Flexible lanthanide MOFs as highly selective and reusable liquid MeOH sorbents

Abstract

A series of new 3-D Ln3+ metal-organic frameworks (MOFs), which are based on the semi-rigid ligand H3CIP [H3CIP = 5-(4-carboxybenzylideneamino)isophthalic acid], [Ln2(CIP) 2(DMF)4-x(H2O)x] (Ln3+ = La3+, Ce3+, Pr3+, Sm3+, Eu 3+, Gd3+, Tb3+, Dy3+, Ho 3+

x = 0-2) are reported. Magnetic susceptibility data for selected compounds indicated the presence of antiferromagnetic interactions, while the photoluminescence properties of the MOFs revealed emission peaks that are red-shifted compared to the emission (405 nm) of the uncoordinated H 3CIP ligand, whereas the Eu3+ and Tb3+ analogues showed emission peaks typical of these lanthanide ions. Single-Crystal-to-Single-Crystal (SCSC) coordinating solvent exchange experiments with acetone and methanol for the Ce3+ analogue afforded compounds that are isostructural with the pristine material and contain one acetone and one water or 1.25 methanol and 0.75 water ligated molecules per Ce3+ respectively. The capability of activated Ce3+ MOF to absorb liquid MeOH was evaluated by means of 1H NMR spectroscopy. The results of the sorption experiments indicated a maximum absorption capacity of 96(2) mg g-1 and fast kinetics, while the sorbent is reusable and is also capable of highly selective sorption of MeOH over EtOH. Overall this work emphasizes the multifunctional nature of lanthanide MOFs and provides insight into the liquid-phase sorption of small organic molecules by such materials demonstrating their high potential as sorbents. © The Royal Society of Chemistry 2013.