Efficient oxidation of hydrazine using amine-functionalized cobalt and nickel porphyrin-modified electrodes

The meso-tetra(para-aminophenyl) porphyrinatocobalt(II) (Co(II)MTpAP) and meso-tetra(para-aminophenyl)porphyrinatonickel(II) (Ni(II)MTpAP) were self-assembled on a glassy carbon electrode (GCE) and were utilized for the oxidation of hydrazine. The oxidation of hydrazine at the self-assembled monolayers (SAMs) of Co(II)MTpAP and Ni(II)MTpAP occurred at ?0.20 and 0.42 V, respectively. When compared to the SAM of Ni(II)MTpAP, Co(II)MTpAP SAM not only decreased the overpotential of hydrazine oxidation but also enormously increased its current. The oxidation of hydrazine was influenced by pH. While increasing the pH, the oxidation potential of hydrazine was shifted towards a less positive potential. Further, an inverted shape cyclic voltammogram (CV) was observed for the oxidation of hydrazine at Co(II)MTpAP-modified GCE, whereas a normal CV curve was observed at Ni(II)MTpAP-modified GCE. The appearance of the inverted shape peak for hydrazine oxidation at the SAM of Co(II)MTpAP is due to the oxidation of axially ligated hydrazine molecules during the reverse potential scan. The hydrazine oxidation was also performed at amine-functionalized cobalt and nickel phthalocyanine-modified electrodes in order to study the influence of a macrocyclic ring. Irrespective of the macrocyclic ring, an inverted shape CV was observed at cobalt phthalocyanine-modified electrode.     

Interaction of aryldiazonium salts with some schiff-base complexes of cobalt and ruthenium

The interaction of aryldiazonium ions with some Schiff-base complexes of cobalt and ruthenium have been studied. With cobalt, one-electron oxidation of [Co(II)Salen] occurred; with [Co(I)Salen] the corresponding Co(III)-aryl complexes were isolated. In the case of ruthenium oxidation also occurs, [Ru(Salen)(CO)py] gave the corresponding monocation. The results, especially for ruthenium, are in contrast to the stabilisation of both nitrosyl and aryldiazonium adducts in analogous porphyrin complexes.     

Electron transfer activity of a cobalt crown carbene complex

The novel cobalt(II) crown carbene complex 12(II) has been prepared and characterised by X-ray crystallography. This complex is reduced in a one-electron process to a cobalt(I) complex that acts as a powerful single electron donor, reducing aryl halides, including aryl chlorides and demonstrating the strong electron-enriching effect on cobalt of the crown carbene ligand. The metal ion is tightly held in a tetrahedral conformation by its enveloping crown ligand—this prevents what would otherwise be expected to be an easy oxidation to cobalt(III) under standard electrochemical conditions. Complex 12 is shown to be an effective catalyst in mediated electrochemical reductions of aryl iodides at room temperature and aryl bromides at 90 °C. The electrochemically produced catalyst [from 10 mol % of added Co(II) complex] also triggers reduction of aryl chlorides, although this seems at the limit of its reactivity. However, when the cobalt(II) complex is reduced by sodium amalgam, this affords stoichiometric quantities of the active cobalt reducing agent, which affords reduction of aryl iodides and bromides as above, but also reduces aryl chlorides at elevated temperatures.     

Anthracene Substituted Co (II) and Cu (II) phthalocyanines; Preparations,Investigation of Catalytical and Electrochemical Behaviors

An approach to investigation of catalytical behaviors of Co (II) and Cu (II) phthalocyanines is reported that is based on changing any parameter to effect these behaviors. Towards this end, new anthracene substituted Co (II) and Cu (II) phthalocyanines were prepared and characterized spectroscopic methods. New cobalt (II) and copper (II) phthalocyanines were used as catalyst for oxidation of different phenolic compounds (such as 2,3‐dichlorophenol, 4‐methoxyphenol, 4‐nitrophenol, 2,3,6‐trimethylphenol) with different oxidants. Then, electrochemical characterization of cobalt (II) and copper (II) phthallocyanines were determined by using cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques. Although copper (II) phthalocyanine showed similar Pc based electron transfer processes, cobalt (II) phthalocyanine showed metal and ligand based reduction reactions as expected.     

Indium tin oxide electrodes modified with tris(2,2'-bipyridine-4,4'-dicarboxylic acid) iron(II) and the catalytic oxidation of tris(4,4'-di-tert-butyl-2,2'-bipyridine) cobalt(II)

Indium tin oxide (ITO) electrodes modified by attachment of tris(2,2'-bipyridine-4,4'-dicarboxylic acid) iron(II) are examined. The mode of attachment is believed to be via the COOH functions in a manner similar to attachment of similar carboxylate-containing compounds to TiO2 surfaces. On the surface the complex resides as a stable electrochemically active monolayer. These modified electrodes can efficiently catalyze the oxidation of certain cobalt complexes, specifically, tris(4,4'-di-tert-butyl-2,2'-bipyridine) cobalt(II). On the unmodified ITO surfaces this cobalt complex is essentially electrochemically inert. The catalytic process approaches diffusional control at very slow scan speeds. Also, the electro-catalysis is sufficiently efficient that the peak oxidation current for Co2+, under certain conditions, exceeds the i(p) for the surface oxidation of the adsorbed Fe2+ by >x100 and the current for the uncatalyzed oxidation of Co2+ by considerably more than that.     

Formation of the second superhydrophobic shell around an encapsulated metal ion: synthesis, X-ray structure and electrochemical study of the clathrochelate and bis-clathrochelate iron(II) and cobalt(II, III) dioximates with ribbed perfluoroarylsulfide substituents

The nucleophilic substitution of six chlorine atoms of the n-butylboron-capped clathrochelate iron and cobalt(II) precursors with perfluoroarylthiolate anions afforded the hexaperfluoroarylsulfide macrobicyclic iron and cobalt(II) tris-dioximates. The complexes obtained are soluble in aromatic and aliphatic hydrocarbons as well as in polar aprotonic solvents due to the presence of the superhydrophobic fluorine-containing molecular periphery. As it follows from the X-ray data for five iron and cobalt mono- and bis-clathrochelates, the geometry of their macrobicyclic frameworks is affected by both the nature of an encapsulated metal ion and that of the ribbed substituents. Bis-capping fragment Co(II)O(6) of the Co(III)Co(II)Co(III) bis-clathrochelate possesses a trigonal antiprismatic geometry, all the Co(II)N(6) coordination polyhedra are trigonal-prismatic, and those of the encapsulated iron(II) and cobalt(III) ions are intermediate between them. The wide range of Co-N distances as well as the significant shifts of the encapsulated cobalt(II) ions from the centres of their N(6)-coordination polyhedra were explained by the Jahn-Teller distortion. The EPR and magnetometry data are also characteristic of the low-spin cobalt(II) complexes with this distortion. The parameters of the (57)Fe M?ssbauer spectra of the iron macrobicycles are characteristic of the low-spin iron(II) complexes. The cyclic voltammograms (CVs) for the complexes studied contain the one-electron oxidation and reduction waves assigned to metal-centered redox-processes. The Fe(2+/3+) and Co(2+/3+) oxidations are quasi-reversible or irreversible. The anionic clathrochelate species resulting from the reversible Co(2+/+) reductions are stable on the CV time scale, whereas their iron(I)-containing analogs are unstable.     

Effect of hydrophobized active carbon on the catalytic activity and adsorptivity of supported cobalt(II)-phthalocyanine

The catalytic activity of cobalt(II)-phthalocyanine [Co(II)Pc] supported on active carbon the oxidation of sulfide ions to elemental sulfur by dioxygen in aqueous solution has been studied. Hydrophobization of the carbon surface facilitates activation of dioxygen by adsorption. The sulfide ion is activated mainly on the supported Co(II)Pc.     

Co(II) and Co(III) complexes of m-benziphthalocyanine

The syntheses and structural elucidations of three different cobalt complexes of m-benziphthalocyanine are reported; both Co(II) and Co(III) complexes can be generated, and the ring undergoes partial oxidation upon metalation with Co(OAc)2x4H2O.     

Enhancing the Deperoxidation Activity of Cobalt(II)Acetylacetonate by the Addition of Octanoic Acid

The homolytic scission of peroxides with catalytic amounts of cobalt(II) complexes is used in several industrial oxidation processes. In this contribution, we report that addition of small amounts of octanoic acid significantly enhances the catalytic deperoxidation activity of the cobalt(II)acetylacetonate complex. We attribute this to the stabilization of the Co? OOR bond upon coordination of octanoic acid, preventing the unimolecular scission. As such, the cobalt peroxo intermediate is forced to enter an alternative catalytic cycle which causes its rapid conversion to the highly reactive cobalt hydroxy. This shift in catalytic cycle results in a higher pre‐exponential rate factor, over‐compensating the higher barrier of the new rate‐determining step.     

Dinuclear Co(III)/Co(III) and Co(II)/Co(III) mixed-valent complexes: synthetic control of the cobalt oxidation level

The reactivity of cobalt(II) salts towards H(3)L (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) was studied in different reaction conditions. Accordingly, the interaction of cobalt(II) acetate with H(3)L in methanol gives rise to the discrete complex [Co(III)(2)L(OAc)(2)(OMe)]*1.5H(2)O.MeOH, 1. Reaction of cobalt(II) acetylacetonate with H(3)L in the presence of dicarboxylic acids was also investigated. Thus, when cobalt(II) acetylacetonate and H(3)L are mixed with terephthalic or malonic acid in 4 : 2 : 1 molar ratios, the mixed valent [Co(II/III)(2)L(acac)(p-O(2)CC(6)H(4)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*2H(2)O*2MeOH, 2 and [Co(II/III)(2)L(acac)(O(2)CCH(2)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*7H(2)O, complexes are isolated. Decreasing the pH of the medium, by addition of a second mol of dicarboxylic acid, leads to [Co(II/III)(2)L(O(2)CCH(2)CO(2))(MeOH)]*2MeOH, 4, while the reaction with terephthalic acid does not proceed. 1, 2 and 4 were crystallographically characterised and all the complexes are dinuclear, with hydrogen bonds that expand the initial nodes. The magnetic characterisation, as well as the NMR spectroscopy, indicates a diamagnetic nature for 1, in agreement with the presence of Co(III), showing the aerial oxidation suffered by the cobalt(II) ions. Nevertheless, are paramagnetic. Temperature variable magnetic measurements were recorded for the crystallographically characterised complexes 2 and 4 and these studies confirm the mixed valence Co(II)/Co(III) nature of the compounds. The best fits of the magnetic data give an axial distortion parameter Delta = 628.7 cm(-1) for 2 and 698.8 cm(-1) for 4, and spin-orbit coupling constant lambda = -117.8 cm(-1) for 2 and -107.0 cm(-1) for 4. Therefore, this study shows that the oxidation degree of the initial cobalt(ii) salt by atmospheric oxygen can be controlled according to the pH of the medium.     

How molecular oxygen binds to bis[trifluoroacetylacetonato(-1)]cobalt(II)--ab initio and density functional theory studies

Cobalt(II) diketonate complexes, such as bis[trifluoroacetylacetonato(-1)]cobalt(II) [Co(tfa)(2)], catalyze the aerobic oxidation of alkenols into functionalized tetrahydrofurans. To gain insight into activation of triplet dioxygen by Co(tfa)(2) in a protic solvent, as used in oxidation catalysis, the electronic structure of aquabis[trifluoroacetylacetonato(-1)]cobalt(II)--Co(tfa)(2)(H(2)O)--and the derived dioxygen adduct were characterized using ab initio (CASSCF, NEVPT2) and density functional theory (BP86, TPSSh, B3LYP) methods. The ground state of Co(tfa)(2)(H(2)O) is a high-spin, quartet state. As dioxygen approaches the cobalt atom, the quartet state couples with a triplet dioxygen molecule and forms a sextet, a quartet, and a doublet spin state with the high-spin state being the lowest in energy. At the equilibrium Co-O(2) distance of 1.9 ?, Co(tfa)(2)(H(2)O)(O(2)) has a doublet superoxo Co(III) ground state with the unpaired electron residing on the oxygen moiety, in a nearly unchanged O(2)π* orbital.     

不同钴含量CoAPO-5分子筛的合成、表征及其催化环己烷氧化性能

用水热法合成了一系列不同含量钴掺杂的磷酸铝分子筛CoAPO-5. 合成的样品用X射线衍射(XRD), 扫描电镜(SEM), 紫外可见漫反射光谱(UV-Vis DRS), 热重分析(TG)仪和电感耦合等离子体发射光谱(ICP-AES)等进行了表征. XRD表征显示, 合成的CoAPO-5分子筛具有较高的结晶度, 分子筛晶胞参数与Co含量之间存在较好的对应关系. UV-Vis漫反射光谱显示合成的CoAPO-5分子筛具有骨架钴的特征三重峰; 焙烧后峰的强度降低, 表明分子筛骨架中Co2+可被氧化成Co3+. SEM表明该分子筛具有典型的AlPO4-5分子筛形貌特征. TG结果也表明Co2+进入了分子筛骨架, 分子筛具有较好的稳定性. 在环己烷氧化反应中CoAPO-5具有较好的催化性能, 环己烷转化率与环己酮选择性均较高; 随着分子筛中钴含量的增加, 环己烷的转化率增加.     

An example of O2 binding in a cobalt(II) corrole system and high-valent cobalt-cyano and cobalt-alkynyl complexes

The novel cobalt corrolazine (Cz) complexes (TBP)(8)CzCoCN (1) and (TBP)(8)CzCo(CCSiPh(3)) (2) have been synthesized and examined in light of the recent intense interest regarding the role of corrole ligands in stabilizing high oxidation states. In the case of 2, the molecular structure has been determined by X-ray crystallography, revealing a short Co[bond]C distance of 1.831(4) A and an intermolecular pi-stacking interaction between Cz ring planes, and this structure has been analyzed in regards to the electronic configuration. By a combination of spectroscopic techniques it has been shown that 1 is best described as a cobalt(III)[bond]pi-cation-radical complex, whereas 2 is likely best represented as the resonance hybrid (Cz)Co(IV)(CCSiPh(3)) <--> (Cz+*)Co(III)(CCSiPh(3)). The reduced cobalt(II) complex, [(TBP)(8)CzCo(II)(py)](-), has been generated in situ and shown to bind dioxygen at low temperature to give [(TBP)(8)CzCo(III)(py)(O(2))](-). For the reduced complex [(TBP)(8)CzCo(II)(py)](-), the EPR spectrum in frozen solution is indicative of a low-spin cobalt(II) complex with a d(z)2 ground state. Exposure of [(TBP)(8)CzCo(II)(py)](-) to O(2) leads to the reversible formation of the cobalt(III)-superoxo complex [(TBP)(8)CzCo(III)(py)(O(2))](-), which has been characterized by EPR spectroscopy. VT-EPR measurements show that the dioxygen adduct is stable up to T approximately 240 K. This work is the first observation, to our knowledge, of O(2) binding to a cobalt(II) corrole.     

UV-Vis, NMR, and time-resolved spectroscopy analysis of photoisomerization behavior of three- and six-azobenzene-bound tris(bipyridine)cobalt complexes

The photoisomerization properties of tris(bipyridine)cobalt complexes containing six or three azobenzene moieties, namely, [Co(II)(dmAB)3](BF4)2 [dmAB = 4,4'-bis[3'-(4'-tolylazo)phenyl]-2,2'-bipyridine], [Co(III)(dmAB)3](BF4)3, [Co(II)(mAB)3](BF4)2 [mAB = 4-[3' '-(4' '-tolylazo)phenyl]-2,2'-bipyridine], and [Co(III)(dmAB)3](BF4)3, derived from the effect of gathering azobenzenes in one molecule and the effect of the cobalt(II) or cobalt(III) ion were investigated using UV-vis absorption spectroscopy, femtosecond transient spectroscopy, and 1H NMR spectroscopy. In the photostationary state of these four complexes, nearly 50% of the trans-azobenzene moieties of the Co(II) complexes were converted to the cis isomer, and nearly 10% of the trans-azobenzene moieties of the Co(III) complexes isomerized to the cis isomer, implying that the cis isomer ratio in the photostationary state upon irradiation at 365 nm is controlled not by the number of azobenzene moieties in one molecule but rather by the oxidation state of the cobalt ions. The femtosecond transient absorption spectra of the ligands and the complexes suggested that the photoexcited states of the azobenzene moieties in the Co(III) complexes were strongly deactivated by electron transfer from the azobenzene moiety to the cobalt center to form an azobenzene radical cation and a Co(II) center. The cooperation among the photochemical structural changes of six azobenzene moieties in [Co(II)(dmAB)3](BF4)2 was investigated with 1H NMR spectroscopy. The time-course change in the 1H NMR signals of the methyl protons indicated that each azobenzene moiety in [Co(II)(dmAB)3](BF4)2 isomerized to a cis isomer with a random probability of 50% and without interactions among the azobenzene moieties.     

Elucidation of a low spin cobalt(II) system in a distorted tetrahedral geometry

We have prepared a series of divalent cobalt(II) complexes supported by the [PhBP(3)] ligand ([PhBP(3)] = [PhB(CH(2)PPh(2))(3)](-)) to probe certain structural and electronic phenomena that arise from this strong field, anionic tris(phosphine) donor ligand. The solid-state structure of the complex [PhBP(3)]CoI (1), accompanied by SQUID, EPR, and optical data, indicates that it is a pseudotetrahedral cobalt(II) species with a doublet ground state-the first of its type. To our knowledge, all previous examples of 4-coordinate cobalt(II) complexes with doublet ground states have adopted square planar structure types. Complex 1 provided a useful precursor to the corresponding bromide and chloride complexes, ([PhBP(3)]Co(mu-Br))(2), (2), and ([PhBP(3)]Co(mu-Cl))(2), (3). These complexes were similarly characterized and shown to be dimeric in the solid-state. In solution, however, the monomeric low spin form of 2 and 3 dominates at 25 degrees C. There is spectroscopic evidence for a temperature-dependent monomer/dimer equilibrium in solution for complex 3. Furthermore, the dimers 2 and 3 did not display appreciable antiferromagnetic coupling that is typical of halide and oxo-bridged copper(II) and cobalt(II) dimers. Rather, the EPR and SQUID data for solid samples of 2 and 3 suggest that they have triplet ground states. Complexes 1, 2, and 3 are extremely oxygen sensitive. Thus, stoichiometric oxidation of 1 by dioxygen produced the 4-coordinate, high spin complex [PhB(CH(2)P(O)Ph(2))(2)(CH(2)PPh(2))]CoI, (4), in which the [PhBP(3)] ligand had undergone a 4-electron oxidation. Reaction of 1 with TlOAr (Ar = 2,6-Me(2)Ph) afforded an example of a 4-coordinate, high spin complex, [PhBP(3)]Co(O-2,6-Me(2)Ph) (5), with an intact [PhBP(3)] ligand. The latter two complexes were spectroscopically and structurally characterized for comparison to complexes 1, 2, and 3. Our data for these complexes collectively suggest that the [PhBP(3)] ligand provides an unusually strong ligand-field to these divalent cobalt complexes that is chemically distinct from typical tris(phosphine) donor ligand sets, and distinct from tridentate borato ligands that have been previously studied. Coupling this strong ligand-field with a pronounced axial distortion away from tetrahedral symmetry, a geometric consequence that is enforced by the [PhBP(3)] ligand, provides access to monomeric [PhBP(3)]CoX complexes with doublet rather than quartet ground states.     

Protonic modulation of redox properties in ionisable [2 x 2] grid-like metalloarrays

The oxidation state of the cobalt centres can be controlled by modification of the protonation state in [2 x 2] grid-like arrays based on ionisable bis(hydrazone) ligands, allowing conversion of the paramagnetic Co(II)(4) into the diamagnetic Co(III)(4) grid.     

Photochemical synthesis of a water oxidation catalyst based on cobalt nanostructures

New cobalt-based nanocomposites have been prepared by photoreduction of Co(2+) salts to generate cobalt nanoparticles deposited on carbon-based materials such as nanocyrstalline diamond and carbon felt. Spontaneous air oxidation converts the metal to Co(2)O(3) which has been tested as a water oxidation catalyst. This work demonstrates that the cobalt oxide nanostructures can be deposited on various carbon surfaces and can catalyze the four-electron oxidation of water to oxygen under anodic bias.     

Synthesis, structural, and spectroscopic characterization and reactivities of mononuclear cobalt(III)-peroxo complexes

Metal-dioxygen adducts are key intermediates detected in the catalytic cycles of dioxygen activation by metalloenzymes and biomimetic compounds. In this study, mononuclear cobalt(III)-peroxo complexes bearing tetraazamacrocyclic ligands, [Co(12-TMC)(O(2))](+) and [Co(13-TMC)(O(2))](+), were synthesized by reacting [Co(12-TMC)(CH(3)CN)](2+) and [Co(13-TMC)(CH(3)CN)](2+), respectively, with H(2)O(2) in the presence of triethylamine. The mononuclear cobalt(III)-peroxo intermediates were isolated and characterized by various spectroscopic techniques and X-ray crystallography, and the structural and spectroscopic characterization demonstrated unambiguously that the peroxo ligand is bound in a side-on η(2) fashion. The O-O bond stretching frequency of [Co(12-TMC)(O(2))](+) and [Co(13-TMC)(O(2))](+) was determined to be 902 cm(-1) by resonance Raman spectroscopy. The structural properties of the CoO(2) core in both complexes are nearly identical; the O-O bond distances of [Co(12-TMC)(O(2))](+) and [Co(13-TMC)(O(2))](+) were 1.4389(17) ? and 1.438(6) ?, respectively. The cobalt(III)-peroxo complexes showed reactivities in the oxidation of aldehydes and O(2)-transfer reactions. In the aldehyde oxidation reactions, the nucleophilic reactivity of the cobalt-peroxo complexes was significantly dependent on the ring size of the macrocyclic ligands, with the reactivity of [Co(13-TMC)(O(2))](+) > [Co(12-TMC)(O(2))](+). In the O(2)-transfer reactions, the cobalt(III)-peroxo complexes transferred the bound peroxo group to a manganese(II) complex, affording the corresponding cobalt(II) and manganese(III)-peroxo complexes. The reactivity of the cobalt-peroxo complexes in O(2)-transfer was also significantly dependent on the ring size of tetraazamacrocycles, and the reactivity order in the O(2)-transfer reactions was the same as that observed in the aldehyde oxidation reactions.     

Metal complex-substituted polysiloxanes as novel coatings for capillary electrophoresis and capillary electrochromatography

Two novel polysiloxane-based polymers, which contain metal complexes, have been prepared. To prepare the Co(TACN)3+(2) (TACN= 1,4,7-triazacyclononane) based polymers, an orthoamide derivative of TACN was added to bromobutane-substituted methylpolysiloxane and hydrolyzed with base. Co(II) was then coordinated to the TACN, followed by cobalt oxidation to make polymer A or followed by N-octyl TACN coordination and cobalt oxidation to make polymer B. In both materials, TACN forms thermodynamically and kinetically stable Co(TACN)3+(2) complexes in which the six coordination sites of the Co(III) are occupied by nitrogens from the TACN. The polymers were coated on fused-silica capillary columns and spherical silica particles, which were used for capillary electrophoresis and capillary electrochromatography, respectively. The open and packed columns showed strong and pH-independent reversed electroosmotic flow.     

Cobalt(II)/(III) complexes bearing a tetradentate thiosemicarbazone: Synthesis,experimental and theoretical characterization,and electrochemical and antioxidant properties

New cobalt complexes, Co1 and Co2 , were synthesized starting from acetylacetone-S-methylthiosemicarbazone. The square planar cobalt(II) and octahedral cobalt(III) complexes were characterized by FT-IR, UV–visible, ¹H NMR, and X-ray diffraction spectroscopies and mass spectrometry. Frontier orbitals of the complexes were theoretically obtained to better understand the complex structures and intermolecular interactions. The electrochemical behaviors of Co1 and Co2 were investigated and the results were evaluated by comparing with each other and with similar published compounds to determine their possible usage in various electrochemical technologies, such as energy storage devices, electrocatalysts, and electrosensors. Metal-based oxidation at around 0 V and metal-based reduction at around −1.0 V indicated that these complexes are valuable for the proposed applications. By determining the trolox equivalent antioxidant capacity and the radical scavenging activity of the cobalt complexes, the compatibility between the antioxidant qualification, redox, and theoretical calculation results was discussed.