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A pure-supramolecular-linker approach to highly connected metal-organic frameworks for CO2 capture Xiaohui Song, Mingxing Zhang, Cong Chen, Jingui Duan, Wenwei Zhang, Yi Pan, and Junfeng Bai J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b07422 • Publication Date (Web): 30 Aug 2019 Downloaded from pubs.acs.org on August 30, 2019
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A pure-supramolecular-linker approach to highly connected metal-organic frameworks for CO2 capture Xiaohui Songa‡, Mingxing Zhangc‡, Cong Chena, Jingui Duand, Wenwei Zhanga, Yi Pana, and Junfeng Bai*a,b State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China b School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an 710119, China c Department of Chemistry, Chongqing Normal University, Chongqing 401331, China d State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemical Engineering, Nanjing Tech University, Nanjing, 210009, China Supporting Information Placeholder a
ABSTRACT: A pure-supramolecular-linker (PSL) approach for the formation of MOFs was initially given, which was demonstrated by syntheses of two highly connected and isostructural MOFs, {Fe3O(TPBTM6-)(Cl)(H2O)2}∞ (TPBTM = N,N’,N’’-tris(isophthalyl)-1,3,5-benzenetricarboxamide) (NJUBai52, NJU-Bai for Nanjing University Bai group) and {Sc3O(TPBTM6-)(OH)(H2O)2}∞ (NJU-Bai53). Very interestingly, they exhibit exceptional thermal stability, water stability and highly selective CO2 capture properties. In particular, NJU-Bai53 with higher uptakes (2.74 wt% at 0.4 mbar and 298 K, 7.67 wt% at 298 K and 0.15 bar) and higher selectivity may be an excellent candidate for CO2 capture.
The past decades have witnessed the rapid development of metal-organic frameworks (MOFs), which represent a new class of porous materials with metal ions or metal clusters linked by organic ligands and have high surface area, structural diversity and tunability, and various applications including CO2 capture, et al.1 In arround 1990s, self-assembly of single metal ion nodes and neutral donor linkers produced many open coordination networks (commonly referred to as coordination polymers), which were usually frail and lacked thermal stability, due to the relatively weak M-N bonds.2 Until the late-1990s, Yaghi’s group initially applied the carboxylate ligands to bind metal-carboxylate clusters termed secondary building units (SBUs) to give MOFs with the amazing property of permanent porosity and signicantly stimulate and expand this fascinating field.3 In contrast to the single-metal nodes known in coordination polymers, SBUs were sufficiently rigid to allow for architectural stability and the strong metal– carboxylate bonds ensured thermal stability of the resulting frameworks.3c, 4 Meanwhile, the introduction of SBUs may increase MOFs’ nodes with connectivity of more than 6, even 12 and facilitates the formation of a wide range of intriguing structures.5 Later on, in 2007, Zaworotko and Eddaoudi, et al. put forward an successful route for highly connected MOFs by employing metal-organic polyhedra (MOPs) as supermolecular building blocks (SBBs).6 SBBs typically start at the nanometre scale and possess high symmetry, making greatly use of the crystal engineering strategy for MOFs that combines even greater levels
of scale with highly specific control over topology.7 The SBB strategy further provides a toolbox of building blocks capable of acting as nodes with rare or even unprecedented connectivity since MOPs offer coordination numbers higher than those possible with simple inorganic metal clusters. The above approaches focus upon the MOFs’ inorganic part of the assembly of single metal ion as nodes for expanding and enriching MOFs. Whether it is possible to utilize organic aggregates or self-assemblies as the starting points or tools for further enriching MOFs structures beyond multidentate carboxylate ligands? We have made a series of a subclass MOFs, amide-functionalized MOFs (AFMOFs) and accidently observed self-assembly of the amide-functional carboxylate ligands within several coordination polymers.8 Herein, we afforded a puresupramolecular-linker approach of self-aggregation of our previous hexacarboxylic acid, TPBTM as a 12-connected supramolecular connector being linked by M3O clusters to form two highly connected and isostructural MOFs with rare (3,3,6,6)-c topology, {Fe3O(TPBTM6-)(Cl)(H2O)2}∞ (NJU-Bai52) and {Sc3O(TPBTM6-)(OH)(H2O)2}∞ (NJU-Bai53). From NJU-Bai52 to NJU-Bai53, the balanced charge on those M3O clusters was finely tuned from Cl- ion to monodentate hydroxide anion, leading to the CO2 uptake of NJU-Bai53 (2.74 wt%) at 0.4 mbar and 298 K, being significantly improved by around 50 times compared with NJU-Bai52 (0.057 wt%) and the CO2 uptake of NJU-Bai53 (7.67 wt%) at 298 K and 0.15 bar, which is larger in comparision to NJU-Bai52 (5.75 wt%) and is the highest among the reported AFMOFs. Moreover, NJU-Bai53 shows higher selectivity, thermal stability, and water stability and might be an excellent candidate for CO2 capture, which have further been confirmed by breakthrough experiments.
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Figure 1. (a) The TPBTM6- ligand self-assembles into PSL by strong π−π stacking and H-bonds, together with Fe3O clusters to construct NJU-Bai52, in which the P-isophthalates form metallamacrocycle and the C-isophthalates bridge these metallamacrocycles. (b) The 2D rhombitrihexagonal nets are pillared through the antiprismatic cores to generate a 3D network.
Solvothermal reaction of TPBTM and FeCl3·6H2O in DMF containing CH3COOH afforded brown cubic crystals of NJUBai52. Single-crystal X-ray diffraction (SCXRD) analysis reveals that NJU-Bai52 crystallizes in the trigonal P3m1 space and the asymmetric unit contains a half TPBTM6- ligand, one and a half Fe ions, a half μ3-O2-, one coordinated H2O molecule, and a half Cl ion. The central O atom links three Fe3+ cations to form a planar Fe3O cluster, in which each pair of Fe centres are bridged by two carboxylate groups from two independent TPBTM6ligands. Unexpectedly, two distorted carboxylate moieties bridging Fe2 and Fe3 make one dihedral angle of the cluster change from ~90° to ~180°, which degrades the symmetry of [Fe3O(COO)6] unit from familiar D3d to C2v. (Figure S2). The charge of the cationic [Fe3O(COO)6], is balanced by one Cl- anion per cluster as supported by X-ray photoelectron spectroscopy (XPS) experiment. Interestingly, as we expected, the TPBTM6- ligand selfassembles into pairs by strong π−π stacking (3.2257(260) Å) and H-bonds (N1-H1A…O9 = 2.0740(157) Å,
