Highly Selective CO₂ Capture in Flexible 3D Coordination Polymer Networks

Abstract

Carbon dioxide capture has been in the center of interests in the scientific community in recent years because of the implications for global warming, and the development of efficient methods for capturing CO 2 from industrial flue gas has become an important issue. It has been revealed that coordination polymer networks (CPNs) with channels or pores can be applied in gas storage, [1, 2] gas separation, [3] ion exchange, [4] and selective adsorption of organic or inorganic molecules. [1e, 5-7] It has been reported that large amounts of CO 2 can be adsorbed in some CPNs, for example 20 wt % at 195 K and 1 bar in [{Cu(pyrdc)(bpp)} 2 ] n (pyrdc = pyridine-2,3-dicarboxylate, bpp = 1,3-bis(4-pyridyl)propane), [8a] 16 wt % at 298 K and 50 atm in [Cu(dhbc) 2 (4,4'-bpy)] (dhbc = 2,5-dihydroxybenzoate, bpy = bipyridine), [8b] 114 wt % at 195 K and 1 bar in SNU-6, [1c] 150 wt % at 298 K and 42 bar in MOF-177, [9a] and 176 wt % at 303 K and 50 bar in MIL-101c. [9b] However, the selective capture of CO 2 , in particular at ambient temperature and pressure, from industrial emission streams that contain other gases such as N 2 , CH 4 , and H 2 O still remains challenging. [1c, 10, 11] Our approach to selectively capturing CO 2 with porous materials is based on the construction of highly flexible 3D coordination polymer networks whose channels or pores open and close depending on the gas type. Compared to N 2 and H 2 , we expected that CO 2 would interact with the host network more efficiently because of its quadrupole moment (À1.4 10 À39 C m 2 ) and open up channels that are closed for other gases. Our design strategy for flexible 3D networks is to use 2D grids formed from square-planar Ni II macrocyclic complexes as linear linkers [3a, 6, 7a,b, 12] and 1,1'-biphenyl-3,3',5,5'tetracarboxylate (bptc 4À ) [13] as a square organic building block, and then to connect the 2D grids with highly flexible alkyl pillars by utilizing alkyl-bridged Ni II bismacrocyclic complexes such as [Ni 2 L 2 ](ClO 4 ) 4 (A) and [Ni 2 L 4 ]-(ClO 4 ) 4 ·8 H 2 O (B, Scheme 1). We previously prepared a 2D pillared bilayer network that behaves like a sponge from other Ni II bismacrocyclic complexes and 1,3,5-benzenetricarboxylate. [6] The formation of either 2D or 3D pillared network depends on how the bismacrocyclic complex connects 2D planes (Chart S1 in the Supporting Information), which is affected by the pore size of the 2D layer and the steric hindrance between the pillars.Herein, we report two flexible 3D coordination polymer networks, [(Ni 2 L 2 )(bptc)]·6 H 2 O·3 DEF (1, DEF = N,N-diethylformamide) and [(Ni 2 L 4 )(bptc)]·14 H 2 O (2), which exhibit highly selective CO 2 adsorption over N 2 , H 2 , and CH 4 gases as well as thermal stability up to 300 8C and air and water stability. The CO 2 adsorption isotherms of 1 and 2 show gate opening and closing phenomena as well as hysteretic desorption, which allow efficient CO 2 capture, storage, and sensing. Compounds 1 and 2 are the first 3D pillared networks assembled from Ni II bismac...

Selective CO2 Adsorption by a Triazacyclononane‐Bridged Microporous Metal–Organic Framework

“…, very close to that for N 2 at 77 K. The isotherm shows a large hysteresis that is generally assigned to guest-directed framework rearrangement leading to a gate-opening structure [40,45] due its flexibility. It is unlikely that this mechanism operates in the case described herein because [1]Cl keeps its crystallinity up to 433 K without structural change.…”

“…It also demonstrates the rigidity of the framework, in contrast to that described previously with tetraazacycloalkanes. [40] To the best of our knowledge, rigid frameworks obtained from flexible building blocks have not been described in the literature.…”

“…In contrast to the frameworks constructed by the reaction of metallo-tetraazacycloalkane with pillared ligands, [40] this material was prepared by self-assembly of the zinc-TACN complex without adding an exogenous ligand. Reaction of an excess of ZnA …”

Direct Synthesis of Imines via Solid State Reactions of Carbamates with Aldehydes

“…Although it is stable, the carbamate can revert to the parent amine and CO 2 by external stimuli, such as heating or pressure. [4][5][6][7][8][9] In contrast, only a few studies on the reactivity of the carbamate salts have been performed, [1] due presumably to the lack of ap-plications in organic syntheses. [6] A wide range of amines has been extensively investigated to develop new liquid absorbents for CO 2 capture.…”

A Highly Porous Metal–Organic Framework: Structural Transformations of a Guest‐Free MOF Depending on Activation Method and Temperature

“…Porous metal-organic frameworks (MOFs) have received considerable attention because of their diverse chemical compositions and architectures as well as their potential applications in gas storage and separation, [1][2][3][4][5] catalysis, [6,7] and in the fabrication of metal nanoparticles. [8][9][10][11] The potential applications of MOFs are attributed to their permanent microporosity and large internal surface areas.…”