The influence of solvent structure on the solvolysis oftrans-dichlorotetra (4-ethylpyridine) cobalt(III) perchlorate

Summary The solvolysis oftrans-Co(4-Etpy)₄Cl₂]ClO₄, was followed spectrophotometrically in water/isopropanol at different temperatures. The activation energy varied nonlinearly with the mole fraction of the co-solvent, ₂. The plot of logk versus D _s ^–1 was also non-linear. These features were attributed to the differential solvation of the initial and transition states. On plotting H versus S, the points fall very close to straight line. The isokinetic temperature was found to be 334K, indicating that the solvolysis reaction is controlled by S and not H. The change in H and S with the mole fraction of the cosolvent shows extrema at the composition range where changes in solvent structure occur. The influence of the solvent structure on the complex ion in the transition state dominates over that in the initial state, where –G _t ⁰ Co(4-Etpy)₄Cl]²⁺>–G _t ⁰ Co(4-Etpy)₄Cl₂]⁺.