Kinetics and mechanism of base hydrolysis of cisα-oxalato(amine)(trien)cobalt(III) and salicylato(amine)(trien)cobalt(III)cations

Oxalato(amine)(trien)cobalt(III) and salicylato(amine)(trien)cobalt(III) perchlorates have been synthesized and tentatively assigned a cis α configuration. The dissociation constants of the complexes have been determined. The base hydrolysis of the complexes have been investigated at 30, 35, 38.6°C and I = 1.0 mol dm⁻³. The rate laws for the oxalato and salicylato complexes are −dln[Complex]_T/dt = k₂[OH⁻] and −dln[Complex]_T = k₁ + k₂[OH⁻] respectively. For the oxalato complex, k₂(30°C) = (2.95 ± 0.05) × 10⁻² dm³ mol⁻¹ s⁻¹, ΔH¹ = (109 ± 4) KJ mol⁻¹, ΔS¹ = (85 ± 13) JK⁻¹ mol⁻¹ and for the salicylato complex, k₁(30°C) = (1.58 ± 0.28) × 10⁻⁴ s⁻¹, ΔH¹ = (166 ± 7) KJ mol⁻¹, ΔS¹ = (229 ± 21) JK⁻¹ mol⁻¹ and k₂(30°C) = (3.56 ± 0.10) × 10⁻³ dm³ mol⁻¹ s⁻¹, ΔH¹ = (101 ± 6) KJ mol⁻¹, ΔS¹ = (42 ± 20) JK⁻¹ mol⁻¹. The base hydrolysis reactions of the complexes were followed in presence of imidazole and ethanolamine, in the presence of added anions and also in D₂O medium. The results are discussed in terms of δ SN₁CB mechanism involving rate limiting CoO bond fission for both k₁ and k₂ paths. However, the possibility of CO bond cleavage in the base hydrolysis of the oxalato complex is not ruled out.     

Kinetics and mechanism of complex formation between O-bonded cis-(diglycinato)bis(ethylenediamine)cobalt(III) and α-cis-(diglycinato) (triethylenetetramine)cobalt(III) with nickel(II) in aqueous medium

Summary The kinetics of reversible complexation of Ni(OH₂) _inf6 ^sup2+ with oxygen-bonded glycinatocobalt(III) substrates N₄-Co(glyH)gly²⁺ [N₄ = (en)₂ or trien; glyH = H₃N⁺CH₂-COO^–] have been investigated by the stopped-flow technique in the 20–35° C range, at pH = 6.08–6.82 and I = 0.3 mol dm^–3. The formation of N₄Co(glyH)glyNi⁴⁺ occurred via the reaction of Ni(OH₂) _inf6 ^sup2+ with the deprotonated form of the cobalt(III) substrates, N₄Co-(glyH)gly²⁺. The rate and activation parameters for the formation and dissociation of the binuclear species are reported. The formation rate constants k _f (at 25° C), activation enthalpy and entropy H , S for N₄Co-(glyH)glyNi⁴⁺ are 320±49, 341 ± 52dm³mol^–1 s^–1, 78 ± 7, 79 ± 5 kJmol^–1 and 64 ± 24, 69 ± 18 JK^–1 mol^–1 for the ethylenediamine and triethylenetetraminecobalt(III) substrates, respectively. This result indicates that the rate and activation parameters are virtually independent of the nature of N₄ moities, which strongly suggests that the formation of mono-bonded species occurs via entry of one of the pendant NH₂ groups into the coordination sphere of nickel(II) via a rate-limiting Ni-OH₂ bond dissociation mechanism (I_d). The binuclear species exist in dynamic equilibrium between the monodentate and chelated forms, with the chelate form predominating. The low values of spontaneous dissociation rate constant for the binuclear species (k _r- 0.095^–1 at 25° C) in comparison with the high values of dissociation rate constants of monodentate nickel(II) complexes reported in the literature also support the chelate nature of the binuclear species.     

Kinetics and mechanism of oxidation of bis(2,2′,6′,2″-terpyridine) iron(II) by manganese(IV)

A study has been made on the oxidation of bis(2,2,6, 2-terpyridine)-iron(II), Fe(tpy) ₂ ²⁺ by manganese (IV) using stopped-flow spectrophotometry in H₂SO₄–H₃PO₄ mixtures. The reaction is first order in each the substrate and the oxidant. The rate of the reaction increases with hydrogen ion concentration. A plausible mechanism is proposed considering the protonated forms of manganese(IV) as reactive oxidizing species. The reaction obeys the rate law

Kinetics and mechanism of the anation of (αβ)-hydroxo(tetraethylenepentamine)cobalt(III) by thiosulfate, the base hydrolysis of the (sulfur-bonded) thiosulfato(tetraethylenepentamine)-cobalt(III) and photochemistry of oxygen and sulfur-bonded thiosulfato complexes

Summary The reaction of ()-(tetren)CoOH²⁺ with S₂O ₃ ^2- in the 7.25–8.28 pH range at 20–40 °C yielded S- (yellow) and O- (purple) bonded thiosulfato(tetren)cobalt(III) complexes, the former in larger quantities. The rate determining step is preceded by diffusion-controlled ion-pair [(tetren)CoOH²⁺,S₂O ₃ ^2- ] formation. Replacement of coordinated OH^- by S₂O ₃ ^2- is interpreted in terms of an internal conjugate base mechanism: (tetren)CoOH²⁺ (tetren-H)CoOH ₂ ²⁺ , the reactive amido conjugate base being generated by intramolecular proton transfer from the coordinated NH site.In acid medium the S-bonded (tetren)Co(S₂O₃)⁺ is highly stable to redox decomposition, in contrast to its pentaammine analogue. The complex however, undergoes base hydrolysis yielding the corresponding hydroxo complex. The rate and activation parameters for the base hydrolysis have been reported. Photolysis of O- and S-bonded isomers of [(tetren)CoS₂O₃]⁺ in acidic medium at 254 and 313 nm, respectively, yielded aquation products accompanied by some decomposition of S₂O ₃ ^2- .     

Synthesis,molecular structure and electrochemistry of cobalt(II) complexes of 2,2′: 6′,2′′-terpyridine macrocycles

The macrocycle L, prepared by template condensation of bis-6,6′′-(α-methylhidrazino)-4′-phenyl-2,2′:6′′,2′-terpyridine with glyoxal, forms a stable crystalline complex of cobalt(II) [Co(L)(H₂O)₂][PF₆]₂ which has been used as a starting material to prepare, for electrochemical studies, a series of seven coordinate cobalt(II) complexes [Co(L)X₂][PF₆]₂ (X=pyridine, 4-cianopyridine, 4-aminopyridine, 4-dimethylaminopyridine, pirazine, imidazole, 1-methylimidazole, 2-methylimidazole, and trimethylphosphite). Cyclic voltammetry of the aquo complex in DMSO show one reversible reduction wave at −1.35 V versus Ag ∣ AgBF₄ reference electrode and controlled potential electrolysis in the presence of trimethylphosphite affords a diamagnetic species which has been assigned as a mononuclear d⁸ Co(I) species. The crystal and molecular structure of [Co(L)(imidazole)₂][PF₆]₂·Me₂CO shows the metal to be in a pentagonal-bipyramidal N₇ environment.     

The precipitation of some actinide element complex ions by using hexammine cobalt(III) cation—VI The precipitation of Np(IV), (V) and (VI) sulfate complex ions with hexammine cobalt(III) cation

Precipitation behaviors of Np(IV), (V) and (VI) in sulfuric acid and ammonium sulfate solutions with hexammine cobalt(III) ion have been studied. The optimum conditions of precipitating Np as crystalline compounds are 0.4 M H₂SO₄ and 0.06 M [Co(NH₃)₆]Cl₃ for Np(IV), larger than 0.5 M (NH₄)₂SO₄ and 0.03 M [Co(NH₃)₆]Cl₃ for Np(V), and the higher the concentrations the better for Np(VI). Np(IV) is completely removed from ammonium sulfate solution.Composition of the Np(IV) compound from the sulfuric acid solution is [Co(NH₃)₆]₂[Np(SO₄)₅]·nH₂O. And composition of the Np(V) compounds is possibly [Co(NH₃)₆][NpO₂(SO₄)₂]·α[Co(NH₃)₆]₂(SO₄)₃·nH₂O (α = 2.20−0.32). Solubilities of the Np(IV), (V) and (VI) compounds in water are found to be 4.9 mgNp/l, 520 mgNp/l, and 250 mgNp/l, respectively.     

Kinetics and mechanism of H+(aq)-assisted aquation of [Cr(N3)(S-pdtra)]− and [Cr(N3(edtrp)]−ions

Two new complex anions, [Cr(N3)(S-pdtra)]– and [Cr(N3)(edtrp)]–, were obtained in solution by N3–/HN3 anation of the aqua analogues (S-pdtra = S-propane-1,2-diamine-N,N,N-triacetate, edtrp = ethylenediamine-N,N,N-tripropionate). Aquation of these species in acidic media leads to the same geometrical isomers as those used for the synthesis. The aquation rate is strongly dependent upon [H] and is substantially higher in D2O than in H2O. Protonation of the coordinated azide was not observed spectrophotometrically. The rate law and activation parameters have been determined and discussed.     

Synthesis, characterization, and electron transfer reaction of some surfactant–cobalt(III) complex ions

Abstract  

The surfactant complex ion cis-[Co(tmd)₂(C₁₂H₂₅NH₂)₂]³⁺ (tmd = 1,3-propanediamine, C₁₂H₂₅NH₂ = dodecylamine) has been synthesized and characterized by elemental analysis and spectral data. In addition we have determined the critical micelle concentration of the surfactant–cobalt(III) complex and studied the kinetics and mechanism of the complex with ferrocyanide anion. The reaction is found to be second order, and the second-order rate constant increases with increasing initial concentration of the surfactant–cobalt(III) complex due to the presence of self-micelles formed by the complex itself. The thermodynamic parameters were determined. The results have been analyzed.     

Kinetics and mechanism of ruthenium(III) catalyzed oxidation of chloromphenicol—An antibiotic drug by diperiodatocuprate(III) in aqueous alkaline medium

The kinetics of ruthenium(III) catalyzed oxidation of chloramphenicol (CHP) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.1 mol l⁻¹ was studied spectrophotometrically. The reaction between DPC and CHP in alkaline medium exhibits 1: 2 stoichiometry (CHP: DPC). The main oxidation products were identified by spot test, IR, NMR, and GC-MS spectral studies. The reaction is first order with respect to ruthenium(III) and DPC concentrations. The order with respect to chloramphenicol concentration varies from first order to zero order as the chloramphenicol concentration increases. As the alkali concentration increases the reaction rate increases with fractional order dependence on alkali concentration. Increase in periodate concentration decreases the rate. A mechanism adequately describing the observed regularities is proposed. The reaction constants involved in the different steps of the mechanism were calculated. The activation parameters with respect to limiting step of the mechanism are computed and discussed. Thermodynamic quantities are determined.     

Kinetics and mechanism of the oxidation of neutralized α-hydroxy acids by tris(pyridine-2-carboxylato)manganese(III)

The kinetics of oxidation of the neutralized -hydroxy acids: lactic, -hydroxyisobutyric, mandelic, benzilic and atrolactic acids by tris(pyridine-2-carboxylato)manganese(III) have been studied. The reactions were carried out in a Na(pic)-picH [Na(pic) = sodium salt of pyridine-2-carboxylic acid and picH = pyridine-2-carboxylic acid] buffer medium in the 4.89–6.10pH range. The oxidation rate was found to be independent of pH, and rate follows the order: benzilate > mandelate >atrolactate>lactate > -hydroxy isobutyrate. The oxidation products are MeCHO, Me2CO, PhCHO, Ph2CO and PhCOMe for the respective reactions. A mechanism is proposed involving intermediate formation of hepta-coordinated MnIII complexes in a fast step. The complexes then decompose to give free radicals and MnII in the rate determining step. The free radicals subsequently react with another molecule of the MnIII species to give the respective carbonyl compounds in a fast step.     

Liquid secondary ion mass spectrometry of several β-diketonates of cobalt(III) and chromium(III)

The positive, liquid secondary ion (LSI) mass spectra of six cobalt(III) and three chromium(III) (β-diketonates ligand = L^?) were examined in a 3-nitrobenzyl alcohol matrix. The complexes of both metals yield clean, matrix-free mass spectra, but there are important differences between them. The cobalt compounds show prominent peaks assignable to the molecular ion, CoL ₃ ⁺ , of the monomeric chelates, together with abundant dimeric ions, such as Co₂L ₄ ⁺ and Co₂L ₃ ⁺ ; in contrast, chromium complexes show protonated monomers, CrL₃H⁺, in addition to ionized monomers, CrL ₃ ⁺ , and only minor formation of dimeric ions. The collisionally-activated dissociation (CAD) mass spectrum of Co₂L ₄ ⁺ shows fragmentation to CoL ₂ ⁺ and Co₂L ₃ ⁺ . That of Co₂L ₃ ⁺ shows fragmentation only to dimeric ions, including Co₂L ₂ ⁺ and, for thienyl or phenyl substituted ligands, to Co₂L₂Ar⁺ or Co₂LAr⁺ (Ar = thienyl or phenyl). Neither Co₂L ₄ ⁺ nor Co₂L ₃ ⁺ dissociates to the CoL ₃ ⁺ ion. The LSI mass spectrum of a mixture of two different cobalt chelates shows dimeric ions containing both types of ligand, which can be explained by ion-molecule reactions in the selvedge region. The differing behaviors of the cobalt and chromium complexes is attributed to the relatively greater stability of the +2 oxidation state for cobalt than for chromium.     

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.     

Kinetics and mechanism of the reduction of diaquatetrakis (2,2′-bipyridine)-μ-oxo diruthenium(III) by ascorbic acid

Summary The kinetics of the oxidation of ascorbic acid by diaquatetrakis (2,2-bipyridine)--oxo diruthenium(III) in aqueous HClO₄ were investigated. The dependence of the second order rate constantk ₂ on [H⁺] is given by k ₂=a+b[H⁺]^–, indicating that both the undissociated form and the monoanion of ascorbic acid are reactive. Marcus theory was used to estimate the redox potential for the Ru^III-O-Ru^III/Ru^III-O-Ru^II couple and a feasible mechanism has been proposed to explain the results.     

Kinetics and mechanism of mercuration of N-(substituted benzylidene)-4-toluidines

In order to investigate the mechanism of mercuration reaction of substituted ben-zylideneanilines, kinetic measurements of these reactions at different temperatures (40-60℃) inmethanol-l,4-dioxane (1/1, V/V) were carried out and Hammett ρ value for C-phenyl substituentsof-0.61 for the N-(substituted benzylidene)-4-toluidine series was obtained. Thermodynamicparameters E_a, △S~≠ were obtained for the reaction of different. N-(substituted benzylidene)-4-toluidines. It was found that this ortho-mercuration was brought about by an internal cyclometal-lation process involving the imino-moiety.     

New chromium(III)–nicotinate complexes. Kinetics and mechanism of nicotinate ligand liberation in acidic media

Two new chromium(III)–nicotinate complexes, cis-[Cr(C₂O₄)₂(O-nic)(H₂O)]⁻ and cis-[Cr(C₂O₄)₂(N-nic)(H₂O)]⁻, were obtained and characterized in solution (where O-nic=O-bonded and N-nic=N-bonded nicotinic acid). The kinetics of nicotinate ligand liberation were studied spectrophotometrically in the 0.1–1.0 m HClO₄ range, at I=1.0 m. The rate equations were determined and a mechanism is proposed. The rate of Cr–O bond breaking is [H⁺] dependent: k_obs=k_HQ_H[H⁺], where k_H is the acid-catalyzed rate constant and Q_H is the protonation constant of the nonbonded oxygen atom in the O-coordinated ligand. The Cr–N bond breaking proceeds via two paths: spontaneous and acid-catalyzed; k_obs=k₀ + k_HQ_H[H⁺], where k₀ and k_H are the spontaneous and acid catalyzed rate constants and Q_H is the protonation constant of the carboxylic group in the N-bonded nicotinic acid. The results demonstrate by comparison that Cr–N bond breaking is a much slower process than Cr–O bond fission.     

Solubility of β-diketonate complexes for cobalt(III) and chromium(III) in supercritical carbon dioxide

The solubilities of tris(2,2,6,6-tetramethyl-3,5-heptanedionate) cobalt(III) (Co(thd)₃) and chromium(III) (Cr(thd)₃) in supercritical carbon dioxide (scCO₂) were measured at temperatures ranging from 313 to 343 K. The measurements were carried out using a circulation-type apparatus with a UV–vis spectrometer. The solubilities of both Co(thd)₃ and Cr(thd)₃ increased as both the density of scCO₂ and the temperature increased, which has the same tendency as cobalt(III) acetylacetonate (Co(acac)₃) and chromium(III) acetylacetonate (Cr(acac)₃) had in our previous work. The solubilities of Cr(thd)₃ were higher than that of Co(thd)₃, and the solubilities of Co(thd)₃ and Cr(thd)₃ were about 50- and 70-fold higher than those of Co(acac)₃ and Cr(acac)₃, respectively. The measured solubilities of the metal complexes were correlated with the equation based on Chrastil's equation. The parameters were determined by correlating the experimental data for each metal complex, and the correlated results well reproduced the experimental data, especially Co(thd)₃. Moreover, the charge density distributions on the molecular surface of CO₂ and the metal complexes used in the measurement were estimated by the quantum chemical calculation and the COSMO-RS to clear the effect of the molecular structure of the metal complexes on the affinity for CO₂.     

Intensity-tunable micelles and films containing bimetal ions—europium(III) and terbium(III)

In this paper, multicolored micelles were prepared by coordination of lanthanide(III) (europium(III) (Eu(III)) and terbium(III) (Tb(III))) ions with block copolymer in different molar ratios of n _Eu(III)/n _Tb(III). The micelles formed by polymer–Eu(III)/Tb(III) could emit higher quantum yield luminescence than the mixture of polymer–Eu(III) micelles and polymer–Tb(III) micelles. The micelles containing Eu(III) and Tb(III) could emit a yellow-green color, and the intensity varied with the molar ratios of n _Eu(III)/n _Tb(III). In the constant concentrations of Eu(III) and 1,10-phenanthroline (Phen), the intensity of ⁵D₀→⁷F₂ increased with the addition of Tb(III), and the intensity of ⁵D₄→⁷F₅ decreased with the increasing of Eu(III) in the constant concentrations of Tb(III) and Phen. All the multicolored micelles could be spin-coated as intensity-tunable films.     

Synthesis of poly(2,2′,3,3′-indole)

New approaches to the synthesis of poly(2,2′,3,3′-indole) were developed based on the photochemical dehydropolycondensation of indole in the presence of iodine and the photochemical polycondensation of 1-(1H-indol-3-yl)-2-iodo-1-ethanone in the absence of catalyst and solvent. A suggested mechanism for the formation of the oligomeric chain in these reactions includes the intermediate formation of 3,3′-diindole with subsequent polycondensation via elimination of hydrogen atoms at position 2 of the dimer pyrrole fragment.