COMPLEX FORMATION OF COPPER(II) WITH AZOLE DERIVATIVE OF FUSED ENAMINE

DOI: https://doi.org/10.17721/1728-2209.2023.1(58).6

Abstract

Background. The development of new organic reagents for spectrophotometric analysis remains an urgent task of recent decades. One of the main requirements for reagents is their high stability during storage, in particular in solution, which eliminates the need for daily preparation of new portions of the reagent and significantly saves time and material costs. At the same time, spectrophotometric reagents must meet the requirements of contrast and sensitivity of reactions. Such compounds include new derivatives of fused enamines, which have already been proposed as reagents for zinc. The aim of the work was to study complex formation of (Z)-2-(Benzo[d]thiazol-2-yl)-2-(5-methyl-3-oxoindolin-2-ylidene)acetonitrile with Cu(II) ions using the method of UV-Vis absorption spectroscopy.

Methods. Complex formation was studied by UV/Vis spectrophotometry. The composition of the complex compound was determined by the methods of spectral data processing - Moland, Staryk and Barbanel. The calculation of the conditional stability constant was carried out by data processing according to the Bent and French's method.

Results. It is shown that for aqueous-organic solutions with a DMSO content of 83%, the absorption spectra of the Cu(II) complex compound contain a band in the range of 560–720 nm with λ_max at 620 nm. The red shift is 90 nm. According to the methods of spectral data processing (Moland, Staryk and Barbanel), it was established that the complex compound CuL⁺ predominates in the solution, the formal stability constant (Bent and French method) is lgK^f = 9,91 ± 0,05. The absorption of solutions at 640 nm increases linearly with increasing content of Cu(II) ions in the solution. LOD (3S) is 0,78 μmol/L.

Сonclusions. Evidence suggests that the azole derivative of fused enamines, specifically (Z)-2-(Benzo[d]thiazol-2-yl)-2-(5-methyl-
3-oxoindolin-2-ylidene)acetonitrile, functions effectively as an organic N, N-reagent for the spectrophotometric determination of Cu(II) ions within a solution. The reaction transpires in a Tris-HCl (pH 7,2) / DMSO (1 : 5) medium and displays a prominent contrast (Δλ = 90 nm). The absorption spectra of the compound have a band within the 560–720 nm range, with a maximum absorption at λ = 620 nm, which causes the solution to appear blue. Utilizing spectral data processing methodologies established by Moland, Staryk and Barbanel, it is ascertained that the complex compound CuL⁺ predominates in the solution. The saturation curves of complex formation, with constant concentrations of either the ligand or the metal ions, suggest the formation of a medium stable compound. This proposition is validated by the value of the calculated conditional stability constant (as per the Bent and French method), represented as lgK^f = 9,91 ± 0,05. Importantly, the complex compound solutions maintain stability and do not exhibit any changes in their inherent properties when conserved in a sealed vial over an extended duration of 6 months. The light absorption of these solutions at 640 nm (with minimal background interference) linearly escalates with an increase in the content of copper ions in the solution. The linearity range of the calibration graph, intended for the spectrophotometric identification of Cu(II), extends from 2 to 20 µmol/l. The reagent shows high sensitivity to Cu(II), the detection limit, calculated according to the 3S criterion, is 50 µg/L. Investigation into the impact of extraneous ions on the analytical signal revealed a low selectivity in the presence of equivalent quantities of Zn(II), and similarly for Co(II) if the sample solution is stored beyond a duration of 30 minutes. Consequently, the examined organic reagent demonstrates promising potential for the analysis of specimens with respect to trace amounts of Cu(II), given that Zn(II) are removed from the sample in advance.