Warren L. Reynolds

D2O effect on ΔH++ and ΔS++ in the ironII-ironIII electron-exchange reaction

Abstract The equilibrium constant of the reaction Fe 3+ + D 2 O → FeOD 2+ + D + has been measured at 0.500 ionic strength at 5°, 15° and 25°. The ΔH and ΔS of this reaction are 9.32 ± 0.56 kcal mole −1 and 17.7 ± 2.0 cal. deg. −1 mole −1 , respectively. The rates of the electron-exchange reactions Fe 2+ + ∗ Fe 2+ → Fe 2+ + ∗ Fe 2+ and Fe 2+ + ∗ FeOD 2+ → FeOD 2+ + ∗ Fe 2+ have been measured at 0 500 ionic strength at 5°, 15° and 25°. The enthalpy and entropy of the latter reaction are 11.5 ± 0.5 kcal, mole −1 and −4.0 ± 1.8 cal. deg. −1 mole −1 , respectively.

Complexes of cobalt(II) with chloride and thiocyanate ions in dimethyl sulfoxide

Abstract The important cobalt(II)-chloride ion complexes which form in dimethyl sulfoxide solutions are Co(DMSO)Cl3− and CoCl42− and their overall formation constants are (4.21±0.58)×108 M−3 and (1.12±0.16)×109 M−4, respectively, at 25°C. The important cobalt(II)thiocyanate ion complexes which form in dimethyl sulfoxide solutions are Co(DMSO)5(NCS)+, Co(DMSO)4(NCS)2, and Co(NCS)42− and their overall formation constants are (465±72) M−1, (5.12±0.48)×10 M−2 and (5.79±0.55)×106 M−4, respectively, at 25°C. A value of 20±4 M−1 was found for the Co(DMSO)62+. ClO4− ion pairing constant. Molar absorptivities of the complexes are reported for selected wavelengths

Solvent-interchange reactions of the penta-amminecobalt(III) ions [Co(NH3)5(OH2)]3+ and [Co(NH3)5(dmf)]3+ in dimethylformamide (dmf)–water media

The rate law for aquation of [Co(NH3)5(dmf)][ClO4]3 is first order with respect to the concentration of the cobalt(III) complex and independent of aluminium(III) or perchloric acid concentration, contrary to a previous report. Tracer experiments have shown more than 95% cobalt(III)–oxygen bond fission, and chromatographic analyses for the formato-complex indicated less than 1% carbon–nitrogen bond fission. It is concluded that aquation proceeds by water molecules replacing intact dimethylformamide (dmf) molecules. Solvent interchange between the aqua- and dimethylformamide complexes has been studied in dmf–water mixtures at 25, 45, and 65 °C. The activation enthalpy for aquation of the dmf complex is independent of the composition of the solvation shell of the complex. The dependence of rate and equilibrium constants on dmf concentration is interpreted in terms of a free dmf-co-ordinated dmf interaction at small dmf contents which decreased the aquation rate constants at a more rapid rate at small dmf contents than at larger dmf contents at all temperatures. This same interaction increased the equilibrium concentration of the dmf complex more rapidly at small dmf than at larger dmf contents at 65 and probably at 45 °C also. Other explanations for preferential solvation of the complexes are considered and rejected. The rate law for aquation is Raq=Kaq′[Co(NH3)5(dmf)3+]xH2O. The activation parameters for kaq′ are satisfactorily constant over the range 0–0.7 mol fraction dmf, viz.ΔH‡= 105 ± 2 kJ mol–1 and ΔS‡=–3 ± 7 J K–1 mol–1. The rate law for ligation is expressed as Rlig=klig′[Co(NH3)5(OH2)3+]xdmf. The activation parameters for klig′ are not constant; ΔH‡lig and ΔS‡lig both decrease with increasing dmf content (xdmf).

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

The aquation rate constant for penta-ammine(dimethyl sulphoxide)cobalt(III) perchlorate has been determined in 71 different solvent media and at three different temperatures for each medium. The average enthalpy and entropy of activation, their standard deviations, and ranges are 24.6 ± 0.4 and 23.6–25.6 kcal mol–1 and 1.1 ± 1.2 and –2.4 to 4.4 cal K–1 mol–1, respectively, without noticeable trends. The aquation rate constant is independent of ionic strength at constant perchlorate-ion concentration, but shows a specific perchlorate-ion effect. These results are discussed in terms of the Id and Bennetto–Caldin mechanisms. It is concluded that there is, at most, only a very small solvent contribution to the activation parameters.

Temperature dependence of isotropic shifts of nickel complexes

Abstract Isotropic proton shifts of octahedral nickel(II) complexes with benzylamine, dimethylformamide, N,N,-dimethylacetamide, N-methylacetamide and n-propanol were determined as functions of the absolute temperature. Apparent non-Curie behavior was found for most of the isotropic shifts. Sources for this behavior were examined and the conclusions drawn are presented.

Rate Constants of Second‐Order Reactions from Kinetic Current Measurements

Kinetic currents have been calculated for the case where the solution contains two electroactive species, one of which may undergo a second order reaction with the reduced form of the other. The results have been applied to the reaction between ferrous versenate and cumene hydroperoxide, assuming the diffusion co‐efficients of all species to be equal. The calculated and observed rate constants are found to differ by 33%, which constitutes reasonable agreement in view of the assumptions made.

Preferential solvation and the composition of the solvation shell of (dimethyl sulphoxide)penta-amminechromium(III) ion in dimethyl sulphoxide–water mixtures

The number of solvent molecules in the solvation shell of the title complex ion has been found to be 10, the stepwise equilibrium constants for the replacement of the 10 water molecules by 10 dimethyl sulphoxide molecules have been obtained, and the free energy increment per replacement step has been found to be ∼+1.42 kJ mol–1.