Sorption comparison of two indium–organic framework isomers with syn–anti configurations

Abstract

Two indium–organic framework isomers, namely [Me2NH2][In(BPDC)2] (InOF-3) and [MeNH3][In(BPDC)2] (InOF-4), have been solvothermally prepared from a biphenyl-3,3′-dicarboxylate ligand (H2BPDC) with changeable conformation, and feature skeletal frameworks with equivalent chemical formulae. For the 2D close-packing InOF-3, each 3-connected [In(O2CR)4] node connects to 3 others through syn-BPDC2− ligands, leading to a 3-connected uninodal layer with a point symbol of {63}. For the 3D microporous InOF-4, the framework is assembled from [In(O2CR)4] nodes bridged by dicarboxylate ligands in the anti- fashion. Careful examination of the structure shows that InOF-4 is a 4-fold interpenetrating network and topologically adopts a diamond-like 4-connected uninodal net with a point symbol of {66}. More importantly, the theoretical calculations and the experimental single component gas uptake measurements reveal that the 3D porous InOF-4 has a better low pressure gas storage capacity than its 2D framework isomer InOF-3, with a saturated N2 uptake of 168.2 cm3 g−1 at 77 K and H2 uptake capacities of up to 126.5 cm3 g−1 (1.13 wt%) at 77 K and 1.0 bar, and 98.1 cm3 g−1 (0.88 wt%) at 87 K and 1.0 bar. Finally, the IAST calculations show us that both microporous materials have an outstanding low-pressure selectivity between CO2 and N2, probably due to their intrinsic structural characteristics.