Binuclear Iron Complexes Research Articles

Structure and properties of bis(1-phenyl-1h-tetrazole-5-thiolate)diiron tetranitrosyl

New tetranitrosyl binuclear iron complex [Fe2(SС7H5N4)2(NO)4] (I) has been synthesized by interaction of aqueous solutions of anionic salts [Fе(S2O3)2(NO)2]3− and [SС7H5N4]−. The latter one was synthesized by reduction of bis-(1-phenyl-1H-tetrazole-5-yl) disulfide with hydrazine hydrate in ethanol at T=25°C. Molecular and crystalline structure of I was determined by X-ray analysis; the complex has binuclear structure of “μ-SCN” type with ∼4.02Å between the iron atoms. Shortened О⋯О contacts (2.81Å) between the NO groups of similar type are observed. Parameters of Mössbauer spectrum for I are: isomer shift δFe=0.311(1) mm/s, quadrupole splitting ΔEQ=1.044(1) mm/s, line width Γ=0.267(1) mm/s at 85K. From SQUID magnetometry data, the temperature and field dependences of the magnetic moment of I are well described in the frame of a simple model of binuclear iron complex with magnetic centers S1=S2=½. In solution, binuclear structure of the complex remains, though the NO groups are non-equivalent. For solutions of I five-line hyperfine structure of spectrum (HFS) is observed, g-factor=2.03. For polycrystals of I, no HFS was observed due to averaged exchange interaction between the electron spins of adjacent complexes. In polycrystals of I, the number of spins per one binuclear complex is <2, this being the evidence of antiferromagnetic exchange interaction of unpaired electrons of two iron atoms. The average number of spins in crystals (0.65) and solutions (0.55) are close. The maximum amount of NO generated by I in 1% dimethylsulfoxide (DMSO) aqueous solution is ∼13.8nM, it halves in 8min after decomposition starts, and reaches ∼3.8nM in anaerobic conditions at Т=25°С, pH 7.0. This is due, according to quantum-chemical calculations, to the presence of a more stable FeNO bond in I than in its isostructural analog – nitrosyl iron complex with 1-methyltetrazole-5-yl (II).

Synthesis of new Fe(II) and Ru(II) η5-monocyclopentadienyl compounds showing significant second order NLO properties

A series of new ruthenium(II) complexes of the general formula [Ru(η5-C5H5)(PP)(L)][PF6] (PP = DPPE or 2PPh3, L = 4-butoxybenzonitrile or N-(3-cyanophenyl)formamide) and the binuclear iron(II) complex [Fe(η5-C5H5)(PP)(μ-L)(PP)(η5-C5H5)Fe][PF6]2 (L = (E)-2-(3-(4-nitrophenyl)allylidene)malononitrile, that has been also newly synthesized) have been prepared and studied to evaluate their potential in the second harmonic generation property. All the new compounds were fully characterized by NMR, IR and UV–Vis spectroscopies and their electrochemistry behaviour was studied by cyclic voltammetry. Quadratic hyperpolarizabilities (β) of three of the complexes have been determined by hyper-Rayleigh scattering (HRS) measurements at fundamental wavelength of 1500 nm and the calculated static β0 values are found to fall in the range 65–212 × 10−30 esu. Compound presenting β0 = 212 × 10−30 esu has revealed to be 1.2 times more efficient than urea standard in the second harmonic generation (SHG) property, measured in the solid state by Kurtz powder technique, using a Nd:YAG laser (1064 nm).

Dinitrosyl iron complexes with glutathione largely relieve rats of experimental endometriosis

A study was made of the effect of binuclear dinitrosyl iron complexes (DNIC) with glutathione in rats with experimental endometriosis. The latter was induced in an autotransplantation model, where two fragments of endometrium with myometrium (2 × 2 mm) from the left uterine horn were grafted to the inner surface of the anterior abdominal wall. After 4 weeks, the test animals received i.p. injections of 0.5 mL DNIC-glutathione at a dose of 12.5 μmol/kg daily for 12 days. This treatment more than halved the total volume of endometrioid tumors. Remarkably, tumor growths from grafts in control rats were often attended by tumors spontaneously arising nearby or in other locations; no such secondary tumors were observed in DNIC-treated animals. The EPR signal with gav = 2.03 characteristic of protein-bound DNIC with thiol ligands was recorded in liver and endometrioid implants of control as well as treated animals. Activation of ribonucleotide reductase, detected by a doublet EPR signal at g = 2.0 with 2.3-mT hyperfine splitting, was found in small tumors. The beneficial effect of DNIC-glutathione was suggested to be due to DNIC breakdown near the tumors, with release of a large amount of molecular nitric oxide and nitrosonium ions that resulted in selective local cytotoxicity.

Synthesis and characterization of oxalate-bridged binuclear iron(III) complex: [(N)2(O)2Fe(μ-ox)Fe(N)2(O)2

In the present work, a novel oxalate-bridged binuclear iron(III) complex of aminophenol derivative, (μ-ox-FeLNEM), where LNEM is deprotonated form of a tetradentate aminophenol ligand and ox stands for oxalate, was synthesized. The iron complex has been characterized by X-ray crystallography, infrared spectroscopy, UV–Vis, magnetic susceptibility studies and cyclic voltammetry techniques. X-ray structure analysis has revealed that each iron(III) is coordinated by two oxygen atoms of the oxalate group, two amine nitrogen’s and two oxygen atoms of phenolate ligand in an octahedral arrangement. The temperature variable magnetic susceptibility exhibits quite strong antiferromagnetic coupling between the two iron(III) centers. Cyclic voltammograms of the complex in dichloromethane at low temperatures showed two quasi-reversible cathodic peaks, corresponding to FeIIIFeIII to FeIIIFeII followed by FeIIIFeII to FeIIFeII process.

Synthesis, characterization and ethylene polymerization behavior of binuclear iron complexes bearing N,N′-bis(1-(6-(1-(arylimino)ethyl) pyridin-2-yl)ethylidene)benzidines

A series of N,N′-bis(1-(6-(1-(arylimino)ethyl)pyridin-2-yl)ethylidene)benzidines and the bi-metallic iron complexes thereof have been synthesized and fully characterized. All iron complexes, when activated by MAO or MMAO, exhibited high activities of up to 1.3 × 107 g mol−1 (Fe) h−1 for the polymerization of ethylene. On comparison with their mononuclear counterparts, such bi-metallic complexes not only retain a relatively high activity at elevated temperatures (up to 70 °C), but also exhibit increased lifetimes. The polyethylenes obtained were characterized by GPC, DSC and high temperature NMR spectroscopy, which indicated multimodal and highly linear features.

The Nature of Spin Crossover and Coordination Core Distortion in a Family of Binuclear Iron(II) Complexes with Bipyridyl‐Like Bridging Ligands

AbstractThe synthesis and characterization of two new binuclear compounds [{Fe(dpia)(NCS)2}2(bpac)]·nCH3OH [n = 0 (1) and 2 (2), dpia = bis(2‐picolyl)amine, bpac = 1,2‐bis(4‐pyridyl)ethyne] are reported. The magnetic susceptibility measurements of the compounds revealed different types of magnetic behavior. Complex 1 displays a two‐step spin crossover (SCO) that suggests the occurrence of a mixed [HS–LS] (HS = high spin, LS = low spin) pair at the plateau temperature (145 K), at which about 50 % of the complexes undergo a thermal spin conversion. The high‐temperature step is very gradual, whereas the low‐temperature step shows a first‐order spin transition with a hysteresis width equal to 17 K. Compound 2 manifests a relatively abrupt one‐step spin change with a narrow hysteresis of 4 K. The single‐crystal X‐ray structure of 1 was solved for the [HS–HS] complex at room temperature. Compound 2 was structurally characterized in both [HS–HS] and [LS–LS] spin states at 290 and 110 K. The magnetic and structural characteristics of 1 and 2 were compared with previously reported related binuclear compounds with 4,4′‐bipyridine and 1,2‐bis(4‐pyridyl)ethene spacer ligands. This analysis confirms a recently proposed idea about the key role of the [FeN6] core structural distortions, which are caused by crystal packing and strain effects of terminal and/or bridging ligands, in the spin‐crossover behavior of binuclear complexes. This study also revealed the predominant role of inter‐ vs. intramolecular interactions in the spin transition cooperativity.

DFT Studies on the Reduction of Dinitrogen to Ammonia by a Thiolate-Bridged Diiron Complex as a Nitrogenase Mimic

We have recently reported that the binuclear iron complexes Cp*Fe(μ-SR1)2(μ,η2-R2N═NH)FeCp* (R1 = Me, Et; R2 = Me, Ph; Cp* = η5-C5Me5) as novel models of nitrogenase could effectively catalyze the N–N bond cleavage of hydrazines, including NH2NH2 (J. Am. Chem. Soc. 2008, 130, 15250−15251). However, the mechanistic aspects involved in the catalytic cycle and the possibility of reducing N2 by these complexes have remained unexplored. In the present study, DFT has been applied for modeling the binding of Cp*Fe(μ-SEt)2FeCp* with N2 and the reduction of the N2 to two NH3 molecules at the diiron centers. The calculations of model system indicate that the hydrogenation (H+ + e–) energetically prefers to occur at the N atoms rather than the Fe or S atoms. The rate-determining step of the reduction of HN═NH could be the isomerization of a μ,η2-HN–NH2 moiety to a μ-HN–NH2 form with a NH-bridging feature, which occurred at the diiron centers. Such a transformation of the binding mode of HN–NH2 might be driven by unequal charge populations on the two Fe atoms. The results show an event of net electron transfer from the ancillary ligands to the Fe atoms and the NHNH2 moiety during the rate-determining step. In view of the experimental observations reported previously, the current computations suggest that the diiron complex Cp*Fe(μ-SEt)2FeCp* is possible to bind N2 and reduce it to NH3 via protonation/reduction. Such a reduction of N2 to NH3 at the diiron centers favorably occurs through the HNNH and HNNH2 forms rather than via the H2NNH2 unit.

Synthesis and structure of binuclear iron(ii) complex with the cage-like ligand as a model of methane monooxygenase

A binuclear iron(II) complex, [FeII2L(OTf)2](OTf) (1), with the cage-like ligand LH = [(PyCH2)2N(CH2)3O]2C6H3COOH containing an immobilized carboxylate was synthe-sized and characterized in order to model an active center of soluble methane monooxygenase (sMMO). Studies on the oxidation of cyclohexane with hydrogen peroxide or O2 involving this complex showed that the complex 1 does not catalyze the indicated reactions. Consideration of crystal structure of complex 1 gives an explanation of its inactivity in the reaction of O2 activation.

Stability and reactivity of active sites for direct benzene oxidation to phenol in Fe/ZSM-5: A comprehensive periodic DFT study

The stability of isolated extraframework Fe 2+ ions in ZSM-5 zeolite and their reactivity in the benzene to phenol oxidation were studied by periodic DFT calculations. Mononuclear iron(II) cations can only be stabilized at very specific exchange sites of ZSM-5 zeolite. Accordingly, iron will be predominantly present as oxygenated/hydroxylated mono- and binuclear iron complexes in Fe/ZSM-5. The reactivity of isolated Fe 2+ does not depend on the local coordination environment around iron, whereas the steric constraints imposed by the zeolite lattice are important for the overall catalytic reactivity. [FeO] +, [HOFe(μ-O)FeOH] 2+, [Fe(μ-O) 2Fe] 2+, [Fe(μ-O)Fe] 2+ extraframework complexes are also potential sites for benzene activation. The reaction is however not catalytic in these cases because the vacant active site cannot be regenerated. The presence of basic extraframework O ligands in these complexes favors phenol dissociation resulting in the formation of stable grafted phenolate species, and ultimately, to the deactivation of the oxygenated iron complexes.

One-step and two-step spin crossover binuclear iron(III) complexes bridged by 4,4′-bipyridine

Two binuclear iron(III) complexes, [L1FeIII(bpy)FeIIIL1](BPh4)2 (1) and [L2FeIII(bpy)FeIIIL2](BPh4)2 (2), were synthesized and characterized, where H2L1 and H2L2 denote bis(salicylicdeneaminopropyl)methylamine and bis(3-methoxysalicylideneaminopropyl)methylamine, respectively, and bpy denotes 4,4′-bipyridine and BPh4− denotes tetraphenylborate. Complexes 1 and 2 consist of one and two crystallographically unique Fe sites, respectively, while they have a similar binuclear complex-cation [LnFeIII(bpy)FeIIILn]2+ (n=1, 2) bridged by 4,4′-bipyridine and two tetraphenylborate ions as the counter anions. The magnetic susceptibility measurements of 1 and 2 showed one-step and two-step spin crossover (SCO), respectively. The four saturated six-membered chelate rings at the aminopropyl moieties of 1 exhibit disorder throughout one-step SCO. The two chelate rings of one Fe site of 2 exhibit disorder but the other two of another Fe site do not. The different SCO behaviors of 1 and 2 were ascribed to one and two crystallographically unique Fe sites and the order/disorder at the saturated six-membered chelate rings of aminopropyl moieties.

One-pot synthesis of Ni(II) and Fe(III) complexes: In situ formation of 2-pyridinemethanol from 2-pyridinecarboxaldehyde

Abstract A cubane-like tetranuclear nickel(II) compound [Ni4(L)4Cl4(H2O)3(C2H5OH)]·H2O (1) and a binuclear iron(III) compound Fe2(L)2Cl4 (2) (HL = 2-pyridinemethanol) have been prepared by solvothermal reaction of metal chloride and 2-pyridinecarboxaldehyde in C2H5OH, in which 2-pyridinecarboxaldehyde was in situ reduced to 2-pyridinemethanol. The single crystal X-ray diffraction analysis suggests that the cluster core of [Ni4(μ3-O)4] in 1 is formed by four Ni(II) and four alkoxide oxygen atoms at alternating corners, and the binuclear iron complex 2 is almost co-planar structure with alkoxide oxygen atom in μ2-mode. The magnetic studies reveal the ferromagnetic behavior for 1 and the anti-ferromagnetic interaction for 2.

Synthesis and characterization of two binuclear iron(III) complexes of aminoethanol derivatives of aminophenol as models for non-heme iron enzymes active sites

Two aminoethanol derivatives of aminophenol ligands were synthesized and characterized by IR and 1H NMR spectroscopies. The binuclear iron(III) complexes of these ligands have been prepared and characterized by IR, 1H NMR and UV–Vis spectroscopic techniques, cyclic voltammetry, single crystal X-ray diffraction and magnetic susceptibility studies. X-ray analysis revealed binuclear complexes, Fe 2(L 2), in which Fe(III) centers are surrounded by two phenolate and hydroxyl oxygen atoms, and amine nitrogens of the ligands. The metal active sites of both complexes are held together by the two above mentioned hydroxyl bridges. Variable temperature magnetic susceptibility indicates antiferromagnetic coupling between the iron centers of both complexes. This exchange coupling is stronger for Fe 2(L ae) 2, such that it shows a room temperature strong coupling between the two iron centers. The investigated complexes undergo irreversible electrochemical oxidation and reduction.

Spin crossover and polymorphism in a family of 1,2-bis(4-pyridyl)ethene-bridged binuclear iron(ii) complexes. A key role of structural distortions

Two polymorphic modifications 1 and 3 of binuclear compound [{Fe(dpia)(NCS)(2)}(2)(bpe)] and pseudo-polymorphic modification [{Fe(dpia)(NCS)(2)}(2)(bpe)]·2CH(3)OH (2), where dpia = di-(2-picolyl)amine, bpe = 1,2-bis(4-pyridyl)ethene, were synthesized, and their structures, magnetic properties, and Mössbauer spectra were studied. Variable-temperature magnetic susceptibility measurements of three binuclear compounds show different types of magnetic behaviour. The complex 1 exhibits a gradual two-step spin crossover (SCO) suggesting the occurrence of the mixed [HS-LS] (HS: high spin, LS: low spin) pair at the plateau temperature (182 K), at which about 50% of the complexes undergoes a thermal spin conversion. The complex 2 displays an abrupt full one-step spin transition without hysteresis, centred at about 159 K. The complex 3 is paramagnetic over the temperature range 20-290 K. The single-crystal X-ray studies show that all three compounds are built up from the bpe-bridged binuclear molecules. The structure of 1 was solved for three spin isomers [HS-HS], [HS-LS], and [LS-LS] at three temperatures 300 K, 183 K, and 90 K. The crystal structures for 2 and 3 were determined for the [HS-HS] complexes at room temperature. The analysis of correlations between the structural characteristics and different types of magnetic behaviour for new 1-3 binuclear complexes, as well as for previously reported binuclear compounds, revealed that the SCO process (occurrence of full one-step, two-step, or partial (50%) SCO) is specified by the degree of distortion of the octahedral geometry of the [FeN(6)] core, caused by both packing and strain effects arising from terminal and/or bridging ligands. The comparison of the magnetic properties and the networks of intra- and inter-molecular interactions in the crystal lattice for the family of related SCO binuclear compounds suggests that the intermolecular interactions play a predominant role in the cooperativeness of the spin transition relative to the intramolecular interactions through the bridging ligand.

Synthesis, electrochemical and antimicrobial studies of mono and binuclear iron(III) and oxovanadium(IV) complexes of [ONO] donor tridentate Schiff-base ligands

Tridentate Schiff bases (H2L1 or H2L2) were derived from condensation of acetylacetone and 2-aminophenol or 2-aminobenzoic acid. Binuclear square pyramidal complexes of the type [M2(L1)2] · nH2O (M = Fe–Cl, n = 0; M = VO, n = 1) were accessed from interaction of H2L1 with anhydrous FeCl3 and VOSO4 · 5H2O, respectively. A similar reaction with H2L2, however, produced mononuclear complexes [ML2(H2O) x ] · nH2O (M=Fe–Cl, x = 0, n = 0; M=VO, x = 1, n = 1). The compounds were characterized using elemental analysis, FT-IR, UV-Vis, and NMR (for ligand only), and mass spectroscopies and solution electrical conductivity studies. Magnetic susceptibility measurements suggest antiferromagnetic exchange in binuclear Fe(III) and VO(IV) complexes. Thermo gravimetric analysis (TGA) provided unambiguous evidence for the presence of coordinated as well as lattice water in [VOL2(H2O)] · H2O. Cyclic voltammetric studies showed well-defined redox processes corresponding to Fe(III)/Fe(II) and VO(V)/VO(IV). In vitro antimicrobial activities of the compounds were investigated against Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas aeroginosa, Escherichia coli, Bacillus subtilis, and Proteus vulgaris. H2L1 and its binuclear complexes exhibited pronounced activity against all the microorganisms tested.

Physicochemical study of binuclear copper(II), oxovanadium(IV), and iron(III) complexes with bis-1′-phthalazinylhydrazone of 2,6-diformyl-4-tert-butylphenol

Binuclear copper(II), oxovanadium(IV), and iron(III) complexes with bis-1′-phthalazinylhydrazone of 2,6-diformyl-4-tert-butylphenol have been prepared. An antiferromegnetic exchange interaction between the paramagnetic centers was found. Redox properties of the complexes were studied by the methods of cyclic and differential pulse voltammetry; the reduction of Cu(II) complexes was shown to proceed in two consecutive one-electron steps.

ChemInform Abstract: Hydroxylation of Alkanes and Arenes Using Molecular Oxygen.

A novel µ-oxo binuclear iron complex [{Fe-(HBpz3)(hfacac)}2O] was found to be effective for dioxygen hydroxylation of alkanes and arenes including pentane and benzene in the presence of Hhfacac and Zn powder.

ChemInform Abstract: Activation of Dioxygen by Catecholate Binuclear Iron Complexes for Alkane Hydroxylation. A Chemical Model for Methane Monooxygenase.

A new model is proposed for methane monooxygenase activation of O 2 on binuclear catecholate iron complexes as catalytic centres in the presence of hydrazobenzene as a reducing agent, to oxidize alkanes (including methane).

On the nature of a compound formed from dinitrosyl-iron complexes with cysteine and responsible for a long-lasting vasorelaxation

The nature of a compound able to induce long-lasting (⩾20 min) relaxation of rat abdominal aorta rings after addition of rapidly (within several minutes) disappeared mono- and binuclear dinitrosyl iron complexes with cysteine (M- and B-DNICs, respectively) (10 μmol) to the Krebs medium has been investigated. It has been found that long-lasting vasorelaxation is not induced either by S-nitrosocysteine formed upon decomposition of DNICs or by accumulation of free nitric oxide molecules or nitrite remaining in the incubation medium. Long-term air bubbling of the Krebs medium initially containing М-DNIC is accompanied by conversion of the complex first into B-DNIC, which represents a Roussin’s red salt cysteine ester and then into a more stable diamagnetic compound Х, which displays an intense absorption band at 278 nm. Compound X is decomposed after treatment with the strong bivalent iron chelator bathophenanthroline disulfonate (BPDS) and N-methyl- d-glucamine dithiocarbamate (MGD). The MGD-induced decomposition of compound Х is concomitant with the formation of EPR-detectable mononitrosyl iron complexes with MGD. Treatment of compound X with cysteine results in its decomposition and the appearance of optical absorption bands characteristic of М- and B-DNICs. Evidently, compound Х, has an iron-nitrosyl origin similar to that of М- and B-DNICs and its formation in oxygenated DNIC solutions is determined by the lowering cysteine content in them. It is hypothesized that compound X represents a cysteine ester of nitrosyl iron complexes, namely, a black Roussin’s salt cysteine ester responsible for long-lasting vasorelaxation initiated by addition of М- and B-DNICs that are rapidly decomposed to compound X to the incubation medium.

Contribution of direct and indirect exchange interaction to binuclear iron complexes

The analysis of temperature dependences of magnetic moment of several new iron nitrosyl complexes in solid phase allowed the value of exchange interaction ( J) between two iron ions to be estimated in each type complexes and a systematic decrease of J together with the increase in the ESR linewidth with a distance between iron ions to be observed. It was found that exchange interaction in the complexes involves two components, namely, direct exchange interaction and indirect one transferred through organic ligands.

Synthesis, crystal structure, magnetic property, and nuclease activity of a binuclear iron(III) complex

A μ-oxo-di-μ-carboxylato-bridged iron(III) complex containing two tridentate nitrogen ligands, {[Fe2(bpma)(bpea)(μ-CH3COO)2 μ-O)] · (ClO4)2 · 0.5CH3OH} (1) (bpma = N, N-bis(2-pyridylmethyl)methyl-amine, bpea = N,N-bis(2-pyridylmethyl)ethylamine), has been synthesized and determined by X-ray diffraction. Complex 1 crystallizes in the monoclinic space group P21/c with a = 10.9434(12) Å, b = 23.118(3) Å, c = 15.8721(18) Å, β = 92.736(2)° and Z = 4. In 1, each Fe(III) has a distorted octahedral geometry with a N3O3 donor set. The Fe(III) atoms are bridged by two carboxyl groups and one μ-oxo oxygen with Fe1–Fe2 separation of 3.064 Å. Susceptibility data of 1 indicate strong intramolecular antiferromagnetic coupling of the high-spin Fe(III) atoms with J = −121.0 cm−1 and g = 2.04. The interaction with calf thymus DNA was investigated by UV absorption and fluorescent spectroscopy. Results show that the complex binds to ct-DNA with a moderate intercalative mode. The interaction between 1 and pBR322 DNA has also been investigated by submarine gel electrophoresis; the complex exhibits effective DNA cleavage activity in the absence of activating agents under similar physiological conditions.