Isoreticular Metal-Organic Polyhedral Networks Based on 5-Connecting Paddlewheel Motifs

A metal-organic polyhedral network with a unique 5-connected topology is expanded into a series using different metal ions or dicarboxylate ligands. The prototype material (ZmID), [Zn(4)(mip)(4)(dabco)(OH(2))(2)] (mip = 5-methylisophthalate, dabco = diazabicyclo[2.2.2]octane), is based on 5-connecting paddlewheel motifs and possesses large cage-like pores (8-20 A diameter). The metal ion is replaced by Co(2+) and/or the dicarboxylate by isophthalate (ip) or 2,7-naphthalenedicarboxylate (2,7-ndc) to give isoreticular frameworks [Zn(4)(ip)(4)(dabco)(OH(2))(2)] (ZID), [Co(4)(ip)(4)(dabco)(OH(2))(2)] (CID), and [Zn(4)(2,7-ndc)(4)(dabco)(OH(2))(2)] (ZND). X-ray powder diffraction and gas sorption studies reveal that ZID and CID have sustainable pore structures and show higher N(2) uptakes than ZmID. ZND is found unstable with respect to the removal of guest solvents. ZmID, ZID, and CID are all similar in terms of the H(2) sorption capacities (1.4-1.5 wt % at 77 K and 1 bar) and isosteric heat of H(2) adsorption (6-7 kJ/mol at low coverage).