Zeolitic
imidazolate frameworks (ZIFs) represent the class of metal–organic
frameworks (MOFs) that possess high porosity, large surface area,
exceptional thermal, and chemical stability. Because of these properties,
ZIFs are being employed extensively in gas separation and selective
CO<sub>2</sub> adsorption. We have chosen the structural modification
approach to enhance the CO<sub>2</sub> binding ability of various
imidazolate (Im) linkers of ZIFs by systematically varying the substituents
at 2, 4, and 5 positions of Im ring with CH<sub>3</sub>, Cl, CN, OH,
NH<sub>2</sub>, and NO<sub>2</sub> functional groups. Density functional
theory (DFT) calculations have been employed to identify and quantify
the CO<sub>2</sub> binding ability of various adsorption sites present
in 137 Im linkers. The study demonstrates that the Im linkers with
asymmetrical substitution, viz. NO<sub>2</sub>/OH, CN/OH, and Cl/OH
combinations are highly promising linkers of ZIFs for efficient CO<sub>2</sub> adsorption. The QTAIM analysis characterizes these interactions
as noncovalent interactions which are stabilized by weak hydrogen
bond and van der Waals (vdWs) interactions. Localized molecular orbital
energy decomposition analysis (LMO-EDA) performed on substituted Im···CO<sub>2</sub> complexes reveals that CO<sub>2</sub> binding is governed
by a combination of H-bonding, electrostatic, and dispersion interactions.
The findings of the study will serve as guide-in principles to synthesize
new adsorbents with enhanced and selective CO<sub>2</sub> adsorption