Coordination Compounds of Certain of Lanthanoides with 2-Furancarboxylic and 2-Furylacrylic Acids. Synthesis, Structure, and Photoluminescent Properties

Abstract— Dissociation constants of 2-furancarboxylic and 2-furylacrylic acids and stability constants of their complexes with Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Ho³⁺, Er³⁺, and Yb³⁺ ions were determined in aqueous ethanol solution (5 : 1 by volume) by pH-potentiometric titration. It was found that the complex formation occurs in the pH range of 3.0–6.5, the stability constants of complex compounds increasing with increasing values of the protonation constant of the ligands. Solid complex compounds with 2-furancarboxylic and 2-furylacrylic acids of the compositions (С₅Н₃О₃)₃Ln·nH₂O and (С₇Н₅О₃)₃Ln·nH₂O (n = 2–4), respectively, have been synthesized. According to IR spectra, Ln³⁺ ions are coordinated to acids bidentately by the carboxyl groups. The range of thermal stability of the complex compounds has been determined by the TG/DTG/DSC methods. Spectral-luminescent properties of the complex compounds of 2-furancarboxylic acid with Eu³⁺ and Tb³⁺ ions have been studied.