Kinetics and mechanism of the oxidation ofbis(2,4,6-tripyridyl-1,3,5-triazine)iron(II) bytrans-1,2-diaminocyclohexanetetraacetatomanganate(III) in acetate buffer

The rapid oxidation ofbis(2,4,6-tripyridyl-1,3,5-triazine)-iron(II), [Fe(TPTZ)₂]²⁺, bytrans-1,2-diaminocyclohexanetetraacetatomanganate(III), [Mn^III(Y)]⁻, in acetate buffers was monitored using stopped-flow spectrophotometry. The reaction is first order in the substrate and evidence was obtained for pre-complexation between the oxidant and the substrate. The reaction rate increases as the pH increases. Characterisation of the products using the radiotracers⁵⁴Mn and⁵⁹Fe indicated that [Mn^II(Y)]²⁻ and [Fe(TPTZ)₂]³⁺ are the final products. The reaction obeys the rate law:

Oxidation of N-(2-hydroxyethyl)ethylenediamine triacetate by tris(polypyridy)iron(III) complexes and the dodecatungstocobaltate(III) ion

Summary The stoichiometry, kinetics and mechanism of oxidation of N-(2-hydroxyethyl)ethylenediamine triacetate by K₅Co^IIIW₁₂O₄₀, Fe(phen) _inf3 ^sup3+ and Fe(bipy) _inf3 ^sup3+ have been studied. Each reaction is first order with respect to the oxidant and the reductant, but retarded by [H⁺] in the 0.20–1.60 mol dm ^–3 range. Simple electron exchanges are thought to occur, leading to the decarboxylation of the substrate.     

Kinetics and mechanism of substitution of bis(2,4,6-tripyridyl 1,3,5-triazine)iron(II) by 2,2′,6,2″-terpyridine

The substitution of bis(2,4,6-tripyridyl 1,3,5-triazine)iron(II), \textFe(TPTZ) ₂ ^{2 +} {\text{Fe(TPTZ)}}_{ 2}^{{ 2 { + }}} by 2,2′,6,2″-terpyridine (terpy) occurs on a time scale of about 6 m. The kinetics of this reaction was followed by stopped-flow spectrophotometry in the pH range of 3.6–5.6 in acetate buffer. The data indicate that the reaction occurs in two consecutive steps: kinetic data for both steps were acquired simultaneously and analyzed independently. The first step is assigned to the reaction between \textFe(TPTZ) ₂ ^{2 +} {\text{Fe(TPTZ)}}_{ 2}^{{ 2 { + }}} and terpy to give Fe(TPTZ)(terpy)²⁺, followed by its reaction with another terpy molecule to give the final product, \textFe(terpy) ₂ ^{2 +} {\text{Fe(terpy)}}_{ 2}^{{ 2 { + }}} . The rate of the reaction increases with increases in [terpy] and pH. The kinetic and activation parameters determined for both steps suggest that they involve both associative and dissociative paths. The ternary complex Fe(TPTZ)(terpy)²⁺ has been prepared, and the kinetics of its reaction with terpy suggest that this reaction is identical with the second step of the \textFe(TPTZ) ₂ ^{2 +} {\text{Fe(TPTZ)}}_{ 2}^{{ 2 { + }}} -terpy system, supporting the proposed mechanism.     

Mechanistic studies of the reaction of bis(2,4,6-tripyridyl 1,3,5-triazine)iron(II) with triazines

Bis(2,4,6-tripyridyl 1,3,5-triazine)iron(II), \textFe(\textTPTZ) ₂ ^{2 +} {\text{Fe(\text{TPTZ})}}_{ 2}^{{ 2 { + }}} reacts with 3-(2-pyridyl)-5,6-bis(4-phenyl-sulfonicacid)-1,2,4-triazine (PDTS) and 3-(4-(4-phenylsulfonicacid)-2-pyridyl)-5,6-bis(4-phenylsulfonic-acid)-1,2,4-triazine (PPDTS) to give \textFe(PDTS) ₃ ^4- {\text{Fe(PDTS)}}_{ 3}^{ 4- } and \textFe(PPDTS) ₃ ^7- {\text{Fe(PPDTS)}}_{ 3}^{ 7- } respectively. Both of these substitution reactions are fast and their kinetics were monitored by stopped-flow spectrophotometry in acetate buffers in the pH range of 3.6–5.6 at 25–45 °C. Both reactions are first order in \textFe(TPTZ) ₂ ^{2 +} {\text{Fe(TPTZ)}}_{ 2}^{{ 2 { + }}} and triazine, and pH has negligible effect on the rate. The kinetic data suggest that these reactions occur in an associative path and a mechanism is proposed considering both protonated and unprotonated forms of PDTS and PPDTS are very similar in reactivity. The kinetic and activation parameters have been evaluated.     

PROTONATION CONSTANTS OF 2,6-BIS(2-PYRIDYL)PYRIDINE AND 2,4,6-TRIS(2-PYRIDYL)-1,3,5-TRIAZINE AND FORMATION CONSTANTS OF THEIR BINARY AND TERNARY IRON(II) COMPLEXES

Abstract

Equilibrium constants involving the ternary mixed ligand iron(II) complex [Fe(TPTZ)(terpy)]²⁺, determined spectrophotometrically at 23° and μ=0.5 M, are reported. Acidity constants of the protonated ligands and formation constants of the binary iron(II) complexes [Fe(TPTZ)₂]²⁺ and [Fe(terpy)₂]²⁺, measured as an adjunct to determining the ternary complex constants, are also reported. The results are of interest in elucidating mixed-ligand complexation effects as well as in confirming or correcting previously reported equilibrium constants of the binary complexes.     

Complexation of cobalt(II) with histidinato(pentaammine)cobalt(III) in aqueous medium. A kinetic and mechanistic study

Summary The kinetics of formation and dissociation of the binuclear complex of Co^II with histidinato(pentaammine)Co^III have been studied at 10.0°Ct°C25°C and I = 0.3 mol dm^–3 (ClO _inf4 ^sup– ). The formation of the binuclear complex, [(NH₃)₅Co^IIILCo^II]⁴⁺ (L = histidinate), in the 5.7–6.8 pH range involves the reaction of Co(OH₂) _inf6 ^sup2+ with the deprotonated, (NH₃)₅CoL²⁺, and monoprotonated, (NH₃)₅CoLH₃₊, forms of the complex. The rate and activation parameters for the formation are consistent with an I _d mechanism. The binuclear species undergoes dissociation to yield the parent Co^III substrate and Co(OH₂) _inf6 ^sup2+ via spontaneous and acid-catalysed paths. Comparison of spontaneous dissociation rate of the binuclear complex with other related systems indicated the chelate nature of the binuclear species.     

Sorption of iron(II) and ruthenium(III)-triazine complexes on silica gel and its analytical applicability

2,4,6-Tri(2′-pyridyl)-s-triazine (TPTZ) complexes with iron(II) and ruthenium(III) were prepared. Their sorption and desorption features on silica gel have been investigated. Both complexes were strongly adsorbed. This has been utilized for separating and preconcentrating iron(II) and ruthenium(III) using TPTZ-impregnated silica gel. The chromatographic behavior of TPTZ on silica gel column was examined and found to be effective modifier for silica gel surface. The sorption capacity of silica gel for those metal-triazine complexes has been determined under static conditions and was found to be 5.28 × 10^–3 mM (Fe(TPTZ)₂²⁺) and 2.9 × 10^–3 mM (Ru(TPTZ)₂³⁺). Saturated methanolic solutions of KI or 25% NaClO₄ solutions desorbed both complexes quantitatively from the silica gel surface.     

Vanadium(V) oxidation of thallium(I) in hydrochloric acid

The reaction between V^V and Tl^I was studied in 4.0 mol dm^–3 HCl at an ionic strength of 4.1 mol dm^–3 at 25° C. The main active species under the reaction conditions were found to be VO _inf2 ^sup+ and TlCl _inf3 ^sup2– for the oxidant and reductant, respectively. A probable mechanism in terms of these species is given, and follows the rate law:

Axial-ligation and macrocyclization of novel (E,E)-dioximes of nickel(II) palladium(II), platinum(II) and cobalt(III)

Summary The synthesis and characterization of new Ni^II, Pd^II, Pt^II and Co^III complexes, with the BF _inf2 ^sup+ -bridged,bis(-di-oximato) ligands are described. The initially formed six-coordinate hydrogen-bonded macrocycles, were used as metal templates to prepare the corresponding BF _inf2 ^sup+ - capped macrocycles. The complexes were characterized by¹H-n.m.r. and i.r. spectroscopy, and by elemental analysis.     

Unusual kinetic role of a water‐soluble iron(III) porphyrin catalyst in the oxidation of 2,4,6‐trichlorophenol by hydrogen peroxide

The oxidation of 2,4,6‐trichlorophenol (TCP) to 2,6‐dichloro‐1,4‐benzoquinone (DCQ) by hydrogen peroxide using iron(III) meso‐tetra(4‐sulfonatophenyl) porphine chloride, Fe(TPPS)Cl, as a catalyst was studied with stopped‐flow UV–vis spectrophotometry and potentiometry using a chloride ion selective electrode. The observations are interpreted by a three‐step kinetic model: the initial reaction of the catalyst with the oxidant (Fe(TPPS)⁺ + H₂O₂ → Cat′) produces an active intermediate, which oxidizes the substrate (Cat′ + TCP → Fe(TPPS)⁺ + DCQ + Cl^?) in the second step. The third step is the transformation of the catalyst into a much less active form (Cat′ → Cat″) and is responsible for the unusual kinetic phenomena observed in the system. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:449–455, 2004.     

Electron transfer reactions of tris(1,10-phenanthroline)cobalt(II) with copper(III) imine-oxime complexes

Summary The kinetics of oxidation of [Co^II(phen)₃]²⁺ (phen = 1,10-phenanthroline) by copper(III) imine-oxime complexes are first-order in each reactant. All reactions proceed via two parallel pathways; one pH independent, the other pH dependent. The second-order rate constant varies with [H⁺] as k₂ = k _inf2 ^supo + k _inf2 ^supH [H⁺]. The rapidity of the electron transfer step, coupled with the relative inertness of [Co^II(phen)₃]²⁺ over the pH range studied and the absence of a bridging atom on the phen ligand, supports an outer-sphere mechanism for this process. Reasonably good agreement between the experimental rate constants and those calculated using the Marcus equation has been obtained.     

Equilibria in complexes of N-heterocyclic molecules,part XXI. Kinetics of reaction of hydroxide with bis [2,4,6-tri (2-pyridyl)-1,3,5-triazine] iron (II) and ruthenium(II)

Summary The kinetics of reaction of HO^– with [Ru(TPT)₂]²⁺ and [Fe(TPT)₂]²⁺ have been studied in detail. The former participates in an equilibrium with HO^– yielding a pseudo-base by attack at the ligand and, at very high concentrations of HO^–, dissociates to yield pure TPT quantitatively. [Fe(TPT)₂]²⁺ dissociates rapidly in basic solution, even at 273 K, however, [Fe(TPT)(TPT · OH)]+ does in fact exist and the Fell and Ru^ll reactions are quite similar, although that of Fell is much faster. The implications of these findings for the dissociation of [Fe(TPT)₂]²⁺ over a wide range of pH are discussed.Patt XX, ref. 1.     

Aqueous polymerization of acrylonitrile initiated by manganese(III) pyrophosphate-thiocyanate redox system: a kinetic study

Summary The kinetics of aqueous polymerization of acrylonitrile monomer (M) initiated by the Mn^III-KNCS redox system have been studied under deaerated conditions in the temperature range 26–40 °C at constant ionic strength. The overall rates of polymerization and the disappearance of Mn^III were determined. The polymerization was initiated by the free radicals arising from the Mn^III-thiocyanate redox reaction. The rate of polymerization was investigated at various concentrations of monomer and initiator. The effects of varying [Mn^III], [NCS^–], pH, total [P₂O _inf7 ^sup4– ], added [Mn^II], metal ions, ClO _inf4 ^sup– , Cl^– and SO _inf4 ^sup2– were examined. Dependence of the rate of polymerization on temperature was studied and activation parameters were computed from an Arrhenius plot. A suitable kinetic scheme consistent with the observed results is proposed and discussed.     

The formation of an antitubercular complex [Fe(CN)5(INH)]3− through mercury(II)‐catalyzed ligand substitution reaction: A kinetic and mechanistic study

The kinetics and mechanism of the formation of an antitubercular complex [Fe(CN)₅(INH)]^3? based on the substitution reaction between K₄[Fe(CN)₆] and isoniazid (INH), i.e., isonicotinohydrazide, catalyzed by Hg²⁺ in aqueous medium was studied spectrophotometrically at 435 nm (the λ_max of the golden‐yellow‐colored complex [Fe(CN)₅(INH)]^3?) as a function of pH, ionic strength, temperature, and the concentration of the reactants and the catalyst. The replacement of coordinated CN^? in [Fe(CN)₆]^4? was facilitated by incoming ligand INH under the optimized reaction conditions: pH 3.5 ± 0.02, temperature = 30.0 ± 0.1°C, and ionic strength I = 0.05 M (KNO₃). The stoichiometry of the reaction and the stability constant of the complex ([Fe(CN)₅(INH)]^3?) have been established as 1:1 and 2.10 × 10³ M, respectively. The rate of catalyzed reaction was found to be slow at low pH values, to increase with increasing pH, to attain a maximum value at 3.50 ± 0.02, and finally to decrease after pH > 3.5 due to less availability of H⁺ ions needed to regenerate the catalytic species. The initial rates were evaluated for each variation from the absorbance versus time curves. The reaction was found to be pseudo‐first order with respect to [INH] and first order with respect to [Fe(CN)₆^4?] at lower concentration, whereas it was found to be fractional order at higher [INH] and [Fe(CN)₆^4?]. The ionic strength dependence study showed a negative salt effect on the rate of the reaction. Based on experimental results, a mechanism for the studied reaction is proposed. The rate equation derived from this mechanism explains all the experimental observations. The evaluated values of activation parameters for the catalyzed reaction suggest an interchange dissociative (I_d) mechanism. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 398–406, 2012     

57Fe 穆斯堡尔谱研究 Ir-Fe 催化剂用于 CO 选择氧化反应

 采用不同浸渍顺序制备了三种 Ir-Fe 催化剂, 其 CO 选择氧化 (PROX) 反应活性差别很大, 其中共浸渍的 Ir-Fe 催化剂活性最高. 吸附量热研究表明, 三种催化剂的 H2 和 CO 吸附存在差别. 通过对三种催化剂还原后、再氧化和反应后准原位 57Fe 穆斯堡尔谱的研究, 得到各种 Fe 物种信息. 结果表明, 三种制备方法影响催化剂中 Ir-Fe 相互作用强度, 导致催化剂中 Fe 物种的氧化还原性能不同. 催化剂中 Fe²⁺(a) 的含量与 CO 转化率呈正比关系, Fe²⁺(a) 是 PROX 反应过程中活化氧的活性中心. 浸渍顺序改变了 Ir-Fe 间相互作用强度, 从而改变 Fe²⁺(a) 物种含量, 影响 PROX 反应活性. Ir-Fe 间的相互作用可以稳定活化氧的 Fe²⁺(a) 物种, 为今后研究金属-金属间的相互作用提供借鉴.     

Kinetics and mechanism of complexation of iron(III) bycis-(salicylato)(methyl/ethylamine)bis(ethylenediamine)cobalt(III) ions

The formation and dissociation of the binuclear complexes of Fe^III withcis-[Co(en)₂(RNH₂)SalH]²⁺ [R=Me, Et and SalH=C₆H₄(OH)CO ₂ ⁻ ] were studied by a stopped-flow technique at 20–35°C, and I=1.0 mol dm⁻³ (ClO ₄ ⁻ ). The formation of the binuclear species, N₅CoSalFe⁴⁺, involves reactions of the phenol form of the Co^III substrates with Fe(OH₂) ₆ ³⁺ and Fe(OH₂)₅OH²⁺. The mechanism of reaction of Fe(OH₂)₅OH²⁺ is essentially Id, while that of Fe(OH₂) ₆ ³⁺ appears to be Ia. The formation rate constant, k₁, for Fe(OH₂) ₆ ³⁺ /N₅CoSalH²⁺ reaction decreases as the amine chain length increases, whereas the same (k₂) for the Fe(OH₂)₅OH²⁺/N₅CoSalH²⁺ reaction does not show any such trend. The binuclear species, N₅CoSalFe⁴⁺, dissociates to yield a Co^III substrate and Fe^III speciesvia a predominantly spontaneous dissociation path and a minor acid catalysed path which are relatively insensitive to the variation in size of the non-labile amine chain length.     

Kinetic study of the Ce(III)‐, Mn(II)‐ or Fe(phen)32+‐catalyzed Belousov–Zhabotinsky reaction with ethyl hydrogen malonate

In a stirred batch reaction, Fe(phen)₃²⁺ ion behaves differently from Ce(III) or Mn(II) ion in catalyzing the bromate‐driven oscillating reaction with ethyl hydrogen malonate [CH₂COOHCOOEt, ethyl hydrogen malonate (EHM)]. The effects of N₂ atmosphere, concentrations of bromate ion, EHM, metal ion catalyst, sulfuric acid, and additive (bromide ion or bromomalonic acid) on the pattern of oscillations were investigated. The kinetic study of the reaction of EHM with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion indicates that under aerobic or anaerobic conditions the order of reactivity toward reacting with EHM is Mn(III) > Ce(IV) ≫ Fe(phen)₃³⁺, which follows the same trend as that of the malonic acid system. The presence of the ester group in EHM lowers the reactivity of the two methylene hydrogen atoms toward bromination or oxidation by Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion. No good oscillations were observed for the BrO₃₋‐CH₂(COOEt)₂ reaction catalyzed by Ce(III), Mn(II), or Fe(phen)₃²⁺ ion. A discussion of the effects of oxygen on the reactions of malonic acid and its derivatives (RCHCOOHCOOR′) with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion is also presented. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 52–61, 2000     

Kinetics and mechanism of ligand exchange of coordinated cyanide in hexacyanoferrate(II) by nitroso‐R‐salt in the presence of mercury(II) as a catalyst

The kinetics of Hg(II)‐catalyzed reaction between hexacyanoferrate(II) and nitroso‐R‐salt has been followed spectrophotometrically by monitoring the increase in absorbance at 720 nm, the λ_max of green complex, [Fe(CN)₅ N‐R‐salt]^3? as a function of pH, ionic strength, temperature, concentration of reactants, and the catalyst. In this reaction, the coordinated cyanide ion in hexacyanoferrate(II) gets replaced by incoming N‐R‐salt under the following specified reaction conditions: temperature = 25 ± 0.1°C, pH = 6.5 ± 0.2, and I = 0.1 M (KNO₃). The stoichiometry of the complex has been established as 1:1 by mole ratio method. The rate of catalyzed reaction is slow at low pH values and then increases with pH and attains a maximum value between 6.5 and 6.7. The rate finally falls again at higher pH values due to nonavailability of [H⁺] ions needed to regenerate the catalytic species. The rate of reaction increases initially with [N‐R‐salt] and attains a maximum value and then levels off at higher [N‐R‐salt]. The rate of reaction shows a variable order dependence in [Fe(CN)₆^4?] ranging from unity at lower concentration to 0.1 at higher concentrations. The effect of [Hg²⁺] on the reaction rate shows a complex behavior and the same has been explained in detail. The activation parameters for the catalyzed reactions have been evaluated. A most plausible mechanistic scheme has been proposed based on the experimental observations. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 222–232, 2005     

Isosaccharinate Complexes of Fe(III)

Prior to this study there were no thermodynamic data for isosaccharinate (ISA) complexes of Fe(III) in the environmental range of pH (>~4.5). This study was undertaken to obtain such data in order to predict Fe(III) behavior in the presence of ISA. The solubility of Fe(OH)₃(2-line ferrihydrite), referred to as Fe(OH)₃(s), was studied at 22?±?2?°C in: (1) very acidic (0.01?mol·dm^?3 H⁺) to highly alkaline conditions (3?mol·dm^?3 NaOH) as a function of time (11?C421?days), and fixed concentrations of 0.01 or 0.001?mol·dm^?3 NaISA; and (2) as a function of NaISA concentrations ranging from approximately 0.0001 to 0.256?mol·dm^?3 and at fixed pH values of approximately 4.5 and 11.6 to determine the ISA complexes of Fe(III). The data were interpreted using the SIT model that included previously reported stability constants for $ {{\text{Fe(ISA}})_{n}}^{3 - n} $ (with n varying from 1 to 4) and Fe(III)?COH complexes, and the solubility product for Fe(OH)₃(s) along with the values for two additional complexes (Fe(OH)₂(ISA)(aq) and $ {\text{Fe(OH)}}_{ 3} ( {{\text{ISA}})_{2}}^{2 - } $ ) determined in this study. These extensive data provided a log₁₀ K ⁰ value of 1.55?±?0.38 for the reaction $ ({\text{Fe}}^{ 3+ } + {\text{ISA}}^{-} + 2 {\text{H}}_{ 2} {\text{O}} \rightleftarrows {\text{Fe(OH}})_{ 2} {\text{ISA(aq}}) + 2 {\text{H}}^{ + } ) $ and a value of ?3.27?±?0.32 for the reaction $ ({\text{Fe}}^{ 3+ } + 2 {\text{ISA}}^{-} + 3 {\text{H}}_{ 2} {\text{O}} \rightleftarrows {\text{Fe(OH)}}_{ 3} ( {\text{ISA}})_{2}^{2 - } + 3 {\text{H}}^{ + } ) $ and show that ISA forms strong complexes with Fe(III) which significantly increase the Fe(OH)₃(s) solubility at pH?<~12. Thermodynamic calculations show that competition of Fe(III) with tetravalent ions for ISA does not significantly affect the solubilities of tetravalent hydrous oxides (e.g., Th and Np(IV)) in ISA solutions.     

Equilibria in complexes ofN-heterocyclic molecules,Part XXIV. The reaction of nucleophiles with tris-(2,2′-bipyrimidine)iron(II) ion and its ruthenium(II) analogue

Summary The reactions of [Fe(bipym)₃]²⁺ and [Ru(bipym)₃]²⁺ with hydroxide ion in aqueous solution have been followed. The [Ru(bipym)₃]²⁺ species undergoes nucleophilic attack at the ligand to yield [Ru(bipym)₂(pyrimidine)(OH)]⁺ and [HCO₂]^– ion, involving cleavage of one pyrimidyl ring. Intermediates can be observed in the reaction of [Fe(bipym)₃]²⁺ with HO^–, N₃ ^– and SCN^–. The kinetics of the first reaction have been followed and the results are compared with those known for the reactions of [Fe(bipy)₃]²⁺, [Fe(phen)₃]²⁺ and similar compounds.Part XXIII: P. A. Williams,Transition Met. Chem., 78/84.