Construction of porous 2D Dy3+ metal organic frameworks: solvent responsive magnetic dynamics under 0 Oe dc field and luminescent sensors for Fe3+ ions

Abstract

Among the recent developments in metal–organic frameworks (MOFs), porous two-dimensional (2D) MOFs have garnered attention due to providing key technical supports, important energy-saving measures and precise chemical sensors for the green and sustainable society. Herein, two rare porous 2D Dy³⁺ MOFs, namely [Dy₄L₆(DMA)₂(H₂O)₃]·7DMA (1, DMA = N,N-dimethylacetamide) and [Dy₂L₃(DMF)₂]·DMF (2, DMF = N,N-dimethylformamide), have been successfully synthesized from reaction with 4,4′-(1,2-diphenylethene-1,2-diyl) dibenzoic acid (H₂L) under different solvent systems. The main distinctions between the crystal structures of 1 and 2 arise from the differing solvent molecules residing within the pores which interact with the surrounding frameworks. These effects lead to different sizes of 1D channels. Importantly, different solvents of coordinated/free DMA molecules in 1 and DMF molecules in 2 induce the conversion of magnetic dynamics. Compound 1 exhibits obvious slow magnetic relaxation behavior under 0 Oe dc field, while zero-field out-of-phase signals of 2 exhibit no peaks in the whole temperature range. Compound 1 was magnetically characterized as a new example that the slow magnetic relaxation process can be observed in a 2D Dy³⁺ layer with 1D channels. Theoretical analysis based on ab initio calculation provides interpretations of magnetic observation. Additionally, compounds 1 and 2 have been tested as efficient fluorescent sensors for Fe³⁺ ions with high selectivity and sensitivity. The fluorescence quenching of 1 and 2 was demonstrated by an approximately 90% reduction in the emission intensity upon binding to Fe³⁺ ions. The emission intensities of 1 and 2 at 464 nm and 443 nm have shown linear responses to Fe³⁺ ion concentration with detection limits of 4.51 × 10⁶ ppb and 6.90 × 10⁶ ppb.