Two structural types of lanthanide MOFs based on long-chain flexible sebacic acid: synthesis, luminescence, sensing, and magnetic properties

Abstract

Five new lanthanide metal–organic frameworks (MOFs) with two different structures—[Dy(Seb)_1.5(H₂O)₂]_n (H₂Seb = sebacic acid, 1) and {[Ln₂(Seb)₃H₂O]·0.5H₂O}_n {Ln = Sm (2a), Eu (2b), Gd (2c) and Tb (2d)}—have been solvo-thermally synthesized and structurally characterized. 1 shows a 2-D sql layer, while 2a–d are isostructural and exhibit a new structural type of 3-D lanthanide sebacates constructed by the combination of long-chain flexible sebacic acid ligands and rare edge-shared chains of LnO₈(H₂O)_x (x = 0, 1) polyhedrons. Luminescent measurements indicated that europium (2b) and terbium (2d) sebacates not only show remarkable red- and green-light luminescent properties, respectively, but also serve as luminescent sensors for the quick and effective detection of Fe³⁺, CrO₄²⁻ and Cr₂O₇²⁻ ions with low detection limits of 4.38–6.92 ppm. Although a few transition metal sebacates have been applied for sensing Fe³⁺ ions, no lanthanide sebacate-based sensors for the detection of Fe³⁺, CrO₄²⁻ and Cr₂O₇²⁻ ions have emerged. Therefore, 2b and 2d are the only examples of a lanthanide sebacate-based sensor capable of sensing Fe³⁺, CrO₄²⁻ and Cr₂O₇²⁻ ions, significantly extending the potential applications of lanthanide sebacates. Moreover, magnetic investigations of 1, 2a, and 2c–d showed that 1 exhibits typical slow relaxation of the magnetization, while 2c exhibits a significant magnetocaloric effect with a −ΔS_m value of 36.32 J (kg K)⁻¹ at 2 K (ΔH = 7 T).