Nanoporous lanthanide-carboxylate frameworks based on 5-nitroisophthalic acid

Abstract

The reactions of lanthanide nitrates with 5-nitroisophthalic acid (ab. 5-H₂nip) in DMF and ethanol (1 : 1) mixed solution gave rise to three nanoporous lanthanide polymers, {[Ln₂(5-nip)₃(DMF)₄](DMF)₂}_n (Ln = Nd (1), Dy (2), Ho (3), 5-nip = 5-nitroisophthalate). Single-crystal X-ray diffraction analyses reveal that they are isomorphous and feature three-dimensional metal–organic frameworks with two-dimensional intersecting channels occupied by guest DMF molecules constructed from the linkage of dimer Ln₂C₆O₁₂ SBUs and 5-nip ligands. The guest DMF molecules can be reversibly removed from 2 as identified using TGA-DSC and PXRD. The heat of adsorption of the guest-free sample of 2 with DMF was measured with a value of 10.3 kJ mol⁻¹ by an RD496-III type microcalorimeter. In addition, the photoluminescent property of 2 was investigated.