Síntese, caracterização e estudo termoanalítico de nicotinato de uranila e picolinato de uranila no estado sólido

Abstract

Among the actinides present in the terrestrial environment, the most abundant are uranium and thorium, which are well distributed in the earth's crust. These metal ions have the ability to form complexes with different ligands, due to its high charge density, uranium tends to constantly occur as a uranyl ion (UO2 2+). Such ions become ideal due to the interactions of complexing agents in the equatorial plane that is perpendicular to [O=U=O]2+, of great value for studies of coordination compounds. As organic ligands in this work, nicotinic acid and picolinic acid were used, which have isomeric structures with alteration in the position of the pyridine ring branching. Nicotinic acid (or niacin), also commonly known as vitamin B3, is a dyslipidemic drug that increases HDL cholesterol by 15-35%. Some derivatives of this vitamin have antibiotic and antimicrobial properties. Thus, the investigation of this work was based on the synthesis and study of coordination compounds formed between the reaction of uranyl with nicotinic and picolinic acids, aiming to determine its minimum formula, its thermal stability and the possible mode of coordination. The synthesized compounds were characterized by simultaneous thermogravimetric analysis, differential scanning calorimetry (TG-DSC) and absorption spectroscopy in the mid-infrared region with Fourier transform (FT-IR). The results showed the formation of uranyl nicotinate complexes with suggested formula [UO2(C6H4NO2)2]·0.25H2O and uranyl picolinate with suggested formula [UO2(C6H4NO2)2]. Spectroscopic studies suggest that coordination occurs through the carboxylate forming a chelating and/or bridging structure.