Synthesis and Luminescent Properties of Eu3+, Gd3+, and Tb3+ Complexes with Quinoline-4-carboxylic Acids

New complex compounds LnL3·nH2O (n = 5–10) have been synthesized on the basis of Eu3+, Gd3+, and Tb3+ salts and quinoline-4-carboxylic acid derivatives obtained via the Pfitzinger reaction. Composition and structure of the ligands and the resulting complex compounds have been confirmed by NMR and IR spectroscopy, thermogravimetry, and complexometric titration. Europium complex with 1,2,3,4-tetrahydroacridine-9-carboxylic acid has exhibited efficient luminescence.