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

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.

[1]  E. Kyuno,et al.  Derivatographic Studies on Transition Metal Complexes. I. Deaquation-Anation Reaction of Aquopentaamminechromium(III) Complexes , 1969 .

[2]  H. Lemay.  Solid-phase dehydration of trans-[Co((+-)pn)2Cl2](H5O2)Cl2 and trans-[Co(en)2Cl2](H5O2)Cl2 , 1968 .

[3]  H. Lemay,et al.  The solid-phase trans-to-cis isomerization of [Co-(NH3)4Cl2]IQ3.2H2O , 1967 .

[4]  D. Watts,et al.  Octahedral Cobalt(III) Complexes in Dipolar Aprotic Solvents. X. The Isomerization ofcis-andtrans-Dichlorobis (ethylenediamine) cobalt(III) Ions, [CoCl2(en)2]+, in Anhydrous Sulfolane , 1967 .

[5]  J. Paulik,et al.  Derivatography A complex method in thermal analysis. , 1966, Talanta.

[6]  S. K. Chopra,et al.  A Method for the Evaluation of Kinetics of Solid State Reactions from Thermogravimetric Curves , 1966 .

[7]  H. Iwasaki,et al.  The Crystal Structure of trans-Dichloro-bis-l-propylenediamine Cobalt(III)Chloride Hydrochloride Dihydrate and the Absolute Configuration of the Complex Ion, [Co l-pn2Cl2] , 1962 .

[8]  A. Nakahara,et al.  The Crystal Structure of Trans-dichloro-diethylenediamine-cobalt. (III). Chloride Hydrochloride Dihydrate, [Coen2Cl2]Cl·HCl·2H2O , 1952 .

[9]  J. Bailar,et al.  The Stereochemistry of Complex Inorganic Compounds. IV. The Introduction of Racemic Organic Molecules into Some Optically Active Complex Ions of Cobalt and Chromium , 1939 .

[10]  J. Bailar.  Some problems in the stereochemistry of coordination compounds: Introductory lecture , 1958 .

[11]  Farrington Daniels,et al.  The Application of Differential Thermal Analysis to the Study of Reaction Kinetics1 , 1957 .