Increasing nuclearity of secondary building units in porous cobalt(ii) metal–organic frameworks: Variation in structure and H2 adsorption

Abstract

Reaction of Co(NO₃)₂·6H₂O with H₂L [H₂L = pyridine-4-(phenyl-3′,5′-dicarboxylic acid)] under different reaction conditions gives three closely-related metal–organic framework polymers, {[Co₂(L)₂(DMF)]·n(solv)}_∞ (1), {[Co(L)]·2DMF}_∞ (2) and {[Co₃(L)₃(DMF)_0.5(H₂O)_1.5]·n(solv)}_∞ (3). Variation in reaction conditions thus has a decisive impact on the materials isolated, producing frameworks based upon either binuclear (1, 2) or trinuclear (3) cobalt cluster nodes. Analysis of their crystal structures shows that all three contain considerable solvent-accessible volumes, an indication of porosity that is confirmed for desolvated 1 and 3, which can store up to 2.75 and 2.33 wt% of H₂ at 78 K and 20 bar, respectively.