Ol'ga Grančičová

The kinetics of aquation of cis-ammine-bromobis(ethylenediamine) cobalt(III) ion in water-organic mixtures

Abstract The aquation kinetics of cis -[CoNH 3 Br(en) 2 ] 2+ were investigated in aqueous mixtures of ethyl alcohol, isopropyl alcohol, t -butylalcohol and acetonitrile. The rate constants, activation enthalpies and entropies were determined. The interpretation of the experimental data, based on electrostatic theory, was possible only when methyl alcohol and ethyl alcohol were used as co-solvents. It was shown that in the mechanism of reaction studied non-electrostatic interactions play an important role.

Kinetics of aquation ofcis- andtrans-chloro-nitrobis-(ethylene-diamine)cobalt(III) ion in binary aqueous mixtures

SummaryKinetics of aquation ofcis- andtrans-[Co(en)2NO2Cl]+ were investigated in aqueous mixtures of MeOH, EtOH,i-PrOH andt-BuOH at 298.1 K. The values of transfer functions corresponding to the transfer of reactant and activated complex from H2O to the solvent mixtures were calculated from kinetic measurements and from solubilities of the complex salt. The results of the analysis of solvent effect are discussed in terms of D and Id mechanisms.

Kinetics of oxidation of pentaammine-isothiocyanato-cobalt(III) ion with peroxodisulphate and periodate in water and water-organic mixtures

SummaryThe kinetics of oxidation of [Co(NH3)5(NCS)]2+ by peroxodisulphate and periodate were investigated at different ionic strengths, and at different temperatures and concentrations of perchloric acid. Rate constants and activation parameters are also reported in mixed water-organic solvents. It was shown that the acid-base equilibria involving S2O8−2, and IO4− ions are important in the reactions studied. Solvent effects on the oxidation are interpreted in terms of the solvation of both the initial state and the activated complex.

Base hydrolysis of pentaammine complexes of cobalt(III) in aqueous-organic mixed solvents

SummaryThe kinetics of base hydrolysis of [Co(NH3)5Cl]2+ and [Co(NH3)5SO4]+ were investigated in aqueous mixtures of MeOH, EtOH,i-PrOH andt-BuOH at 298.1K. The values of transfer functions of the transition state corresponding to the transfer from water to the mixed media were calculated from solubilities of the complex salt and from kinetic measurements. The results of the analysis of the medium effect on the solvation of the initial and transition state are discussed in terms of the SNl CB and Id mechanisms.

Fluorescence Dynamics of Coumarin C522 as a Function of Micelle Confinement along with Cyclodextrin Supramolecular Complex Formation

Our aim is to doubly confine a molecule of coumarin C522 in a host-guest supramolecular complex with β-cyclodextrin in a reverse sodium dioctyl sulfosuccinate (AOT) micelle using nonpolar n-heptane and polar water solvents. Varying the volumes of coumarin C522 and β-cyclodextrin dissolved in water allows us to control the water-pool diameters of the reverse micelle in n-heptane with values of w=3, 5, 10, 20, and 40, where w is the ratio of water concentration to AOT concentration in n-heptane. To study the fluorescence dynamics of coumarin C522, the spectral steady-state and time-resolved dependences are compared for the two systems coumarin C522(water)/AOT(n-heptane), denoted C522/micelle, and coumarin C522/β-cyclodextrin(water)/AOT(n-heptane), referred to as C522/CD/micelle. The formation of the supramolecular host-guest complex CD-C522 is indicated by a blue shift, but in the micelle, the shift is red. However, the values of the fluorescence maxima at 520 and 515 nm are still way below the value of 535 nm representing bulk water. The interpretation of the red shift is based on two complementary processes. The first one is the confinement of CD and C522 by the micelle water pool and the second is the perturbation of the micelle by CD and C522, resulting in an increase of the water polarity. The fluorescence spectra of the C522/micelle and C522/CD/micelle systems have maxima and shoulders. The shoulder intensities at 440 nm, representing the C522 at n-heptane/AOT interface, decrease as the w values decrease. This intensity shift suggests that the small micelle provides a stronger confinement, and the presence of CD shifts the equilibrium from n-heptane towards the water pool even more. The fluorescence emission maxima of the C522/micelle and C522/CD/micelle systems for all w values clearly differentiate two trends for w=3-5, and w=10-40, suggesting different interaction in the small and large micelles. Moreover, these fluorescence maxima result in 7 and 13 nm differences for w=3 and w=5, respectively, and provide the spectral evidence to differentiate the C522 confinement in the C522/micelle and C522/CD/micelle systems as an effect of the CD molecule, which might be interpreted as a double confinement of C522 in CD within the micelle. The ultrafast decay in the case of w=3 ranges from 9.5 to 16 ps, with an average of 12.6 ps, in the case of the C522/micelle system. For C522/CD/micelle, the ultrafast decay at w=3 ranges from 9 to 14.5 ps, with an average of 11.8 ps. Increasing w values (from 10 to 40) result in a decrease of the ultrafast decay values in both cases to an average value of about 6.5 ps. The ultrafast decays of 12.6 and 11.8 ps for C522/micelle and C522/CD/micelle, respectively, are in the agreement with the observed red shift, supporting a double confinement in the C522/CD/micelle(w=3) system. The dynamics in the small and large micelles clearly show two different trends. Two slopes in the data are observed for w values of 3-5 and 10-40 in the steady-state and time-resolved data. The average ultrafast lifetimes are determined to be 12.6 and 6.5 ps for the small (w=3) and the large (w=40) micelles, respectively. To interpret the experimental solvation dynamics, a simplified model is proposed, and although the model involves a number of parameters, it satisfactory fits the dynamics and provides the gradient of permittivity in the ideal micelle for free water located in the centre (60-80) and for bound water (25-60). An attempt to map the fluorescence dynamics of the doubly confined C522/CD/micelle system is presented for the first time.

Solvent Effect on the Kinetics of Oxidation of [Co(en)2SCH2CH2 NH2]2+ by S2O8 2−

The effect of the solvent on rate of the oxidation of [Co(en)2SCH2CH2NH2]2+ by S2O82− in aqueous mixtures of methanol (MeOH), tert-butyl alcohol (ButOH), acetonitrile (AN), ethylene glycol (EG) and ethylene carbonate (EC) has been analysed as regards initial and transition state contributions. From kinetic measurements and solubilities of the reactants, the Gibbs transfer functions, ΔGt°, corresponding to transfer of reactants and activated complex from water to water-organic mixtures were evaluated. The trends of the transfer functions are discussed in terms of ion-solvent interactions and the structural effects in the solvent mixtures.

Kinetics of aquation of cis- and trans-chloro-nitrobis(ethylenediamine) cobalt(III) ion in aqueous mixtures of ethylene carbonate and propylene carbonate

SummaryThe kinetics of aquation of cis- and trans-[Co(en)2-NO 2Cl] + were investigated in quasi-isodielectric aqueous mixtures of ethylene carbonate (EC) and propylene carbonate (PC) over a range of temperatures. Transfer Gibbs energies of reactant and transition state from H2O to aqueous mixtures of EC were evaluated from kinetic measurements and the solubilities of the complex salt. An analysis of the solvent effect on the solvation of the initial (IS) and transition (TS) state reveals that their stabilization by non-aqueous cosolvent is due to predominant ion-dipole and dispersion interactions.

Kinetics of aquation of cis-aquabromo-bis(ethylenediamine) complexes of cobalt(III) and chromium(III) in binary aqueous mixtures

SummaryThe kinetics of aquation of cis-[Co(en)2(H2O)Br]2+ and cis-[Cr(en)2(H2O)Br]2+ (en = ethylenediamine) were investigated in aqueous mixtures of MeOH, EtOH, i-PrOH and t-BuOH. The values of transfer functions corresponding to the transfer of reactants and activated complex from water to the solvent mixtures were evaluated from kinetic measurements and from solubilities of the complex salt. Analysis of the solvent effect confirmed a common Id mechanism for the aquation of the CoIII and CrIII complexes.

Salt and medium effects in the aquation ofcis-amminebromobis(ethylenediamine)cobalt(III) ion

SummaryThe aquation kinetics ofcis-[Co(NH3)Br(en)2]2+ were studied in aqueous and mixed aqueous-nonaqueous solvents in the presence of KBr, KCl, LiCl, NaNO3 and NaClO4 as supporting electrolytes. It was found that the association between the complex ion and Cl−, Br− and NO3− ions takes place. The association constants, KIP, were evaluated from kinetic measurements. The kinetic parameters in the studied media are related to the influence of the cosolvents on the solvation spheres of the reactants and activated complex.

Solvent effects on the aquation of cationic, anionic and nonionic chlorocobalt(III) complexes

The kinetics of aquation of α- and β- cis[Co(edda)Cl2]−, α- cis[Co(edda)(H2O)Cl] and α- cis[Co(trien)Cl2]+ were investigated in aqueous mixtures of t-BuOH, MeOH, DMSO, ethylene carbonate and urea. The transfer Gibbs energy values for the reactants, evaluated from the solubility of the complexes, confirm the decisive role of the reactant solvation on the aquation rate.