Showing papers on "Aquation published in 1975"

Volumes of activation for aquation of tris(1,10-phenanthroline)iron(II) complexes in aqueous solution

Abstract: Activation volumes for aquation of the tris(1,10-phenanthroline)iron(II) cation and of its 5-nitro- and 4,7-dimethyl derivatives in 1M-H2SO4 at 35 °C are +15·4 ± 0·4, +17·9 ± 0·3, and +11. 6 ± 0·6 cm3 mol–1 respectively. These values are consistent with a dissociative mechanism for aquation of these complexes.

Kinetics of the 1 : 1 equilibration of thiocyanate with the molybdenum(V) aquo-dimer

Abstract: Equilibration kinetic studies on the complexing of thiocyanate with the molybdenum(V) aquo-dimer [Mo2O4]2+, (I), have been carried out using the temperature-jump technique. With excess thiocyanate the reaction exhibits more than one relaxation effect, and the mechanism cannot be expressed in terms of a single process. With [Mo2O4]2+ in excess (ca. 5 : 1) only one relaxation time corresponding to the formation of the 1 : 1 complex [Mo2O4(NCS)]+ is observed, and this is independent of hydrogen-ion concentration in the range 0·5–2·0M, I= 2·0M, (LiClO4). Relaxation times, τ, can be expressed in terms of equilibrium concentrations of reactant as in (i), where rate constants K1 and k–1 for the formation and aquation of the 1 : 1 complex are, at 25 °C, (2·9 τ–1=K1([Mo2O42+]e+[NCS–]e)+K–1(i)± 0·1)× 104 l mol–1 s–1 and 120 ± 10 s–1 respectively. Activation parameters from data at 15–35 °C are ΔH1‡= 11·3 ± 0·9 kcal mol–1, ΔS1‡=–0·3 ± 3·1 cal K–1 mol–1, ΔH–1‡= 13·7 ± 2·5 kcal mol–1, and ΔS–1‡=–3·0 ± 8·0 cal K–1 mol–1. The kinetic value of the equilibrium constant (k1/k–1) at 25 °C, I= 2·0M(LiClO4), is 240 l mol–1, which is in good agreement with that obtained spectrophotometrically.

The Photolyses of Chloropentammine and Chloropentakis(alkylamine) Chromium(III) Complexes in Acetone/Water Mixtures

Abstract: The photochemistry of the [Cr(RNH2)5Cl]2+ ions where R = H,CH3,C2H5,n-C3H7,n-C4H9 has been investigated in water and in acetone/water solutions at pH 3. In water and in 33 w/w% acetone/water, the predominant reaction for each ion was found to be amine aquation to give predominantly cis-[Cr(RNH2)4(H2O)Cl]2+. Photolysis of [Cr(CH3NH2)5Cl]2+ in acidified acetone yielded a solvent substituted product [Cr(CH3NH2)4(S)Cl]2+ which has predominantly the cis-configuration but the extents of water and acetone substitution were not established. The amine quantum yields are almost solvent independent, only slightly wavelength dependent, and they decrease significantly in going from R = H to R = n-C4H9. The chloride quantum yields, which are of the order of 10−4 at 565 nm, are about an order of magnitude smaller than had been previously reported for [Cr(NH3)5Cl]2+; they are several times larger at 401 nm. The chloride quantum yields show a significant decrease upon changing the solvent from water to 33% acetone/water.T...

Kinetics of aquation of penta-amminechlororuthenium(III) dichloride and cis-dichlorobis(ethylenediamine)ruthenium(III) chloride hydrate in mixed water–organic solvents

Abstract: Kinetic data are reported for the spontaneous aquations of [Ru(NH3)5Cl]Cl2 and cis-[Ru(en)2Cl2]Cl in a variety of mixed water–organic solvents. Plots of log kH2O against Grunwald–Winstein Y values are linear with gradients ca. 0.25, suggesting essentially SN1 mechanisms. The Hg2+-catalysed aquation of [Ru(NH3)5Cl]2+ has also been studied in both aqueous solution and in a variety of mixed water–organic solvents. Kinetic data in aqueous solution are consistent with pre-equilibnum formation of a chloro-bridged intermediate, [(NH3)5Ru–Cl–Hg]4+, followed by dissociation to release [HgCl]+ and the rapid pick up of water. Plots of log kHg2+ against Y values for the Hg2+-catalysed aquation in mixed solvents are markedly non-linear. This unusual behaviour is discussed in terms of the pre-equilibrium mechanism.

Kinetic and equilibrium studies on iron(II) and iron(III) pentacyanoferrates

Abstract: The results of a kinetic investigation of the reaction of [FeII(CN)5(py)]3–(py = pyridine) with CN– and HCN are reported, together with a linear free-energy treatment of data obtained for aquation reactions of species of the type [FeII(CN)5X](X = an uncharged or univalent anion). Equilibrium studies of [FeII(CN)5OH2]3– and [FeIII(CN)5OH2]2– with a number of substituents have confirmed the class (b) or ‘soft’ character of the iron centre in these complexes.

Base hydrolysis and mercury(II)-catalysed aquation of bis(ethylenediamine-NN′)(ethylenediamine-N)halogenocobalt(III) complexes

Abstract: The kinetics of base hydrolysis of the complexes cis-[CoX(en)2(en-N)]2+(X = Cl or Br) have been studied at 25 °C and I= 0.1M(Na[ClO4]) and kOHCl=(6.3 ± 0.3) and kOHBr=(4.1 ± 0.2)× 101 l mol–1s–1. The main product is [Co(en)2(en-N)OH]2+(ca, 97%) rather than [Co(en)3]3+. The ionization constants for the equilibria (i) and (ii) are pKlm 5.05 and pK2m 7.23. The mercury(II)-catalysed aquations have also been studied at 25 °C [Co(en)2(Hen-N)OH2]4+[graphic omitted][Co(en)2(Hen-N)OH]3++ H+(i), [Co(en)2(Hen-N)OH]3+[graphic omitted][Co(en)2(en-N)OH]2++ H+(ii)(I= 3.94M and [H+]= 0.94M) and kHgCl=(5.6 ± 0.3)× 10–3 and kHgBr=(5.0 ± 0.15)× 10–3 l mol–1 s–1. The major product (ca, 95%) is the complex [Co(en)2(Hen-N)OH2]4+. In dimethyl sulphoxide solution the complex [CoCl(en)2(en-N)]2+, in the presence of n-butylamine, undergoes cyclisation to [Co(en)3]3+. The reaction is first order in the complex and n-butylamine concentrations with k= 1.19 × 10–3 l mol–1 s–1 at 25 °C.

Kinetics of aquation and base hydrolysis of the macrocyclic complex trans-chloro(5,12-dimethyl-1,4,8,11-tetra-azacyclotetradeca-4,11-diene)nitrocobalt(III) perchlorate

Abstract: The macrocyclic complex trans-[Co(dtcd)(NO2) Cl][ClO4](dtcd = 5,12-dimethyl- 1,4,8,11 -tetra-azacyclotetradeca-4,11 -diene) has been prepared and its hydrolysis kinetics investigated. At 25 °C and 0.1 M-HNO3 the aquation occurs with kaq= 4.4 × 10–4 s–1 to give the trans-[Co(dtcd)(NO2)(OH2)]2+ cation. The activation parameters are ΔH‡= 77.4 kJ mol–1 and ΔS‡=–49.8 J K–1 mol–1 at 298 K. Hydrolysis of the chloride in the pH range 7.7–8.9 follows the rate expression kobs.=kaq+k2[OH–]. At 25 °C (I= 0.1 M Na[ClO4])k2= 2.5 × 102 l mol–1 s–1 and the activation parameters for base hydrolysis are ΔH‡= 69 kJ mol–1 and ΔS‡=+24.5 J K–1 mol–1. Base hydrolysis of the nitro-group has been studied at 25 °C and 0.1 M–NaOH and k= 2.1 l mol–1 s–1. Slow decomposition of the complex occurs, possibly as a result of hydrolysis of the imine linkages; however, this decomposition (koba.= 2.2 × 10–3 s–1) is much slower than nitro-hydrolysis. The analogous complex trans-[Co(htcd)(NO2)Cl][ClO4](htcd = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradeca-4,11-diene) exhibits similar kinetic behaviour for base hydrolysis of the chloride. At 25 °C (I= 0.1M), k2= 2.2 × 102 l mol–1 s–1 and kaq= 5.5 × 10–4 s–1. The additional methyl substituents in the macrocyclic ligand have little or no effect on the hydrolysis rates.

The mercury(II)-induced aquation of trans-Chloroamminebis(dimethylglyoximato)cobalt(III) complex

Abstract: The pseudo first-order rate constants for the mercury(II)-induced aquation of trans-[Co(Hdmg)2(NH3)Cl] (Hdmg = dimethylglyoximate ion) have been measured in aqueous and aqueous ethanol solutions (ethanol- water mole ratio 1 : 5.1) containing various excess amounts of mercury(II)ion at 273.2 K. Association constants of the complex formed with mercury(II) ion and rate constants for dissociation of the activated complex in both solutions have been calculated. The kinetic results are discussed in terms of formation of an activated complex Co-C1-Hg, followed by a simple rate-determining aquation in which HgCl+ acts as the leaving group.

Aquation of chloropentaamminecobalt(III) Perchlorate in chloride‐ion containing water–nonaqueous solvent mixtures

Abstract: The equilibrium quotients for the formation of Co(NH3)5Cl2+ from Co(NH3)5OH23+ and Cl− were 3.74±0.25 M−1 and 6.07±0.54 M−1 at 45.0°C in 10:1 mole ratio water: dimethyl sulfoxide and in 25 w/w % aqueous ethanol, respectively, and those forthe formation of the ion pair Co(NH3)5OH23+ . Cl− were 1.21±0.20 M−1 and 1.58±0.17 M−1, respectively, in the same solvents. The aquation and anation rateconstants were determined at 45.0°C for these two solvents over the range of chloride-ion concentrations 0.0 ≤ [Cl−] ≤ 0.9 M. The aquation rate constant was essentially independent of chloride-ion concentration in each solvent over this range. The inverse of the pseudo-first-order anation rate constant was linearly dependent on the inverse of the chloride-ion concentration in each solvent. The least squares relationships between (1/kan) and (1/[Cl−]) gave intercepts and ratios of intercept to slope which were analyzed interms of Id and D mechanisms. It was concluded that the data were not satisfied by a D mechanism, but that they were consistent with an Id mechanism.

Aquation of penta-ammine(dimethyl sulphoxide)cobalt(III) perchlorate in ethanol–water–perchlorate media

Abstract: Rates of aquation of penta-ammine(dimethyl sulphoxide)cobalt(III) perchlorate have been measured in a variety of ethanol–water–perchlorate-ion media. The pseudo-first-order rate constant for aquation is independent of the perchloric acid concentration, ionic strength, and nature of the cation but is dependent on perchlorate-ion concentration and on the ethanol : water ratio. The average enthalpy and entropy of activation are 25.4 ± 0.3 kcal mol–1 and 1.9 ± 1.0 cal K–1 mol–1, respectively. There is little evidence of solvent assistance for the leaving and entering groups in the transition state.

Infra-red and Raman spectral study of the aqueous nickel(II)–nitrite system. Evidence for photochemical alteration of the chemical equilibrium

Abstract: Infra-red and Raman spectra of aqueous nickel(II)–nitrite systems have been obtained for a wide range of compositions. Stability constants for the nickel(II)–nitrite system have been measured by infra-red and Raman techniques. The infra-red and Raman data give completely different stability constants. Raman studies indicate the existence of Ni(NO2)2(H2O)4 exclusively with β2= 0.15 ± 0.02 in excellent agreement with previous work. Infra-red data indicate the more usual step-wise formation of the complexes Ni(NO2)(H2O)+5, Ni(NO2)2(H2O)4 and Ni(NO2)3(H2O)–3 with β1= 2.2 ± 0.5, β2= 0.45 ± 0.2 and β3= 0.65 ± 0.2 but the existence of higher order complexes could not be excluded. To rationalize the difference between the two sets of data it is postulated that visible light in the 400–600 nm region alters the chemical equilibrium through rapid photochemical aquation. The infra-red data more closely describe the nickel(II)–nitrite system in the absence of light.

The uncatalysed and mercury(II)- and thallium(III)-catalysed elimination of chloride from the µ-amido-µ-chloro-bis[tetra-amminecobalt(III)] complex

Abstract: The kinetics of the mercury(II)- and thallium(III)-catalysed elimination of chloride from the title complex (I), equation (i), have been studied in aqueous HClO4 solution, I= 2·0M(NaClO4). Both reactions are independent [graphic omitted] of [H+] in the range 0·5–2·0M. With mercury(II) there is a less than first-order dependence on [Hg2+] which cannot be satisfactorily accounted for in terms of a 1 :1 adduct. Instead the dependence can be explained by considering Hg2+-catalysed conversion of (II) into (III) and applying the steady-state approximation for (II). From the treatment (at 25 °C), k1= 3·02 × 10–3 s–1, ΔH‡1= 19·2 ± 0·5 kcal mol–1, ΔS‡1=–5·7 ±1·8 cal K–1 mol–1, and k2/k–1= 0·028. At 25 °C ratios k3/k2= 1·57 × 103 I mol–1 and k4/k2= 1·3 × 103 I mol–1 are measures of the effectiveness of Hg2+ and HgCl+ as catalysts for (II)→(III). Thallium(III) produces only a mild catalytic effect, a first-order dependence on [Tl3+] is observed, and k5/k2= 15 I mol–1 is a measure of the effectiveness of Tl3+ as a catalyst. It is concluded that Tl3+ is a relatively weaker catalyst compared to Hg2+ for (II)→(III) than for the catalysed aquation of mononuclear chloro-complexes.

Investigation of the effects of added salts on the rate of hydrolysis of sulphur trioxide–trimethylamine

Abstract: The first-order rate constant for aquation of sulphur trioxide–trimethylamine, Me3N·SO3, at 336 K increases when tetra-n-butylammonium bromide is added, but decreases when either potassium or lithium bromide is added. This behaviour is examined in the light of similar trends for the dissociative aquation of the tris(5-nitro-1,10-phenanthroline)iron(II) cation.