Estudo da viabilidade de sensores vapocrômicos de complexos de coordenação de cobre(II) com ligantes fumarato e pirazol

Abstract

There is great interest in the study of copper coordination compounds due to their characteristics such as high availability, low cost and high coordination plasticity. copper(II) has the most stable oxidation state, it is able to coordinate in various ways with ligands producing diverse molecular geometries. One of these ligands is fumarate, a dicarboxylate widely used in industry, the other is pyrazole, a nitrogenous ligand. copper(II) coordination compounds are interesting in the use of vapochromic chemical sensors that detect toxic substances present in the environment. Therefore, in this work the complexes [Cu(pz)6]2+ (A1), [Cu(fum)2(pz)2]2- (A2) and [Cu(fum)3]-4 (A3) were synthesized and characterized by vibrational spectroscopy in the infrared region and melting point. Vibrational spectroscopy in the infrared region confirmed the formation of the complexes and made it possible to infer their coordination modes. In the [Cu(pz)6]2+ complex, the displacement of the ring respiration band (φ) and the presence of three CH bands at 810, 777, 688 cm-1 indicated the presence of monodentate pyrazole. The vibrational stretching modes in the [Cu(fum)2(pz)2]2- and [Cu(fum)3]4- complex demonstrated that the fumarate is chelatingly coordinated to the metal center. Furthermore, vibrational spectroscopy in the infrared region confirmed the coordination of ammonia to the metallic center for the three samples. The study of the decomposition temperature allowed analyzing the thermal stability of these materials and the results indicated that the A3 sample is the most thermally stable. The vaprochromic character was observed with the color change of the samples after exposure to ammonia vapors. The analysis of the colors of the complexes before and after contact with ammonia indicated that there were modifications in the luminosity (L), green-red, blue-yellow coordinate, hue angle and chroma of the complexes. The ΔE00 values indicated that all the complexes present a color perceptible by the human eye, being feasible in the application of sensors.