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Intermediate-Spin Iron(III) Complexes Having a Redox-Noninnocent Macrocyclic Tetraamido Ligand
Inorganic Chemistry ( IF 4.6 ) Pub Date : 2018-03-16 00:00:00 , DOI: 10.1021/acs.inorgchem.8b00037
Takahiko Kojima 1, 2 , Fumiya Ogishima 1 , Takahisa Nishibu 1 , Hiroaki Kotani 1 , Tomoya Ishizuka 1 , Toshihiro Okajima 3 , Shunsuke Nozawa 4 , Yoshihito Shiota 5 , Kazunari Yoshizawa 2, 5 , Hiroyoshi Ohtsu 6 , Masaki Kawano 6 , Takuya Shiga 1 , Hiroki Oshio 1
Affiliation  

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 13 were measured in both CH3CN solutions and BN pellets to observe comparable rising-edge energies for the three complexes, and Mössbauer spectra of 13 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.

中文翻译:

具有氧化还原非清大环四胺基配体的中间自旋铁(III)配合物

合成了具有二苯并四乙基四酰胺基大环配体(DTTM 4-)(NEt 42 [Fe III(DTTM)Cl](1)的铁(III)配合物,并通过晶体学,光谱学和电化学方法进行了表征。复杂1具有在一个方底金字塔形结构小号= 3 / 2的自旋态。在室温下,在CH 2 Cl 2中测得的循环伏安图中,络合物在+0.36和+0.68 V(vs SCE)处显示两个可逆氧化还原波。1的逐步氧化使用化学氧化剂可以使我们观察到每个步骤具有清晰的等吸收点的清晰明显的光谱变化,其中氧化发生在苯二胺基部分而不是铁中心。在CH 2 Cl 2中1 Ru当量的[Ru III(bpy)3 ](ClO 43(bpy = 2,2'-联吡啶)进行单电子氧化,得到方形锥体(NEt 4)[Fe(DTTM) )Cl](2),它处于S = 1的自旋态,涉及一个配体基团,并且显示出略微扭曲的方金字塔形结构。复杂2展示了在900 nm处的间隔电荷转移带,该间隔带是根据随时间变化的密度泛函理论计算而分配的,表明该络合物处于II a类混合价配体-自由基体系,H ab = 884 cm – 1。的双电子氧化1由2当量的[(4-溴-PH)3 Ñ •+ ]酸盐(SbCl 6)的CH 22,得到二-电子-氧化物质1,的[Fe(DTTM)CL](3),这是在小号= 1 / 2的自旋态; 复杂3呈现出扭曲的方形锥体结构。的X射线吸收近边结构光谱1 - 3在两个CH测定3 CN溶液和BN粒料观察可比上升边缘能量为三个配合物以及穆斯堡尔谱1 - 3显示出几乎相同的异构体位移和四分裂参数,表明这三个配合物的铁中心完好无损,处于中间自旋铁(III)状态。因此,在配合物23中,很明显在配体基团的未配对电子与铁(III)中心的未配对电子之间存在反铁磁耦合。
更新日期:2018-03-16
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