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

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

doi:10.3389/fmats.2019.00218

Abstract

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 Me2NH2+ and Et2NH2+ 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 Schlafli symbol of 66 (dia). The gas sorption properties of solvent-free I were also investigated in detail.

Highlights

One of the most valuable features of porous metal-organic frameworks (MOFs) may lie in the formation of robust crystalline organic/inorganic hybrid materials with various functionalities (Farha and Hupp, 2010; Furukawa et al, 2013; Nguyen et al, 2013; Foo et al, 2014; Kim and Huh, 2016; Qin et al, 2017; Diercks et al, 2018)
We reported several functional MOFs with Lewis basic sites for heterogeneous catalysis for organic transformations and selective adsorption of CO2 over other competing gases (Gu et al, 2010, 2011; Kim et al, 2013, 2017, 2018)
A room temperature ionic liquid (RTIL)-based [EMIM][BF4] was chosen and added into the reaction mixture of DEF solution to lead to parallelogram shaped large X-ray quality crystals of I after thermal reaction at 120◦C for 7 d (Figure 2d)

Summary

Introduction

One of the most valuable features of porous metal-organic frameworks (MOFs) may lie in the formation of robust crystalline organic/inorganic hybrid materials with various functionalities (Farha and Hupp, 2010; Furukawa et al, 2013; Nguyen et al, 2013; Foo et al, 2014; Kim and Huh, 2016; Qin et al, 2017; Diercks et al, 2018). There are several MOF systems containing a ditopic azobenzene-4,4’-dicarboxylate (ABDC2−) bridging ligand in which the azo group (-N=N-) can potentially act as Lewis basic sites (Nguyen et al, 2011; Zhuang et al, 2011; Lyndon et al, 2013; Gong et al, 2015; Liu et al, 2016; Zhao et al, 2016; Yuan et al, 2017; Xu et al, 2018; Yang et al, 2018).

Results

Conclusion