Fe Pc Research Articles

Hetero trinuclear oxo-bridged complexes of ruthenium porphyrin and iron phthalocyanine

New diamagnetic hetero bi- and trinuclear oxo-bridged metal complexes of formula (L)(Pc)Fe-O-Ru(TPP')(O) and (L)(Pc)Fe-O-Ru(TPP')-O-Fe(Pc)(L) have been prepared from Ru(TPP')(O)2 and Fe(Pc)(L)2 (TPP' = tetrakis(4-methoxyphenyl)porphyrinate, Pc = phthalocyanate ion, L = monodentate ligand). The trinuclear complex binds a variety of ligands (4,4'-bipy, 4-MePy, P(OEt)3, pip, NH3, 1-MeIm, P(Me)2Ph) trans to the oxo-bridge. 1H NMR spectra are characterized by large ring current shifts (rcs) due to the TPP' and Pc ions. The complexes show an unusually weak Pc Q band in their visible spectra at 700 nm and two CT bands in the near-IR region from 1000 to 1500 nm, which are sensitive to the trans ligand. The trinuclear complex can be reversibly oxidized to the +1 and +2 ions, formally Fe(IV)-O-Ru(IV)-O-Fe(III) and Fe(IV)-O-Ru(IV)-O-Fe(IV) at 0.4 and 0.76 V. The +1 ion is chemically obtained by reaction of the neutral species with (Cp)2Fe+ for L = 4-MePy and this reaction is reversed upon addition of L' = P(Me)2Ph. Reductive cleavage by hydroquinone, phosphines and phosphites are the slowest of all RuTPP[O(FeN4)]2 systems studied to date (t1/2 = 8 h at 40°C).Key words: ruthenium, iron, porphyrin, phthalocyanine, oxo.

Giant negative magnetoresistance of one-dimensional conductor TPP[Fe(Pc)(CN) 2] 2

We found the giant negative magnetoresistance in TPP[Fe(Pc)(CN) 2 ] 2 below 50K. The magnetic susceptibility shows a highly anisotropic Curie behavior. Under the field along the α-axis (the c-axis), we observed the large (small) negative magnetoresistance and the large (small) magnetic susceptibility. This experimental results suggest the π-d interaction between the one-dimensional conduction electrons and the local magnetic moments. We proposed the field-induced reduction of the spin scattering of the conduction electrons by the local moments as the origin of the negative magnetoresistance. In the isostructural compound TPP[Co(Pc)(CN) 2 ] 2 without magnetic moments, we observed large positive magnetoresistance. The experimental result of the Co-compound suggests that the local moments are essential for the mechanism of the negative magnetoresistance of the Fe-compound.

Iron(II) Phthalocyanine-Modified Carbon-Paste Electrode for Potentiometric Detection of Ascorbic Acid

A chemically modified electrode constructed by incorporating iron(II) phthalocyanine [Fe(II)Pc] into carbon-paste matrix was used as a sensitive potentiometric sensor for detection of ascorbic acid. The resulting electrode exhibits catalytic properties for the electrooxidation of ascorbic acid, and lowers the overpotential for the oxidation of this compound. The faster rate of electron transfer results in a near-Nernstian behavior of the modified electrode, and makes it a suitable potentiometric sensor for detection of ascorbic acid. A linear response in concentration range from 10−6 to 10−2 M (0.18–1800 μg ml−1) was obtained with a detection limit of 5 × 10−7 M for the potentiometric detection of ascorbic acid. The modified electrode was used for the determination of ascorbic acid in vitamin preparations. The recovery was 97.2–102.4% for the vitamin added to the preparations with a relative standard deviation of less than 5%. The modified electrode exhibited a fast response time (<10 s),had good stability, and had an extended lifetime.

Hetero trinuclear oxo-bridged complexes of ruthenium porphyrin and iron phthalocyanine

New diamagnetic hetero bi- and trinuclear oxo-bridged metal complexes of formula (L)(Pc)Fe-O-Ru(TPP')(O) and (L)(Pc)Fe-O-Ru(TPP')-O-Fe(Pc)(L) have been prepared from Ru(TPP')(O)2 and Fe(Pc)(L)2 (TPP' = tetrakis(4-methoxyphenyl)porphyrinate, Pc = phthalocyanate ion, L = monodentate ligand). The trinuclear complex binds a variety of ligands (4,4'-bipy, 4-MePy, P(OEt)3, pip, NH3, 1-MeIm, P(Me)2Ph) trans to the oxo-bridge. 1H NMR spectra are characterized by large ring current shifts (rcs) due to the TPP' and Pc ions. The complexes show an unusually weak Pc Q band in their visible spectra at 700 nm and two CT bands in the near-IR region from 1000 to 1500 nm, which are sensitive to the trans ligand. The trinuclear complex can be reversibly oxidized to the +1 and +2 ions, formally Fe(IV)-O-Ru(IV)-O-Fe(III) and Fe(IV)-O-Ru(IV)-O-Fe(IV) at 0.4 and 0.76 V. The +1 ion is chemically obtained by reaction of the neutral species with (Cp)2Fe+ for L = 4-MePy and this reaction is reversed upon addition of L' = P(Me)2Ph. Reductive cleavage by hydroquinone, phosphines and phosphites are the slowest of all RuTPP[O(FeN4)]2 systems studied to date (t1/2 = 8 h at 40°C).Key words: ruthenium, iron, porphyrin, phthalocyanine, oxo.

M(mu-CN)Fe(mu-CN)M' chains with phthalocyanine iron centers: redox, spin-state, and mixed-valence properties.

Dinuclear complexes with M-CN-ZnPc and M-CN-FePc-CN arrays and trinuclear complexes with M(mu-CN)Fe(mu-CN)M' arrays containing central metal phthalocyaninato (Pc) and external Cp(dppe)Fe or Cp(PPh3)2Ru building blocks (M) and having all possible orientations of the bridging cyanide ligands were subjected to electrochemical and preparative redox reactions. The species with unpaired electrons show characteristic MMCT bands in the near-IR spectra, the energies of which depend in a typical fashion on the nature of the building blocks and the orientation of the cyanide bridges and can be correlated with the redox potentials. Cyclic voltammetry has revealed electronic communication between the external organometallic units. An analysis of the MMCT spectra allows the assignment of the odd-electron complexes as class II mixed-valence species. The magnetic moments of the complexes with central Fe(III)Pc units are characteristically higher than the spin-only value for one unpaired electron. A Mössbauer investigation has shown that the M-CN-Fe(III)Pc-NC-M complexes undergo a low-spin-to-high-spin crossover of the Fe(III) component above room temperature.

M(mu-CN)Fe(mu-CN)M' chains with phthalocyanine iron centers: preparation, structures, and isomerization.

The molecular building blocks Fe(II)Pc (Pc = phthalocyaninato2-), Fe(III)Pc, ZnPc, Cp(dppe)Fe, and Cp(PPh3)2Ru were combined in the cyanide-bridged dinuclear reference compounds with M-CN-ZnPc and M-CN-FePc-CN arrays containing Fe(II)Pc and Fe(III)Pc. The linear trinuclear species with the M(mu-CN)Fe(mu-CN)M' backbone were prepared for both Fe(II)Pc and Fe(III)Pc centers, for terminal Fe/Fe, Fe/Ru, and Ru/Ru combinations and for all three possible cyanide orientations (M-CN-Fe-NC-M', M-CN-Fe-CN-M', and M-NC-Fe-CN-M'). The 15 complexes obtained were identified from their IR spectra and six structure determinations. The preferred orientation of the cyanide bridges could be established starting from the [Fe-NC-Fe(III)Pc-CN-Fe]+ complex, which is labile in solution and isomerizes to the corresponding [Fe-CN-Fe(III)Pc-NC-Fe]+ complex. A kinetic analysis of this isomerization has yielded an activation barrier of roughly 110 kJ/mol.

Giant Negative Magnetoresistance in One-Dimensional π-d System : TPP[Fe(Pc)(CN)2]2 (TPP = tetraphenylphosphonium, Pc = phthalocyanine)

We found the giant negative magnetoresistance in the one-dimensional π-d system TPP[Fe(Pc)(CN)2]2 below 50K. The large negative magnetoresistance was observed for the field along the a-axis, while the small one along the c-axis. We also observed the anisotropic Curie behavior of the magnetic susceptibility. The large (small) magnetoresistance was observed in the field orientation for the large (small) magnetic susceptibility. The reduction of the spin-flip scattering of the itinerant electrons by the local moments under the magnetic field was proposed as the origin of the negative magnetoresistance. In the isostructural compound TPP[Co(Pc)(CN)2]2 we observed the large positive magnetoresistance. This positive magnetoresistance cannot be explained in terms of the orbital effects under the field.

A one-dimensional macrocyclic π‐ligand conductor carrying a magnetic center. Structure and electrical, optical and magnetic properties of TPP[Fe(Pc)(CN)2]2 {TPP = tetraphenylphosphonium and [Fe(Pc)(CN)2] = dicyano(phthalocyaninato)iron(iii)}

A conducting partially oxidized salt of TPP[Fe(Pc)(CN)2]2, which contains paramagnetic iron(III), has been obtained by electrocrystallization of TPP[Fe(Pc)(CN)2]. The crystal is composed of one-dimensional TPP arrays surrounded by slipped-stacked one-dimensional Fe(Pc)(CN)2 chains. This structure is isomorphous with TPP[Co(Pc)(CN)2]2, in which the central metal is non-magnetic cobalt(III). The electrical conductivity at room temperature, ca. 10 Ω−1 cm−1, is about one order of magnitude lower than that of the Co analogue. On lowering the temperature, the conductivity shows a much steeper decline compared with the temperature dependence of the conductivity of TPP[Co(Pc)(CN)2]2. The band width, estimated from both thermoelectric power measurements (which show apparent metallic behavior at high temperatures) and an extended Huckel calculation, is found to be the same as that obtained for TPP[Co(Pc)(CN)2]2. This is consistent with observations from the single-crystal reflectance spectra, in which both partially oxidized salts show almost the same plasma edge. On the other hand, the magnetic susceptibility of TPP[Fe(Pc)(CN)2]2 is quite different from that of TPP[Co(Pc)(CN)2]2; both of the magnetic moments originated from FeIII and the π-radical seem to be localized in TPP[Fe(Pc)(CN)2]2, while the moments originated from the π-radical in TPP[Co(Pc)(CN)2]2 are interacting with each other to lead to temperature-independent Pauli-like susceptibility. At low temperatures, a decrease in the susceptibility has been observed, suggesting the existence of antiferromagnetic interactions.

Phthalocyanine Molecular Conductors with Paramagnetic Iron(III)

Paramagnetic Fe(III) has been introduced into molecular conductors based on axially substituted metal phthalocyanine for the purpose of constructing a system which has magnetic spins on the conduction paths. Some crystals have been obtained from the electrochemical oxidation of [Fe(III)(Pc)(CN) 2] −. The crystal structures are the same as the cases where the metal ion is Co(III), but their physical properties are quite different.

Use of cobalt(II) phthalocyanine to improve the sensitivity and stability of glassy carbon electrodes for the detection of cresols, chlorophenols and phenol

A cobalt(II) phthalocyanine-modified glassy carbon electrode (CoPc-GCE) was used for the detection of o-, m- and p-cresols, and of 2-chlorophenol, 4-chlorophenol and phenol. Modification of the glassy carbon electrode with CoPc increases the oxidation currents of these species and increases the stability of the electrode. CoPc-GCE showed less fouling by the oxidation products of these compounds than the unmodified GCE. Comparison of some first row transition metal phthalocyanines showed the following trend for the enhancement of the currents for the oxidation of cresols and phenols: Co(II)Pc > Mn(II)Pc > Fe(II)Pc > Ni(II)Pc > Cu(II)Pc > H 2Pc > Zn(II)Pc > GCE. When [Co(II)TSPc] 4− (TSPc=tetrasulfo Pc) was added to aqueous solutions containing the cresols and phenols, an enhancement of the oxidation currents was also observed.

Synthesis, electrochemical, and electrical properties of (phthalocyaninato)iron complexes with azopyridines

Syntheses of phthalocyaninatoiron complexes, Fe(Pc b)L 2 and [Fe(Pc tb) L] n where Pc b = tetra- tert-butylphthalocyaninato, L = 4,4′-azopyridine (4,4′-APy) or octafluoro-4,4′-azopyridine (4,4′-FAPy), were carried out. These complexes were characterized with TG/DTA, 1H NMR, UV-visible spectroscopy, and cyclic voltammetry. Vpltammetric measurements of soluble Fe(Pc b)L 2 in benzene solutions revealed that coordination of axial ligands on Fe(Pc b) greatly influenced oxidation potentials of the central metal moiety. The correlation between conductivities of polymeric [Fe(Pc b)L] n complexes and bandgaps determinedby the voltammetric measurements was identified.

Electrical properties of iodine-doped materials comprised of (phthalocyaninato)iron and azopyridines

The preparation and electrical properties of iodine-doped phthalocyaninatoiron polymers [Fe(Pc)L]I y n and[Fe(Pc b)L]I y n Pc = phthalocyaninato, Pc b = tetra- tert-butylphthalocyaninato, L = 4,4′-azopyridine(4,4′-APy) and octafluoro-4,4′-azopyridine (4,4′-FAPy) were investigated The stoichiometry of polymer complexes was determined by TG/DTA. The iodine-doped [Fe(Pc)(4,4′-APy)]I y n complexes were semiconducting materials in the range of 10 −4 to 10 −10S/cm.

Reaction of μ-oxobis(phthalocyaninatoiron(III)) in pyridine/water. Evidence for a slow reacting oxophthalocyaninatoiron(IV) compound

The reaction of μ-oxobis(phthalocyaninatoiron(III)) in pyridine containing small amounts of water has been investigated. The reaction occurs in two consecutive steps. The first step is a disproportionation equilibrium ( K = 1.0×10 −3 mol dm −3 at 35 °C) yielding [(py) 2Fe(II)(pc)] and the ferryl compound [(py)Fe(IV)(pc)O]. The spectrum of the latter in the 600–700 nm range shows the shape characteristic of phthalocyaninato derivatives with a high intensity Q band ( ϵ = 7.5 × 10 4) at 670 nm. During the succedding step, that requires several hours to be completed, the FeO oxygen is transferred to peripheral sites of the macrocycle, very likely to form C-OH groups. This fact does not modify appreciably the electronic properties of the complex, if compared to those of [(py) 2Fe(pc)], and can be revealed only by FAB experiments which show the presence of phthalocyaninato derivatives of mass 568 + 16 and 568 + 32 (568 being the mass of the molecular ion [Fe(pc) +]. The first step of this reaction representes a convenient method for preparing pyridine solutions of the ferrylic species, suitable for reactivity studies.

Equilibrium and kinetic study of piperidine binding to phthalocyaninatoiron(II) in dimethyl sulfoxide

The reaction between piperidine (Pip) and phthalocyaninatoiron(II) ([Fe(pc)]) in dimethyl sulfoxide (dmso) has been studied at 20.0 °C, from both equilibrium and kinetic viewpoints. In excess of Pip, the adduct [Fe(pc)(Pip) 2] is formed via two consecutive pseudo-first-order processes. The observed rate constants have the general form: k obs= k 1f[Pip] + k 1r with k 1f′ = (8.7 ± 0.2) × 10 3 dm 3 mol −1 s −1 and k 1f″ = (8.3 ± 0.2) × 10 1 dm 3 mol −1 s −1, for the binding of the first and second Pip molecule, respectively. Equilibrium experiments yield K 1′ = (1.0 ± 0.1) × 10 5 dm 3 mol −1 and K 1″ = (1.3 ± 0.1) × 10 3 dm 3 mol −1 for the stepwise formation of the [Fe(pc)(dmso)(Pip)] and [Fe(pc)(Pip) 2] adducts, respectively. From the values of the second-order rate constants ( k 1f′ and k 1f″) and of the equilibrium constants ( K 1′ and K 1″), the dissociation rate constants have been estimated to be k 1r′= (8.7 ± 1) × 10 −2 s −1 and k 1r″ = (6.4 ± 0.7) × 10 −2 s −1. Present results are discussed in the light of related previous studies.

Ac Impedance, sem and edax study of the passivation of a carbon cathode in LiAlCl 4SOCl 2 electrolyte

The cathodic passivation of porous carbon electrodes in a LiAlCl 4SOCl 4 electrolyte and the effect of ferro-phthalocyanine (FePc) were studied by ac impedance, scanning electron microscopy and X-ray energy dispersion analysis. It was found that the reduction mechanism of SOCl 2 at earlier stages of discharge is different from that at later stages. The cause of complete passivation of porous electrodes seems to be the deposition of a large quantity of solid materials containing elemental sulphur. An FePc additive in the electrolyte has little effect on the porous carbon electrodes before discharge. However, upon cathodic polarization the nature of the primary film was found to be modified by addition of the FePc, resulting in the decrease of the rate of formation of deposits on the inner surfaces of pores and delay of the passivation of the porous carbon electrode.

Interaction of cyanide with iron(II) phthalocyanine: kinetics and equilibria

The kinetics and equilibria for the reaction between cyanide and iron(II) phthalocyanine [Fe(pc)](H2pc = phthalocyanine) in dimethyl sulfoxide (dmso) were studied at 25 °C. The complex [Fe(pc)(CN)2]2– is formed in two consecutive pseudo-first-order processes with k2f= 17.5 ± 0.8 dm3 mol–1 s–1 and k3f= 0.20 ± 0.05 dm3 mol–1 s–1, where k2f and k3f are the rate constants for the binding of the first and second cyanide ligands, respectively. The equilbrium constants were fund to be K2= 3.0 × 103 dm3 mol–1 and K3= 5.7 × 102 dm3 mol–1, for the formation of [Fe(pc)(CN)(dmso)]– and [Fe(pc)(CN)2]2–, respectively.

Electrochromism in the transition-metal phthalocyanines. Part 3.—Molecular organisation, reorganisation and assembly under the influence of an applied electric field. Response of [Fe(pc)] and [Fe(pc)Cl

The electrochromic behaviour of α-[Fe(pc)] and [Fe(pc)Cl] has been studied, using cyclic voltammetry, electronic absorption spectroscopy and Mossbauer spectroscopy, the latter on 57Fe-enriched [Fe(pc)] films. [Fe(pc)] films have been shown to cycle reversibly ca. 103 times between neutral (blue) and reduced (purple-red) states (negative voltages), but decompose when oxidised repeatedly (positive voltages) in aqueous KCI electrolytes. When oxidised then reduced in < ca. 1 s [Fe(pc)Cl] is formed. This indicates that the Cl– ion adds as a ligand during the electrochromic oxidation and this takes place concomitantly with a lattice reorganisation. [Fe(pc)] films on oxidation produce red [FeIII(pc˙)Cl2] and contain a (pc˙) phthalocyanine radical anion. On reduction to neutral they become [Fe(pc)Cl].[Fe(PC)Cl] films have been shown to reduce electrochromically from an initial green film to a purple reduced film without first becoming [Fe(pc)]. However, on reoxidation to neutral, a blue [Fe(pc)] film is formed; this then behaves like a normal [Fe(pc)] film. These studies show that the axial Cl–on [Fe(pc)Cl], once removed, passes out of the lattice during the electrochromic reduction, and that under the influence of the field the lattice reorganises, assembling predominantly as the α-[Fe(pc)] phase.This is the first attempt to explain widespread lattice reorganisation that involves metallophthalocyanines with axial ligands attaching and detaching under controlled voltage.

Reactivity of chloro(phthalocyaninato)iron(III) in pyridine–water

The reaction of [Fe(pc)Cl](pc = phthalocyaninate) in water-containing pyridine (py) has been followed by spectrophotometric and conductometric techniques. It is a two-step process: the first step is first-order on [H2O] and is accompanied by an increase in conductance, the second is kinetically independent of water and does not involve ionic species. The complex [Fe(pc)(py)2] is formed during both steps and about 70–80% of the initial iron(III) is finally recovered in this form. The infinite-time conductance is quantitatively explained in terms of 100% formation of py·HCI. Addition of PPh3 has a remarkable effect: when added to py before[Fe(pc)Cl] the second step tends to vanish as the concentration of PPh3 increases and, for [PPh3] 4 × 10–3 mol dm–3 the overall reaction appears as a one-step process; if the phosphine is added after the first step and before the second two consecutive reactions take place, the first kinetically phosphine-dependent, the second independent of PPh3. Virtually quantitative oxidation to OPPh3 occurs when the complex is allowed to react with a slight excess of PPh3. The observations are explained in terms of a rapid Cl– release from [Fe(pc)Cl(py)] to give [Fe(pc)(py)2]+, Cl– which, in turn, undergoes substitution of an axial py by water. A hydroxo species forms which readily dimerises and the dimer disproportionates to give [Fe(pc)(py)2] and the iron(IV) species [Fe(pc)O(py)]. Considerations based on the instability of analogous oxoporphyrinatoiron(IV) species and on the nearly 75% overall yield of [Fe(pc)(py)2] lead to the suggestion that the iron(IV) compound is in the form of a µ-peroxo or di-µ-oxo dimer.

X-Ray crystal structure of µ-oxo-bis[(1-methylimidazole)-phthalocyaninatoiron(III)] and comments on the molecular structure and chemistry of oxo-bridged iron phthalocyaninate dimers

Single-crystal X-ray work has been carried out on crystals containing the 1-methylimidazole adduct of µ-oxo-bis[(phthalocyaninato)iron(III)], [{Fe(pc)(mim)}2O]·[Fe(pc)(mim)2]·3Me2CO. The crystals are monoclinic, space group C2/c, with a= 35.236(5), b= 14.173(2), c= 23.220(3)Å, β= 103.56(10)° and Z= 4. The structure was solved and refined using all data including zero intensities (5739). Only the atoms of the µ-oxo dimer were refined anisotropically because of data limitations. The Fe atoms in [{Fe(pc)(mim)}2O] are nominally centred in the phthalocyanine plane, with an average Fe–N(pc) of 1.92(3)Å and six-co-ordinate, with Fe–O 1.749(1)Å and Fe–N(mim) 2.039(7)Å. The Fe–O–Fe angle is 175.1°. X-Ray data for [Fe(pc)(mim)2] are as expected for six-co-ordinate low-spin nitrogen-containing base adducts of [Fe(pc)]. The crystal data are discussed in the light of similar results on [{Fe(pc)(mim)}2C] and related compounds.

Nitrosyl–nitro redox couples with metal phthalocyanines: synthesis and characterization of nitro derivatives of cobalt and iron phthalocyanine, dioxygen activation, oxygen-atom transfer and stoichiometric and catalytic oxidation of terminal olefins

The complexes [Co(pc)(NO2)(py)]·dce, [Co(pc)(NO2)(py)]·thf, and [Fe(pc)(NO2)(py)](pc = phthalocyaninate, py = pyridine, dce = 1,2-dichloroethane and thf = tetrahydrofuran) have been isolated as stable crystalline materials. Their molecular and electronic structures have been investigated by IR and UV/VIS spectra, X-ray powder patterns, thermogravimetric and magnetic susceptibility measurements and Mossbauer spectra. The complexes should be regarded as six-co-ordinate low-spin cobalt(III) and iron(III) species. Reference is also made to their corresponding five-co-ordinate nitrosyl derivatives, [Co(pc)(NO)] and [Fe(pc)(NO)]. The Co(pc)– and Fe(pc)–NO/NO2 systems have been studied with regard to their dioxygen activation and oxygen-atom-transfer reactions, in the oxidation of terminal olefins to the corresponding methyl ketones. Whereas oxidation with the Co(pc)–NO/NO2 redox couple is nearly stoichiometric, catalytic and selective oxidation occurs with the parallel Fe(pc) system.