Ethylenediamine Cobalt Research Articles

Effect of solvent on the reactions of coordination complexes. Part 1.—Kinetics of solvolysis of cis-(bromo)(benzimidazole)bis(ethylenediamine)cobalt(III) in methanol–water media

The kinetics of the solvolytic aquation of cis-(bromo)(benzimidazole)bis(ethylenediamine)cobalt(III) have been investigated at 35, 40, 45, 50.2 and 54.8 °C in aqueous methanol media of methanol content 0–80 wt %. The pseudo-first-order rate constant decreases with increasing methanol content. Plots of log ksaqvs. D–1s(where Ds is the dielectric constant of the solvent mixture) and log ksaqvs. the Grunwald–Winstein Y parameter or revised YCl(1-adamantyl Chloride) parameter are non-linear. The plot of log ksaqvs. the molefraction of methanol (XMeOH), which deviates from linearity at 35, 40 and 45 °C, is an excellent straight line (r= 0.998) at 50 and 54.8 °C over the entire composition range studied. It is evident that the solvation phenomenon plays dominant role and that the rate of aquation is mediated by the dual solvent vectors, the overall basicity and acidity of the solvent mixtures. At 25 °C the calculated values of the transfer free energy of the dissociative transition state, cis-{[Co(en)2(bzmH)]3+}*, relative to that of the initial state, cis-[Co(en)2(bzmH)Br]2+, for the transfer of the ions from water to the mixed solvent were positive at all solvent compositions (except 80 % MeOH), exhibiting a maximum at XMeOH= 0.46. This reflects the propensity of the said tripositive transition state and the dipositive initial state towards solvation interaction with the medium. In contrast to the activation free energy, which varies linearly with XMeOH, the plots of activation enthalpy and entropy against XMeOH exhibit maxima at XMeOH= 0.12 and 0.46 and minima at XMeOH= 0.02 and 0.25; thereafter both ΔH‡ and ΔS‡ decrease steeply to significantly low values at XMeOH= 0.69 (ΔH‡= 80.1 ± 4.3 kJ mol–1 and ΔS‡=–91 ± 13 J K–1 mol–1), manifesting the effect of solvent-shell reorganisation around the complex ion both in the initial state and in the transition state as the composition is varied.

High-performance liquid chromatography of some bis(ethylenediamine)cobalt(III) complexes

Chromatographic separation of the complexes cis- and trans-Co(en)2(S2O3)2−, cis- and trans-Co(en)2(SO3)2−, cis- and trans-Co(en)2Cl2+,cis-Co(en)2(N3)2+, cis-Co(en)2(SO3)(N3)0, Co(en)2(S2O3)(N3)0, and Co(en)2(S2O3)(OH2)+ (en = ethylenediamine) was carried out by high-performance liquid chromatography. Good separations were achieved on a μ-Bondapak C18 reversed-phase octadecyldimethylsilane (ODS) column using tributylmethylammonium cations and octylsulphonate anions. The efficiency and speed of the separations were superior to those obtained on a Partisil SCX ion exchange column.

KINETICS OF ACID DISSOCIATION OF MALONATO-AND SUCCINATOBIS (ETHYLENEDIAMINE)COBALT(III)

Abstract Acid-catalysed dissociation of malonato- and succinatobis(ethylenediamine) cobalt(III) has been studied kinetically in aqueous acidic media (0.05–1.0 mol dm−3) over a temperature range of 40–80°C. The variation of observed pseudo-first-order rate constants on [acid] suggests the operation of two concurrent paths with kobs [dbnd] ko + kH+[H+], where ko and kH+ are the appropriate rate constants for spontaneous and acid-catalysed pathways respectively. The influence of basicity and chelate ring size of the carboxylato chelate on the rate and activation parameters for the acid-catalysed path has been discussed. Analysis of the rate data corresponding to kH+ suggests a dissociative mechanism involving the protonated complex.

Kinetics of oxidation of bis(ethylenediamine)mercaptoacetatocobalt(III) and cysteinatobis(ethylenediamine)cobalt(III) ions by peroxodisulphate in aqueous-nonaqueous mixed solvents

The kinetics of oxidation in the first step was studied for coordination-bonded sulphur in the cysteinatobis(ethylenediamine)cobalt(III) and bis(ethylenediamine)mercaptoacetatocobalt(III) ions using peroxodisulphate as oxidant. The effect of the acid-base equilibria of the reactants was established based on the dependences of the rate constant and the thermodynamic activation parameters ΔH and ΔS on perchloric acid concentration. The effect of ionic strength at various perchloric acid concentrations, was examined for the two complex ions. The combined effect of perchloric acid and sodium perchlorate was investigated in water-tert-butyl alcohol and water-ethylene glycol solutions. The transfer functions were calculated from the changes in the solubility of the reactants on passing from aqueous to the mixed aqueous-nonaqueous solutions, and the role of solvation during the oxidation of the complexes by peroxodisulphate was assessed based on the dependences of the transfer functions on the nonaqueous component content of the solvent system.

Effect of acid-base equilibria of reactants and the effect of waterorganic mixtures on the kinetics of oxidation of cysteinsulphenatobis(ethylenediamine)cobalt(III) ion by periodate

The kinetics of oxidation of cysteinsulphenatobis(ethylenediamine)cobalt(III) ion by periodate were investigated in mixtures containing up to 40%t-BuOH andi-PrOH. The effect of acid-base equilibria on the rate constants and activation parameters ΔH≠, ΔS≠ and the effect ionic strength on the rate constant at different concentrations HClO4 are also reported. The solvent effects on the oxidation at the different pH are interpreted in terms of solvation of the initial and transition states.

Steric changes at labelled NH2 sites during the base-catalysed ammoniation of the trans-azido(dimethyl sulphoxide)bis(ethylenediamine)cobalt(III) ion

A quantitative evaluation of the acid dependence of the kinetics of ammoniation of trans-[CoN3(en)2(dmso)][ClO4]2(en = ethylenediamine, dmso = dimethyl sulphoxide) to give trans(70%)-and cis(30%)-[CoN3(en)2(NH3)][ClO4]2 in liquid ammonia is presented. The reaction follows the normal conjugate-base mechanism, consisting of a fast pre-equilibrium, followed by the rate-determining elimination of dmso. Independent methods are presented for the assignment of the 1H n.m.r. resonances of co-ordinated ethylenediamine in the trans complexes. The large difference in exchange rates of the protons at either side (near dmso or N3) of the Co(en)2‘plane’ make it possible to study the ammoniation reaction in liquid N2H3 of a complex selectively deuteriated at the N3-side. In this complex the remaining hydrogens function as 1H n.m.r. labels. In the trans-[CoN3(en)2(NH3)]2+ reaction product the position of the labels indicates inversion at the active amido-site and rotation of the chelate ring not involved in acid dissociation during the ammoniation. The results lead to a proposal for the stereochemistry of the five-co-ordinate intermediate involving N-donor π bonding.

The Preparation and Properties of Ethylenediamine(2-methyl-8-quinolinolato)cobalt(III) Complexes

Abstract Ethylenediaminebis(2-methyl-8-quinolinolato)cobalt(III) complexes and bis(ethylenediamine)(2-methyI-8-quinolinolato)cobalt(III) complexes have been isolated and characterized by analytical and spectroscopic methods. In the former complexes, the NMR spectra indicate that the two nitrogen atoms of the coordinated 2-methyl-8-quinolinolato ligands are in the trans positions, whereas the two oxygen atoms are in the cis positions.

Dinuclear complexes of transition metals containing carbonate ligands. Part 3. Kinetics and mechanism of bridge cleavage in the di-µ-hydroxo-bis[bis(ethylenediamine)cobalt(III)] ion in weakly basic aqueous solution containing carbonate ions

The kinetics of the reaction of the title dinuclear ion [(en)2Co(µ-OH)2Co(en)2]4+ with aqueous carbonate have been followed spectrophotometrically at 340 nm over the ranges 8.26 ⩽ pH ⩽ 9.4, 35 ⩽θc⩽ 45 °C, and 0.05 ⩽[CO32–]⩽ 0.2 mol dm–3 at an ionic strength of 0.5 mol dm–3(LiClO4). During the reaction the complete cleavage of the hydroxo-bridges occurs and the sole reaction product is [Co(en)2(CO3)]+. The rate of the bridge cleavage is completely independent of pH as well as total carbonate in solution. The rate data required a consecutive reaction treatment to resolve the kobs. values into the components k1 and k2 which have been assigned to the first and second bridge cleavages of the title complex. At 25 °C and I= 0.5 mol dm–3, the values of k1 and k2 are (1.7 ± 0.3)× 10–3 and (0.46 ± 0.05)× 10–3s–1 with the Eyring–Polyani parameters ΔH1≠= 101 ± 9 kJ mol–1, ΔS1≠= 28.5 ± 28.0 J K–1 mol–1 and ΔH2≠= 90.8 ± 5.4 kJ mol–1, ΔS2≠=–13.0 ± 18.4 J K–1 mol–1 respectively. The reaction has also been studied without any added carbonate over the range 8.21 ⩽ pH ⩽ 9.25 at 40 °C and I= 0.5 mol dm–3. The rate constants are found to be independent of pH here also and have average values of (1.05 ± 0.06)× 10–3 and (2.98 ± 0.03)× 10–4s–1 respectively. The higher values for the rate constants in carbonate-containing solutions indicate a mechanism involving some form of carbonate catalysis during the bridge cleavage.

INFLUENCE OF FEEDING FREQUENCY ON PASSAGE OF FLUID AND PARTICULATE MARKERS IN STEERS FED A CONCENTRATE DIET

Four beef steers were used to study the influence of feeding a 75% concentrate diet twice (2 ×) versus eight times (8 ×) daily on fluid and particulate passage rate estimates. Passage of ruthenium phenanthroline was not altered by feeding frequency; however, particulate dilution rates differed (P < 0.05) when determined by rumen sampling compared with fecal sampling in 2 ×, but not in 8 × steers. Passage of cobalt ethylenediamine tetracetic acid determined from fecal sampling was higher (P < 0.05) in 8 × than in 2 × steers, but ruminal estimates did not differ. Molar proportions of acetate and butyrate were higher (P < 0.05) and propionate lower (P < 0.05) in 8 × than in 2 × steers. Key words: Feeding frequency, particulate and fluid passage, rumen fermentation

Solvent effects on the kinetics of oxidation of cysteinatobis(ethylenediamine)cobalt(III) ion by peroxodisulphate

The kinetics of oxidation of cysteinatobis(ethylenediamine)cobalt(III) ion, [Co(CysOS)(en)2]+, by peroxodisulphate were investigated at different ionic strengths, adjusted with various electrolytes, and at different temperatures and concentrations of perchloric acid. Rate constants and activation parameters are also reported for this oxidation in mixtures containing up to 40% acetone, t-butyl alcohol, isopropyl alcohol, or acetonitrile. The solubilities of [Co(CysOS)(en)2]ClO4 and KClO4 have been determined in water and aqueous acetone and aqueous t-butyl alcohol at 298.2 K. From these values, Gibbs free energies of transfer for [Co(CysOS)(en)2]+ and S2O82– have been estimated. The solvent effects on the oxidation have been divided into their initial-state and transition-state components.

Kinetics and mechanisms of the reactions of thiosulphato-amine complexes of cobalt(III). Part I. Isomerization and base hydrolysis ofcis andtrans isomers of dithiosulphatobis(ethylenediamine) cobalt(III) ion in aqueous solution

Investigations were carried out on the isomerization and base hydrolysis ofcis andtrans forms of dithiosulphatobis-(ethylenediamine)cobalt(III) ions. Thecis form isomerizes to thetrans form in neutral aqueous medium, rates being 1.15, 2.30 and 4.0×10−5s−1, respectively at 42, 50 and 58 °C. Thetrans complex isomerizes to thecis form in basic solution only, the rate varying with pH in a sigmoid pattern. In presence of OH−, an acid-base equilibrium of the complex ion sets in, but only the basic form takes part in the isomerization reaction. Hydrolysis of thecis isomer proceeds through a base-dependent path only, but that of thetrans isomer proceeds both through base-dependent and base-independent paths. The mechanisms are associative in nature. Thetrans form reacts faster thancis in all cases.

A study of some reactions of acetylacetonatobis(ethylenediamine)cobalt(III) ion in sodium hydroxide solution

Abstract The reactions of acetylacetonato cobalt (III) ion in sodium hydroxide solutions have been studied spectrophotometrically over a range of temperatures and hydroxide ion concentrations. The activation enthalpy, ΔH≠ was 70.6 kJ mol−1 and the activation entropy, ΔS≠ was − 119 JK−1mol−1, with a rate law of kobs = k2 [OH−]2. A mechanism involving initial de-chelation of the acetylacetone ligand is suggested. The rate of exchange of methyl hydrogen of the acetylacetone ligand was studied, using proton nuclear magnetic resonance. The rate law was kobs = k [OH−]. Initial de-chelation is also suggested as a mechanism for this process. The 13C nuclear magnetic resonance spectrum of the complex is reported.

The Preparation and Properties of Ethylenediamine(8-quinolinolato)cobalt(III) Complexes

Abstract Bis(ethylenediamine)(8-quinolinolato)cobalt(III) chloride dihydrate and ethylenediaminebis(8-quinolinolato)cobalt(III) chloride dihydrate have been isolated and characterized. The 1H-NMR spectrum of the latter complex indicates that the two oxygen atoms of the coordinated 8-quinolinolato ligands are in the cis positions.

The kinetics of the solvolysis of the 1,2-chloroazido-bis(ethylenediamine)cobalt(III) ion in water and in water + isopropanol

Rates of solvolysis of the 1,2-chloroazido-bis(ethylenediamine)cobalt(III) ion have been measured in water and in water + isopropanol in the composition range mole fraction of isopropanol 0–0.2. Although log (rate constant) varies linearly with the reciprocal of the dielectric constant, comparison with other co-solvents shows that the slope of these plots varies with the co-solvent used. The influence of solvent structure on the reaction is shown by comparing the variation with solvent composition of the transition-state parameters for the solvolysis with the physical properties of the solvent mixture. The application of a free-energy cycle to the loss of the Cl– in the transition state shows that changes in solvent structure have a much greater effect on the transition state than on the initial state.

The synthesis and kinetics of isomerization and solvent exchange of the trans-Chloro(dimethyl sulfoxide)bis(ethylenediamine)cobalt(III) ion in dimethyl sulfoxide

The synthesis and characterization of trans-[CO(en)2(Me2SO)Cl](ClO4)2 are described. Its rate of isomerization to the cis isomer has been measured in Me2SO in the range 293-313 K: ktc = 1.54 × 10-3s-1 at 298.2 K, ΔH‡ = 105 kJ mol-1, ΔS‡ = 55 J mol-1 K-1. The solvent exchange rate has been measured by 1H n.m.r. spectroscopy in (CD3)2SO at 308.2K: kex = ktt+ktc = 7.0xl0-3 s-1. These and other data show that trans-to-cis isomerization requires solvent exchange, each act of which leads to substantial rearrangement, c. 90% cis (308.2 K). Differences between non-aqueous and aqueous systems in the steric course of substitution are discussed.

Spectroscopy of cobalt–ethylenediamine–oxygen adducts in the supercages of zeolites

The complex [Co(en)3]2+(en = ethylenediamine) can be synthesized in the supercages of faujasite-type zeolites by adsorption of gaseous en. On dehydrated cobalt–zeolites additional heating is necessary to enhance the mobility of Co2+ from the small cages to the supercages. Upon heating, [Co(en)3]2+ decomposes to [Co(en)2]2+ and to [Co(en)]2+. The mono and tris complexes are not capable of binding O2 whereas the bis complex forms the 1 : 1 superoxo-complex [Co(en)2(O2)]2+ and the 2 : 1 monobridged peroxo-complex [{Co(en)2}2(O2)]4+ with O2. The former is preferentially formed when not more than one cobalt atom is in each supercage, the latter when more than one cobalt, statistically, is in each supercage. The 1 : 1 superoxo-complex is unstable, and its formation is only partially reversible. The amount of electron transfer from cobalt to O2 is estimated to be 0.46 e, indicating a weak σ-donor ligand trans to O2– in the complex. When [Co(en)3]2+ and physisorbed en are present in the supercages the interaction with O2 is complex and involves oxidation of en with formation of water.

Kinetics and mechanism of substitution in trans-dichlorobis(ethylenediamine)-cobalt(III) chloride by organic bases in non-aqueous solvents

Kinetics of substitution of a chloride in trans- dichlorobis(ethylenediamine)cobalt(III) cation by five organic bases (piperidine, diethylamine, cyclohexylamine, butylamine and benzylamine) in methanol, dimethylformamide and mixtures of the two solvents are reported. Rates are high in methanol but appreciably smaller in dimethylformamide and increase with the increase in methanol content in the mixtures. A retardation was observed by the addition of amine hydrochloride to the methanolic medium. These observations have been explained on the basis of catalysis by methoxide ion and a mechanism (SN1CB) in terms of a rapidly established acid-base equilibrium resulting in a conjugate base, which dissociates in the rate- determining step, has been proposed. Activation parameters have been evaluated on the basis of the rate data at four different temperatures.

Stereoselective association between acetylacetonatobis(ethylenediamine)cobalt(III) cation and malonate anion as studied by the rate of amine hydrogen exchange

The rate of amine hydrogen exchange for acetylacetonatobis(ethylenediamine)cobalt(III){[Co(acac)en)2]2+} in the presence of malonate ion indicates that the malonate ion associates with the complex from the side opposite to acac and hydrogen bonds only to trans hydrogens in the direction approximately parallel to the two-fold axis of the complex.

Oxidation kinetics of trans-aqua-bis(ethylenediamine)-isothiocyanatocobalt(III) ion with peroxodisulphate

Oxidation kinetics of trans-aqua-bis(ethylenediamine)cobalt(III) ion with peroxodisulphate have been investigated in 0.01M-HClO4 medium within the ionic strength and temperature intervals 0.0411 to 0.4415M and 315.5 to 336.9 K, respectively. From the temperature dependence of the rate constants extrapolated to zero ionic strength the extrapolated values of thermodynamic activation parameters have been calculated. The data obtained by investigation of the primary salt effect have been confronted with relations valid for ionic reactions.

Catalytic conversion of NO into N2 and N2O by dinitrobis(ethylenediamine)cobalt(III) cation

In the presence of various amines, nitric oxide was catalytically converted into N2 and N2O by dinitro-bis(ethylenediamine)cobalt(III) cation complex in aqueous solution.