Structures And Luminescence Properties Of Rare Earth Complexes Based On Tetradentate Carboxylate

The design and construction of coordination complexes have attracted extensive interest in the materials science fields in recent years,owing to their potential applications in various areas,such as gas adsorption,molecular magnetism,luminescent sensor and so on.The rational selection of ligands is vitally important in the construction of coordination complexes.3,3′,5,5′-azobenzenetetracarboxylic acid（H₄ABTC）is a conjugated ligand,which has many carboxyl groups,diverse coordination modes and strong coordination ability.The complexes with unique novel structures and specific performances can be easily synthesized by the ligand of H₄ABTC.In this paper,a series of rare earth metal organic complexes based on H₄ABTC and Eu（III）/Tb（III）/Dy（III）/Y（III）have been synthesized.Their structures and properties have been characterized.The luminescence properties of[Eu₂（HABTC）₂（H₂O）₄]·3H₂O}_n（1）have been studied.1.Ninenovelcomplexes,namely{[Eu₂（HABTC）₂（H₂O）₄]·3H₂O}_n（1）,[Tb₂（HABTC）₂（H₂O）₄]·3H₂O}_n（2）,{[Eu（HABTC）（H₂O）₃]·2H₂O}_n（3）,{[Tb（HABTC）（H₂O）₃]·2H₂O}_n（4）,{[Eu（ABTC）_1.5（H₂O）₄]·2H₂O}_n（5）,{[Tb（ABTC）_1.5（H₂O）₄]·2H₂O}_n（6）,{[Dy（ABTC）_1.5（H₂O）₄]·2H₂O}_n（7）,{[Y₂（ABTC）₃（H₂O）]₂·2H₂O}_n（8）and{[Y₂（ABTC）₂（CO₂）（H₂O）₃]₂·3（CH₃）₂NH·6H₂O}_n（9）are synthesized based on the promising multifunctional tetracarboxylate ligand3,3′,5,5′-azobenzenetetracarboxylic acid（H₄ABTC）.Among them,complexes 1,2 have the same structure and exhibit the 2D bilayer network with 1D channels.The 2D bilayers are further connected by the strongπ???πstacking interaction to form a 3D supramolecular framework.The complexes 3,4 have the same structure and complexes 5,6,7 have the same structure.They display the 3D framework with 1D open channels.And,complexes 8 and 9exhibit the 3D framework with 1D open channels,respectively.In addition,their structures and purity are characterized by IR spectra,X-ray single crystal diffraction and powder X-ray diffraction（PXRD）analysis.Then the thermal stability of these complexes was studied by thermogravimetry（TG）.All above results indicate that these nine complexes have good stability.2.The luminescence properties of{[Eu₂（HABTC）₂（H₂O）₄]·3H₂O}_n（1）were investigated.1 can act as a promising dual-functional luminescent sensor with highly photo-stability and reusability for detecting and recognizing trace 2,4,6-trinitrophenol（TNP）and CrO₄^2-ions through luminescence quenching with high selectivity and sensitivity in aqueous solutions.Most importantly,we selected three different water systems and measured the concentration of TNP and CrO₄^2-in these water phases,and all obtained good recovery.Experimental and theoretical calculations indicate that the luminescence quenching property of 1 in the existence of TNP can be assigned to both photo-induced electron and resonance energy transfer processes as well as electrostatic interactions of 1 with TNP.And the change in the luminescence intensity of 1 in presence of CrO₄^2-ions might be attributed to resonance energy transfer mechanism and molecular interactions.Owing to its excellent detection performance,1 is a promising dual-functional luminescent sensor for the long-term,in-field and reliable sensing of TNP and CrO₄^2-in the aqueous phase.