Structure Controlling Factors of Oxido-Bridged Dinuclear Iron(III) Complexes.

Ryusei Hoshikawa,Masahiro Mikuriya,Kosuke Yoshida,Ryoji Mitsuhashi,Hiroshi Sakiyama,Takashi Okuno

doi:10.3390/molecules26040897

Ryusei Hoshikawa, Masahiro Mikuriya + Show 4 more

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https://doi.org/10.3390/molecules26040897

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Abstract

Oxido bridges commonly form between iron(III) ions, but their bond angles and symmetry vary with the circumstances. A large number of oxido-bridged dinuclear iron(III) complexes have been structurally characterized. Some of them belong to the C2 point group, possessing bent Fe–O–Fe bonds, while some others belong to the Ci symmetry, possessing the linear Fe–O–Fe bonds. The question in this study is what determines the structures and symmetry of oxido-bridged dinuclear iron(III) complexes. In order to gain further insights, three oxido-bridged dinuclear iron(III) complexes were newly prepared with 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) ligands: [Fe2OCl2(bpy)4][PF6]2 (1), [Fe2O(NO3)2(bpy)4][PF6]2·0.6MeCN·0.2(2-PrOH) (2), and [Fe2OCl2(phen)4][PF6]2·MeCN·0.5H2O (3). The crystal structures of 1, 2, and 3 were determined by the single-crystal X-ray diffraction method, and all of them were found to have the bent Fe–O–Fe bonds. Judging from the crystal structure, some intramolecular interligand hydrogen bonds were found to play an important role in fixing the structures. Additional density functional theory (DFT) calculations were conducted, also for a related oxido-bridged dinuclear iron(III) complex with a linear Fe–O–Fe bond. We conclude that the Fe–O–Fe bridge tends to bend like a water molecule, but is often stretched by interligand steric repulsion, and that the structures are mainly controlled by the intramolecular interligand interactions.

Highlights

The iron(III)–oxido bond is easy to form, and the oxido ligand tends to bridge iron(III) ions
The precipitation has been identified by X-ray diffraction [1] to have the same structure of the natural ore goethite, α-Fe(O)(OH), in which iron(III) ions are bridged by the oxido and hydroxido ligands to form a polymeric structure [2]
All of the complexes were characterized by elemental analysis and a single-crystal X-ray diffraction study

Summary

Introduction

The iron(III)–oxido bond is easy to form, and the oxido ligand tends to bridge iron(III) ions. The precipitation has been identified by X-ray diffraction [1] to have the same structure of the natural ore goethite, α-Fe(O)(OH), in which iron(III) ions are bridged by the oxido and hydroxido ligands to form a polymeric structure [2]. The oxy-form of hemerythrin has a (μ-oxido)bis(μ-carboxylato)diiron(III) unit at the active site [3], and the two-electron-reduced dioxygen species (hydroperoxido ligand) is bound to one of the iron(III) ions and to the bridging oxido ligand. In another example, some (μ-oxido)diiron(III) complexes are known to cause characteristic renal injuries [4]

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Conclusion