Oxo-bridged Binuclear Iron Research Articles

Kinetics of the reduction of μ–oxo–tetrakis(1, 10–phenanthroline) diiron (iii) complex by thiourea in aqueous phenanthrolinium buffer

The homovalent oxo-bridged binuclear iron(III) complex ion [Fe 2 O(phen) 4 Cl 2 ] 4+ (phen = 1, 10–phenanthroline) aquates to [Fe 2 O(phen) 4 (H 2 O) 2 ] 4+ in aqueous phenanthrolinium buffer solution (pH 3.25–4.50). The reaction of [Fe 2 O 2 (phen) 4 (H 2 O) 2 ] 4+ with thiourea in this buffer solution to give [Fe(phen) 3 ] 2+ , sulphite ion and urea was studied spectrophotometrically at 510 nm and found to be first order in [Fe 2 O 2 (phen) 4 (H 2 O) 2 ] 4+ and of mixed zero and first order in thiourea, i.e. reaction order with respect to thiourea varies from one to zero on increasing the thiourea concentration from 1.0–7.0 × 10 -2 mol dm -3 . The reaction is characterized by adduct formation. Changes in pH from 3.25 to 4.50 and ionic strength from 0.10 moldm -3 to 0.60 moldm -3 of the reaction solution were found to have no effect on the reaction rate. Catalysis and retardation were observed with the addition of Mg 2+ and CH 3 COO - ions respectively. A plausible mechanism consistent with the results obtained is proposed. Keywords: kinetics, mechanism, oxo-bridged, phenanthrolinium buffer, thiourea

Synthesis and characterization of a novel oxo-bridged binuclear iron(iii) complex: its catalytic application in the synthesis of benzoxazoles using benzyl alcohol in water

A novel oxo-bridged binuclear iron(iii) complex was found to be an efficient catalyst in the synthesis of benzoxazoles from benzyl alcohols.

Synthesis, characterization and catalytic activities of μ–oxo-bridged binuclear iron complexes encapsulated in SBA-15

Fe 3+ bipyridine complexes were successfully anchored on the inner surface of the mesopores of SBA-15 and compared with those immobilized on the surface of SiO 2. FT-IR, ESR, and XAFS measurements were used to characterize the structure of the formed μ–oxo-bridged binuclear Fe bipyridine complexes inside the mesopores of SBA-15, which were observed to be the active species for the oxidation of cyclohexane. Furthermore, binuclear Fe complexes anchored inside the mesopores of SBA-15 were found to show much higher activity than those anchored on the surface of SiO 2. The effect of the presence of the Si OH groups on the surface of SiO 2 on the selectivity for the oxidation of cyclohexane into cyclohexanone also was investigated.

Synthesis, Structure and Property of Oxo-Bridged Binuclear Iron(III) Complex [Fe(phen)(H2O)3]2O?2SO4

An oxo-bridged binuclear iron(III) complex, [Fe(phen)(H2O)3]2O⋅2SO4, has been synthesized and structurally characterized by elemental analysis (EA), IR, TG-DSC and X-ray. Its crystal structure has been determined by X-ray crystallography. It crystallizes in the orthorhombic system, space group P21212, with lattice parameters a = 17.650(4), b = 8.5133(17), c = 9.971(2) A; V = 1498.2(5) A3, ρcalcd = 1.763 g/cm3 and Z = 4 for R1 = 0.0601. The crystal structure indicated that two octahedrally coordinated iron(III) ions bridged with oxygen atoms formed a non-linear complex. The bond angle of Fe–O–Fe is 163.9(4)∘. The data of EA and IR are in good agreement with the crystal structure. The thermal gravity (TG) data indicate that there are four decomposition steps with three endothermic peaks. The final product of the thermal decomposition may be Fe(C2H8N2)SO4.

Study of the Crystal Structure of Oxo‐bridged Binuclear FeIII Complex with Chiral Salen Ligand

AbstractA oxo‐bridged binuclear iron complex with chiral salen ligand [Fe2L2]O (H2L = R, R'‐N, N'‐bis (3,5‐di‐tert‐butylsalicylaldene)‐1, 2‐cyclohexanediamine) has been synthesized and the structure has been determined by X‐ray diffraction analysis. The title complex crystallizes in triclinic system with space group P‐1. Crystal data: a = 1.42555(14) nm, b = 1.54889 (15) nm, c = 1.83662 (17) run, = 103.873(2)°, β = 100.506(2)°, 7=101.840(2)°, V = 3.7371 nm3, Dc = 1.082 g/cm3 and Z = 2. In the complex, each iron center is penta‐coordination and in distorted square‐pyramidal environment. Two Fem atoms are intramolecularity bridged by an oxygen atom with Fe‐Fe nonbond distance of 0.3517(3) nm.

Synthesis, crystal structure and magnetic properties of oxo-bridged binuclear iron(III) complex [Fe(phen) 2PhCOO] 2OCl 2·7H 2O

An oxo-bridged binuclear iron(III) complex, [Fe(phen) 2PhCOO] 2OCl 2·7H 2O, was synthesized and the crystal structure indicated that two octahedrally coordinated iron(III) ions bridged with oxygen atoms formed a non-linear complex. The bond angle of FeOFe is 155.6°. The studies of magnetic properties showed that there was strong antiferromagnetic superexchange coupling ( J = −80.8 cm −) between two S = 5 2 iron(III) ions.

Mixed-valence Fe(III)Fe(IV) dimers. Preparation and physical properties of oxidation products of oxo-bridged binuclear iron(III) complexes

Polycrystalline samples of the oxidation products of nine oxo-bridged binuclear iron(III) complexes [Fe 2L 2O] +[I 3] −X ( I–VIII) and [Fe 2L 2(OH) 2] + (BF 4) − ( IX), where L 2− = some substituted tetraisothiosemicarbazide ligands, X = iodine or iodinechloroform solvates, are investigated over the temperature range 4.2–300 K using EPR, Mössbauer and magnetic susceptibility measurements. The results of the investigation show that oxidation of the μ-oxo [Fe(III) 2L 2O] dimers gives the mixed-valence Fe(III)Fe(IV) dimers. The 57Fe Mössbauer spectra of these compounds in the temperature range 300-80 K exhibit a single quadrupole doublet which indicates delocalization of the ‘extra’ electron between iron sites, at least within the Mössbauer time scale of about 10 −7 s. The presence of the antiferromagnetic exchange interaction in these dimers is evidenced by variable-temperature (4–300K) magnetic susceptibility data. These data are least-squares fit to the theoretical equation for a spin Hamiltonian which includes the isotropic exchange interaction between two iron centers ( JS 1 S 2, J ∼ 30–50 cm −1), the axial zero-field splitting of the iron centers with the parameter D ∼ 10 cm −1, and the interdimer exchange interaction (| z′ J inter| ∼ 1–9 cm −1). The ground state with S = 1 2 for all dimers is proved by the value of the magnetic moment at 4.2 K. Practically symmetric signals with g values ∼ 2.0 are observed in X- and Q-band EPR spectra at room temperature. Analysis of the temperature dependence of the spectra detected in the temperature range 100–300 K for I–VIII and 300-40 K for IX compounds showed that the spectra are due to transitions within the excited spin states with the total quantum number S > 1 2 . The linewidth increases as the S value decreases and the signal due to S = 1 2 is not detected. It is proposed that the observed peculiarities of the EPR spectra are connected with the intramolecular electron transfer which is accompanied by some fluctuations of the dimer structure. The absence of the signals at low temperature indicates that the period of this fluctuation coincides with the EPR time scale (10 −10 s).

Complex formation between the protein components of methane monooxygenase from Methylosinus trichosporium OB3b. Identification of sites of component interaction.

Kinetic, spectroscopic, and chemical evidence for the formation of specific catalytically essential complexes between the three protein components of the soluble form of methane monooxygenase from Methylosinus trichosporium OB3b is reported. The effects of the concentrations of the reductase and component B on the hydroxylation activity of the reconstituted enzyme system has been numerically simulated based on a kinetic model which assumes formation of multiple high affinity complexes with the hydroxylase component during catalysis. The formation of several of these complexes has been directly demonstrated. By using EPR spectroscopy, the binding of approximately 2 mol of component B/mol of hydroxylase (subunit structure (alpha beta gamma)2) is shown to significantly change the electronic environment of the mu-(H/R)-oxo-bridged binuclear iron cluster of the hydroxylase in both the mixed valent (Fe(II).Fe(III)) and fully reduced (Fe(II).Fe(II)) states. Protein-protein complexes between the reductase and component B as well as between the reductase and hydroxylase have been shown to form by monitoring quenching of the tryptophan fluorescence spectrum of either the component B (KD approximately 0.4 microM) or hydroxylase (two binding sites, KDa approximately 10 nM, KDb approximately 8 microM). The observed KD values are in agreement with the best fit values from the kinetic simulation. Through the use of the covalent zero length cross-linking reagent 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC), the binding sites of the component B and reductase were shown to be on the hydroxylase alpha and beta subunits, respectively. The alpha and beta subunits of the hydroxylase are cross-linked by EDC suggesting that they are juxtaposed. EDC also caused the rapid loss of the ability of the monomeric component B to stimulate the hydroxylation reaction suggesting that cross-linking of reactive groups on the protein surface had occurred. This effect was inhibited by the presence of hydroxylase and was accompanied by a loss of the ability of the component B to bind to the hydroxylase. Thus, formation of a component B-hydroxylase complex is apparently required for effective catalysis linked to NADH oxidation. When present in concentrations greater than required to saturate the initial hydroxylase complex, component B inhibited both the rate of the enzymic reaction and the cross-linking of the reductase to the hydroxylase. This suggests that a second complex involving component B can form that negatively regulates catalysis by preventing formation of the reductase-hydroxylase complex.

Purification of a high specific activity methane monooxygenase hydroxylase component from a type II methanotroph

The purification of the hydroxylase component of a 3 component methane monooxygenase from the type II methanotroph Methylosinus trichosporium OB3b is reported. The enzyme (240 kDa) has an (αβγ) 2 subunit structure as observed for hydroxylases isolated from other Type I and Type II methanotrophs, but it exhibits a 5 to 10 fold higher specific activity and is isolated in 2 to 10 fold higher yield. EPR and Mössbauer spectra of the hydroxylase show that it contains a coupled iron center containing an even number of iron atoms. The spectra are similar to those of proteins known to contain oxo-bridged binuclear iron centers. The presence of such a center is unprecedented in a monooxygenase and suggests that a novel mechanism is utilized.

Identification of a hydroxide ligand at the iron center of ribonucleotide reductase by resonance Raman spectroscopy.

The resonance Raman spectrum of protein B2 of ribonucleotide reductase from Escherichia coli shows several features to its oxo-bridged binuclear iron center. A peak at 492 cm-1 is assigned to the symmetric stretch of the Fe-O-Fe moiety on the basis of its 13-cm-1 shift to lower energy upon 18O substitution. The 18O species shows an additional peak at 731 cm-1, which is a good candidate for the asymmetric stretch of the Fe-O-Fe moiety. Its exact location in the 16O species is obscured by the presence of a protein tryptophan vibration at 758 cm-1. A third resonance-enhanced peak at 598 cm-1 is identified as an Fe-OH vibration on the basis of its 24-cm-1 shift to lower energy in H2 18O, its 2-cm-1 shift to lower energy in D2O, and its pH-dependent intensity. A hydrogen-bonded mu-oxo bridge similar to that in hemerythrin is suggested by the unusually low frequency for the Fe-O-Fe symmetric stretch and the 3-cm-1 shift to higher energy of vs(Fe-O-Fe) in D2O. From the oxygen isotope dependence of vs(Fe-O-Fe), an Fe-O-Fe angle of 138 degrees can be calculated. This small angle suggests that the iron center consists of a tribridged core as in hemerythrin. A model for the binuclear iron center of ribonucleotide reductase is presented in which the hydroxide ligand sites provide an explanation for the half-of-sites reactivity of the enzyme.

Crystal structures and magnetism of binuclear iron(III) complexes with a linear oxo-bridge, [Fe2O(bbimae)2X2][NO3]2{bbimae =2-[bis(benzimidazol-2-ylmethyl)amino]ethanol, X = Cl or NCS}

The crystal structures of the oxo-bridged binuclear iron(III) complexes [Fe2O(bbimae)2X2][NO3]2{X = Cl (1) or NCS (2); bbimae = 2-[bis(benzimidazol-2-ylmethyl)amino]ethanol} have been determined by X-ray diffraction methods. Crystals of (1) are monoclinic with a=11.949(3), b=15.901(4), c= 11.326(2)A, β=109.36(2)°, space group P21/n, and Z= 2. Crystals of (2) are orthorhombic with a=16.384(2), b=19.804(2), c=13.600(2)A, space group Pbca, and Z= 4. Both crystals are composed of centrosymmetric dimeric cations with a linear Fe–O–Fe bond and nitrate counter ions. The iron–iron and iron–oxo distances are 3.563(1) and 1.7816(7)A for (1) and 3.559(1) and 1.7795(8)A for (2). Mossbauer spectra reveal the presence of high-spin iron(III) atoms in both complexes. The magnetic moments of 1.81(295 K) and 0.73 B.M. (98 K) for (1) and 1.82 (295 K) and 0.89 B.M. (98 K) for (2) indicate an antiferromagnetic interaction between the two iron(III) atoms. The –J value was evaluated as 103 cm–1 for (1), which falls in the range (95–110 cm–1) of previously reported oxo-bridged complexes with Fe–O–Fe bond angles in the range 139–180°

Preparation and physical properties of oxidation products of oxo-bridged binuclear iron(III) complexes. Mixed-valence diiron(III, IV) complexes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPreparation and physical properties of oxidation products of oxo-bridged binuclear iron(III) complexes. Mixed-valence diiron(III, IV) complexesRonald G. Wollmann and David N. HendricksonCite this: Inorg. Chem. 1977, 16, 4, 723–733Publication Date (Print):April 1, 1977Publication History Published online1 May 2002Published inissue 1 April 1977https://doi.org/10.1021/ic50170a001RIGHTS & PERMISSIONSArticle Views318Altmetric-Citations35LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Mössbauer and Magnetic Study of Mononuclear and Oxo-bridged Binuclear Iron(III) Complexes of 1,10-Phenanthroline and 2,2′-Bipyridine

Abstract The oxo-bridged binuclear iron(III) complexes [L2(NCS)Fe–O–Fe(NCS)L2]2+ (L=1,10-phenanthroline or 2,2′-bipyridine) were prepared recently in spite of the earlier report that they could not be prepared. The unperturbed and perturbed Mössbauer spectral and magnetic susceptibility data on these compounds are reported here and compared with those for the well characterized oxo-bridged compounds [L2XFe–O–FeXL2]2+ (X=Cl−, Br−, SO42−,/2 or NO3−). The effect of Fe–X bond (X=Cl−, Br−, SO42−/2, NO3−, or NCS−) on the Mössbauer parameters was investigated, and the results are discussed in terms of the bonding properties of these anionic ligands. The data indicate that the electronegativity of the X ligands has no significant effect on the Mössbauer parameters. Another system, the mononuclear iron(III) complexes [FeL2(NCS)2](NCS), investigated in this work showed no Mössbauer resonance at or above 223 K and below this temperature the unperturbed spectra exhibited a broad asymmetric singlet. Magnetic susceptibilities and magnetically perturbed Mössbauer spectra indicated that iron(III) ion in these mononuclear complexes was paramagnetic with S=5⁄2.

Spectral investigation of the products of reactions of cyanide ion with oxo-bridged binuclear iron(III) complexes of 1,10-phenanthroline and 2,2′-bipyridine

Reactions of cyanide ion with aqueous solutions of oxo-bridged binuclear complexes of iron(III) and 1,10-phenanthroline or 2,2′-bipyridine, [L2(H2O)Fe–O–Fe(H2O)L2]4+(L = phen or bipy), are pH and temperature dependent. In the range 45–50 °C and pH 4·0, the complexes [FeIII(phen)2(CN)2]CN and [FeIII(bipy)2(CN)2]CN are formed, respectively. At room temperature and pH 1·2–1·5, the reduction products [FeII(phen)2(CN)2] and [FeII(bipy)2(CN)2] are obtained, respectively. Addition of cyanide ion to the binuclear complexes at pH 3·8–4·2 and room temperature results in a green solution, which rapidly becomes yellow. The green solution is believed to be due to the ion [L2(CN)Fe–O–Fe(CN)L2]2+, which in solution may undergo rapid decomposition to [FeIIIL2(CN)2]+.

Electron Spin Resonance of the Thermally Excited Quintet State of an Oxo-Bridged Binuclear Iron(III) Complex

Electron Spin Resonance of the Thermally Excited Quintet State of an Oxo-Bridged Binuclear Iron(III) Complex

Crystal and molecular structure of an oxo-bridged binuclear iron(III) complex

Crystal and molecular structure of an oxo-bridged binuclear iron(III) complex