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

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 degrees 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 N-2 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.