Cobalt Phthalocyanine Complexes Research Articles

Self‐Assembled Monolayers of Cobalt and Iron Phthalocyanine Complexes on Gold Electrodes: Comparative Surface Electrochemistry and Electrocatalytic Interaction with Thiols and Thiocyanate

AbstractThe self‐assembling of the octa(hydroxyethylthio)‐metallophthalocyanine {MOHETPc (M=Co and Fe)} complexes and their similar analogues, octabutylthiometallophthalocyanine {MOBTPc (M=Co and Fe)} complexes on gold electrodes are investigated. Comparative surface voltammetric insights into their distinct self‐assembling properties with respect to the passivation of Faradaic processes and surface coverages, including their solution electrochemistry, suggest different orientations and non‐cleavage of their CS bonds. In the pH 2−9 range, the reversible [M(III)Pc(−2)]+ / [M(II)Pc(−2)] redox couples show potential shifts close to −59 mV / pH. The gold electrodes modified with the SAMs of these species show electrocatalytic activity towards the oxidation of thiols (L‐cysteine, homocysteine and penicillamine) and thiocyanate in acidic media with detection limits in the region of 10−7–10−6 mol dm−3. These monolayers are stable and easily reproducible.

Catalytic activity of iron and cobalt phthalocyanine complexes towards the oxidation of cyclohexene using tert-butylhydroperoxide and chloroperoxybenzoic acid

Cyclohexene oxidation using tert-butylhydroperoxide (TBHP) or chloroperoxybenzoic acid (CPBA) in the presence of iron(II) polychlorophthalocyanine (Cl16PcFe), iron(II) phthalocyanine (PcFe) and cobalt(II) phthalocyanine (PcCo), results in the formation of the following products: cyclohexene oxide, 2-cyclohexene-1-ol and 2-cyclohexene-1-one. Adipic acid was also formed after long reaction times. The selectivity for 2-cyclohexene-1-one is favoured when Cl16PcFe or PcCo catalysts are employed, while PcFe is selective towards the formation of 2-cyclohexene-1-ol. The Cl16PcFe catalyst is transformed into a μ-oxo dimer (Cl16PcFeIIIOIIIFePcCl16) during the oxidation process. The catalytic process using the unsubstituted PcCoII and PcFeII catalysts involved PcMIII species as an intermediate. The active form of the Cl16PcFe catalyst was stable to degradation in that it was still active even after 4 weeks of continued catalysis.

Synthesis, spectral and electrochemical properties of a new family of pyrrole substituted cobalt, iron, manganese, nickel and zinc phthalocyanine complexes

A new family of pyrrole substituted metallophthalocyanine complexes, namely cobalt(II), iron(II), manganese(III), nickel(II) and zinc(II) tetrakis-4-(pyrrol-1-yl)phenoxy phthalocyanines (noted as M ( TPhPyrPc ), where M is the metallic cation) have been synthesized and fully characterized. In particular, the UV-visible spectra of the iron and nickel complexes showed extensive aggregation even at low concentrations. The cyclic voltammetry of the cobalt, iron and manganese complexes showed three to four redox couples assigned to metal and ring based processes. Spectroelectrochemistry of the manganese derivative confirmed that the synthesized complex is Mn III( TPhPyrPc -2) and that the reduction of Mn II( TPhPyrPc -2) to be centred on the ring and rather than on the metal, forming the Mn II( TPhPyrPc -4) species. Also, the electrochemical polymerization of these newly synthesized pyrrole-substituted phthalocyanines has been demonstrated in the case of the cobalt complex and the electrocatalytic activity of the obtained film has been tested towards the oxidation of L-cysteine.

Phthalocyanine modified TiO2 or WO3-catalysts for photooxidation of sulfide and thiosulfate ions upon irradiation with visible light

The photooxidation of Na2S or Na2S2O3, catalyzed by Al2O3, TiO2 or WO3 superficially modified with metal-free phthalocyanine complex (Pc), cobalt phthalocyanine complex (CoPc) and copper phthalocyanine complex (CuPc), has been studied upon irradiation with visible light. The rates of the substrate photooxidation, catalyzed by the phthalocyanine complexes supported on TiO2 or WO3, are much higher than those registered with the same complexes, anchored on Al2O3. The high photocatalytic activity of the samples is explained by an electron transfer from the conduction band of the excited phthalocyanine semiconductor particles to the conduction band of the TiO2 or WO3 supports. The increase of the quantum yield of the photocatalytic redox process comes as a result of the additional formation of superoxide radicals on the TiO2 or WO3 conduction bands. A complete oxidation of Na2S or Na2S2O3 to sulfates has been registered in the presence of the studied photocatalysts.

New Rigid Conducting Composites for Electrochemical Sensors

In this work, a novel sonogel-carbon material, obtained via a sonocatalytic procedure, is proposed as a matrix for the preparation of composite electrodes. This material combines the electrical properties of graphite with the mechanical resistance of the sonogel network; an electroactive phase is incorporated inside to give a system with peculiar redox properties. Ni/Al-Cl hydrotalcite and cobalt phthalocyanine complex were used to this end. The electrochemical behaviour of the sonogel-carbon-Ni/Al-Cl and of the sonogel-carbon-cobalt phthalocyanine composites is studied by cyclic voltammetry. These electrodes are stable and lead to repeatable responses. The responses have been compared with those of similar electrodes without added graphite. Key points of the electrochemical behaviour have been identified and discussed and the electrocatalytic capabilities have been investigated on oxidisable substrates, on methanol and on cysteine.

Electrocatalytic activity of cobalt phthalocyanine stabilized by different matrixes.

The behavior of cobalt phthalocyanine complexes incorporated inside an hydrotalcite-like clay (HT) or a sonogel-carbon composite has been investigated in order to develop chemically modified electrodes suitable for use as amperometric detectors. The electrocatalytic oxidation process of cysteine at this new electrode has been studied by cyclic voltammetry. For comparison, the oxidation of cysteine catalyzed by the cobalt phthalocyanine complex as a redox mediator, either dissolved in solution or entrapped inside the HT structure, has been followed by polarography. The sonogel-carbon composite electrode is stable and its response is repeatable. Cysteine oxidation is actually induced by the electrogenerated Co(III) complex, and the relevant anodic peak current varies linearly with cysteine concentration within the range 9.0x10(-4) to 1.0x10(-2) mol L(-1).

Cyclic voltammetric studies of octabutylthiophthalo-cyaninato-cobalt(II) and its self-assembled monolayer (SAM) on gold electrode

The synthesis of thiol-derivatized cobalt phthalocyanine complex, 2,3,9,10,16,17,23,24-octa (butylthiophthalocyaninatocobalt(II) ( CoOBTPc ) is described. Cyclic voltammetric data of this complex in DMF showed five quasi-reversible and reversible, diffusion-controlled redox couples, comprising both the phthalocyanine ring and central metal redox processes. The CoOBTPc complex forms a self-assembled monolayer (SAM) on gold electrode. The investigation of the integrity of this SAM, using the established cyclic voltammetric methods in aqueous alkaline solutions, gave evidence about the formation of a stable and easily reproducible monolayer. However, due to its susceptibility to destruction via oxidative and reductive desorptions, its potential application as an electrochemical sensor in alkaline pH is limited to a potential window of between −0.20 and +0.55 V vs Ag / AgCl .

Photooxidation of sodium sulfide and sodium thiosulfate under irradiation with visible light catalyzed by water soluble polynuclear phthalocyanine complexes

The catalytic and photocatalytic activities of polynuclear water soluble phthalocyanine complexes, [CoPc(COOH) n ] poly, [ZnPc(COOH) n ] poly, [AlPc(COOH) n ] poly, and [Pc(COOH) n ] poly, have been investigated in the oxidation of Na 2S and Na 2S 2O 3. The studied complexes represent two-dimensional polymers, formed of condensed phthalocyanine macrocycles. The average number of the phthalocyanine units in them is, respectively: [CoPc(COOH) n ] poly≈4, [ZnPc(COOH) n ] poly≈4, [AlPc(COOH) n ] poly≈3, [Pc(COOH) n ] poly≈4. No visible bathochromic shifting is observed in the Q-band electron transition ( λ=665–680 nm) of the polynuclear complexes with respect to their mononuclear analogues. This fact is an indication of low π–π electron delocalization in excited state between the phthalocyanine units of the polynuclear complexes. The catalytic and photocatalytic activity per mole of the polynuclear complexes is 2–5 times higher than that of the respective mononuclear phthalocyanine complexes. In the dark or upon irradiation with visible light the cobalt(II) phthalocyanine complexes catalyze only the oxidation of Na 2S, which is proceeding incompletely to thiosulfate. The zinc, aluminum and non-metal polynuclear phthalocyanine complexes are active catalysts only in the case of irradiation with visible light. The photooxidation of substrates like Na 2S and Na 2S 2O 3 with the previously mentioned photosensitizers is proceeding completely, whereupon the valence state of the sulfur in the final products is S 6+. In this case the photooxidation process involves singlet oxygen. The high photocatalytic activity of the polymers might be explained by the proceeding of a intra-molecular triplet–triplet energy transfer between the phthalocyanine macrocycles in accordance with the mechanism of Dexter.

Catalytic Oxidative Polymerization of Vinyl Monomers Using Cobalt Phthalocyanine Complex and an Exploratory Investigation on the Polymerization of Vinyl Acetate

This is the first report on the oxidative polymerization of vinyl monomers using cobalt(II) phthalocyanine pyridine {CoIIPc(Py)} complex. The mechanism of polymerization is described and it has been supported from the kinetic data, UV−vis, ESR and 1H NMR studies. It is found that the rate of polymerizations (Rp) and number-average molecular weights (M̄n) of the vinyl polyperoxides are higher for CoIIPc(Py) catalyzed polymerization compared to the usual free radical, AIBN, initiated polymerization. This is supported by their activation energy of initiation (Ei) and total activation energy (Ea) of polymerization. The peroxide macroinitiator has been used for the polymerization of vinyl acetate. The polymerization obeys classical kinetics. The K2 values of the peroxide macroinitiator has been determined, which reveals that it can also be used at higher temperature for the polymerization compared to monomeric peroxide initiator, benzoyl peroxide. The “active” poly(vinyl acetate) has also been synthesized, which contains peroxy segments at the chain ends.

Electrocatalytic behavior of substituted cobalt phthalocyanines towards the oxidation of cysteine

Ring substituted cobalt phthalocyanine complexes of the form CoPc(X)4, (where X=NH2, NO2, C(CH3)3, SO3H and COOH) are compared for their catalytic activities towards the oxidation of cysteine. The potential for the electrocatalytic oxidation of cysteine is closely related to the CoIII/CoII couple of the CoPc(X)4 complexes in acidic media and to the CoII/CoI couple in basic media. The catalytic currents and the oxidation potential for cysteine are dependent on the pH of the solution, the potential becoming less positive as the pH increases and the catalytic currents decreasing with increase in pH, for the same concentration of cysteine. The magnitudes of the catalytic currents (after ten scans) for cysteine oxidation at pH 8.3 and on electrodes modified with the CoPc(X)4 complexes increased with the nature of the ring substituent as follows: NO2<NH2<SO3H<C(CH3)3<COOH.

Functional metallomacrocycles and their polymers, Part 37.: Oxidative decomposition of 2,4,6-trichlorophenol by polymer-bound phthalocyanines

Oxidative decomposition of 2,4,6-trichlorophenol (TCP) catalyzed by iron, manganese, and cobalt octacarboxyphthalocyanines and their polymer-bound derivatives was studied in aqueous solution. Iron octacarboxyphthalocyanine scarcely had catalytic activity in oxidative decomposition of TCP by H 2O 2, while extremely high catalytic activity was observed in the presence of water-soluble polymers having pyridinium side chains. When iron octacarboxyphthalocyanine complex was covalently bound to the water-soluble cationic polymer, it revealed much higher catalytic activity. 2,6-Dichloro- p-benzoquinone was formed in the initial period of the reaction and was decomposed to further low molecular weight compound. Formic acid, oxalic acid, chloropropenic acid, and two coupling products were found in the resulting solution by GC–MS analysis. Catalytic activity of polymer-bound iron phthalocyanine was strongly influenced by pH and the maximum activity was observed at pH 7. The pH-dependence of the catalytic activity was explained by the dissociation of TCP. Enhancement in catalytic activity by polymer chain was also observed in manganese and cobalt phthalocyanine complexes. Highly efficient dechlorination of TCP was concomitantly achieved by the polymer-bound iron and manganese phthalocyanine complexes, while polymer-bound cobalt phthalocyanine complex hardly cause the dechlorination.

Oxidation and photooxidation of sulfide and thiosulfate ions catalyzed by transition metal chalcogenides and phthalocyanine complexes

The catalytic and photocatalytic activities of supported cobalt or zinc phthalocyanine complexes, bulk MoS 2, MoS 2 deposited on Al 2O 3, potassium intercalated MoS 2 (K 0.33 H 2O 0.66 MoS 2), CdS and polycrystalline nickel phosphorus trisulfide (NiPS 3) have been investigated in the oxidation of sodium sulfide and Na 2S 2O 3. The phthalocyanine complexes and the metal chalcogenides do not catalyze, in the absence of light, the complete oxidation of the sulfide ion to sulfate ion. The final product of the catalytic oxidation is the formed thiosulfate. No oxidation of Na 2S 2O 3 has been registered in the dark in the presence of any of the catalytic samples. Their activity was enhanced upon irradiation with visible light. Thiosulfate appears to be the final product also of the photooxidation of the sulfide ion catalyzed by metal chalcogenides. They do not catalyze the further photooxidation of Na 2S 2O 3. The only photocatalysts which favour with their presence the oxidation of the sulfide and thiosulfate ions to sulfate ion, are the zinc phthalocyanine complexes. In this case, the photooxidation process involves singlet oxygen.

Oxidation and photooxidation of sulfur-containing compounds in the presence of immobilized phthalocyanine complexes

Immobilized cobalt(II) and zinc(II) phthalocyanine and SALEN complexes have been studied as catalysts or photocatalysts for oxidation of 2-mercaptoethanol and sodium thiosulfate. The complexes have been anchored on silica or intercalated in the galleries and cavities of layered double hydroxides (HT) and NaX zeolite. Both the degree of monomerization of phthalocyanine complexes and their activity as catalysts or photocatalysts, after intercalation within supports with well defined intracrystalline cavities, are higher than those observed for the complexes supported on SiO 2. The coadsorption of water in the galleries and cavities of hydrotalcite and the zeolite retards the diffusion of dioxygen and sulfur-containing compounds towards the active catalytic sites. For this reason the activity of the immobilized catalyst samples for the oxidation and photooxidation is lower than that of the complexes in homogeneous phase. After hydrophobic modification of hydrotalcite and NaX zeolite by dodecylsulfate or tetrabutylammonium ions the catalysts sample activity is increased 2–8 ×, because of the improved diffusion of the reactants towards the phthalocyanine molecules intercalated within the bulk of the supports. The degree of photodestruction of the zinc phthalocyanine complexes in the volume of the hydrotalcite or the faujasite is lower in comparison to that in homogeneous phase owing to the retarded diffusion of dioxygen towards the photoactive molecules. After hydrophobic modification of the catalysts samples the diffusion of dioxygen and quantum yield of the generated 1O 2∗ ( 1 Δ g) are promoted and the degree of photodestruction of the immobilized phthalocyanine complexes is increased. The stability of zinc phthalocyanine complexes intercalated within the bulk of hydrotalcite or NaX zeolite is quite higher than that in the homogeneous phase due to deactivation of the singlet dioxygen on the walls of the supports.

ChemInform Abstract: Transition‐Metal Complexes as Catalysts of Active Oxygen Species Formation in Autooxidation Reactions. Part 2. Oxidative Degradation of Nucleic Acids by Cobalt and Iron Phthalocyanine Complexes.

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Determination of CO 2( g) by enhancement of luminol—cobalt(II) phthalocyanine chemiluminescence: Analysis of atmospheric air and human breath

Two related continuous-flow sensing strategies are presented for the determination of CO 2( g) in gas mixtures. A continuous monitoring scheme is described for the determination of the analyte in atmospheric air, and a discrete sample introduction approach for the determination of the same analyte in human breath. The same chemical system is used in both cases, which is based on the CO 2( g) enhancement of luminol chemiluminescence in the absence of added oxidant and in the presence of cobalt(II) phthalocyanine complex as rate modifier. A specially designed reaction cell is at the heart of these determinations. The main analytical virtues of these approaches are simplicity, fast response, and a wide linear concentration range amenable to determination (in log-log relationships from about 50 ppm to 800 ppm v/v, and from 1% to 100% v/v CO 2( g).

Oxidation and photooxidation of sulfur-containing compounds in the presence of water soluble phthalocyanine complexes

Water soluble cobalt(II) 2,9,16,23-tetrasulfophthalocyanine, zinc(II) 2,9,16,23-tetrasulfophthalocyanine, zinc(II) tetracarboxyphthalocyanine, and non-metallic sulfophthalocyanine complexes were studied as catalysts and photocatalysts for oxidation of sulfide, sulfite and thiosulfate ions by dioxygen. The cobalt phthalocyanine complexes exhibit high catalytic activity only in the oxidation of compounds containing sulfur in low oxidation state (sulfides). Oxidation is not complete and the activity of these complexes is not enhanced upon irradiation with visible light. Zinc and non-metallic phthalocyanine complexes demonstrate high catalytic activity only on irradiation with visible light. During interaction between dioxygen and the long-living triplet state of these complexes a chemically more reactive singlet dioxygen is formed which further interacts with compounds containing sulfur of various oxidation state. Upon photooxidation catalyzed by zinc or non-metallic phthalocyanine complexes the alkali sulfides, sulfites and thiosulfates are completely oxidized to sulfates. Aggregation of charged phthalocyanine complexes in aqueous medium decreases their effectiveness as photocatalysts because of lowering of the quantum yield of singlet dioxygen. In the presence of quaternary ammonium salts the equilibrium monomer-dimer is shifted to the monomeric form of the complexes, the photocatalytic activity being enhanced in this case. The mechanism of photocatalytic oxidation of sulfur-containing compounds and the catalyst destruction are briefly discussed.

Some recent studies on the use of electrochemical sensors in nonaqueous solution chemistry

AbstractFour recent studies in the authors' laboratory on the use of electrochemical sensors in nonaqueous solutions are reported. (1) Si3N4‐ and Ta2O5‐type ISFETs proved to be useful in nonaqueous solutions as sensors for pH and for proton solvation, because of their more rapid response than a conventional glass electrode. They were used to study the acid–base equilibria in γ‐butyrolactone and to determine the proton transfer activity coefficients between different solvents. (2) A univalent cation‐sensitive glass electrode was used to study the solvation of lithium ions in mixed solvents applicable to lithium batteries. (3) A membrane of polyacrylamide coupled to a cobalt phthalocyanine complex and coated onto a platinum electrode functioned as a sensor for fluoride and cyanide ions in aprotic solvents. It was used to determine the solubility products of alkali and alkaline earth metal fluorides and cyanides in acetonitrile and propylene carbonate. (4) A new method is proposed for the estimation of the liquid junction potential between different solvents, and a comparative study has been made between the new method and some conventional methods.

Catalytic oxidation of 2-mercaptoethanol by cobalt(II)-phthalocyanine complexes intercalated in layered double hydroxides

Complexes of cobalt(II)-2,9,16,23-phthalocyanine tetracar☐ylic acid and cobalt(II)-2,9,16,23-phthalocyanine tetrasulfonic acid were intercalated into the interlayer space of hydrotalcite by anion exchange. Intercalation compounds of various concentrations of the cobalt phthalocyanine complexes were prepared in this way. The distribution of the complexes in hydrotalcite was studied by means of electron spin resonance spectroscopy. The intercalation compounds were used as catalysts for 2-mercaptoethanol oxidation in aqueous solution. The catalyst effectiveness decreased upon increasing the concentration of the intercalated cobalt phthalocyanine complexes. Aggregation and crystallization of the phthalocyanine molecules on the hydrotalcite surface and formation of low active μ-peroxo complexes between closely ion-exchanged complexes resulted in a decrease in the turnover frequency of the oxidation.

Substituted cobalt phthalocyanine complexes as carriers for nitrite-sensitive electrodes

A new poly(vinyl chloride) membrane electrode based on lipophilic 2,9,16,23-tetra- tert-butylphthalocyanine-cobalt is described which demonstrates excellent selectivity toward the nitrite ion. The resulting electrodes displayed a near-Nernstian response for nitrite in the concentration range 10 −5-0.1 M with the selectivity sequence nitrite ⪢ thiocyanate ⪢ iodide ⪢ perchlorate ⪢ bromide ⪢ nitrate ⪢ chloride. The UV/Vis spectra and a.c. impedance studies showed that the excellent selectivity for nitrite was related to the unique interaction between the central cobalt ion and nitrite.

Functional metallomacrocycles and their polymers. Part 31. Autoxidation of thiol by temperature-sensitive polymer catalyst containing cobalt(II) phthalocyanine complex

Copolymers (I-IV) of 2-acryloylamino-9,16,23-tri( t-butyl)phthalocyanine (APc( t-Bu) 3) and acrylamide derivatives were prepared and their catalytic activity for oxidation of 2-mercaptoethanol was examined. Copolymers (II and IV) of APc( t-Bu) 3 and N-isopropylacrylamide revealed a lower critical solution temperature phenomenon at 29°C in carbonate buffer, that is to say, the copolymers dissolving in buffer solution below 29°C separated out as precipitate above 29°C. The catalytic activity of polymer IV, which was prepared by metalation of copolymer II, markedly changed around 29°C. Copolymer IV served as a homogeneous catalyst of autoxidation of 2-mercaptoethanol below 29°C. In contrast, the catalytic activity drastically decreased above 29°C because of separation as precipitate.