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Modifying Cage Structures in Metal–Organic Polyhedral Frameworks for H 2 Storage

2011; Wiley; Volume: 17; Issue: 40 Linguagem: Inglês

10.1002/chem.201101341

1521-3765

Yong Yan, Alexander J. Blake, William Lewis, Sarah A. Barnett, Anne Dailly, Neil R. Champness, Martin Schröder,

Hydrogen Storage and Materials

Abstract Three isostructural metal–organic polyhedral cage based frameworks (denoted NOTT‐113, NOTT‐114 and NOTT‐115) with (3,24)‐connected topology have been synthesised by combining hexacarboxylate isophthalate linkers with {Cu 2 (RCOO) 4 } paddlewheels. All three frameworks have the same cuboctahedral cage structure constructed from 24 isophthalates from the ligands and 12 {Cu 2 (RCOO) 4 } paddlewheel moieties. The frameworks differ only in the functionality of the central core of the hexacarboxylate ligands with trimethylphenyl, phenylamine and triphenylamine moieties in NOTT‐113, NOTT‐114 and NOTT‐115, respectively. Exchange of pore solvent with acetone followed by heating affords the corresponding desolvated framework materials, which show high BET surface areas of 2970, 3424 and 3394 m 2 g −1 for NOTT‐113, NOTT‐114 and NOTT‐115, respectively. Desolvated NOTT‐113 and NOTT‐114 show high total H 2 adsorption capacities of 6.7 and 6.8 wt %, respectively, at 77 K and 60 bar. Desolvated NOTT‐115 has a significantly higher total H 2 uptake of 7.5 wt % under the same conditions. Analysis of the heats of adsorption ( Q st ) for H 2 reveals that with a triphenylamine moiety in the cage wall, desolvated NOTT‐115 shows the highest value of Q st for these three materials, indicating that functionalisation of the cage walls with more aromatic rings can enhance the H 2 /framework interactions. In contrast, measurement of Q st reveals that the amine‐substituted trisalkynylbenzene core used in NOTT‐114 gives a notably lower H 2 /framework binding energy.