Determination of Acid–Base and Complexing Parameters of Chlorine-Substituted Trifluorobenzoylacetone in Water Medium

Abstract

In this work, we study the behavior of 1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedione (ClTFBA) using a spectrophotometric technique under various conditions. Acid–base characteristics have been studied in citrate-phosphate buffer and hydrochloric acid solutions. Dissociation constants were determined in the pH range 3.0–8.0 for three ionic strengths (I = 0.1, 0.5, and 1.0 M; NaCl). Protonation equilibria have been investigated in concentrated HCl by the nonlinear Cox–Yeats method. The interaction between ClTFBA and rare-earth metals was examined in glycine and acetate buffers. Stability constants of monocomplexes were obtained for trivalent metalsSc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The received formation constants lie from 4.5 to 11.8 logarithmic units. Analysis of the results shows that the thermodynamic stability of complexes increased from Ce­(III) to Lu­(III) and has a linear correlation with the ionic potential. The relationship described in this work demonstrates the electrostatic nature of the M­(III)–ClTFBA bonds. Pronounced ionic character, observed for complexes with Ce, Pr, Nd, Sm, Eu, and Gd, points to high charge carrier mobility for these compounds and iterates the appropriateness to use the studied complexes to generate new organic light-emitting diode materials. Equilibrium and spectral characteristics were reproduced by density functional theory (DFT) and time-dependent DFT calculations performed using different basis sets and exchange–correlation functionals.

Interaction of Rare-Earth Metals and Some Perfluorinated β-Diketones

“…Table 4 demonstrates the values of log K for Odonor ligands 56,57 and similar β-diketones. 48 The stability of complexes nonmonotonically increases from cerium to lutetium. For each ligand, the minimum values of log K were observed for Ce 3+ and La 3+ (4.5−4.9 log units) and the maximum values for Sc 3+ (11.6−12.7 log units).…”

“…Curves REMs versus log K and log K versus ionic potential ( Z / R , where Z = charge of ion, 3+ for all rare-earth atoms, and R = ionic radius , ) are depicted in Figure . Table demonstrates the values of log K for O-donor ligands , and similar β-diketones . Some types of stability constants ( K = [ML 2+ ]/[M 3+ ]­[L – ]) for lanthanide­(III) thenoyltrifluoroacetone complexes can be found in the literature.…”

“…The protonation process has several mechanisms. The typical parameters of protonation of the dicarbonyl fragment are observed for benzoyl-and naphthyltrifluoroacetone: the equilibrium parameters are close to those for similar diketones (−pK H = 2.2−2.5 47,48 ), the solvation coefficient is about 0. Complexation with REMs.…”

“…47 At the same time, the substitution of H on a Cl atom in the para position of the phenyl group of benzoyltrifluoroacetone has little effect on pK a . 48 Theoretical calculations of the spectral, acid−base, and complexing properties were performed using these enol forms of the ligands (enol form b). Nevertheless, the energy of tautomeric transformation is very small compared to the energy of complexation or the acid−base reaction.…”

“…The protonation process has several mechanisms. The typical parameters of protonation of the dicarbonyl fragment are observed for benzoyl- and naphthyltrifluoroacetone: the equilibrium parameters are close to those for similar diketones (−p K H = 2.2–2.5 , ), the solvation coefficient is about 0.50, and the spectral changes were observed in region 280–380 nm. Furoyltrifluoroacetone has a small value of −p K H (1.65 vs 2.3 for others) and lower m * (0.40), and the spectral changes were observed in a short region 270–290 nm (Figure S2).…”