KINETICS OF STRUCTURAL INTERCONVERSIONS .I. COBALT(2) CHLORIDE-PYRIDINE-NITROMETHANE

A kinetic examination of the octCo(py)4Cl2 = tetCo(py)2Cl2 + 2py equilibrium in nitromethane and pyridine (py) has been carried out. The experimental data appear to fit the mechanism, Co(py)4Cl4 ⇌ Co(py)3Cl2 + py (3) and Co(py)3Cl2 ⇌ Co(py)2Cl2 + py (k4 k-4) (4), where reaction 3 equilibrates rapidly compared to reaction 4. The rate constant k-4 in nitromethane at ¨ = 0.1 (Et4NC1O4) and 25.0˚ is (7.2 ± 0.5) × 104 M−1 sec−1, and ΔH± and ΔS± are 5.4 ± 0.8 kcal/mole and -18 ± 3 eu, respectively. The corresponding rate constant in pyridine is (3.1 ± 0.3) × 103 M−1 sec−1, and the. activation parameters are 2.6 ± 1.0 kcal/mole and -34 ± 4 eu. Factors affecting the kinetics in the two solvents are discussed. © 1969, American Chemical Society. All rights reserved.