Tuning the interpenetration of metal–organic frameworks through changing ligand functionality: effect on gas adsorption properties

Abstract

Among metal–organic frameworks (MOFs), the interpenetrated MOFs commonly affect the gas adsorption properties. Herein, a cyano-containing 2-connected ligand, 4-(6-(4-cyanophenyl)-[2,3′-bipyridin]-4-yl)benzoic acid (HL1), was used to construct two novel MOFs ([Co(L1)₂] and [Zn(L1)₂]), and as a result, two two-fold interpenetrated MOFs were expectantly obtained. Both interpenetrated MOFs possess quasi-hexagonal channels and reveal good CO₂ gas adsorption capacities at 273 K, attributable to the nitrile groups in the frameworks of MOFs. In contrast to CO₂, both interpenetrated MOFs only have very low N₂ gas adsorption capacities at 77 K, suggesting potential application in gas separation. More interestingly, when simple modification of the ligand functional group (from the cyano group to the carboxyl group), a new non-interpenetrated MOF ([Co₂(L2)₂(H₂O)]) with rugby-like channels is constructed by using 3-connected 4,4′-([2,3′-bipyridine]-4,6-diyl) dibenzoic acid (H₂L2), which is ascribed to the change in ligand functionality (from the cyano group to the carboxyl group). Significantly, this non-interpenetrated MOF reveals much high N₂ gas adsorption capacity at 77 K, and moderate CO₂ gas adsorption capacity at 273 K owing to the absence of the nitrile groups in the MOF. Furthermore, the magnetic properties of two Co-based MOFs and photoluminescence of three MOFs have also been investigated. The present work provides a promising approach to design and construct interpenetrated/non-interpenetrated MOFs by changing ligand functionality and to tune gas adsorption properties.