Derivatographic Studies on Transition Metal Complexes. III. The Thermal <i>trans-cis</i> Isomerization of [CoCl2pn2](H5O2)Cl2 in Solid-Phase

Abstract

Abstract The thermal decomposition of trans-[CoCl2pn2](H5O2)Cl2 in solid-phase was measured by derivatography and the isothermal method with a thermobalance. It was found by the latter that dehydration and dehydrochlorination took place with partial isomerization below 170°C. The rate of isomerization gradually increased with temperature until it became equal to the rate of dehydration and dehydrochlorination above 170°C. The activation energies for dehydration and dehydrochlorination and for isomerization were calculated from the isothermal measurement below 170°C to be 10 kcal/mol and 23 kcal/mol, respectively. The activation energy obtained from DTA curve analysis at about 144°C in the derivatogram was 33 kcal/mol. The reaction was explained in terms of “aquation-anation” mechanism. Since the trans-cis isomerization in anhydrous state at 180°C gave a larger activation energy in DTA analysis, the “twisting” mechanism might be preferable to “aquation-anation” for the reaction.