Kinetics of aquation of the trans-dichlorobis (N-methylethylenediamine) cobalt(III) ion in a water-methanol media

Abstract

The trans-[Co(meen)2C12]C1 complex was prepared and characterized by elemental analysis, and u.v. vis. and i.r. spectroscopies. The kinetics of the primary aquation of trans-[Co(meen)2C12] + in H20 and H20-MeOH have been investigated over a wide range of solvent compositions and temperatures (45-60 ~ Plots of rate constants (log k) versus the reciprocal of the dielectric constant of the medium (D~ -1) and Grunwald Winstein values of the solvent (Y) were non-linear. The variation of enthalpies (AH*) and entropies (AS*) of activation with solvent composition have been determined. Plots of AH* or AS* versus the mole fraction of the solvent exhibit a maximum at x2 ca. 0.1 and a minimum ofx 2 ca. 0.3; a linear plot of AH* versus AS* is obtained. Furthermore, the cycle relating the free energy of activation in H20 to that in H20-MeOH shows that changes in the solvent structure in H20-MeOH mixtures generally stabilize the five-coordinate cation in the transition state, more than the cation in the initial state as the mole fraction of MeOH increases. The results are discussed and compared with other related systems.

Medium effects on the initial and the transition states upon the solvolysis of trans‐dichlorobis(N‐methyl‐ethylenediamine)cobalt(III) complex in water‐mixed solvents

“…Plots of log(optical density) against time for the solvolysis in water + cosolvent were always linear, for extents of reaction exceeding 85%, as found for the other cosolvents 2–5. For 25, 35, 40, 45, 50, and 55°C such plots were determined for a range of solvent compositions up to 60% v/v.…”

“…The trans ‐[Co(meen) 2 Cl 2 ] + complex was prepared as described previously 2. Analar n ‐propanol and tert ‐butyl alcohol were used and the other materials were used as previously described 2.…”

“…The trans ‐[Co(meen) 2 Cl 2 ] + complex was prepared as described previously 2. Analar n ‐propanol and tert ‐butyl alcohol were used and the other materials were used as previously described 2. The rates of solvolysis were followed spectrophotometrically by using the method as described for water and cosolvent mixtures 2.…”

“…Analar n ‐propanol and tert ‐butyl alcohol were used and the other materials were used as previously described 2. The rates of solvolysis were followed spectrophotometrically by using the method as described for water and cosolvent mixtures 2. The mixtures were prepared using double distilled water from all‐pyrex apparatus.…”

“…The kinetics of the solvolysis of trans ‐dichlor‐ obis( N ‐methyl‐ethylenediamine)cobalt(III) complex, trans ‐[Co(meen) 2 Cl 2 ] + (where meen = N ‐methyl‐ ethylenediamine), have been studied in methanol, iso ‐propanol, acetonitrile, urea, and DMSO as cosolvents added to water 2–5. This paper is a continuation of the studies of solvation of trans ‐[Co(meen) 2 Cl 2 ] + complex, where the kinetics of its solvolysis have been measured in n ‐propanol and tert ‐butyl alcohol as cosolvents added to water to study the nature and effect of hydrophobic interaction around a nonpolar group such as methyl group.…”