Thermal racemization of tris(1,10-phenanthroline) chromium(III)

The thermal racemization of (+)₅₈₉-Cr phen₃(ClO₄)₃ has been examined under a variety of medium conditions. The racemization rate constant in water at 75°C, for example, is 8·5 × 10⁻⁵ sec⁻¹, with an energy and entropy of activation of 23·5 kcal mole⁻¹ and −10·9 e.u., respectively. The effect of acid, hydroxide, and various other added ions on the rate constant has been investigated, and the results compared with other tris-phenanthroline systems. An intramolecular twist process is considered the most probable mechanism of racemization.