Ultrasensitive sorption behavior of isostructural lanthanide–organic frameworks induced by lanthanide contraction

Abstract

Reactions of lanthanide nitrate and the trigonal-planar ligand 1,3,5-benzenetrisbenzoic acid (H₃BTB) gave rise to a family of lanthanide–organic frameworks (LOFs) formulated as Ln(BTB)(H₂O), where Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Yb. Single-crystal X-ray diffraction (XRD) analysis of Pr-LOF reveals a three-dimensional network with an ultramicroporous structure. Powder XRD and thermogravimetric analyses show that these LOFs are isostructural and can firmly stabilize up to 550 °C. Influenced by the opposite effects of ionic radius and molecular weight from La(III)–Yb(III), the related LOFs with the highest uptake of CO₂ and CH₄ happen to be Nd-LOF and Sm-LOF, respectively. Moreover, the isotherms of N₂ at 77 K and benzene vapor at 298 K further evidence that lanthanide contraction greatly affects the adsorption performance of the resulting materials, bringing about stepwise and hysteretic sorption behavior for La-LOF to Pr-LOF but type I isotherms for the rest of the LOFs. This work represents the first systematic study of a family of lanthanide-based metal–organic frameworks with ultrasensitive sorption behavior induced by the lanthanide contraction.