Tuning MOF Stability and Porosity via Adding Rigid Pillars

High stability and permanent porosity are the premise
of general applicability for metal–organic framework materials
(MOFs). By varying degrees of success on increasing the connectivity
of the linear pillar 4,4′-bipyridine (bpy), two isostructural
flexible frameworks [M2(obb)2(DMF)2]·2DMF (1, M = Zn or Cu; H2obb = 4,4′-oxybis­(benzoic
acid), DMF = N,N-dimethylformamide) with no gas sorption are structurally
modified into two rigid frameworks [Zn2(obb)2(bpy)]·DMF (2) and [Cu2(obb)2(bpy)0.5(DMF)]·2DMF (3) with notable
gas sorption and separation properties. Especially for 3, it exhibits gas selective uptake for the adsorption of CO2 over N2 and CH4 under 273 K and has an interesting
physically lock effect in benzene and cyclohexane sorption. The results
provide a successful strategy on tuning framework stability of flexible
structures via adding rigid pillars.