Thermoanalytical, magnetic and structural investigation of neutral Co(II) complexes with 2,2'-dipyridylamine and salicylaldehydes

Cobalt(II) complexes of 2,2'-dipyridylamine (dpamH) and substituted salicylaldehyde ligands (X-saloH, where X = 5-NO2, CH3, Br and Cl) with the general formula [Co(X-salo)(2)(dpamH)] (1-4), were synthesized and characterized by physicochemical methods and by spectroscopy (IR and UV-Vis). The octahedral geometry around Co2+ ion and the bidentate chelating mode of the anion X-salo(-) were proved by single-crystal X-ray diffraction analysis for the complexes [Co(5-CH3-salo)(2)(dpamH)] (2) and [Co(5-Cl-salo)(2)(dpamH)] (4). The variable-temperature (76-303 K) magnetic susceptibility measurements showed a paramagnetic nature of the complexes, in accordance with their molecular structure. The simultaneous TG/DTG-DTA technique was used to analyze their thermal behavior under inert atmosphere, with particular attention to determine their thermal degradation pathways, which was found to have a multi-step nature, accompanied by the release of the ligand molecules, as it is partially confirmed by analyzing the amount of gases evolved during heating under experimental conditions comparable with those of TG by using a TG-MS device. Finally, the decomposition kinetics, analyzed by applying the Vyazovkin's advanced isoconversional method and referred to the elimination of the ligand molecules in the range 200-400 A degrees C (process that was found to be common in all four complexes), confirmed the stability order assessed on the basis of the decomposition temperatures only.