Comparative Study on Temperature-Dependent CO2 Sorption Behaviors of Two Isostructural N-Oxide-Functionalized 3D Dynamic Microporous MOFs

By functionalization of the achiral carboxylate-based pyridine-N ligand 2,2′-bipyridine-3,3′-dicarboxylate (H2bpda) with N-oxide groups, the axially chiral ligand 2,2′-bipyridine-3,3′-dicarboxylate 1,1′-dioxide (H2bpdado) has been obtained. On the basis of H2bpdado and auxiliary N-donor ligands, two isostructural 3D dynamic porous Cu(II) metal–organic frameworks (MOFs), {[Cu0.5(bpdado)0.5(L)0.5]·3H2O}n (L = 1,2-bis(4-pyridyl)ethane (bpa), trans-1,2-bis(4-pyridyl)ethene (bpe) for 1 and 2, respectively), have been synthesized, which contain N-oxide “open donor sites” (ODSs) and carboxyl sites on the pore surfaces. The modification of pyridine-N into the N-oxide group not only transforms the nonporous structure into a porous framework but also endows the N-oxide group with unique charge-separated plus electron-rich character, which may provide an enhanced affinity toward CO2 molecules. Interestingly, both 1 and 2 present reversible structural transformation upon dehydration and rehydration. The adsorption pr...