Two lanthanide metal–organic frameworks constructed from tris(4-carboxyphenyl)phosphane oxide with gas adsorption and magnetic properties

Abstract

Two lanthanide metal–organic frameworks (LOFs), namely, {[Eu(L³⁻)(H₂O)]·5H₂O}_n (1) and {[Dy(L³⁻) (H₂O)]·2CH₃CN}_n (2), have been synthesized based on tris(4-carboxyphenyl)phosphane oxide (H₃L) and further characterized by powder X-ray diffraction (PXRD), IR spectroscopy, elemental analyses and thermogravimetric (TG) analyses. X-ray diffraction analyses showed that complexes 1 and 2 are isostructural, and thus the structure and gas adsorption properties of complex 1 and the magnetic properties of 2 were described as a representative in detail. Complex 1 appears to have a 3D 6-connected {4¹²·6³} net based on binuclear {Eu₂(COO)₂} SBUs. Furthermore, the adsorption properties of 1 have been investigated using N₂, H₂, CO₂ and CH₄ gases. 1 has high CO₂ uptake and exhibits highly selective adsorption of CO₂ over CH₄ at room temperature, which allows 1 to have a potential application in gas separation and purification. Finally, its full magnetic properties revealed that complex 2 displays antiferromagnetic coupling between Dy^III ions and single-molecule magnet (SMM) behavior. According to the Arrhenius law, the anisotropy barrier (U_eff) and pre-exponential factor (τ₀) were extracted by fitting of the alternating current data, giving the values of 53.5 K and 3.1 × 10⁻⁷ s, respectively. The afforded α parameter is less than 0.10, suggesting a single relaxation process.