Shape‐Memory Effect Enabled by Ligand Substitution and CO<sub>2</sub> Affinity in a Flexible SIFSIX Coordination Network
Bai‐Qiao Song, Mohana Shivanna, Mei‐Yan Gao, Shi‐Qiang Wang, Chenghua Deng, Qing‐Yuan Yang, Sousa Javan Nikkhah, Matthias Vandichel, Susumu Kitagawa, Michael J. Zaworotko
Abstract
Abstract We report that linker ligand substitution involving just one atom induces a shape‐memory effect in a flexible coordination network. Specifically, whereas SIFSIX‐23‐Cu, [Cu(SiF 6 )(L) 2 ] n , (L=1,4‐bis(1‐imidazolyl)benzene, SiF 6 2− =SIFSIX) has been previously reported to exhibit reversible switching between closed and open phases, the activated phase of SIFSIX‐23‐Cu N , [Cu(SiF 6 )(L N ) 2 ] n (L N =2,5‐bis(1‐imidazolyl)pyridine), transformed to a kinetically stable porous phase with strong affinity for CO 2 . As‐synthesized SIFSIX‐23‐Cu N , α, transformed to less open, γ, and closed, β, phases during activation. β did not adsorb N 2 (77 K), rather it reverted to α induced by CO 2 at 195, 273 and 298 K. CO 2 desorption resulted in α′, a shape‐memory phase which subsequently exhibited type‐I isotherms for N 2 (77 K) and CO 2 as well as strong performance for separation of CO 2 /N 2 (15/85) at 298 K and 1 bar driven by strong binding (Q st =45–51 kJ/mol) and excellent CO 2 /N 2 selectivity (up to 700). Interestingly, α′ reverted to β after re‐solvation/desolvation. Molecular simulations and density functional theory (DFT) calculations provide insight into the properties of SIFSIX‐23‐Cu N .