- Two supramolecular complexes based on polyoxometalates and Co-EDTA units via covalent connection or non-covalent interaction
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Two new 3D network organic-inorganic hybrid supramolecular complexes {[Na6(CoEDTA)2(H2O)13]·(H2SiW12O40)·xH2O}n (1) and [CoH4EDTA(H2O)]2(SiW12O40)·15H2O (2) (H4EDTA=Ethylenediamine tetraacetic acid) have been successfully synthesized by solution method, and characterized by infrared spectrum (IR), thermogravimetric-differential thermal analysis (TG-DTA), cyclic voltammetry (CV) and single?crystal X-ray diffraction (XRD). Both of the complexes are the supramolecules, but with different liking mode, they are two representative models of supramolecule. complex (1) is a 3D infinite network supramolecular coordination polymer with a rare multi-metal sturcture of sodium-cobalt-containing, which is mainly linked through coordinate-covalent bonds. While complex (2) is normal supramolecule, which linked by non-covalent interactions, such as H-bonding interaction, electrostatic interaction and van der waals force. Both of complex (1) and (2) exhibit good catalytic activities for catalytic oxidation of methanol, when the initial concentration of methanol is 3.0?g?m?3, flow rate is 10?mL?min?1, and the quality of catalyst is 0.2?g, for complex (1) and complex (2) the maximum elimination rates of methanol are 85% (150?°C) and 92% (120?°C), respectively.
- Teng, Chunlin,Xiao, Hanxi,Cai, Qing,Tang, Jianting,Cai, Tiejun,Deng, Qian
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p. 146 - 153
(2016/08/30)
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- Magnetic resonance imaging of the manipulation of a chemical wave using an inhomogeneous magnetic field
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The effects of applied magnetic fields on the traveling wave formed by the reaction of (ethylenediaminetetraacetato)cobalt(II) (Co(II)EDTA2-) and hydrogen peroxide have been studied using magnetic resonance imaging (MRI). It was found that the wave could be manipulated by applying pulsed magnetic field gradients to a sample contained in a vertical cylindrical tube in the 7.0 T magnetic field of the spectrometer. Transverse field gradients decelerated the propagation of the wave down the high-field side of the tube and accelerated it down the low-field side. This control of the wave propagation eventually promoted the formation of a finger on the low-field side of the tube and allowed the wave to be maneuvered within the sample tube. The origin of these effects is rationalized by considering the Maxwell stress arising from the combined homogeneous and inhomogeneous magnetic fields and the magnetic susceptibility gradient across the wave front.
- Evans, Robert,Timmel, Christiane R.,Hore,Britton, Melanie M.
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p. 7309 - 7314
(2007/10/03)
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- Magnetic resonance imaging of a magnetic field-dependent chemical wave
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The magnetic field dependence of the travelling wave formed during the reaction of (ethylenediaminetetraacetato)cobalt(II) (Co(II)EDTA2-) and hydrogen peroxide was studied using magnetic resonance imaging (MRI). The reaction was investigated in a vertical tube, in which the wave was initiated from above. The wave propagated downwards, initially with a flat wavefront before forming a finger. Magnetic field effects were observed only once the finger had formed. The wave propagation was accelerated by a magnetic field with a negative gradient (i.e., when the field was stronger at the top of the tube than at the bottom) and slightly decelerated by positive field gradients.
- Evans, Robert,Timmel, Christiane R.,Hore,Britton, Melanie M.
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- Kinetics and mechanism of the reduction of the molybdatopentaamminecobalt(III) ion by aqueous sulfite and aqueous potassium hexacyanoferrate(II)
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A detailed investigation on the oxidation of aqueous sulfite and aqueous potassium hexacyanoferrate(II) by the title complex ion has been carried out using the stopped-flow technique over the ranges, 0.01≤[S(IV)]T≤0.05 mol dm-3, 4.47≤pH≤5.12, and 24.9≤θ≤37.6°C and at ionic strength 1.0 mol dm-3 (NaNO3) for aqueous sulfite and 0.01≤[Fe(CN)64-]≤0.11 mol dm-3, 4.54≤pH≤5.63, and 25.0≤θ≤35.3°C and at ionic strength 1.0 or 3.0 mol dm-3 (NaNO3) for the hexacyanoferrate(II) ion. Both redox processes are dependent on pH and reductant concentration in a complex manner, that is, for the reaction with aqueous sulfite, kobs={(k1K1K2K3+k 2K1K4[H+])[S(IV)]T]/ ([H+]2+K1[H+]+K1K 2) and for the hexacyanoferrate(II) ion, kobs={(k1K3K4K5+k 2K3K6[H+])[Fe(CN)6 4-]T)/([H+]2+K3[H +]+K3K4). At 25.0°C, the value of k′1 (the composite of k1K3) is 0.77±0.07 mol-1 dm3 s-1, while the value of k′2 (the composite of k2K4) is (3.78±0.17)×10-2 mol-1 dm3 s-1 for aqueous sulfite. For the hexacyanoferrate(II) ion, k′1 (the composite of k1K5) is 1.13±0.01 mol-1 dm3 s-1, while the value of k′2 (the composite of k2K6) is 2.36±0.05 mol-1 dm3 s-1 at 25.0°C. In both cases there was reduction of the cobalt(III) centre to cobalt(II), but there was no reduction of the molybdenum(VI) centre. k22, the self-exchange rate constant, for aqueous sulfite (as SO32-) was calculated to be 5.37×10-12 mol-1 dm3 s-1, while for Fe(CN)64-, it was calculated to be 1.10×109 mol-1 dm3 s-1 from the Marcus equations.
- Holder, Alvin A.,Dasgupta, Tara P.
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p. 279 - 289
(2008/10/08)
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- Kinetics and mechanism of oxidation of ascorbic acid by cobalt(III) complexes in micellar media
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The kinetics of oxidation of L-ascorbic acid (H2A) by Co(bipy)33+, Co(edta)- and Co(atda) (tmd) complexes have been studied spectrophotometrically in the presence of cationic, cetyl trimethylammonium bromide (CTAB) and anionic, sodium dodecylsulphate (SDS) surfactants in weakly acidic and basic media. The rate of ascorbic acid oxidation is influenced by the ionic nature of the micelle, hydrophobicity of the coordinated ligands and the overall charge of the complex used. Ascorbic acid oxidation byCo(bipy)33+ is slowed down in the presence of SDS while rate acceleration is observed in CTAB micellar medium. CTAB micelles also lead to rate enhancement in ascorbic acid oxidation by Co(edta)- complex. However, micellar effect is not very pronounced in the case of neutral Co(atda) (tmd) complex as oxidant Based on kinetic results it can be inferred that the hydrophobic interactions are dominant in the case of Co(bipy)33+ and electrostatic interactions play an important role for Co(edta)- complex.
- Makote, Rajendra D.,Chatterjee
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- Photolysis of Cobalt(III) Aminopolycarboxylates: Dimerization of Decarboxylated Fragments of Ligands
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When solutions of (nitrilotriacetato)ethylenediaminecobalt(III) are irradiated by the UV light in the region of the ligand-to-metal charge-transfer (LMTC) absorption band, a considerable portion (28% at the photolysis efficiency of 51%) of the photochemical process follows the pathway of the metal ion reduction and decarboxylated aminopolycarboxylate liganddimerization. This results in the formation of ethylenediaminetetraacetatocobalt(II) ions. Two mechanisms of dimerization with the participation of primary organocobalt photoproducts are discussed.
- Poznyak, A. L.,Stopolyanskaya, L. V.
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p. 1080 - 1082
(2008/10/08)
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- Chiral discrimination in the reduction of [Co(edta)]- by [Co(en)3]2+ and [Ru(en)3]2+. X-ray structure of [Λ-Co(en)3][Δ-Co(edta)]2Cl·10H 2O
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The structure of the salt [Λ-Co(en)3][Δ-Co(edta)]2Cl·10H 2O has been determined by X-ray crystallography. The salt crystallizes in the orthorhombic space group P21212 (No. 18) with Z = 2, a = 21.046(3) A?, b = 12.813(2) A?, c = 8.158(1) A?, and R = 0.035 for 5263 reflections. The complex ions participate in a network of hydrogen bonds which is interpreted to suggest a mechanism for chiral discrimination. Outer-sphere reduction of [Co(edta)]- by [Ru(en)3]2+ takes place with a second-order rate constant of 6 × 103 M-1 s-1 at 25°C and 0.10 M ionic strength. Chiral induction in the reaction results in a 2% enantiomeric excess with a ΔΛ preference, significantly smaller than the 10% ΔΛ induction found with [Co(en)3]2+ as reductant. This difference in chiral induction between the two reductants is ascribed to differences in chiral recognition in the assembly of electron-transfer precursor complexes.
- Warren, Robert M. L.,Haller, Kenneth J.,Tatehata, Akira,Lappin, A. Graham
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p. 227 - 232
(2008/10/08)
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- Novel Enantioselective Photocatalysis by Chiral, Helical Ruthenium(II) Complexes
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The enantioselective photoreduction of the helical substrates of rac- (acac- = acetylacetonato) and rac-- (edta4- = ethylenediaminetetraacetato) with the newly synthesized helical photocatalysts Δ- (or rac)-2+ -2,2'-bipyridine>, and Λ- (or Δ)-3>2+ -2,2'-bipyridine> was realized in the helical-shape recognition reaction with a maximum enantiomer rate ratio (kΔ/kΛ) of 14.7 in 90percent v/v EtOH-H2O at 25 degC.
- Ohkubo, Katsutoshi,Hamada, Taisuke,Ishida, Hitoshi
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p. 1423 - 1425
(2007/10/02)
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- Kinetic Salt Effects on the Outer-sphere Electron-transfer Reaction between Hexacyanoferrate(II) and Pentaammineaquocobalt(III)
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The kinetic salt effects in sodium nitrate solutions, up to 5 mol dm-3, on the reaction between hexacyanoferrate(II) and pentaammineaquocobalt(III) have been studied.The experimental trends of the association constant of the reactants, KIP, and the electron transfer rate constant, ket, can be explained within the framework of dielectric continuum models. -To further support this explanation, the KIP, and ket values of the reaction between octacyanomolibdate(IV) and pentaammineaquocobalt(III) in a 0.5 mol dm-3 solution of sodium perchlorate have been determined. - The methodology employed in the present work could be used as a general method for analyzing medium and salt effects on electron transfer processes, when one of the reactants shows irreversible behaviour; from the electrochemical point of view.
- Galan, M.,Jimenez, R.,Sanchez, F.
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- Electron-transfer reactions of encapsulated transition metal complexes. Oxidation of (4,4′-bipyridine)pentaammineruthenium(II) by (ethylenediaminetetraacetato)cobaltate(III)
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The encapsulation of pentaammine(ligand)ruthenium(II) (ligand = pyrazine or bipyridine) with cyclodextrins was investigated. The equilibrium constants ranged from ~20 to 100. The effect of encapsulation on electron-transfer rates was also determined, and a specific orientation of reactants within the precursor complex is discussed.
- Johnson, Michael D.,Reinsborough, Vincent C.,Ward, Sean
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p. 1085 - 1087
(2008/10/08)
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- Micellar Accelerated Reduction of Ethylenediaminetetraacetatocobaltate(III) by 1-Benzyl-1,4-dihydronicotinamide
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The electrostatic and hydrophobic effects of ionic micelles on the reduction of ethylenediaminetetraacetatocobaltate(III) (-) by 1-benzyl-1,4-dihydronicotinamide (BNAH) were investigated with dodecyltrimethylammonium chloride (DTAC) and/or sodiu
- Yamashita, Kohichi,Chiba, Masahiro,Ishida, Hitoshi,Ohkubo, Katsutoshi
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p. 410 - 415
(2007/10/02)
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- Temperature and pressure effects on the outer-sphere electron-transfer reaction between hexacyanoferrate(II) and pentaamminecobalt(III) complexes in aqueous solution. Comparison of experimental and theoretical volumes of activation
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The kinetics of a series of outer-sphere electron-transfer reactions of the type Co(NH3)4(NH2R)X(3-n)+ + Fe(CN)64- → Co2+ + 4NH3 + NH2R + Xn- + Fe(CN)63- (X = N3-, R = H; X = Cl-, R = H, CH3, i-C4H9) were studied as a function of temperature and pressure. It was possible to separate the ion-pair formation constant and the electron-transfer rate constant in a kinetic way, and the corresponding thermodynamic and activation parameters were determined. For the electron-transfer process, the rate and activation parameters lie in the ranges 0.06 ≤ k × 102 ≤ 20 s-1, 84 ≤ ΔH? ≤ 118 kJ mol-1, +11 ≤ ΔS? ≤ 113 J K-1 mol-1, and +19 ≤ ΔV? ≤ +34 cm3 mol-1. The experimentally observed activation volumes are in good agreement with those predicted theoretically on the basis of an average λ? value of 0.48 ± 0.07. The results are discussed in reference to related studies reported in the literature.
- Krack,Van Eldik
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p. 1700 - 1704
(2008/10/08)
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- Significant Phosphine Ligand Effect on the Photochemical Reactivity of (1+) (N-N=1,10-phenanthroline or 2,9-dimethyl-1,10-phenanthroline; L=tertiary phosphine)
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Photo-induced electron-transfer reactions between (1-) and (1+) have been investigated.Although (1+) exhibits rather low photochemical reactivity, substituting PPh3 by a bulky and/or donative phosphine significantly enhances the reactivity.In the case of N-N=dmphen, introducing a donative phosphine, P(C6H4OMe-p)3, instead of PPh3 remarkably increases the photochemical reactivity, but in the case of N-N=phen, substituting PPh3 by a donative and bulky phosphine such as P(C6H11)3 much improves the photochemical reactivity.A kinetic study has also been carried out and it is concluded that this reaction proceeds via a dynamic quenching mechanism.Phosphine ligand effects are discussed in terms of the lifetime of the excited copper(I) complexes and the facility of formation of the encounter complex.
- Sakaki, Shigeyoshi,Hashimoto, Satoru,Koga, Genji,Ohkubo, Katsutoshi
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p. 1641 - 1644
(2007/10/02)
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- Electron transfer. 88. Cobalt(III)-bound phosphite and hypophosphite
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Phosphite and hypophosphite coordinate to cobalt(III) in (NH3)5CoIII through oxygen, rather than through phosphorus. The resulting complexes undergo electron-transfer reactions with Ru(NH3)62+ much more slowly than with Eu2+ or V2+, indicating that the latter two reactants preferentially utilize ligand bridging. Reductions with Cr2+ are shown to be accompanied by transfer of the phosphorus-containing ligands, and reaction of the protonated phosphite (biphosphito) derivative (pKA = 3.06 at 23°C) proceeds through a combination of acid-independent and inverse-acid paths, both routes yielding the same phosphito-bound Cr(III) product. The hypophosphito, but not the biphosphito, complex reacts with Ce(IV), producing Co2+ in an induced electron-transfer process. The yield of Co2+ falls off progressively as [CeIV] is increased, pointing to a sequence in which a Co(III)-bound P(II) radical is formed in initial attack by Ce(IV) but subsequently undergoes partition between competing reaction paths, i.e. internal electron transfer to Co(III) vs external oxidation by a second Ce(IV) center. The hypophosphito complex, but not the biphosphito complex, smoothly decomposes in basic media via an internal redox reaction, yielding Co(II) quantitatively, along with a 1:1 mixture of phosphite and hypophosphite. This transformation, which fails with mixtures of (NH3)5Co(H2O)3+ and H2PO2-, appears to be catalyzed specifically by OH-. Deuterium-labeling experiments disclose a solvent isotope effect, kH2O/kD2O, of 1.14-1.23 and a substrate isotope effect, kH2P/kD2P, of 2.1-2.3, in better accord with a hydride-transfer mechanism than with a homolytic process or removal of hydrogen as H+. The proposed sequence entails a hydroxide-induced hydride shift from phosphorus to Co(III), yielding a protonated Co(I) species, which then reacts very rapidly with a second Co(III), yielding two Co(II) species and releasing hypophosphite. The suggested mechanism is similar to those proposed for a number of conversions preceding through organometallic species and is also analogous to the Cannizzaro reaction of aldehydes in basic media.
- Linn Jr.,Gould
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p. 3442 - 3446
(2008/10/08)
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- Stereoselectivity as a probe of reaction mechanism in the oxidation of [Co(en)3]2+ and its derivatives by [Co(edta)]-
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Stereoselectivities in the oxidations of [Co(en)3]2+, [Co(sen)]2+, [Co(sep)]2+, [Co((±)-bn)3]2+, and [Co((±)-chxn)3]2+ by [Co(edta)]- have been examined under a variety of conditions. For the conformationally restricted complexes [Co((±)-bn)3]2+ and [Co((±)-chxn)3]2+ the stereoselectivity shows a trend from 15% ΔΔ for [Co((±)-bn)3-lel3]2+ (25% ΔΔ for [Co((±)-chxn)3-lel3]2+) to 25% ΔΛ for [Co((±)-bn)3-ob3]2+ (16% ΔΛ for [Co((±)-chxn)3-ob3]2+). For [Co(en)3]2+, [Co(sen)]2+, and [Co(sep)]2+, stereoselectivities are 11% ΔΛ, 10% ΔΛ, and 18% ΔΛ, respectively. Kinetic studies are consistent with outer-sphere reactions. The stereoselectivities are correlated with ion-pairing stereoselectivities for the interactions of [Co(edta)]- with the appropriate cobalt(III) amine complexes, supporting an important role for precursor complex structure in determining the chiral induction. The trends in the data are explained in terms of a balance of interactions along the C2 and C3 axes of the reductant complexes.
- Osvath, Peter,Lappin, A. Graham
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p. 195 - 202
(2008/10/08)
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- New Photoreduction Catalysis by + (N-N = 2,9-Dimethyl-1,10-phenanthroline or 4,4',6,6'-Tetramethyl-2,2'-bipyridine) and Its Application to Cobalt(III) Complexes
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The copper(I) complexes + photocatalytically reduce cobalt(III) complexes such as 2+, - (edta = ethylenediaminetetra-acetate), and (acac = acetylacetonate), upon irradiation with near-u.v. light corresponding to the metal-to-ligand charge-transfer absorption band (about 360 nm) of the copper(I) copmlex.This is a new type of photocatalytic reduction by copper(I) complexes.The photosensitising mechanism is discussed on the basis of the Stern-Volmer relationship.The dmphen complex has a higher activity than that of the tmbipy analogue, and the reactivity of the cobalt(III) complexes decreases ine the order 2+ > - > .The results are discussed in terms of the lifetime of the exciter copper(I) complex and the irradiation potentials of the cobalt(III) complexes.
- Sakaki, Shigeyoshi,Koga, Genji,Sato, Fumio,Ohkubo, Katsutoshi
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p. 1959 - 1962
(2007/10/02)
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- Kinetics of reduction of cobalt(III) complexes by viologen radicals
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The second-order rate constants are reported for reduction of 11 cobalt(III) complexes by viologen radicals, derived from diquaternary salts of 4,4′-bipyridine and 2,2′-bipyridine. Rate constants vary from 1.5 × 102 to 6.0 × 108 M-1 s-1, and an excellent correlation with the Marcus expression for 14 redox reactions is observed. These data conform, on the basis of a unity transmission coefficient, to a self-exchange rate constant for the viologens (X2+/+ couple) of 1.5 × 106 M-1 s-1. It is suggested however that this value is about 102 too low.
- Tsukahara,Wilkins
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p. 3399 - 3402
(2008/10/08)
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- MICELLAR-PROMOTED STEREOSELECTIVE PHOTOREDUCTION OF POTASSIUM ETHYLENEDIAMINETETRAACETATOCOBALTATE(III) BY A LONG-CHAIN CHIRAL RUTHENIUM(II) COMPLEX.
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This work decribes the micellar-accelerated chiroselective photoreduction of potassium ethylenediaminetetraacetatocobaltate(III), KCo(edta), by the following longchain chiral ruthenium(II) complex with ionic or nonionic surfactants of cetyltrimethylammonium bromide (CTAB), polyoxyethylene (9. 5) octylphenol (Triton X), and sodium dodecylsulfate (SDS).
- Ohkubo,Arikawa
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- Photochemical and thermal decomposition of (ΔΔ,ΛΛ)-(μ-hydroxo)(μ-peroxo) bis[bis(ethylenediamine)cobalt(III)] ions in basic aqueous solution
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The title ion in aqueous basic solution does not undergo deoxygenation in the dark, but it does on irradiation with ultraviolet light to give the photoinduced equilibration (Equation Presented) The quantum yield determined in the presence of excess EDTA is ca. 2.2 × 10-3 on irradiation at 366 nm at 5°C and is virtually independent of pH (8.1-10.4). The yield on irradiation at 515 nm at ca. 25°C is -6. The ligand(O2)-to-metal charge-transfer excited state is relevant to the deoxygenation reaction. Continuous irradiation leads to subsequent irreversible decomposition to give cobalt(III) species including [CoIII(en)2(H2O)2]3+. Such an irreversible decomposition is much slower in the dark (ca. 5 × 10-7 s-1 at 5°C, pH 8.9, and I = 0.1 M (NaClO4); 1 M = 1 mol dm-3).
- Kikkawa, Masahiro,Sasaki, Yoichi,Kawata, Satoshi,Hatakeyama, Yoshihiro,Ueno, Fumio B.,Saito, Kazuo
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p. 4096 - 4100
(2008/10/08)
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- Electron-transfer reactions of tris(picolinato)vanadate(II), a LOMI reagent
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Reductions of Co(edta)-, Co(NH3)63+, Co(en)33+, and Co(sep)3+ by tris(picolinato)vanadate(II), V(pic)3-, take place with second-order rate constants 7.7 × 104 M-1 s-1, 8.0 × 103 M-1 s-1, 8.2 × 102 M-1 s-1, and 8.4 × 104 M-1 s-1, respectively, at 25.0°C and at 0.5 M ionic strength. Application of the Marcus theory to the latter three results leads to a self-exchange rate for V(pic)30/- of 3.1 × 106 M-1 s-1. For Co(edta)- the observed rate is an order of magnitude slower than predicted by the Marcus theory and reasons for this discrepancy are proposed.
- Lannon, A. Martin,Lappin, A. Graham,Segal, Michael G.
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p. 4167 - 4170
(2008/10/08)
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- Kinetics and mechanism of the forward and reverse reactions between (pyridine)pentaammineruthenium(III) or (4,4′-bipyridine)pentaammineruthenium(III) and (ethylenediaminetetraacetato)cobaltate(II)
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Kinetic measurements of the forward and reverse reactions for Ru(NH3)5L3+ + CoEDTA2- ? Ru(NH3)5L2+ + CoEDTA- have been carried out at 25.0°C, pH 6.0, and ionic strength 0.10 M. For L = pyridine or 4,4′-bipyridine, the rate constants are 32 ± 1 and 77 ± 4 M-1 s-1 (forward reactions) and 236 ± 5 and 156 ± 3 M-1 s-1 (reverse reactions). The mechanisms of these reactions are discussed in the context of Marcus' cross relation for outer-sphere processes corrected for electrostatic effects.
- Phillips, James,Haim, Albert
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