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

Abstract

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)(OH2)(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 angstrom diameter). The metal ion is replaced by Co2+ and/or the dicarboxylate by isophthalate (ip) or 2,7-naphthalenedicarboxylate (2,7-ndc) to give isoreticular frameworks [Zn-4(ip)(4)(dabco)(OH2)(2)] (ZID), [Co4O4(dabco)(OH2)(2)] (CID), and [Zn-4(2,7-ndc)(4)(dabco)(OH2)(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 H2 adsorption (6-7 kJ/mol at low coverage).