A Mixed-Valence Octanuclear Iron−Oxo Pyrazolate: Assessment of Electronic Delocalization by Structural and Spectroscopic Analysis

Abstract

A formally FeIII7FeII complex, containing an inner Fe4O4-cubane and four peripheral Fe-centers, is derived from the one-electron reduction of its FeIII8 precursor. Spectroscopic analysis of the former reveals that the redox activity of this Fe8-system is confined within its cubane core. The resulting (Fe4O4)3+-cubane, which is valence-delocalized in the NMR, Mössbauer and IR, but valence-trapped in the X-ray photoelectron spectroscopy (XPS) timescale, is better described as a Robin-Day class-II system by the analysis of its near infrared (NIR) intervalence charge transfer (IVCT) band profile.

Water‐Soluble Derivatives of Octanuclear Iron–Oxido–Pyrazolato Complexes – an Experimental and Computational Study

“…[20–21] We have previously reported the reduction of organosoluble [Fe 8 ] 0 to [Fe 8 ] − species by electrochemical and chemical means – stoichiometric addition of [BH 4 ] − . [10, 11] …”

“…In one case, the first reduction product, [Fe 8 (μ 4 -O) 4 (μ-4-Cl-pz) 12 Cl 4 ] − , has been isolated and fully characterized: It is readily recognized by its near-IR intravalence charge transfer (IVCT) band and shift of the ν (Fe-O) stretch in the IR, but is structurally indistinguishable, within experimental error, from its all-Fe III parent compound. [11] Visual inspection of a three-dimensional model of the [Fe 8 (μ 4 -O) 4 (μ-pz) 12 Cl 4 ] complex, or the space-filling diagram (Figure 1c), shows that its approximately spherical surface is defined by H- and Cl-atoms, rendering it highly hydrophobic. Consequently, [Fe 8 (μ 4 -O) 4 (μ-4-R-pz) 12 X 4 ] complexes with R=H, Cl, Br and CH 3 are all soluble in common organic solvents (methylene chloride, chloroform, tetrahydrofuran, acetone, toluene, acetonitrile, etc.)…”

Water Oxidation Reaction Mediated by an Octanuclear Iron‐Oxo Cluster

“…[1] In recognition of this, many groups have been using chelating ligands containing carboxylate functions and other functionalities in order to determine which parameters are important in controlling the speciation of iron. These studies have led to a wide variety of polyiron clusters containing bridging oxygen atoms and Fe 4 , Fe 6 , Fe 8 , Fe 10 , Fe 11 , Fe 12 , and Fe 16 centers. [2][3][4][5][6][7][8][9] It has been demonstrated that the hydrolysis of iron salts can be controlled by organic ligands so as to yield soluble molecular aggregates with nanometer dimensions, which can often be isolated in crystalline form and structurally characterized.…”

“…Though some work has been carried out directly in aqueous environments, the use of non-aqueous media with a low water content has led to the synthesis of an unexpected variety of polynuclear clusters. [2][3][4][5][6][7][8][9] Of particular relevance to the present study is a family of octanuclear [Fe 8 (μ 4 -O) 4 (μ-4-R-pz) 12 X 4 ] (Fe 8 ) clusters (R = CH 3 , H, and Cl; X = Cl, Br; pz = pyrazolate), which were generated in one-pot reactions of FeX 3 , 4-R-pz, and base in air. [10][11][12][13][14] Notably, spectroscopic and electrochemical properties relative to those of the previously reported Fe 8 clusters based on pyrazolate ligands.…”

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A one-pot synthetic procedure yields the octanuclear Fe III complex [Fe 8 (μ 4 -O) 4 (μ-4-tBu-pz) 12 Cl 4 ] (2). The molecular structure of 2 resembles the building units of iron-containing minerals like magnetite, ferrihydrite and maghemite.

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