Highly thermostable lanthanide metal–organic frameworks exhibiting unique selectivity for nitro explosives

Abstract

Three isostructural 3D metal–organic frameworks [Ln(L)_1.5(DEF)]_n (Ln = Gd (1), Eu (2), Tb (3), H₂L = 9,9-diethylfluorene-2,7-dicarboxylic acid) have been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction. The main framework of compounds 1–3 show high thermal stability to 400 °C but with a distortion or shrinking of the crystal lattice between 200 °C and 250 °C. The high red emission intensity and the microporous instinct of the solvent-free [Eu(L)_1.5]_n (2a) indicate that it can be potentially used as luminescent sensor. It was then applied in the detection of organic solvent molecules. Notably, it exhibits high sensitivity for 2,4,6-trinitrophenol (TNP) with K_sv constant 6.24 × 10⁴ M⁻¹ through luminescence quenching experiments.