AUTHOR=Choi In-Hwan , Yoon Suk Bin , Jang So-Young , Huh Seong , Kim Sung-Jin , Kim Youngmee 

TITLE=Gas Sorption Properties of a New Three-Dimensional In-ABDC MOF With a Diamond Net

JOURNAL=Frontiers in Materials

VOLUME=6

YEAR=2019

URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2019.00218

DOI=10.3389/fmats.2019.00218

ISSN=2296-8016

ABSTRACT=<p>The pseudotetrahedral node, [In(O<sub>2</sub>CR)<sub>4</sub>]<sup>−</sup>, often found in In<sup>III</sup>-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 In<sup>III</sup> ion and four anionic carboxylate bridging ligands. Thus, In-MOFs with this pseudotetrahedral node tend to bear a counter-cation near each In<sup>III</sup> center in the frameworks. Generally, dialkylammonium-based cations such as Me<sub>2</sub><inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula> and Et<sub>2</sub><inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula> directly derived from <italic>N</italic>,<italic>N</italic>-dimethylformamide (DMF) or <italic>N</italic>,<italic>N</italic>-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 (H<sub>2</sub>ABDC) 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][BF<sub>4</sub>]), and the resulting three-dimensional (3D) In-ABDC MOF, [EMIM][In(ABDC)<sub>2</sub>]·DEF·H<sub>2</sub>O (<bold>I</bold>), was structurally characterized by X-ray diffraction. The 3D framework indicates a 4-connected uninodal net with Schläfli symbol of 6<sup>6</sup> (<bold>dia</bold>). The gas sorption properties of solvent-free <bold>I</bold> were also investigated in detail.</p>