Thermal Analysis of Cobalt(III) Complexes of Dimethylglyoxime

Abstract

Thermal decompositioonf electrolyte cobalt(III) complexes[Co(Hdmg)₂B₂]X and nonelectrolyte cobalt(III) complexes[CoX(Hdmg)₂B]n the solid state was studied by thermogravimetry(TG) and differential thermal analysis(DTA), where H2dmg is dimethylglyoxime, B is aniline and its derivatives, and X is Cl, Br, I, SCN, NO₂, NO₃, or ClO₄ ion. In the case of the electrolyte complexes[Co(Hdmg)₂B₂]Xan, endothermicp henomenond ue to the replacement of the axial ligand (base B) by the outer-sphere anion (X) was observed and the formationo f [CoX(Hdmg)₂B] as confirmed.
The observationo f the endothermicp he nomenonr evealed that the replacementr eaction temperature depends on the basicity of axial base in the case of the chloride complexes [Co(Hdmg)₂B₂]Cl. On. the other hand, in the case of the nonelectrolytec omple xesh aving no outer-spherea nion such as [CoX(Hdmg)₂B] and analogousn onelectrolyte Fe(II), Ni(II) and Cu(II) complexesa n exothermicp henomenonw as observed. When solid NH₄Cl was addedt o the electrolytec hloridec omplexes[Co(Hdmg)₂B₂]Cl a, new green compoundw as formed as the secondr eplacementp roduct, and two endothermicp eaks were observe di n the DTA curve of the complex. The electronic and infrared spectra of the green compound suggest that the constitutional formula is H[CoCl₂(Hdrng)₂].