Large Entropic Effect in Flexible Crystalline Media for Gas Separation

Changing channels : The novel dynamic gas‐separation mechanism is demonstrated by a GC study for a flexible single crystal [Cu 2 (bza) 4 (pyz)] n , 1 . The single‐crystal host 1 , because of its flexibility, can separate various gases by adjusting its channel structure according to the features of the guest gaseous molecules. magnified image To develop the application of the adsorption ability of our flexible single‐crystal host [Cu 2 (bza) 4 (pyz)] n ( 1 ) (bza=benzoate; pyz=pyrazine) possessing a 1D channel, we study the separation ability of a 1 packed column for various organic vapors and inorganic gases. A 1 packed column can detect various organic molecules with sharp signals although steric or nonpolar molecules give broad signals. Interestingly, 1 separates various organic mixtures even if the mixture contains nonpolar molecules. Comparing the separation properties with columns of other separation media, including zeolite, activated carbon, activated alumina, and silica gel, suggests that a 1 packed column separates various gaseous molecules under moderate conditions. Additionally, the eluted order of similar molecules, such as N 2 /O 2 and methanol/ethanol using the 1 packed column is different from the others (zeolite, activated carbon, activated alumina, and silica gel), which suggests a difference in the separation mechanism of 1 . From GC measurements, the estimated changes in Gibbs free energy by gas adsorption, under diluted gas conditions, exhibits a large entropy dependence caused by regularity in the generated adsorption state, which enables the dynamic control of gas adsorption selectivity. Therefore, it is suggested that single‐crystal host 1 , because of its flexibility, can separate various gases by adjusting its channel structure according to the features of the guest gaseous molecules. This generates active controllability of the adsorption potential in addition to the intrinsic adsorption interaction.