Thermal behaviors of N-pyrrolidine-N '-(2-chlorobenzoyl)thiourea and its Ni(II), Cu(II), and Co(III) complexes

Abstract

The N-pyrrolidine-N'-(2-chlorobenzoyl)thiourea, HL, and their Ni(II), Cu(II), and Co(III) complexes (NiL2, CuL2, and CoL3) have been synthesized and characterized. The thermal decomposition reactions of all the compounds have been investigated by DTA/TG combined systems. The mass spectroscopy technique has been used to identify the products during pyrolytic decomposition. The pyrolytic final products have been analyzed by X-ray powder diffraction method. After comparison of thermogravimetric and mass results of HL, NiL2, CuL2, and CoL3, the decomposition mechanism of these compounds have been suggested. The thermal stability of the Ni(II) and Cu(II) complexes according to the thermogravimetric curves follows the sequence: NiL2 < CuL2. The values of the activation energy, E (a), have been obtained using model-free (Kissenger-Akahira-Sunose, KAS, Flyn-Wall-Ozawa, FWO, and Isoconversional) methods for all decomposition stages. The E (a) versus the extent of conversion, alpha, plots show that the values of E (a) varies as alpha. Thirteen kinetic model equations have been tested for selecting correct reaction models. The optimized value of E (a) and Arrhenius factor, A, have been obtained using the best model equation. The thermodynamic functions (Delta H*, Delta S*, and Delta G*) have been calculated using these values.