The effect of the functional groups is correlated to the heat of adsorption and selectivity . The electronegative functional group such as Cl offers electrostatic interactions with the polar gas molecules such as CO2 molecules that can be trapped at the pore opening. On the other side, nonpolar gas such as (CH4) undergoes penetration through the pore without adsorption. Thus, the materials offer high selectivity. Using DFT and GCMC, theoretical calculation revealed that the terminal group's rotation tunes the linker swing motion ZIF-90 . The Nitro group of 2nitroimidazole linkers offers a strong Lewis acid-base interaction . On the other side, the interaction of H atoms of the benzimidazole and the oxygen atoms of CO2 enabled high selectivity . Adsorption of CO2 was enhanced two-fold after solvent assisted ligand exchange (SALE) of ZIF-8 with an imidazole linker containing electron withdrawing groups such as -NO2 and -SH . Electron withdrawing groups in the linker of ZIF crystal enhanced the acidity for the hydrogen atoms on linker offering hydrogen bond interactions with the oxygen atoms of CO2 (Figure ) .