Tunable Crystalline Organic Cage for Selective Sorting of Ortho-Monohalotoluene Isomers

A highly flexible 4,4′-oxybis benzaldehyde-based imine cage (Oba-cage) has selectively adsorbed the ortho-isomer from all other monohalotoluene (X-toluene, X = F, Cl, and Br) isomers with moderate to excellent uptake 52%, 71%, and 93% for ortho-fluorotoluene (oFT), ortho-chlorotoluene (oCT), and ortho-bromotoluene (oBT), respectively. The structural changes demonstrated by the Oba-cage with different solvents appear to favor the discrimination of only the ortho-isomer from other monohalotoluene isomers through host-guest hydrogen bonding interactions. In addition, the uptake of these ortho isomers by the Oba-cage increases with the size of the halogen substituents. We believe that this work provides interesting insights for designing efficient molecular sieves for the selective separation of halo-toluene to lower the high energy bill of these industrial separations.