Ótom Anselmo de Oliveira

Synthesis, characterization and thermogravimetric study of zinc group halides adducts with imidazole

Abstract The synthesis, characterization and thermogravimetric study of the adducts ZnCl 2 ·2Imi, ZnBr 2 ·2Imi, CdCl 2 ·Imi, CdCl 2 ·2Imi, CdBr 2 ·2Imi, CdBr 2 ·3Imi, CdI 2 ·2.5Imi, HgCl 2 ·2Imi, HgBr 2 ·1.5Imi and HgI 2 ·1.5Imi (Imi = imidazole) is reported. The following sequence of thermal stability is observed for the synthesized adducts: Zn>Hg>Cd. It is also verified that larger cations, as well as larger anions, result in a smaller number of imidazole molecules in the coordination sphere of the considered cation and that hard acids exhibit stronger bonds to imidazole than soft acids, and this fact is reflected in the thermal stability sequence. ZnCl 2 ·2Imi behaves as a non-electrolyte in acetonitrile and ethanol, whereas ZnBr 2 ·2Imi is a non-electrolyte in acetonitrile and a 1:1 electrolyte in ethanol. CdI 2 ·2.5Imi is a non-electrolyte in acetonitrile and a 1:2 electrolyte in ethanol.

A calorimetric study of (cobalt(II) chloride + acetonitrile) compared with other techniques

Abstract The enthalpies of dissolution of cobalt(II) chloride, acetonitrile, and adducts in ethanol at 298.15 K have been calorimetrically measured to determine the standard enthalpy of the reaction: CoCl 2 (s) + n CH 3 CN(l) = Co(CH 3 CN) n Cl 2 (s); which gave the following ΔH R θ /(kJ·mol −1 ) values: Co(CH 3 CN) 3 Cl 2 , −(47.32±0.76); Co(CH 3 CN) 2 Cl 2 , −(34.07±0.80); and Co(CH 3 CN)Cl 2 , −(22.92±0.78). For the same sequence of adducts, the standard enthalpies of formation of the adducts were calculated: −294.8, −265.3, and −238.0 kJ·mol −1 . Special attention was devoted to the standard enthalpy of the partial and total decomposition reaction: Co(CH 3 CN) n Cl 2 (s) = CoCl 2 (s) + n CH 3 CN(g), as well as to comparing our results with those of d.s.c. and vapour-pressure measurements.

Estudo Cinético por TG e DSC da Decomposição Térmica de Alguns Adutos de Haletos de Cádmio

By DSC data, the kinetical parameters Ea , n and A were calculated for the thermal decomposition of the adducts CdCl2.2dmf, CdCl2.dmf and CdBr2.dmf (dmf= dimethylformamide) by using Rogers and Smith method. The found values were : Ea = 85, 176 and 101 kJ mol-1 , n= 0.23, 0.25, and 0.17, A= 2.40x109, 1.89x1019 and 1.07x109 respectively. By TGA data, the kinetical patameters for the thermal decomposition of the adduct CdCl2.1,5 dmeu (dmeu=dimethylethyleneurea) were calculated by using five different methods.

Synthesis, characterization and thermal degradation kinetics of cadmium halide adducts with imidazole

The synthesis, characterization and a nonisothermal thermal degradation kinetic study performed for the adducts CdCl2·Imi, CdCl2·2Imi, CdBr2·2Imi and CdBr2·3Imi (Imi = imidazole) are reported. For cadmium bromide the maximum number of imidazole molecules per cadmium cation to produce a stable (from a thermodynamic point of view) compound is three, at least for compounds prepared at room temperature and pressure. The kinetic study performed by the Coats–Redfern and Száko methods using thermogravimetric data shows that for all compounds the activation energy values associated with the release of imidazole molecules decreases as the thermal degradation process proceeds.The synthesis, characterization and a nonisothermal thermal degradation kinetic study performed for the adducts CdCl2·Imi, CdCl2·2Imi, CdBr2·2Imi and CdBr2·3Imi (Imi = imidazole) are reported. For cadmium bromide the maximum number of imidazole molecules per cadmium cation to produce a stable (from a thermodynamic point of view) compound is three, at least for compounds prepared at room temperature and pressure. The kinetic study performed by the Coats–Redfern and Szako methods using thermogravimetric data shows that for all compounds the activation energy values associated with the release of imidazole molecules decreases as the thermal degradation process proceeds.

Thermochemical study of the reaction between some lanthanoid trifluoromethanesulfonates and dimethylacetamide (DMA) in ethanolic solution

Abstract Calorimetric studies involving the reaction of lanthanoid trifluoromethanesulfonate complexes with dimethylacetamide in ethanolic solution were performed, in order to determine the dissolution standard enthalpies and acid-base enthalpies for the reaction of the hydrated salts with DMA. Comparisons with dimethylformamide (DMF) reactions were made.

Synthesis, characterization and tg-dsc study of lanthanide trifluoroacetate-2-azacyclononanone compounds

The synthesis, characterization and tg-dsc study of Ln(tfa)3 · 3aza where Ln = La, Pr, Nd, Sm, Eu, Gd, Tb and Er, tfa = trifluoroacetate and aza = 2-azacyclononanone are reported. The obtained X-ray powder diffraction patterns show that the compounds are divided in two isomorphous groups: La, Pr, Nd and Eu, Sm, Gd, Tb and Er. For all compounds, the thermodegradation under nitrogen gave the respective oxifluorides (LnOF) as the final product. The melting temperature intervals are 105–110°C, 100–112°C, 90–95°C, 79–101°C, 65–70°C, 75–90°C, 64–76°C and 50–65°C for the La, Pr, Nd, Sm, Eu, Gd, Tb and Er compounds, respectively, and it is verified that the lanthanide contraction induces a weaker intermolecular interaction between adjacent molecules in the solid state.