Novel 2D isomorphic lanthanide complexes based on a bifunctional 5-(pyridin-3-yloxy)isophthalic acid: synthesis, structure, fluorescence and magnetic properties

Abstract

Five novel isostructural two-dimensional lanthanide complexes [Ln₂(μ₃-L)₂(μ₄-L)(H₂O)₃]_n·nH₂O, (Ln = Eu (1), Gd (2), Tb (3), Dy (4), Ho (5); H₂L = 5-(pyridin-3-yloxy)isophthalic acid) have been hydrothermally synthesized. They are characterized by IR spectroscopy, X-ray diffraction and thermogravimetric analyses. Complexes 1–5 crystallize in the monoclinic space group P2₁/c and display a 2D layered structure. They have good thermal stability, and the skeleton structure can be maintained up to 500 °C. The solid-state fluorescence of complexes 1 and 3 shows the strong characteristic red luminescence of Eu(III) and the green luminescence of Tb(III) respectively, and they exhibit a fluorescence quenching effect on addition of acetone in aqueous solution. The detection limits are 3.59 × 10⁻⁴ M and 2.08 × 10⁻⁶ M, respectively. Moreover, complex 3 also exhibits fluorescence quenching effects on Fe³⁺ and CrO²⁻ in aqueous solution with detection limits of 4.81 × 10⁻⁸ M and 4.06 × 10⁻⁸ M, respectively, which are lower than those of most reported complexes. Therefore, complex 3 is a multifunctional visual fluorescent probe in aqueous solution.