Gas adsorption and structural diversity in a family of Cu(II) pyridyl-isophthalate metal–organic framework materials

A family of Cu(II)-based metal–organic frameworks (MOFs) has been synthesized using three pyridyl-isophthalate ligands, H2 L1 (4′-(pyridin-4-yl)biphenyl-3,5-dicarboxylic acid), H2 L2 (4′′-(pyridin-4-yl)-1,1′:4′,1′′-terphenyl-3,5-dicarboxylic acid) and H2 L3 (5-[4-(pyridin-4-yl)naphthalen-1-yl]benzene-1,3-dicarboxylic acid). Although in each case the pyridyl-isophthalate ligands adopt the same pseudo-octahedral [Cu2 (O2 CR)4 N2 ] paddlewheel coordination modes, the resulting frameworks are structurally diverse, particularly in the case of the complex of Cu(II) with H2 L3 , which leads to three distinct supramolecular isomers, each derived from Kagomé and square nets. In contrast to [Cu(L2 )] and the isomers of [Cu(L3 )], [Cu(L1 )] exhibits permanent porosity. Thus, the gas adsorption properties of [Cu(L1 )] were investigated with N2 , CO2 and H2 , and the material exhibits an isosteric heat of adsorption competitive with leading MOF sorbents for CO2 . [Cu(L1 )] displays high H2 adsorption, with the density in the pores approaching that of liquid H2 .This article is part of the themed issue ‘Coordination polymers and metal–organic frameworks: materials by design’.