Shape‐Memory Effect Enabled by Ligand Substitution and CO₂ Affinity in a Flexible SIFSIX Coordination Network

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(SiF6)(L)2]n, (L = 1,4‐bis(1‐imidazolyl)benzene, SiF62‐ = SIFSIX) has been previously reported to exhibit reversible switching between closed and open phases, the activated phase of SIFSIX‐23‐CuN, [Cu(SiF6)(LN)2]n (LN = 2,5‐bis(1‐imidazolyl)pyridine), transformed to a kinetically stable porous phase with strong affinity for CO2. As‐synthesized SIFSIX‐23‐CuN, α, transformed to less open, γ, and closed, β, phases during activation. β did not adsorb N2 (77 K), rather it reverted to α induced by CO2 at 195, 273 and 298 K. CO2 desorption resulted in α’, a shape‐memory phase which subsequently exhibited type‐I isotherms for N2 (77 K) and CO2 as well as strong performance for separation of CO2/N2 (15/85) at 298 K and 1 bar driven by strong binding (Qst = 45‐51 kJ/mol), high CO2 capacity (209 cm3/g) and excellent CO2/N2 selectivity (up to 700). Interestingly, α’ reverted to β after resolvation/desolvation. Density functional theory (DFT) calculations provide insight into the properties of SIFSIX‐23‐CuN.