The pseudotetrahedral node, [In(O2CR)4]−, often found in InIII-based metal-organic frameworks (MOFs) without a cluster-based secondary building unit (SBU) is a negatively charged center due to charge mismatch between an 8-coordinate InIII ion and four anionic carboxylate bridging ligands. Thus, In-MOFs with this pseudotetrahedral node tend to bear a counter-cation near each InIII center in the frameworks. Generally, dialkylammonium-based cations such as Me2NH+2 and Et2NH+2 directly derived from N,N-dimethylformamide (DMF) or N,N-diethylformamide (DEF) solvents during MOF formation reactions play a significant role to form a stable framework through charge matching. If these cations thermally derived from DMF or DEF were not suitable for crystal growth of In-MOFs, it becomes very challenging to obtain high quality single crystals for X-ray structure determination of the frameworks. In this context, high quality crystals of In-ABDC MOF were not easily prepared from a ditopic azobenzene-4,4'-dicarboxylic acid (H2ABDC) through a thermal reaction in DMF or DEF. We successfully overcome this problem by employing a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), and the resulting three-dimensional (3D) In-ABDC MOF, [EMIM][In(ABDC)2]·DEF·H2O (I), was structurally characterized by X-ray diffraction. The 3D framework indicates a 4-connected uninodal net with Schläfli symbol of 66 (dia). The gas sorption properties of solvent-free I were also investigated in detail.
Bibliographical noteFunding Information:
Funding. This work was supported by the Basic Science Research Program of the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2018R1D1A1B07043017 and 2018R1D1A1B07045327) and by RP-Grant 2018 of Ewha Womans University.
© Copyright © 2019 Choi, Yoon, Jang, Huh, Kim and Kim.
- azobenzene-4,4'-dicarboxylic acid
- carbon dioxide sorption
- hydrogen sorption
- metal-organic framework