Kinetics and mechanism of the base hydrolysis of thecis-chlorobis(ethylenediamme)(benzimidazole)cobalt(III) cation

Summary The hydrolysis ofcis-[CoCl(en)₂(bzmH)]²⁺ (en=ethylenediamine, bzmH=benzimidazole) has been studied over the pH range 8.31–11.58 at I=0.1 mol dm^–3 and 25°. Potentiometric titration of aqueous solutions of the [Co(en)₂(bzmH)OH₂]³⁺ complex obtained by silver(I) catalysed aquation of the chloro-complex give pK₁=5.81 and pK₂ = 8.84 for Equilibria (1) and (2) at 25° and I=0.1 mol dm^–3. Spectrophotometric titration of the hydroxy complex also gives a value of pK₂=8.88 for the ionisation of the coordinated benzimidazole. The kinetic data can be interpreted in terms of base hydrolysis ofcis-[CoCl(en)₂(bzmH)]²⁺ (k_OH=220 dm³ mol^–1s^–1) andcis-[CoCl(en)₂(bzm)]⁺ (k_OH=14.9 dm³ mol^–1s^–1). Comparisons with the corresponding imidazole and pyridine complexes are made.     

Kinetics of reduction of hydroxycuprate(III) in KOH solution

The solution of an unstable copper(III) complex, hydroxycuprate(III) i.e. Cu(OH)^– ₄, has been obtained by oxidising a copper anode in 0.5–3 M KOH solution. The kinetics of the copper(III) reduction in KOH solution has been studied spectrophotometrically and is first order with respect to copper(III), and the pseudo-first order rate constant increases as the KOH concentration increases. The kinetic data is explained by a scheme according to which a Cu^III intermediate, in equilibrium with Cu(OH)^– ₄, reacts with OH^–. On the basis of the kinetic data, the molar absorptivity of the Cu(OH)^– ₄ solution has been determined.     

Mechanistic aspects of the reduction of ruthenium(III) catalyzed

The kinetics of Ru_III catalyzed reduction of hexacyanoferrate(III) [Fe(CN)₆]^3–, by atenolol in alkaline medium at constant ionic strength (0.80 mol dm^–3) has been studied spectrophotometrically, using a rapid kinetic accessory. The reaction between atenolol and [Fe(CN)₆]^3– in alkaline medium exhibits 1:2 stoichiometry [atenolol:Fe(CN)₆ ^3–]. The reaction showed first order kinetics in [Fe(CN)₆]^3– concentration and apparent less than unit order dependence, each in atenolol and alkali concentrations. Effect of added products, ionic strength and dielectric constant of the reaction medium have been investigated. A retarding effect was observed by one of the products i.e., hexacyanoferrate(II). The main products were identified by i.r., n.m.r., fluorimetric and mass spectral studies. A mechanism involving the formation of a complex between the atenolol and the hydroxylated species of ruthenium(III) has been proposed. The active species of oxidant and catalyst were [Fe(CN)₆]^3–and [Ru (H₂O)₅OH]²⁺, respectively. The reaction constants involved in the mechanism were evaluated. The activation parameters were computed with respect to the slow step of the mechanism, and discussed.     

One electron oxidation of Ni(II)-iminodiacetate by carbonate radical

Reactions of carbonate radical (CO₃ ^–), generated by photolysis or by radiolysis of a carbonate solution with nickel(II)-iminodiacetate (Ni(II)IDA) were studied at pH 10.5 and ionic strength (I)==0.2 mol·dm^–3. The stable product arising from the ligand degradation in the complex is mainly glyxalic acid. Time-resolved spectroscopy and transient kinetics were studied using flash photolysis. From the kinetic data it was suggested that the carbonate radical initially reacts with Ni(III)IDA with a rate constant (2.4±0.4)·10⁶ dm³·mol^–1·s^–1 to form a Ni(II)IDA species which, however, undergoes a first-order transformation (k=2.7·10²·s^–1) to give a radical intermediate of the type Ni(II)RNHCHCO ₂ ^– ) which rapidly forms an adduct containing a Ni–C bond. This adduct decays very slowly to give rise to glyoxalic acid. From a consideration of equilibrium between Ni(II)IDA and Ni(III)IDA, the one electron reduction potential for the Ni(III)IDA/Ni(II)IDA couple was determined to be 1.467 V.     

Synthesis and Thermal Decomposition of the Macrocyclic Dinuclear Ni(II) Complex

Crystal of the complex Ni₂L (ClO₄)₂ was obtained by reaction of Ni(ClO₄)₂ and macrocyclic ligand H₂L, where L^2– is the dinucleating macrocycle with two 2,6-di(aminomethyl)-4-methyl phenolate entities combined by the same two lateral chains, –(CH₂)₂–NH–(CH₂)₂–, at the amino nitrogens. The thermal decomposition processes of the title complex were studied in a dynamic atmosphere of dry argon using TG-DTG. The kinetic analysis of the first and second thermal decomposition steps were performed via the TG-DTG curves, and the kinetic parameters were obtained from analysis of the TG-DTG curves with integral and differential methods. The most probable kinetic function was suggested by comparison of the kinetic parameters.This revised version was published online in November 2005 with corrections to the Cover Date.     

Kinetics and mechanism of metal ion catalysis. Part III. Osmium(VIII) catalysed oxidation of m-hydroxybenzaldehyde by Fe(CN)6 3− in alkaline medium

Os^VIII-catalysed oxidation of m-hydroxybenzaldehyde by alkaline Fe(CN)₆ ^3– has been studied in the 0.01–0.05 M [OH^–] range. Higher [OH^–] concentrations were not possible as the substrate turned yellow at [OH^–] > 0.05 M. The very low solubility of the substrate in H₂O restricted the kinetic study to [OH^–] < 0.01 M. A mechanism, consistent with the results is proposed.     

Kinetics and mechanism of the oxidation of nitrilotris(methylenephosphonato)chromium(III) by periodate

The kinetics of oxidation of nitrilotris(methylenephosphonato)chromium(III), Cr^IIINTMP, by periodate to yield Cr^VI have been studied spectrophotometrically over the 5.80–6.85 pH range at 22–33 °C. The reaction rate, which is first-order with respect to [Cr^IIINTMP] and [IO^– ₄] and inversely dependent on [H⁺], obeys the rate law:-d[Cr^IIINTMP/dt=kKK_h[IO^- ₄] [Cr^III]_T/K_h+ [H⁺] +KK_h[IO^- ₄] The values of the intramolecular electron transfer, k, and the formation constant of the intermediate complex, K, were determined at various temperatures. The hydrolysis constant for Cr^IIINTMP, K _h , was determined spectrophotometrically and is in agreement with the value estimated from the kinetic data. The activation parameters were calculated from the temperature dependence of the specific rate constants. A mechanism is proposed in which the hydroxo complex, [CrHNTMP(OH)]^3–, is the reactive species. The results support a mechanism where intramolecular electron transfer is the rate-determining step.     

The kinetics and mechanism of the substitution reactions oftrans-tetracyanodioxotungstate(IV) ions with monodentate ligands

Summary The kinetics of the substitution reactions of the protonated forms oftrans-tetracyanodioxotungstate(IV) ions with pyridine and thiocyanate ions were studied. The kinetic results were compared with those of the reactions with N ₃ ^– and F^– ions and a linear free energy relationship was obtained which was interpreted as additional evidence for a dissociative mechanism. Infrared data for this type of complex are reported and discussed in terms of thetrans influence of various monodentate ligands.     

Thermodynamics and Kinetics of Reaction of (Oxo)(hydroxo)molybdenumtetraphenylporphyrin with Pyridine

The reaction of meso-tetraphenylporphyrin with Mo(VI) oxide in boiling phenol resulted in a stable complex O=Mo(OH)TPP. Thermodynamics and kinetics of the reaction between (oxo)(hydroxo)molybdenumtetraphenyporphyrin with pyridine in toluene were studied by spectrophotometric method. This reaction was found to occur in three equilibrium elementary stages: replacement of OH^– by Py (K ₁=9.1 × 10³ l/mol, k ₁=5.25 s^–1 mol^–1 l), the formation of dication (dipyridine)(hydroxo)molybdenumtetraphenylporphyrin as a result of cleavage of a double bond Mo=O (K ²=39.3 l/mol, k ₂=1.83 × 10^–2 s^-1 mol^–1 l), and the formation of cationic complex[Mo(Py)₃TPP]³⁺ · 3OH^– (K ₃=1.0 l/mol, k ₃=1.19 × 10^–3 s^–1 mol^–1 l).__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 5, 2005, pp. 380–386.Original Russian Text Copyright © 2005 by Tipugina, Lomova, Motorina.     

Kinetics and mechanism of exchange of cyanide in hexacyanoferrate(II) by N-methylpyrazinium ion in the presence of mercury(II) as a catalyst

The kinetics of the mercury(II) catalysed ligand exchange of the hexacyanoferrate(II) complex with the N-methylpyrazinium ion (Mpz⁺) in a potassium hydrogen phthalate buffer medium has been investigated at 25.0 ± 0.1 °C, pH = 5.0 ± 0.02 and ionic strength, I = 0.1 M (KNO₃). The reaction was followed spectrophotometrically in the aqueous medium by measuring the increase in absorbance of the intense blue complex [Fe(CN)₅Mpz]^2– at its _max 655 nm. The effect of pH, and the concentrations of [Fe(CN)₆ ^4–] and Mpz⁺ on the reaction rate have been studied and analysed. The varying catalytic activity of mercury(II) as a function of concentration has also been explained. The kinetic data suggest that substitution follows an interchange dissociative (I _d) mechanism and occurs via formation of a solvent-bound intermediate. The effects of the dielectric constant of the medium on the reaction rates have been used to visualize the formation of a polar activated complex and an interchange dissociative mechanism for the reaction. A mechanism has been proposed in order to interpret the kinetic data. Kinetic evidence is reported for the displacement of CN^– by Mpz⁺ in [Fe(CN)₆ ^4–]. Activation parameters for the catalysed and uncatalysed reaction have been evaluated, and lend further support to the proposed mechanism.     

Kinetics and mechanism of acid and base hydrolysis ofcis-chloro-(benzotriazole)bis(ethylenediamine)cobalt(III) andcis-chloro-(N-methylbenzotriazole)bis(ethylenediamine)cobalt(III) cations

Summary The kinetics of acid hydrolysis ofcis-[CoCl(btzH)(en)₂]²⁺ andcis-[CoCl(btzMe)(en)₂]²⁺ complexes (where btzH = benzotriazole, btzMe =N-methylbenzotriazole and en = ethylenediamine) have been investigated in HClO₄ at ionic strength 1 = 0.25 mol dm^–3 in the 30–40° range. In the 1.0 x 10^–1 to 1.0 X 10^–3 mol dm^–3 acid strength range, the rate of aquation of the [CoCl(btzH)(en)₂]²⁺ cation follows the relationship:-d ln[complex]/dt = k₁ + k₂K_NH[^H+]^–1, where k₁ and k₂ are aquation rate constants of the acid independent and acid dependent steps respectively, and K_NH is the acid dissociation constant of the coordinated benzotriazole.cis-[CoCl(btzMe)-(en)₂]²⁺ undergoes acid independent hydrolysis presumably due to the absence of a labile N-H proton. The base hydrolysis could be followed for thecis-[CoCl(btzMe)(en)₂]²⁺ complex only by measuring hydrolysis rates at 0°.     

Cesium dimethyltetrachloroplatinate,a complex of dimethylplatinum(IV). Synthesis and some reductive elimination reactions involving the monomethylplatinum(II) complex as an intermediate

The reduction of Pt(IV) complexes followed by the oxidative addition of dimethyl sulfate to Pt(II) affords Cs₂PtMe₂Cl₄, a complex of dimethylplatinum(IV). On treatment with such nucleophiles as Cl^–, Br^–, I^–, and PtCl₄ ^2– in aqueous solutions at 368 K this complex undergoes reductive elimination to give MeX and Pt^IIMe as a transient species. The latter is further converted to methane upon protolysis, whereas in the presence of an oxidant (Na₂PtCl₆) it gives rise to the Pt^IVMe species. The kinetics of decomposition of Cs₂PtMe₂Cl₄ in aqueous HCl-KCl systems (2M or 3M in Cl^–; [Pt^IVMe₂][Cl^–]) were studied. The reaction takes place as anS _N 2 attack of X^– on the carbon atom of a methyl group located with thetrans position with respect to the aqua-ligand of the [PtMe₂Cl₃(H₂O)]^– complex.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 389–395, February, 1993.     

Kinetic,solvation and reactivity studies of iron(II) complexes of monoxime and dioxime ligands

Complexes of Fe^II with monoxime and dioxime ligands have been isolated and characterised. Kinetic results and rate laws are reported for acid aquation and base hydrolysis of these complexes in H₂O and in MeOH–H₂O mixtures. Kinetics of acid catalysed aquation of Fe^II–monoxime complexes follow a rate law with k_obs = k₂[H⁺] + k₃[H⁺]², while kinetics of acid dissociation and base hydrolysis of the Fe^II–dioxime complex follow rate laws with k_obs = k₂[H⁺] and k_obs = k₂[OH⁻]. Acid aquation and base hydrolysis mechanisms are proposed. The solubilities of Fe^II–monoxime and –dioxime complex salts are reported and transfer chemical potentials of their complex cations are calculated. Solvent effects on reactivity trends have been analysed into initial and transition state components. These are determined from transfer chemical potentials of reactant and kinetic data. Rate constant trends from these complexes are compared and discussed in terms of ligand structure and solvation properties. Our kinetic results give information relevant to the application of these ligands as analytical reagents for trace Fe^II in acidic and neutral media, in water and in aqueous alcohols.     

Comparative studies on hydrolysis of bis(p-nitrophenyl) phosphate catalyzed by short- and long-alkyl-multiamine metallomicelles

Four short- and long-alkyl-multiamine ligands L¹–L⁴ have been synthesized and characterized. The catalytic efficiency of complex CuL¹ and functional metallomicelles CuL²–CuL⁴ were comparatively investigated for the hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) in buffered solution at 30 °C. The ternary kinetic model for metallomicellar catalysis was suggested to analyze the experimental data. The kinetic and thermodynamic parameters k^′_N, K_T and pK_a were obtained. The results indicated that the complexes with 1:1 ratio of ligands L²–L⁴ to copper(II) ion were the kinetic active catalysts, and the deprotonized Cu(II) complex formed by activated water molecule was the real active species for BNPP catalytic hydrolysis. The real rate constant of the reaction catalyzed by CuL¹–CuL⁴ was 4.00 × 10⁻⁶, 7.44 × 10⁻⁵, 1.42 × 10⁻⁴ and 4.10 × 10⁻⁴ s⁻¹, respectively. The effects of ligand and microenvironment on the hydrolytic reaction of BNPP have been discussed in detail.     

Kinetics of tetraamminecopper(II)-catalysed oxidation of sulphur(IV) by peroxodisulphate in ammonia buffer

The kinetics of tetraamminecopper(II)-catalysed oxidation of SO^2– ₃ to SO^2– ₄ in ammonia buffers and in a nitrogen atmosphere obeys the rate law: –d[S^IV]/dt = k ₂[Cu^II][SO₃ ^2–][NH₃]^–1. There is spectrophotometric evidence for the formation of the intermediate complex [Cu(NH₃)₃(SO₃)] in a pre-equilibrium.     

Determination of the nature of the diperiodatocuprate(III) species in aqueous alkaline medium through a kinetic and mechanistic study on the oxidation of iodide ion

The nature of the diperiodatocuprate(III) (DPC) species present in aqueous alkaline medium has been investigated by a kinetic and mechanistic study on the oxidation of iodide by DPC. The reaction kinetics were studied over the 1.0 × 10^–3–0.1 mol dm^–3 alkali range. The reaction order with respect to DPC, as well as iodide, was found to be unity when [DPC] [I^–]. In the 1.0 × 10^–3–1.0 × 10^–2 mol dm^–3 alkali region, the rate decreased with increase in the alkali concentration and a plot of the pseudo-first order rate constant, k versus 1/[OH^–] was linear. Above 5.0 × 10^–2 mol dm^–3, a plot of k versus [OH^–] was also linear with a non-zero intercept. An increase in ionic strength of the reaction mixtures showed no effect on k at low alkali concentrations, whereas at high concentrations an increase in ionic strength leads to an increase in k. A plot of 1/k versus [periodate] was linear with an intercept in both alkali ranges. Iodine was found to accelerate the reaction at the three different alkali concentrations employed. The observed results indicated the following equilibria for DPC.[Cu(H₂IO₆)₂]^3- [Cu(H₂IO₆)]^- + H₂IO₆ ^3- [Cu(H₂IO₆)] + OH^- [Cu(HIO₆)]^- + H₂OA suitable mechanism has been proposed on the basis of these equilibria to account for the kinetic results.     

Kinetics of ammoniation of some halobis(ethylenediamine)-rhodium(III) perchlorates in liquid ammonia

Summary The ammoniation ofcis-[Rh(en)₂Cl₂] · (ClO₄) in liquid NH₃ was studied at constant ionic medium of 0.20 m perchlorate in the 0 to 35° range. The complex reacts in two distinct steps to givecis-[Rh(en)₂(NH₃)₂] · (ClO₄)₃, with the intermediate formation ofcis-[Rh(en)₂(NH₃)Cl] · (ClO₄)₂. Both steps follow a conjugate-base mechanism. Activation parameters were obtained for the acid-base preequilibrium and the rate-determining step. The entropies of activation for the rate-determining step are 0 and –42 JK^–1mol^–1 for the first and second ammoniations respectively. These values are considerably lower than those found for the cobalt(III) analogues. The entropy changes for the acid-base equilibria are –84 and –36 JK^–1mol^–1 respectively, which is less negative than those values found for the cobalt(III) analogues. Trans-[Rh(en)₂I₂] · (ClO₄) ammoniates totrans-[Rh(en)₂(NH₃)I] · (ClO₄)₂. The contribution of spontaneous ammoniation to the overall reaction oftrans-[Rh(en)₂I₂] · (ClO₄) is negligible, so the uniqueness oftrans-[Co(en)₂Cl₂] · (ClO₄) among cobalt(III) complexes in this respect is not reproduced for thetrans-dihalotetraamine structure in rhodium(III) complexes. A comparison of cobalt(III) and rhodium(III) amines with respect to activation parameters and the influence of formal charge of the metal complex on reactivity indicates a more associative type of activation for rhodium(III).     

Polarographic behaviour of 2-benzilidenimino-benzohydroxamic acid (2-BIBH) and 2-BIBH-Mo(VI) system

The polarographic behaviour of 2-benzilideniminobenzohydroxamic acid (2-BIBH) solutions and of 2-BIBH solutions in the presence of Mo(VI) have been studied by using differential pulse polarography and cyclic voltammetry. The polarographic characteristics of the resulting waves have been studied and possible mechanisms of the processes involved have been proposed. A linear relationship has been observed betweenI _p and Mo(VI) concentration in the range 2×10^–6 to 1.6×10^–5 M when using 3×10^–4 M 2-BIBH. Standard deviations of 5.6×10^–8 and 1.2×10^–8 M were found for 3×10^–6 and 8 × 10^–6 M Mo(VI), respectively.     

Kinetics of the thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O

The thermal decomposition of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O was studied under isothermal conditions in flowing air and argon. Dissociation of the above complex occurs in three stages. The kinetics of the particular stages thermal decomposition have been evaluated. The R_N and/or A_M models were selected as those best fitting the experimental TG curves. The activation energies,E, and lnA were calculated with a conventional procedure and by a new method suggested by Kogaet al. [10, 11]. Comparison of the results have showed that the Arrhenius parameters values estimated by the use of both methods are very close. The calculated activation energies were in air: 96 kJ mol^–1 (R_1.575, stage I); 101 kJ mol^–1 (Ain1.725 stage II); 185 kJ mol^–1 (A _2.9, stage III) and in argon: 66 kJ mol^–1 (A _1.25, stage I); 87 kJ mol^–1 (A _1.825, stage II); 133 kJ mol^–1 (A _2.525, stage III).     

Synthesis, characterization and interaction of a new chiral trinuclear complex [bis(aquodiaminotryptophanato) CuII–Sn2IV]chloride with calfthymus DNA

The new chiral trinuclear complex, [bis(aquodiaminotryptophanato)Cu^II–Sn₂^IV] chloride (1) was synthesized by employing a well-designed three-step pathway under anhydrous conditions. Interaction of the complex (1) with calf-thymus DNA was studied by spectrophotometry, cyclic voltammetry and viscosity measurements. The kinetic studies of calf-thymus DNA binding were carried out at 260 nm (λ_max of calf-thymus DNA) under pseudo-first order conditions. The rate constants, k_obs, were evaluated by the linear least squares regression method. The absorption spectra of the complex with calf-thymus DNA shows ‘hyperchromism’ which is attributed to the electrostatic interaction with calf-thymus DNA. The electrochemical behavior of complex (1) was studied in DMSO/H₂O (5:5) solution and showed a quasireversible Cu^II/Cu^I redox couple. The voltammetric studies of the complex in the absence and in the presence of DNA exhibit a shift in the formal potential E ⁰ and ratio of cathodic to anodic peak currents i_pa/i_pc indicating strong binding of the complex to calf-thymus DNA. The viscosity of DNA decreases with increasing concentration of the complex, suggesting that complex (1)binds to calf-thymus DNA by electrostatic association.