New Heteroligand Europium and Gadolinium Formate Triazole Dicarboxylates: Synthesis, Structures, and Luminescence Properties

Complexes {(NMe 2 H 2 )[Ln(TDA)(HCOO)] ∙ 0.5H 2 O)} are prepared by the solvothermal synthesis in a water–dimethylformamide (1 : 1) system from a mixture of 1,2,3-triazole-4,5-dicarboxylic acid (H 3 TDA), NaOH, and Ln(NO 3 ) 3 (Ln = Eu, Gd). The crystal structure of the europium complex is determined by X-ray structure analysis (CIF file CCDC no. 1939689). This compound is shown to be the ionic metal-organic framework, where the cavities in the anionic structure of [Eu(TDA)(HCOO)] – are partially occupied by the dimethylammonium cations and water molecules. The study of the luminescence spectra of the gadolinium derivative gives the energy of the triplet level of the H 3 TDA ligand (~25 300 cm –1 ), the value of which makes it possible to efficiently sensitize the luminescence of rare-earth metal ions, in particular, Eu 3+ . The decay kinetics and the emission and excitation spectra of the heterometallic derivatives {(NMe 2 H 2 )[Gd 1 – x Eu x (TDA)(HCOO)] ∙ 0.5H 2 O)} are studied. The dilution of europium with gadolinium results in a substantial decrease in the concentration quenching of the europium luminescence and an increase in the observed lifetimes of the excited state of Eu 3+ .