Outer-sphere electron-transfer reactions with the participation of platinum(IV) haloammines

The kinetics of some outer-sphere electron-transfer reactions with the participation of the complexes [Pt(NH₃)_nX_6–n]² (n=6–0, X=Cl^–, Br^–) and dipyridyl complexes of Os(II), Ru(II), Ir(III), and Cr(II) have been investigated by means of luminescence-quenching measurements and flash photolysis. Estimates of the values of the Pt(IV)/Pt(III) one-electron potential and the change in the free energy of activation of electron self-exchange processes of the type Pt(IV) Pt(III) have been obtained on the basis of an analysis of the dependence of the rate constant on the change in the free energy accompanying the electrontransfer process.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 455–462, July–August, 1990.     

Adsorptive stripping voltammetric measurements of trace amounts of platinum(II) and ruthenium(III) in the presence of 1-(2-pyridylazo)-2-naphthol

An extremely sensitive stripping voltammetric procedure for low level measurements of platinum (II, IV) or ruthenium (III, IV) is reported. The method is based on the interfacial accumulation of the platinum (II) or ruthenium (III)-1-(2-pyridylazo)-2-naphthol complex on the surface of a hanging mercury drop electrode, followed by the reduction of the adsorbed complex during the cathodic scan. The peak potential was found to be –0.8 V vs. Ag/AgCl electrode and the reduction current of the adsorbed complex ions of platinum (II) or ruthenium (III) was measured by differential pulse cathodic stripping voltammetry. The optimum experimental conditions were: 1.5×10^–7 mol/l of 1-(2-pyridylazo)-2-naphthol solution of pH 9.3, preconcentration potential of –0.2 V, accumulation time of 3 min and pulse amplitude of 50 mV with 4 mV s^–1 scan rate in the presence of ethanol-water (30% v/v) — sodium sulphate (0.5 mol/l). Linear response up to 6.4 × 10^–8 and 5.1 × 10^–8 mol/l and a relative standard deviation (at 1.2×10^–8 mol/l) of 2.4 and 1.6% (n=5) for platinum (II) and ruthenium (III) respectively were obtained. The detection limits of platinum and ruthenium were 3.2×10^–10 and 4.1×10^–10 mol/l, respectively. The electronic spectra of the Pt(II) — PAN and Ru(III) — PAN complexes were measured at pH 9.3 and the stoichiometric ratios of the complexes formed were obtained by the molar ratio method. The effects of some interfering ions on the proposed procedure were critically investigated. The method was found suitable for the sub-microdetermination of ruthenium (IV) and platinum (IV) after their reduction to ruthenium (III) and platinum (II) with sulphur dioxide in acid media. The applicability of the method for the analysis of binary mixtures of ruthenium (III) and (IV) or platinum (II) and (IV) has also been carried out successfully. The method is simple, rapid, precise, and promising for the determination of the tested metal ions at micro-molar concentration level.     

High performance liquid chromatographic separation and UV determination of cobalt, copper iron and platinum in pharmaceutical preparations using bis(isovalerylacetone)ethylenediimine as complexing reagent

The reagent bis(isovalerylacetone)ethylenediimine(H₂IVA₂en) has been examined for HPLC separation and UV determination of cobalt, copper, iron and platinum using off-line precolumn derivatization and extraction in chloroform. The complexes of cobalt(II), cobalt(III), iron(II), iron(III) and the reagent have been subsequently separated on a Microsorb C-18 column. The complexes were eluted isocratically using ternary mixtures of methanol/water/acetonitrile. Detection was achieved by UV monitoring. Detection limits for Co(II), Co(III), Fe(II) and Fe(III) were 2.5–5.0 ng/injection, based on 0.5–1.0 g/ml with 5 l/injection. The concentration of cobalt(II) and cobalt(III) in aqueous solution have been determined. The presence of oxovanadium(IV), platinum(II), and nickel(II) did not affect the determinations. The HPLC method developed has been applied to the determination of cobalt, copper, iron and platinum in pharmaceutical preparations at the 30 g/g to 15 mg/g level and the obtained results were compared to those of atomic absorption spectrometry.     

The reductions of chloro-, bromo- and iodopentacyanocobaltate(III) anions by titanium(III) in aqueous acidic solution

Summary The reduction of chloro-, bromo- and iodopentacyanocobaltate(III) anions by aquatitanium(III) has been studied in aqueous solution with ionic strength, I = 1.0 mol dm^-3 (LiCl, KBr or KI) at T = 25 °C. The dependence of the observed second-order rate constant, k _obs, on [H⁺] has been investigated over the acid range 0.005–0.100 mol dm ^–3 and is of the general limiting form: k _obs k ₀ + k[H ⁺] ^–1, where k ₀ is appreciable in all cases and k is a composite rate constant. Using values of K _a (associated with the Ti^III hydrolytic equilibrium constant), obtained from the kinetic data for the Ti^III/Co^III redox reactions, and comparison of the rate constants obtained with those for the corresponding V^II reductions of the same Co^III complexes, it is concluded that the Ti^III reductions of these halopentacyanocobaltate(III) complexes proceed via an outer-sphere mechanism.Author to whom all correspondence should be directed, who is presently on leave of absence from Obafemi Awolowo University.     

Influence of the nature of the lower free orbital of platinum(IV) bipyridyl complexes on the kinetics and the mechanism of electron transfer processes in which they participate

The kinetics of outer-sphere electron transfer reactions with the participation of [PtEn_xbipy_2–xCl₂]²⁺ complexes (x = 0–2) have been studied. The formal potential and the internal barrier of self-exchange reactions with the electron Pt(IV) Pt(III) have been estimated. A correlation has been shown to exist between the parameters of outer-sphere and intramolecular electron transfer.A. I. Gertsen Russian Fedagogical University, Leningrad. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 5, pp. 695–698, November–December, 1991. Original article submitted May 20, 1991.     

Highly sensitive spectrophotometric determination of trace amounts of platinum(IV) with the molybdate-basic dyes-poly(vinyl alcohol) system

Three highly sensitive spectrophotometric methods for the determination of platinum(IV) have been developed, based on its colour reactions with molybdate and basic dyes (BD) in aqueous solution in the presence of poly(vinyl alcohol). Platinum(IV) reacts with molybdate and BD to form ion — association complexes of composition (BD)₂[Pt (MoO₄)₃]. The molar absorptivities are between 6.83 × 10⁵ and 9.51 × 10⁵ dm³mol^–1cm^–1, the highest value being found with nile blue. Suitable conditions for the reactions and the effects of foreign ions were investigated. The methods can be applied to the spectrophotometric determination of trace amounts of platinum(IV) in some catalysts and ores.     

Interaction of Aluminium (III) with the f-Family Ions Np(VI), Pu(VI), Np(V), Np(IV), Pu(IV), Nd(III), and Am(III) in the Course of Simultaneous Hydrolysis

The interaction of Np(VI), Pu(VI), Np(V), Np(IV), Pu(IV), Nd(III), and Am(III) with Al(III) in solutions at pH 0–4 was studied by the spectrophotometric method. It was shown that, in the range of pH 3–4, the hydrolyzed forms of neptunyl and plutonyl react with the hydrolyzed forms of aluminium. In the case of Pu(VI), the mixed hydroxoaqua complexes (H₂O)₃PuO₂(-OH)₂Al(OH)(H₂O)₃ ²⁺ or (H₂O)₄PuO₂OAl(OH)(H₂O)₄ ²⁺ are formed at the first stage of hydrolysis. Np(VI) also forms similar hydroxoaqua complexes with Al(III). The formation of the mixed hydroxoaqua complexes was also observed when Np(IV) or Pu(IV) was simultaneously hydrolyzed with Al(III) at pH 1.5–2.5. The Np(IV) complex with Al(III) has, most likely, the formula (H₂O) _n (OH)Np(-OH)₂Al(OH)(H₂O)₃ ³⁺. At pH from 2 to 4.1 (when aluminium hydroxide precipitates), the Np(V) or Nd(III) ions exist in solutions with or without Al(III) in similar forms. When pH is increased to 5–5.5, these ions are almost not captured by the aluminium hydroxide precipitate.     

Synthetic and kinetic studies on copper(II), nickel(II) and cobalt(III) complexes of 1,4,7,10,13-pentaazacyclohexadecane ([16]aneN5)

Summary The pentadentate macrocycle 1,4,7,10,13-penta-azacyclo-hexadecane [16]aneN₅=(3)=L} has been prepared and a variety of copper(II), nickel(II) and cobalt(III) complexes of the ligand characterised. The copper complex [CuL](ClO₄)₂, on the basis of its d-d spectrum, appears to be square pyramidal, while [NiL(H₂O)](ClO₄)₂ is octahedral. The copper(II) and nickel(II) complexes dissociate readily in acidic solution and these reactions have been studied kinetically. For the copper(II) complex, rate=k_H[complex][H⁺]² with k_H =4.8 dm⁶ mol^–2s^–1 at 25 °C and I=1.0 mol dm^–3 (NaClO₄) with H=43 kJ mol^–1 and S ₂₉₈ =–89 JK^–1 mol^–1. Dissociation rates of the copper(II) complexes increase with ring size in the order: [15]aneN₅ < [16]aneN₅ < [17]aneN₅. For the dissociation of the nickel(II) complex, rate=k_H[Complex][H⁺] with k_H=9.4×10^–3 dm³mol^–1 s^–1 at 25 °C and I =1.0 mol dm^–3 (NaClO₄) with H=71 kJ mol^–1 and S ₂₉₈ =–47 JK^–1mol^–1.The cobalt(III) complexes, [CoLCl](ClO₄)₂, [CoL(H₂O)]-(ClO₄)₃, [CoL(NO₂)](ClO₄)₂, [CoL(DMF)](ClO₄)₃ (DMF=dimethylformamide) and [CoL(O₂CH)](ClO₄)₂ have been characterised. The chloropentamine [CoCl([16]aneN₅)]²⁺ undergoes rapid base hydrolysis with k_OH=1.1× 10⁵dm³ mol^–1s^–1 at 25°C and I=0.1 mol dm^–3 (H=73 kJ mol^–1 and S ₂₉₈ =98 JK^–1 mol^–1). Rapid base hydrolysis of [CoL(NO₂)]²⁺ is also observed and the origins of these effects are considered in detail.     

Photochemical properties of peroxo complexes of titanium,intermediate products in the photocatalytic liquid-phase oxidation of alcohols

A study has been made of the photochemical reactions of titanium(IV) peroxo complexes formed in the reaction of titanium tetrachloride with hydrogen peroxide in alcoholic solutions and which are characterized by intense charge transfer bands at 360–425 nm. Irradiation of the solutions with light of = 254 nm leads to the decomposition of the titanium(IV) peroxo complexes, the formation of titanium(III) compounds, as well as the oxidation of the alcohol to aldehyde. In the irradiated frozen solutions associated complexes of titanium(III), organic free radicals formed from the alcohol molecule, as well as peroxy radicals have been identified by EPR. Irradiation with light corresponding to the longwave band of the peroxo complexes leads to their decomposition but titanium(III) compounds and alcohol oxidation products are not formed in this case. In irradiated frozen solutions the formation of paramagnetic titanium(IV) complexes containing the fragment Ti...O ₂ has been established, as well as other paramagnetic particles identified tentatively as coordinated Ti...O ₂ ^· radicals or radical pairs. It is shown that the decomposition of hydrogen peroxide in the presence of titanium(IV) compounds is photocatalytic.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 24, No. 1, pp. 67–74, January–February, 1988.     

Kinetics and mechanism of formation and dissociation of copper(II) and nickel(II) complexes of the Schiff base bis(acetylacetone)ethylenediimine in aqueous-organic solvent media

Summary In NH₄NO₃+NH₄OH buffered 10% (v/v) dioxan-water media (pH 7.0–8.5), thePseudo-first-order rate constant for the formation of the title complexes M(baen),i.e. ML, conforms to the equation 1/k_obs=1/k+1/(kK_o.s · T_L), where T_L stands for the total ligand concentration in the solution, K_o.s is the equilibrium constant for the formation of an intermediate outer sphere complex and k is the rate constant for the formation of the complex ML from the intermediate. Under the experimental conditions the free ligand (pK_a>14) exists virtually exclusively in the undissociated form (baenH₂ or LH₂) which is present mostly as a keto-amine in the internally hydrogen-bonded state. Although the observed formation-rate ratio k^Cu/k^Ni is of the order of 10⁵, as expected for systems having normal behaviour, the individual rate constants are very low (at 25°C, k^Cu=50 s^–1 and k^Ni=4.7×10^–4s^–1) due to the highly negative S values (–84.2±3.3 JK^–1M^–1 for CuL and –105.8±4.1 JK^–1M^–1 for NiL); the much slower rate of formation of the nickel(II) complex is due to higher H value (41.2±1.0 kJM^–1 for CuL and 78.2±1.2 kJM^–1 for NiL) and more negative S value compared to that of CuL. The K_o.s values are much higher than expected for simple outer-sphere association between [M(H₂O)₆] and LH₂ and may be due to hydrogen bonding interaction.In acid media ([H⁺], 0.01–0.04 M) these complexes M(baen) dissociate very rapidly into the [M(H₂O)₆]²⁺ species and baenH₂, followed by a much slower hydrolytic cleavage of the ligand into its components,viz. acetylacetone and ethylenediamine (protonated). For the dissociation of the complexes k_obs=k₁[H⁺]+k₂[H⁺]². The reactions have been studied in 10% (v/v) dioxan-water media and also ethanolwater media of varying ethanol content (10–25% v/v) and the results are in conformity with a solvent-assisted dissociativeinterchange mechanism involving the protonated complexes.     

Kinetics of the Ru(III) catalyzed oxidation of formaldehyde and acetaldehyde by alkaline hexacyanoferrate(III)

The kinetics of ruthenium(III) catalyzed oxidation of formaldehyde and acetaldehyde by alkaline hexacyanoferrate(III) has been studied spectrophotometrically. The rate of oxidation of formaldehyde is directly proportional to [Fe(CN) _3– ⁶ ] while that of acetaldehyde is proportional tok[Fe(CN) _3– ⁶ ]/{k +k[Fe(CN) _3– ⁶ ]}, wherek, k andk are rate constants. The order of reaction in acetylaldehyde is unity while that in formaldehyde falls from 1 to 0. The rate of reaction is proportional to [Ru(III)] _T in each case. A suitable mechanism is proposed and discussed.

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Die Kinetik der Ru(III)-katalysierten Oxidation von Formaldehyd und Acetaldehyd mittels alkalischem Hexacyanoferrat(III)

Zusammenfassung Die Untersuchung der Kinetik erfolgte spektrophotometrisch. Die Geschwindigkeitskonstante der Oxidation von Formaldehyd ist direkt proportional zu [Fe(CN) _3– ⁶ ], währenddessen die entsprechende Konstante für Acetaldehyd proportional zuk[Fe(CN) _3– ⁶ ]/{k +k[Fe(CN) _3– ⁶ ]} ist, wobeik,k undk Geschwindigkeitskonstanten sind. Die Reaktionsordnung für Acetaldehyd ist eine erste, die für Formaldehyd fällt von erster bis zu nullter Ordnung. Die Geschwindigkeitskonstante ist in jedem Fall proportional zu [Ru(III)] _T . Es wird ein passender Mechanismus vorgeschlagen.

     

Spectrofluorimetric determination of trace amounts of Tb(III) using acetylacetone in ethanol solution

Summary The spectrofluorimetric determination of terbium(III) in ethanol (95%) solution of acetylacetone (3×10^–4 mol/l) was studied. Intensive fluorescence of terbium(III) (=545 nm) was observed after excitation of the system (=310 nm). The method proposed is satisfactory for the determination of terbium(III) in the range of 4 to 40 ng/ml (2.5×10^–8 to 2.5×10^–7 mol/l). The effect of other rare earths, common metal ions and anions upon the intensity of the fluorescence emitted by terbium(III) is discussed.

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Spektrofluorimetrische Bestimmung von Tb(III)-Spuren mit Acetylaceton in Ethanollösung

     

Fluorescence enhancement of terbium(III) by nucleotides and polyhomonucleotides in the presence of phenanthroline

Summary The fluorescence enhancement of terbium(III) by nucleotides (AMP, ADP, ATP, GMP, GDP, GTP) and polyhomonucleotides [poly(A), poly(G), poly(C), poly(U)] in the presence of phenanthroline (phen) was studied. Investigation of the composition of the terbium(III)/ANP(AMP, ADP, ATP)/phen complexes and conditions of optimization suggest a 1:2 molar ratio of terbium(III) and phen for the ternary complexes. The results showed that the presence of phen enhanced the net fluorescence of terbium(III)/ANP, poly(A), poly(C) or poly(U) from several fold to more than one-hundred fold, while it has little effect on the fluorescence of terbium(III)/GNP(GMP, GDP and GTP) or the poly(G) system. The possibility of spectrofluorimetric measurements of these compounds were studied under optimal conditions (pH 7.0 in tris-HCl buffer; E_x=298 nm, E_m=543.5 nm). The detection limits were 2.0×10^–7, 6.0×10^–7 and 1.0×10^–6 mol/l for AMP, ADP and ATP, respectively. The relative standard deviations (6 replicates) were within 2.0% in the middle of the linear range.     

Synthesis and Spectroscopic Studies of Chosen Heteropolytungstates and Their Ln(III) Complexes

The heteropolytungstates [(Na)P₅W₃₀O₁₁₀]^4– (I), [(Na)Sb₉W₂₁O₈₆]^18– (II) and [(Na)As₄W₄₀O₁₄₀]^27– (III) and the monovacant Keggin structure of the general formula [XW_11–xMo_xO₃₉]^n– (X-Si, P; n = 7 for P and 8 for Si) (IV) as well as their europium(III) complexes were studied. The structures of I–IV as well as the europium(III) encrypted [(Eu)P₅W₃₀O₁₁₀]^12– (VI), [(Eu)Sb₉W₂₁O₈₆]^16– (VII), [(Eu)As₄W₄₀O₁₄₀]^25– (VIII) and sandwiched [Eu(XW_11–xMo_xO₃₉)₂]^n– (n =11 for P and n = 13 for Si) (V) complexes were synthesized and spectroscopically characterized. The complexes were studied using UV-Vis absorption and luminescence, as well as the laser-induced europium ion luminescence spectroscopy. Absorption spectra of Nd(III) were used to characterize the complexes formed. Excitation and emission spectra of Eu(III) were obtained for solid complexes and their solutions. The relative luminescence intensities of the Eu(III) ion, expressed as the ratio of the two strongest lines at 594 nm and 615 nm, = I₆₁₅/I₅₉₄, which is sensitive to the environment of the primary coordination sphere about the Eu(III) ion, was calculated. In the case of the sandwiched [Eu(XW_11–xMo_xO₃₉)₂]^n– complexes a linear dependence of the luminescence quantum yield of Eu(III) ion, , (calculated using [Ru(bpy)₃]Cl₂ as a standard) on the content of Mo (number of atoms, x) in the [Eu(XW_11–xMo_xO₃₉)₂]^n– structure was observed.     

Thermochemical investigation

The stoichiometry of the thermal decomposition and the stereochemistry of the following compounds was studied: NiR₄Cl₂ (I), NiR₄Br₂ (II), NiR₄I₂·2H₂O (III) and NiR₄(NCS)₂ (IV) (R=3-pyridylcarbinol, ronicol). In complexes I and II the loss of the volatile ligands (on the TG curves) occurs in three steps (–2R, –R, –R), in complex III in four steps (–2H₂O, –2R, –R, –R) and in complex (IV) in one step (–4R). According to the quasi-equilibrium decomposition temperatures, the thermodynamic stability of NiR₄X₄ complexes can be ordered in the sequence (according to X):Cl相似文献   

Electronic and ESR spectroscopic study of thiocyanate-containing coordination compounds of titanium(III) in alcohol solutions

In an investigation of electronic and ESR spectra, it has been established that titanium(III) with the thiocyanate ion (in ethanol) forms distorted tetrahedral and octahedral complexes. The tetrahedral compounds, which are hydroxo complexes of titanium(III) that contain one hydroxyl group and three thiocyanate ions in the coordination sphere, give signals in the ESR spectra with g_o=1.960, A_o=15.0·10^–4 cm^–1 g=1.958, A ^Ti =26.4·10^–4cm^–1, g= 1.691, A^Ti=9.0·10^–4 cm^–1. In the ESR spectra of liquid solutions, additional splitting on the nitrogen atoms is manifested(A _o ^N =2.2·10^–4 cm^–1), which indicates bonding of thiocyanate ions through the nitrogen atom. The pseudo-octahedral complexes of titanium(III), containing from two to six thiocyanate ions in the coordination sphere, are characterized by d-d absorption bands in the 520–590 nm region; and at 77°K, they give anisotropic ESR signals. On the basis of the temperature dependences of the equilibrium constants for the reaction of conversion of the tetrahedral complexes to the octahedral complexes, and also the lifetimes of the tetrahedral complexes, values have been estimated for the heat of reaction (H=26.8 kJ/mole) and the entropy change (S=–1.66 kJ/mole·°K) of the equilibrium process, and also the activation energy for the reaction of titanium(III) thiocyanate formation (E=37 kJ/mole).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 5, pp. 560–567, September–October, 1985.     

Quantum chemical investigation of the reaction of phosphine with alcohol in the coordination sphere of platinum(IV) and platinum(II)

The CNDO method has been used to investigate a new autocatalytic reaction of reduction of alcohol solutions of platinum(IV) halides by phosphine, leading to the formation of products of O-phosphorylation — trialkyl phosphites — at low temperature (20–50°C) and products of C-phosphorylation — trihydroxyalkylphosphines — at high temperature (60–90°C). It was shown by comparing the metalligand and ligand-ligand bond energies in haloalcohol phosphine complexes of platinum(IV) and platinum(II) that alkoxylation proceeds through a step of deprotonation of the alcohol with nucleophilic assistance and introduction of phosphine at the metal-oxygen bond, whereas hydroxyalkylation includes a step of -elimination of alkoxide hydrogen and insertion of phosphine at the metalcarbon bond. Autocatalysis is due to the fact that the indicated key steps on platinum(II) are significantly more profitable with respect to the energy difference of the bonds broken (metal-ligand) and formed (ligand-ligand).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 4, pp. 301–312, July–August, 1992.     

On the mechanism of racemisation of dichlorobis(ethylenediamine)-metal chlorides [metal = cobalt(III) or chromium(III)] in the solid state

Summary In the solid state l-cis-[M(en)₂Cl₂]Cl [M=cobalt(III) or chromium(III)] undergoes thermal racemisation smoothly at 158 °C without anycis-trans interconversion. The values of k_rac, H and S are 6 × 10^–6s^–1, 218 kJM^–1 and 156.1 JK^–1M^–1 for the cobalt(III) complex and 3.5 × 10^–5s^–1, 229.7 kJM^–1 and 197.9 JK^–1M^–1 for the chromium(III) complex, respectively. The results are only in accord with a rhombic twist mechanism of the type originally proposed by Ray and Dutt for [M(AA)₃] complexes.     

Kinetics and mechanism of distribution of Am(III) and Eu(III) between thenoyltrifluoroacetone-triphenylarsine oxide mixture in chloroform and aqueous nitrate medium

The kinetics of distribution of Am(III) and Eu(III) between thenoyltrifluoroacetone (HTTA) and triphenylarsine oxide (Ph₃AsO) mixture in chloroform and aqueous nitrate medium has been investigated using a stirred Lewis cell at ionic strength of 0.1M. The effect of the concentration of HTTA, Ph₃AsO, H⁺ and NO ₃ ^– on the rate of distribution of Am(III) and Eu(III) was studied. The results were interpreted by reaction mechanisms where the rate-determining steps are the parallel reactions of Am(OH)²⁺ or Eu(OH)²⁺ with one HTTA molecule and one Ph₃AsO molecule in the aqueous medium. The values at 25 °C of the rate constantk _HLL (HL=HTTA andL=Ph₃AsO) are 1.6±0.3·10⁶M^–2·s^–1 and 2.3±±0.3·10⁸M^–2·s^–1 for Am(III) and Eu(III), respectively.     

The base hydrolysis ofmer-[Co(1,5-diamino-3-azapentane)(amino acidate)X]+ (X = Cl or NO2) complexes and base hydrolysis of complexed peptides in the coordination sphere of the [Co(dien)]3+ moiety

Summary A variety ofmer-[Co(dien)(AA)X]⁺ (AA = amino acidate, dien = 1,5-diamino-3-azapentane) andmer-[Co(dien)(dipeptideOR)X]²⁺ complexes (X = Cl or NO₂) have been prepared and characterised. Base hydrolysis of the peptide bond in the carbonyl bonded glycyl peptides has been studied at 25°C and I = 0.1 mol dm^–3. The rate constants k_OH for peptide bond hydrolysis fall within the 0.67–0.88 mol dm^–3s^–1 range. Base hydrolysis of the complexed peptide isca. 2×10⁴ times faster than for the uncomplexed peptide ligand at 25 °C. The base hydrolysis of the chloro- and nitro-ligands in these complexes has also been studied. Very rapid hydrolysis occurs if the dien ligand adopts amer-configuration and the reactions are 10²–10⁴ times faster than for analogous complexes where the dien ligand adopts afac-configuration. These results are in agreement with Tobe's criteria for rapid base hydrolysis in cobalt(III) complexes.The following abbreviations are used thoughout this paper; dien 1,5-diamino-3-azapentane - dpt 1,7-diamino-4-azaheptane - glyO glycinate - glyOH glycine - glyOR glycine ester - glyNH₂ glycine amide - glyglyO glycylglycinate - glyglyOR glycylglycine ester - glyglyglyOH triglycine - -alaO -alaninate