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Ligand Functionalization and Its Effect on CO 2 Adsorption in Microporous Metal–Organic Frameworks
Author(s) -
Liu Hui,
Zhao Yonggang,
Zhang Zhijuan,
Nijem Nour,
Chabal Yves J.,
Peng Xiangfang,
Zeng Heping,
Li Jing
Publication year - 2013
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201201081
Subject(s) - sbus , ligand (biochemistry) , adsorption , isostructural , crystallography , metal organic framework , powder diffraction , microporous material , materials science , thermogravimetric analysis , surface modification , chemistry , inorganic chemistry , crystal structure , organic chemistry , biochemistry , receptor
We report two new 3D structures, [Zn 3 (bpdc) 3 (2,2′‐dmbpy)] (DMF) x (H 2 O) y ( 1 ) and [Zn 3 (bpdc) 3 (3,3′‐dmbpy)]⋅(DMF) 4 (H 2 O) 0.5 ( 2 ), by methyl functionalization of the pillar ligand in [Zn 3 (bpdc) 3 (bpy)] (DMF) 4 ⋅(H 2 O) ( 3 ) (bpdc=biphenyl‐4,4′‐dicarboxylic acid; z , z ′‐dmbpy= z , z ′‐dimethyl‐4,4′‐bipyridine; bpy=4,4′‐bipyridine). Single‐crystal X‐ray diffraction analysis indicates that 2 is isostructural to 3 , and the power X‐ray diffraction (PXRD) study shows a very similar framework of 1 to 2 and 3 . Both 1 and 2 are 3D porous structures made of Zn 3 (COO) 6 secondary building units (SBUs) and 2,2′‐ or 3,3′‐dmbpy as pillar ligand. Thermogravimetric analysis (TGA) and PXRD studies reveal high thermal and water stability for both compounds. Gas‐adsorption studies show that the reduction of surface area and pore volume by introducing a methyl group to the bpy ligand leads to a decrease in H 2 uptake for both compounds. However, CO 2 adsorption experiments with 1′ (guest‐free 1 ) indicate significant enhancement in CO 2 uptake, whereas for 2′ (guest‐free 2 ) the adsorbed amount is decreased. These results suggest that there are two opposing and competitive effects brought on by methyl functionalization : the enhancement due to increased isosteric heats of CO 2 adsorption ( Q st ), and the detraction due to the reduction of surface area and pore volume. For 1′ , the enhancement effect dominates, which leads to a significantly higher uptake of CO 2 than its parent compound 3′ (guest‐free 3 ). For 2′ , the detraction effect predominates, thereby resulting in reduced CO 2 uptake relative to its parent structure 3′ . IR and Raman spectroscopic studies also present evidence for strong interaction between CO 2 and methyl‐functionalized π moieties. Furthermore, all compounds exhibit high separation capability for CO 2 over other small gases including CH 4 , CO, N 2 , and O 2 .