Besides the functional groups of the linker, the ligand dipole moment is also a key factor for CO2 adsorption (Figure ) . Data analysis showed an exponential relationship between the ligand dipole moments and the isosteric heat of adsorption (qst) of CO2 (Figure ). The high ligand dipole moment showed a 5-to 7-fold improvement in the selectivity for CO2 adsorption for CO2/CH4, CO2/N2, and CO2/CO mixtures (Figure ).