NMR and DFT-study of new luminescent Eu3+ complexes based on calix[4]arenes with 1,2,3-triazole and 1,3-diketone groupsстатьяИсследовательская статья
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Дата последнего поиска статьи во внешних источниках: 15 февраля 2024 г.
Аннотация:The present work introduces two calix[4]arenes (cone and 1,3-alternate isomers) bearing pairs of 1,2,3-triazole and 1,3-diketone groups as binding sites of Eu3+ (La3+) ions. Combination of UV-Vis, 1H NMR spectroscopy and DFT calculations allowed to evaluate the structure of the lanthanide complexes and specify the groups participating in the coordination. It was found that cone calix[4]arene forms the 2:1 (ligand : Ln3+) complex arisen from the coordination of Ln3+ ions via both 1,2,3-triazole and 1,3-diketonate groups as well as the 2:2 complex form, where Ln3+ ions are coordinated via 1,3-diketonate groups only. The quantum chemical calculations reveal that the 2:2 complex is more thermodynamically favorable than the 2:1 one, which correlates with the NMR data. It is worth considering the coordination of Ln3+ ions with both triazole and 1,3-diketonate groups as the reason for the specific slowed down ligand exchange for 2:1 and 2:2 complex forms. The comparative analysis of the Eu3+-centered luminescence reveals the cone calix[4]arene as more efficient antenna for Eu3+ ions than the 1,3-alternate calix[4]arene, where 1,2,3-triazole and 1,3-diketone substituents are localized at the opposite sides of the macrocycle. The growing degree of accumulation of the 2:1 complex is followed by an increase in Eu3+-centered luminescence for both calix[4]arene ligands.