22541-53-3Relevant academic research and scientific papers
Nucleation, growth, and repair of a cobalt-based oxygen evolving catalyst
Surendranath, Yogesh,Lutterman, Daniel A.,Liu, Yi,Nocera, Daniel G.
, p. 6326 - 6336 (2012)
The mechanism of nucleation, steady-state growth, and repair is investigated for an oxygen evolving catalyst prepared by electrodeposition from Co2+ solutions in weakly basic electrolytes (Co-OEC). Potential step chronoamperometry and atomic force microscopy reveal that nucleation of Co-OEC is progressive and reaches a saturation surface coverage of ca. 70% on highly oriented pyrolytic graphite substrates. Steady-state electrodeposition of Co-OEC exhibits a Tafel slope approximately equal to 2.3 × RT/F. The electrochemical rate law exhibits a first order dependence on Co2+ and inverse orders on proton (third order) and proton acceptor, methylphosphonate (first order for 1.8 mM ≤ [MePi] ≤ 18 mM and second order dependence for 32 mM ≤ [MePi] ≤ 180 mM). These electrokinetic studies, combined with recent XAS studies of catalyst structure, suggest a mechanism for steady state growth at intermediate MePi concentration (1.8-18 mM) involving a rapid solution equilibrium between aquo Co(II) and Co(III) hydroxo species accompanied with a rapid surface equilibrium involving electrolyte dissociation and deprotonation of surface bound water. These equilibria are followed by a chemical rate-limiting step for incorporation of Co(III) into the growing cobaltate clusters comprising Co-OEC. At higher concentrations of MePi ([MePi] ≥ 32 mM), MePO 32- equilibrium binding to Co(II) in solution is suggested by the kinetic data. Consistent with the disparate pH profiles for oxygen evolution electrocatalysis and catalyst formation, NMR-based quantification of catalyst dissolution as a function of pH demonstrates functional stability and repair at pH values >6 whereas catalyst corrosion prevails at lower pH values. These kinetic insights provide a basis for developing and operating functional water oxidation (photo)anodes under benign pH conditions.
Kinetic Investigation of the Oxidation of Bromide Ions by Cobalt(III). Part 2. - The Influence of Pyridine and Hydrocarbon on the Reaction in Acetic Acid Solvent
Schlosserova, Julia,Hronec, Milan,Vesely, Vaclav
, (1986)
The kinetics of cobalt(III) acetate reduction in acetic acid have been studied under nitrogen at 60-93 deg C in the presence of bromide, p-xylene and pyridine.At high p-xylene concentration the initial rate of reaction obeys the rate low with k
Azetidines as intermediates in polyamine synthesis - Structure and reactions of a quadridentate ligand incorporating an azetidine ring
Harrowfield, Jack M.,Gyu, Hwan Jang,Kim, Yang,Thuery, Pierre,Vicens, Jacques
, p. 1241 - 1243 (2002)
Reaction of the tris(benzene sulfonate) of 1,1,1-tris-(hydroxymethyl)ethane with neat 1,2-ethanediamine under relatively mild conditions leads to formation in good yield (60%) of a quadridentate amine incorporating a four-membered, azetidine ring, the nature of the tetramine being established by determination of the crystal structures of two of its cobalt(III) complexes and the reactivity of the azetidine ring being explored in further reactions with 1,2-ethanediamine.
Kinetics of the Iron(II) Reduction of Glycinatobis(malonato)-, trans-Bis(malonato)bis(pyridine)-, Nitrilotriacetato(malonato)-, and Nitrilotriacetato(oxalato)cobaltates(III)
Viswanathan, Ramakrishnan,Vijayaraghavan, Venkatapuram Raman.
, p. 3243 - 3246 (1986)
The kinetics of the iron(II) reduction of glycinatobis(malonato)-, trans-bis(malonato)bis(pyridine), nitrilotriacetato(malonato)-, and nitrilotriacetato(oxalato)cobaltates(III) have been studied in aqueous perchlorate medium at I=1.0 mol dm-3 (LiClO4) and 30 deg C in the +> range 0.01-0.90 mol dm-3.The reductions are found to be second order.The reduction of 2- and - is accelerated by H+, while the reduction of 2- and 2- is independent of +> in the range 0.1+>-3.The reduction of 2- is, however, faster at +>-3.The activation parameters for the reduction of 2-, -, 2-, and 2- are respectively as follows: ΔH=49.8+/-4.8, 51.2+/-2.6, 41.1+/-3.2, and 41.4+3.6 kJ mol-1, ΔS=-98.3+/-8.3, -93.7+/-7.2, -119.2+/-9.7, and -114.6+/-9.6 J K-1 mol-1.The proposed mechanism invokes (L-py2 or gly) formed in a H+-assisted step as the reactive species for the bis(malonato) complexes. 2- is proposed to be present as - while 2- remains unaffected by H+.
INTRAMOLECULAR ELECTRON TRANSFER AT METAL SURFACES. 3. INFLUENCE OF BOND CONJUGATION ON REDUCTION KINETICS OF COBALT(III) ANCHORED TO ELECTRODES VIA THIOPHENECARBOXYLATE LIGANDS.
Li,Liu,Weaver
, p. 1233 - 1239 (1984)
Unimolecular rate constants, k//e//t, are reported for the one-electron electroreduction of pentaamminecobalt(III) anchored to mercury, gold, or copper electrodes via various thiophenecarboxylate ligands where the thiophene sulfur acts as the surface bind
Kinetics and Mechanism of Oxidation of S2O32? by a Co-Bound μ-Amido-μ-Superoxo Complex
Singh, Bula,Das, Ranendu Sekhar,Banerjee, Rupendranath,Mukhopadhyay, Subrata
, p. 88 - 97 (2016)
In acetate buffer media (pH 4.5–5.4) thiosulfate ion (S2O32?) reduces the bridged superoxo complex, [(NH3)4CoIII(μ-NH2,μ-O2)CoIII(NH3)4]4+ (1) to its corresponding μ-peroxo product, [(NH3)4CoIII(μ-NH2,μ-O2)CoIII(NH3)4]3+ (2) and along a parallel reaction path, simultaneously S2O32? reacts with 1 to produce the substituted μ-thiosulfato-μ-superoxo complex, [(NH3)4CoIII(μ-S2O3,μ-O2)CoIII(NH3)4]3+ (3). The formation of μ-thiosulfato-μ-superoxo complex (3) appears as a precipitate which on being subjected to FTIR shows absorption peaks that support the presence of Co(III)-bound S-coordinated S2O32? group. In reaction media, 3 readily dissolves to further react with S2O32? to produce μ-thiosulfato-μ-peroxo product, [(NH3)4CoIII(μ-S2O3,μ-O2)CoIII(NH3)4]2+ (4). The observed rate (k0) increases with an increase in [TThio] ([TThio] is the analytical concentration of S2O32?) and temperature (T), but it decreases with an increase in [H+] and the ionic strength (I). Analysis of the log At versus time data (A is the absorbance of 1 at time t) reveals that overall the reaction follows a biphasic consecutive reaction path with rate constants k1 and k2 and the change of absorbance is equal to {a1 exp(–k1t) + a2 exp(–k2t)), where k1 > k2.
Measurement of solvent dynamics effects on the electron transfer reaction of Co(NH3)4ox+ in mixed solvents: A quantitative approach
Anbalagan,Geethalakshmi,Poonkodi
, p. 1918 - 1927 (2003)
For reactions involving electron transfer or nucleophilic attack on the transition state/excited state of metal complex in aquo-organic solvent mixtures, a linear relationship between logarithms of rate constant and solvent empirical parameters can be derived. Fe(CN)64- reduction of Co(NH3)4ox+ and ligand to metal charge transfer (LMCT) excited-state redox reaction of Co(NH3)4ox+ were studied in varying compositions of aqueous mixtures of methanol (MeOH) and 1,4-dioxane (Diox). A quantitative estimation of relative importance of the components was attempted. A number of empirical solvent parameters were used in the multiple regression equations. The correlation analysis showed significant information on the effect of solvent-solvent and solvent-solute interactions on reactivities. The addition of MeOH or Diox to the medium brings about marked structural changes in the prevailing water structure by making progressive desolvation between partners of the transition state/geminate radical pair which in all probability is highly solvated in the water medium. The positive sign of multiparametric coefficients suggested that the solvent mixture strongly solvates the transition state, and the negative sign of the coefficients shows the specific solvation of incipient reactants.
Formation of an observable intermediate during the reduction of [Co (III)(NH3)5CN]2+ by ?CR1R2(OH) radicals
Herscu-Kluska, Ronit,Cohen, Haim,Meyerstein, Dan
, p. 2821 - 2826 (2005)
?CR1R2OH, Ri = CH 3 or H, react with the complex [CoIII(NH3) 5CN]2+ to form an observable intermediate probably via bonding to the nitrogen of the cyanide. This intermediate isomerizes to form a second intermediate. The second intermediate decomposes into Co 2+(aq), 5NH4+, CN- and R 1R2CO. The plausible structures of the intermediates are discussed. The radicals ?CH3, ?CH 2CHO, CH(OH)CO2-, CH2C(CH3)2OH,CO2- and CH3O2 are considerably less reactive towards this complex, the formation of intermediates in their presence is not observed.
The solid-state electrochemistry of metal octacyanomolybdates, octacyanotungstates, and hexacyanoferrates explained on the basis of dissolution and reprecipitation reactions, lattice structures, and crystallinities
Schr?der, Uwe,Scholz, Fritz
, p. 1006 - 1015 (2000)
The electrochemical behavior of solid microparticles of metal (Ag+, Cd2+, Co2+, Cr2+, Cu2+, Fe2+, Mn2+, Ni2+, Pb2+, and Zn2+) octacyanomolybdates, octacyanotungstates, and hexacyanoferrates has been studied by voltammetry, electrochemical quartz crystal microbalance, and microscopic diffuse reflectance spectroelectrochemical measurements. The solid microparticles have been immobilized on the surface of graphite electrodes prior to the electrochemical measurements. A comparative study of the cyclic oxidation and reduction of these compounds in the presence of potassium ions revealed that any interpretation of the electrochemistry requires the solubility equilibria of the reduced compounds to be taken into account, such as in the case of the silver salts {Ag3K[X]} and {Ag4[X]} (with X = Fe(II)(CN)6/4-, M(IV)(CN)8/4- (M = Mo, W)). Because {Ag4[X]} has a lower solubility than {Ag3K[X]}, the electrochemistry is accompanied by a conversion of solid {Ag3K[X]} into solid {Ag4[X]}. Two distinct voltammetric signal systems are generated by these two compounds according to {Ag3K[X]} ? {Ag3-[X]} + K+ + e- and {Ag4[X]} ? {Ag3[X]} + Ag+ + e-. When silver ions are present in the solution adjacent to the microparticles, the silver octacyanometalates and silver hexacyanoferrate show a chemically reversible and very stable voltammetric behavior. Despite the fact that the electrochemistry is based upon a single-electron/single-ion transfer reaction ({Ag4[X]} ? {Ag3[X]} + Ag+ + e-), more than one electrochemical signal is observed because of the simultaneous presence of amorphous and crystalline particles. This study shows that the interplay of solubility equilibria and electrochemical equilibria is generally observed for the other metal octacyanomolybdates, octacyanotungstates, and hexacyanoferrates as well.
Outer-sphere Redox Reactions in Sterically Hindered Pentaam(m)inecobalt(III) Complexes. A Temperature and Pressure Dependence Kinetic Study
Martinez, Manuel,Pitarque, Mari-Angel,Eldik, Rudi van
, p. 3159 - 3164 (1994)
Outer-sphere redox reactions between (3+) and (4-) have been studied as a function of pH, temperature and pressure.The effect of the size of the alkyl substituent on the amine, RNH2, has been investigated for both the aqua- and the hydroxo-species in order to establish possible correlations between size and ion-pair formation constant, electron-transfer rate constant, and thermal and pressure activation parameters.The values obtained (at 45 deg C and ambient pressure) indicate that the ion-pair formation constant decreases with increasing size of R (75, R = H; 40, Me; 23 dm3 mol-1, Et), whereas the electron-transfer rate constant increases in this direction (0.11, R = H; 9.3, Me; 35 s-1, Et).The activation enthalpies do not change, either with decreasing charge on the cobalt complex or with the size of the amine (87, R = H; 79, Me; 84 kJ mol-1, Et).As for the activation volume, although a slight increase is observed on increasing the size of R (26.5, R = H; 29.4, Me; 33.1 cm3 mol-1, Et), it is clear that solvational changes during electron transfer are mainly responsible for the values obtained.
