Abstract
Abstract The thermal ligand-exchange reaction was investigated by derivatographic and isothermal methods for the following complex thiocyanates: cis-[CoCl2en2]SCN, cis-[CoClBren2]SCN·H2O, cis-[CoBr2en2]SCN·H2O and the corresponding trans-complexes, and several corresponding triethylenetetramine complexes cis-α-[CoXYtrien]SCN·H2O, where X and Y represent Cl− and Br− ion, respectively. cis-Complexes, except for cis-[CoCl2en2]SCN were found to exhibit obviously the ligand-exchange reaction in which Cl− or Br− is substituted by SCN− just after the liberation of lattice water takes place. On the other hand, cis-[CoCl2en2]SCN showed only partial ligand-exchange reaction accompanied by immediate thermal decomposition even at higher temperature than in the other monohydrates. In contrast, all the anhydrated trans-complexes trans-[CoCl2en2]SCN, trans-[CoClBren2]SGN and trans-[CoBr2en2]SCN did not give such a reaction upon heating. The activation energies of cis-[CoClBren2]SCN·H2O were found to be Ea=26±2 kcal/mol for dehydration and Ea=54±2 kcal/mol for ligand-exchange. The thermal ligand-exchange reaction proceeded in cis-type complexes without change in the geometrical configuration of the original complexes. No racemization or inversion could be observed in the optically active complex.
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