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  • 1
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of thiocyanate anation ofcis-β-diaqua-(3,6-diazaoctane-1,8-diamine)cobalt(III) in aqueous medium (1985)
    Springer
    Transition metal chemistry 10 (1985), S. 252-254 
    Details
    ISSN: 1572-901X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Kinetic studies of the anation of the title complex by NCS− show that it occurs in a stepwise manner leading to thecis-β-dithiocyanato complex, both steps having a common rate equation (1): (1) $$k_{obs} = k' + \frac{{k \cdot Q[NCS^ - ]}}{{1 + {\text{Q[NCS]}}}}.$$ The variation ofpseudo-first-order rate constant with pH shows that for the first step k increases with increase in pH (in the 1.8–2.8 range) whereas it remains fairly constant for the second step. Acis-labilisation effect of the hydroxo-group arising from the protic equilibrium of the parent complex is operative and the reaction proceeds through a dissociative interchange process. The activation parameters corresponding to the k' and k paths for each of the steps have been evaluated and compare well with those reported for similar systems.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00621080
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  • 2
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of acetate and succinate anations ofcis-tetraamminediaquacobalt(III) in aqueous acidic media (1986)
    Springer
    Transition metal chemistry 11 (1986), S. 76-80 
    Details
    ISSN: 1572-901X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The complexcis-tetraamminediaquacobalt(III) reacts with acetate ion to formcis-tetraamminediacetatocobalt(III). Kinetic evidence shows that the reaction proceeds in a single step process in the pH range 4.0–5.2, but it splits to a biphasic one at pH 5.4. The acetate anation is governed by the rate law: $${\text{k}}_{{\text{obs}}} = {\text{k}}_{\text{0}} + \frac{{{\text{kQ[OAc}}^ - {\text{]}}}}{{1 + {\text{Q[OAc}}^ - {\text{]}}}}$$ where kobs, k0, k and Q denote the observed rate constant, the back aquation rate, the interchange rate and the ion-pair formation constant, respectively. The ΔH≠] and ΔS≠ values associated with the interchange rate are 137 ± 8 kJ mol−1 and 137 ± 12 JK−1mol−1, respectively. The title complex reacts with succinate ions (HSuc−1 and Suc2−) to form tetraamminesuccinatocobalt(III) and no evidence has been obtained for any significant build-up of the monodenate succinato intermediate. It is concluded that the step in which the succinate ion chelates is rapid. The kinetics of the first stage of the reaction involving coordination of succinate ion to cw-[Co(N-H3)4(OH2)2]3+ have been investigated at pH=2.5–4.0, I=0.5 mol dm−3 (NaClO4) and at temperatures 30–50 °C. The interpretation given is consistent with the formation of ion-pairs between the diaqua complex and the succinate ions, HSuc− and Sue2−. The reaction is believed to proceed through a dissociative interchange mechanism.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00618608
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  • 3
    Digitale Medien
    Digitale Medien
    Solvatochromism and piezochromism of metal→ligand chargetransfer bands of ternary diimine complexes of tungsten(0), molybdenum(0), and iron(II) (1988)
    Springer
    Transition metal chemistry 13 (1988), S. 107-112 
    Details
    ISSN: 1572-901X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The solvatochromic behaviour of W(CO)4(LL), LL=a diazabutadiene or a pyridine Schiff base, and of Mo(CO)4 (butane-2,3-dionedihydrazone) is described. Pressure effects on the charge-transfer spectra of these compounds, the [Mo(CO)4(fz)]2− anion {fz=ferrozine; 3-(2-pyridyl)-5, 6-bis-(4-sulphonatophenyl)-1,2,4-triazine}, and Fe(bipy)2(CN)2 are reported. Solvent sensitivities are discussed in terms of the nature of the ligands and of the central metal atom, and the idea of a correlation between these solvent sensitivities and piezochromic behaviour developed for these and related ternary irondiimine-cyanide species.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01087799
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  • 4
    Digitale Medien
    Digitale Medien
    The kinetics of oxidation of N(2-hydroxyethyl)ethylenediaminetriacetatocobaltate(II) by peroxodisulfate ion in aqueous acidic solutions (1981)
    Springer
    Transition metal chemistry 6 (1981), S. 47-50 
    Details
    ISSN: 1572-901X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Peroxodisulfate ion readily oxidises CoII-YOH [YOH =N(2-hydroxyethyl)ethylenediaminetriacetate] with the formation of an intermediate complex. The kinetics of the electron-transfer step follow the rate law: Rate = 2kHKH[H+][S2O8]2-[CoII-YOH]/(1 + KH[H+]) where [S2O8]2− is the total peroxodisulfate concentration, kH is the rate constant for the electron-transfer process, and KH is the pre-equilibrium protonation constant. Activation parameters have been evaluated. The intermediate, which was identified spectrophotometrically, slowly rearranges to the quinquedentate species Co(YOH)(H2O). The rate of this rearangement has also been measured.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01143469
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  • 5
    Digitale Medien
    Digitale Medien
    Kinetics of the peroxodisulphate and hydrogen peroxide oxidations oftrans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetatocobaltate(II) in acidic and basic buffer media (1983)
    Springer
    Transition metal chemistry 8 (1983), S. 91-93 
    Details
    ISSN: 1572-901X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Kinetics of the oxidation of Co(cydta)2− (H4cydta=trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid) by peroxodisulphate (S2O 8 2− ) and by hydrogen peroxide have been studied in the ranges of pH 3.6–5.8 (acetate buffer) and 6.0–8.0 (phosphate buffer), respectively. For the first oxidant, the reaction was shown to exhibit second-order kinetics, first-order in each of the reactants. No pH dependence on rate was observed. The hydrogen peroxide reaction was also second-order, being first-order in each of the reactants. The rate of reaction showed inverse [H+] dependence. The rate law is given by $${\text{d[Co(cydta)}}^-- {\text{]/dt = 2\{ k}}_{{\text{H}}_{\text{2}} O_2 } {\text{ + k}}_{{\text{H}}O_2 - } {\text{K}}_{\text{a}} {\text{[H}}^{\text{ + }} {\text{]}}^{--1} {\text{\} [Co(cydta)}}^{{\text{2}}--} {\text{][H}}_{\text{2}} {\text{O}}_{\text{2}} {\text{]}}$$ . At 30 °C (I, 0.5 M), the ratio of $$k_{HO_2 - } /k_{H_2 O_2 } \sim 10^5 $$ . The corresponding activation parameters obtained from the temperature-dependence of rate are ΔH≠= (136±9) kJ mol−1, ΔS≠=(119±10) JK−1 mol−1 (for the peroxodisulphate system) and ΔH≠=(75±2) kJ mol−1, ΔS≠ =(−78±4) JK−1 mol−1 (for the hydrogen peroxide system).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01036087
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  • 6
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of the reactions ofcis-tetraaminediaqua-cobalt(III) with nitrite, azide and salicylate ions in aqueous acidic media (1984)
    Springer
    Transition metal chemistry 9 (1984), S. 68-73 
    Details
    ISSN: 1572-901X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Kinetic studies of the anation of the title complex by NO 2 − show that it occurs in a stepwise manner leading to thecis-dinitro-complex both steps having a common rate equation:-d[complex]/dt = a[NO 2 − ]/{[NO 2 − ] + b}. The variation ofpseudo-first-order rate constant (kobs) with [NO 2 − ] indicates that the reaction proceeds through ion-pair interchange path. Activation parameters calculated by the Eyring equation are: ΔH 1 ≠ = (65±7) kJ mol−1 and ΔS 1 ≠ = (−82±11) JK−1 mol−1 for the formation of [Co(NH3)4(NO2)(H2O)]2+, and ΔH 2 ≠ = (97±1) kJ mol−1 and ΔS 2 ≠ = (6±2) JK−1 mol−1 for the formation of [Co(NH3)4(NO2)2]+. Anation of the title complex by N 3 − at pH 4.1 also occurs in a stepwise manner ultimately producing thecis-diazido species. At a fixed pH the reaction shows a first-order dependence on [N 3 − ] for each step. pH-variation studies at a fixed [N 3 − ] show that the hydroxoaqua-form of the complex reactsca. 16 times faster than the diaqua form. Evidence is presented for an ion-pair preequilibrium at high ionic strength (I = 2.0 mol dm−3). Activation parameters obtained from temperature variation studies are: ΔH 1 ≠ = (121±1) kJ mol−1 and ΔS 1 ≠ = (104±3) JK−1 mol−1 (for the first step anation), and ΔH 2 ≠ = (111±2) kJ mol−1 and ΔS 2 ≠ = (74±9) JK−1 mol−1 (for the second step anation). The reaction ofcis-tetraaminediaquacobalt(III) ion with salicylate (HSal−) has been studied in aqueous acidic medium in the temperature range 39.8–58.2°C. The reaction is biphasic corresponding to the anation of two salicylate ions. The kinetic results for the first phase reaction are compatible with the equation: kobs = kIPQ[HSal−]/(1 + Q[HSal−]) where Q denotes ion-pair formation constant and kIP is the first-order rate constant for the interchange reaction. The activation parameters obtained from the temperature dependence of rate are: ΔH≠ = (138±3) kJ mol−1 and ΔS≠ = (135±4) JK−1 mol−1. The reaction seems to take place by a dissociative interchange mechanism.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00619005
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  • 7
    Digitale Medien
    Digitale Medien
    Electrochemical and chemical reduction studies of molybdenum(VI)-and molybdenum (V)-ethylenediaminetetraacetic acid complexes (1980)
    Springer
    Transition metal chemistry 5 (1980), S. 117-120 
    Details
    ISSN: 1572-901X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The electrochemical reduction characteristics of the molyb-denum(VI)-and molybdenum(V)-ethylenediaminetetraacetate complexes, [(MoO3)2Y]4− and [Mo2O4Y]2− respectively have been investigated as a function of pH and free ligand concentration. The nature of chemical reduction of these two complexes with sodium borohydride and sodium dithionite have also been studied in acetate and borate buffers. The electroactive species undergoing electrode reductions have been ascertained by analysing polarograms of the complexes. A mechanism has been proposed to account for the differences observed in the reactivities of these two complexes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01396886
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  • 8
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of the reduction of dodecatungstocobaltate(III) by α-hydroxyacids in aqueous acid solution. Evidence for alkali metal ion catalysis (1991)
    Springer
    Transition metal chemistry 16 (1991), S. 160-164 
    Details
    ISSN: 1572-901X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The kinetics of the redox reaction of dodecatungstocobaltate(III) [abbreviated as CoIIIW] with three α-hydroxy-carboxylic acids:e.g., mandelic, glycolic and lactic acid, were investigated in the 0–5.4 pH range where the complex remains stable and does not decompose. All reactions are first-order both in oxidant and reductant over the experimental pH range. A specific metal ion effect has been observed. Oxidations of the molecular form of the three acids and the anionic form of mandelic acid are catalysed by alkali metal ions and follow a general rate law: $$ - d[Co^{III} W]/dt = 2(k_s + k_c [M^ + ])[R][Co^{III} W]$$ where ks and kc account for the spontaneous and catalysed paths respectively, M+ is either an alkali metal ion (Li+, Na+ or K+) and [R], the reductant concentration. The oxidation of lactate and glycolate ions occurs only in the presence of alkali cations. The cation catalytic order: K+〉Na+〉Li+ observed in this study is in accord with the polarizability of the cations. An outer-sphere alkali cation-bridged mechanism is suggested for the electron transfer step.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01032824
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  • 9
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of the reaction oftrans-cyclohexane-1,2-diamine-N N N' N'-tetra-acetatomanganate(III) with substituted thioureas in aqueous medium (1991)
    Springer
    Transition metal chemistry 16 (1991), S. 355-357 
    Details
    ISSN: 1572-901X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The kinetics of reduction of [MnIII(cydta)]− (where H4cydta=trans-cyclohexane-1,2-diamine-N N N' N'-tetraacetic acid) by some thiourea reductants have been studied in aqueous solution by stopped-flow techniques in the pH ranges 2.5–4.5 and 9.2–10.2. An initial increase in absorbance followed by a steady decrease indicated the formation of a precursor complex prior to the electron transfer step. The reactions are first order in both oxidant and reductant. The observed increase in rate in going from low to high pH is attributed to the difference in reactivities of the aqua and hydroxo species of the MnIII complex; the higher reactivity of the latter is consistent with the formation of a ligand-bridged activated species prior to electron transfer. The reactivity order for the thiourea derivatives follows the order of their reported substituent effects.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01024082
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  • 10
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of the oxidation of some carboxylates by a nickel (III) oxime-imine complex (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 29 (1997), S. 225-230 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the oxidation of formate, oxalate, and malonate by |NiIII(L1)|2+ (where HL1 = 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime) were carried out over the regions pH 3.0-5.75, 2.80-5.50, and 2.50-7.58, respectively, at constant ionic strength and temperature 40°C. All the reactions are overall second-order with first-order on both the oxidant and reductant. A general rate law is given as - d/dt|NiIII(L1)2+| = kobs|NiIII(L1)2+| = (kd + nks |R|)|NiIII(L1)2+|, where kd is the auto-decomposition rate constant of the complex, ks is the electron transfer rate constant, n is the stoichiometric factor, and R is either formate, oxalate, or malonate. The reactivity of all the reacting species of the reductants in solution were evaluated choosing suitable pH regions. The reactivity orders are: kHCOOH 〉 kHCOO-; kH2ox 〉 kHox- 〉 kox2-, and kH2mal 〉 kHmal- 〈 kmal2- for the oxidation of formate, oxalate, and malonate, respectively, and these trends were explained considering the effect of hydrogen bonded adduct formation and thermodynamic potential. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 225-230, 1997.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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