Chelation of rare earth metals by perfluorinated β-diketones bearing nitrogen heterocycles rings

Abstract

Aqueous equilibria of three substituted perfluorinated 1,3-diketones with pyrrole, pyrazole, and pyridine rings have been extensively studied in aqueous solutions. Thermodynamic characteristics of dissociation, protonation, and chelation processes have been investigated by UV–Vis spectroscopy using non-linear regression analysis. Acid-base parameters were discovered in the acidity range from highly acidic media (C(HCl) = 10 M) to alkaline pH region. Dissociation constants (pKa) have been determined in glycine-HCl, phosphate-citrate, and TRIS-HCl buffered media. Protonation activities were studied by the Cox-Yates approach in concentrated hydrochloric acid solutions. First formation constants of ML complex species with trivalent ions of Sc3+, Y3+, La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Dy3+, Tb3+, Ho3+, Er3+, Tm3+, Yb3+, and Lu3+ have been obtained in the pH within 3.0–5.6 (I = 0.5 M, NaCl). True stability constants have been calculated using determined acid-base parameters considering side reactions. The “True” formation constants lie from 3.7 to 6.9 logarithmic units and have a linear relationship with the ionic (Coulomb) potential of metals. DFT and TD-DFT simulations have been performed for the modeling of the data obtained.