunsuke Nozawa,
- Yoshihito ShiotaYoshihito ShiotaInstitute for Materials Chemistry and Engineering, Kyushu University, Motooka, Nishi-Ku, Fukuoka 819-0395, JapanMore by Yoshihito Shiota,
- Kazunari YoshizawaKazunari YoshizawaCREST, Japan Science and Technology Agency, 4 Chome-1-8, Kawaguchi, Honcho, Saitama 332-0012, JapanInstitute for Materials Chemistry and Engineering, Kyushu University, Motooka, Nishi-Ku, Fukuoka 819-0395, JapanMore by Kazunari Yoshizawa,
- Hiroyoshi OhtsuHiroyoshi OhtsuDepartment of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, JapanMore by Hiroyoshi Ohtsu,
- Masaki KawanoMasaki KawanoDepartment of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, JapanMore by Masaki Kawano,
- Takuya ShigaTakuya ShigaDepartment of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, JapanMore by Takuya Shiga, and
- Hiroki OshioHiroki OshioDepartment of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, JapanMore by Hiroki Oshio
Abstract
An iron(III) complex having a dibenzotetraethyltetraamido macrocyclic ligand (DTTM4–), (NEt4)2[FeIII(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 CH2Cl2 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 [RuIII(bpy)3](ClO4)3 (bpy = 2,2′-bipyridine) in CH2Cl2 afforded square-pyramidal (NEt4)[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 Hab = 884 cm–1. Two-electron oxidation of 1 by 2 equiv of [(4-Br-Ph)3N•+](SbCl6) in CH2Cl2 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 CH3CN 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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