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

Abstract

Complexes {(NMe2H2)[Ln(TDA)(HCOO)] ∙ 0.5H2O)} 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 (H3TDA), NaOH, and Ln(NO3)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 H3TDA ligand (~25 300 cm–1), the value of which makes it possible to efficiently sensitize the luminescence of rare-earth metal ions, in particular, Eu3+. The decay kinetics and the emission and excitation spectra of the heterometallic derivatives {(NMe2H2)[Gd1 – xEux(TDA)(HCOO)] ∙ 0.5H2O)} 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 Eu3+.