Coordination Compounds of Lanthanides with 3-Hydroxy-4-oxo-4H-pyran-2,6-dicarboxylic Acid: Synthesis, Structure, and Photoluminescent Properties

Complex compounds of 3-hydroxy-4-oxo-4 H -pyran-2,6-dicarboxylic (meconic) acid (H 3 Mec) with europium(III), gadolinium(III), terbium(III), dysprosium(III), erbium(III), thulium(III) and ytterbium(III) ions were synthesized by the ion exchange method in aqueous solution. The hydrates of the complex compounds [Ln(HMec)(H 2 O)]· n H 2 O ( n = 0‒4) are solid amorphous substances (Sm 3+ , Eu 3+ , Gd 3+ , and Tm 3+ complexes) and fine crystalline substances (Tb 3+ , Dy 3+ , Er 3+ , and Yb 3+ complexes) with colors characteristic of lanthanide ions. The region of thermal stability of the complexes was determined by the TG/DTG/DSC methods. The Ln 3+ ions are coordinated monodentately to the ionized carboxyl groups and the oxygen atom O 1 of the pyrone ring. The coordination of Ln 3+ to the С 3 ‒OH group and the С 4 =О ketogroup of the second ligand molecule leads to the formation of a polymer chain. The triplet level of the ligand ( 3 T*) was determined from the phosphorescence spectrum of the Gd 3+ complex compound (77 K). The spectral-luminescent properties of Sm 3+ , Eu 3+ , Tb 3+ , Dy 3+ , and Tm 3+ complexes were studied.