A 2D flexible cobalt-MOF: reversible solid-state structural transformation, two-step and gate-opening adsorption behaviours, and selective adsorption of C 2 H 2 over CO 2 and CH 4 .

A new 2D flexible cobalt(II) framework (Co-MOF) exhibits a reversible solid-state structural transformation upon guest molecule removal/uptake. After activation, Co-MOF-α with 1D porous channels transformed into Co-MOF-β (0D voids) accompanied by a shift in metal and carboxylate coordination modes, the rotation of organic linkers and the contraction of interstitial spaces. Gas adsorption experiments reveal that Co-MOF-β exhibits a two-step CO 2 adsorption isotherm and close-to-open (type F-IV) isotherms for C 2 H 2 , C 2 H 4 and C 2 H 6 at 195 K. Moreover, it shows typical type I adsorption isotherms for the above gases and the selective uptake of C 2 H 2 over CH 4 and CO 2 at room temperature.