Spectrometric study of solute–solvent interactions for the solvolysis of chloropentaamine cobalt(III) complex in binary aqueous mixtures

Abstract

Kinetic studies of solvent structure effects and solute-solvent interactions on the solvolysis of [Co(NH 3 ) 5 Cl] 2+ complex ion have been investigated spectrophotometrically in binary aqueous mixtures. Three cosolvents were used (acetonitrile, dimethylsulfoxide, and urea) over a wide range of temperatures. Nonlinear plots were found for log(rate constant) against the reciprocal of the relative permitivity of the medium. The enthalpy and entropy of activation ( H # and S # ) exhibited extrema in the same composition region where the physical properties indicate sharp changes in the structure of the solvent, confirming that the solvent structure is an important factor in determining the solvolytic reactivity. C 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: [416][417][418][419][420][421][422] 2008

Comparison of the leaving groups during the study of the aquation of halopentaammine cobalt(III) complex in tartarate at different percentage of tert-butanol

“…The dielectric constant values of different compositions are obtained from Akerlof data [24]. As shown in Figures 2 and 3, the plots were found to be non-linear in accordance with the general observations found in the aquation of a large number of other cobalt(III) complexes [25,26] in water-cosolvent mixtures, which led to a conclusion, that the contribution of the non-electrostatic part of solvent effect, overcomes the electrostatic component part. Also, this parameter measures macroscopic property, while specific solute-solvent interactions occur on a microscopic scale is completely neglected.…”

Studies on ion-pairing effects of the kinetics of aquation of bromopentaammine cobalt(III) complex in malonate media

“…Also Log kip was plotted against reciprocal of the dielectric constant D at 25 o C, where the dielectric constant values of different compositions are obtained from Akerlof data [18]. As shown in Figure(3), the plot was found to be non linear in accordance with the general observations found in the aquation of a large number of other cobalt(III) complexes [19][20] in water-cosolvent mixtures, which led to a conclusion, that the contribution of the non electrostatic part of solvent effect, overcomes the electrostatic component part. Also, these parameter measures macroscopic properties, while specific solute-solvent interactions occur on a microscopic scale are completely neglected.…”

Kinetic Studies of Solute-Solvent Interactions in the Solvolysis of Trans- [Co (4-Teri-Butylpyri Dine)4C12)Clo4 in Organic-Aqueous Mixtures

“…The left-hand side of Eqn (3) plotted versus the mole fractions of dioxane and DMSO as shown in Figure 4, indicating negative values for all compositions investigated. These negative values can be compared with similar negative values obtained for the solvolyses of these complexes in mixtures of alcohols with water [16,17,24]. In all these cases, irrespective of whether the cosolvent, when added to water, increases or decreases the relative permittivity, or enhances or destroys structure in the solvent, it is found that the Co 3 þ cation in the transition state is more stable in the mixture than the Co 3 þ cation in the initial state.…”

“…Good linear plots were obtained for log(rate constant) against the reciprocal of the absolute temperatures for the same composition of the cosolvents. It was found that the rate constant in water -dioxane mixtures is higher than that in water -DMSO mixtures; this trend can be attributed to the properties of the medium, such as the structure of the solvent, ionizing power, basicity and dielectric constant which greatly influence the solvolysis rate of the complex [16,17].…”

“…For the present complex, good straight lines were obtained from the plots of DH 6 ¼ against DS 6 ¼ for different solvent compositions in both of the binary aqueous systems as shown in Figure 3, where compensating changes in DH 6 ¼ and DS 6 ¼ occur [16,17]. From these plots, the isokinetic temperatures were estimated as 315 K and 314 K for dioxane and DMSO respectively, which are close to the experimental values.…”