The thermal and spectral properties of trans-[chloro-bis(dimethylglyoximato)Co(III)] complexes containing heterocyclic donor ligands

The thermal decompositions of the complexes [Co(dmgH)₂(LN)Cl] (where LN: btz, benzotriazole; ind, indole; car, carbazole; qui, quinoline) have been investigated in an atmosphere of static nitrogen in the temperature range 25–1000 °C by means of TG and DTA. Though the complexes are similar but the kinetics of their thermal decompositions are different. The solid intermediate and the resultant products of thermolysis have been identified by means of elemental analysis and spectrometrical data. The schemes of destruction of these complexes are suggested. On heating, these compounds first release halogen part, then heterocyclic nitrogen ligand and finally dimethylglyoxime. The final product of the thermal decomposition was Co₃O₄ for the complexes I–IV. According to the decomposition temperature, the thermal stability of the complexes can be ordered in the sequence: III>II>IV>I. By means of IR spectral analysis, the stereochemistry around Co(III) ion in the compounds have been studied. The btz, ind, car and qui were coordinated to Co(III) through the nitrogen atom of their heterocyclic ring and the chloride ion is coordinated to central metal ion.