Reversible Switching between Nonporous and Porous Phases of a New SIFSIX Coordination Network Induced by a Flexible Linker Ligand
Bai‐Qiao Song, Qing‐Yuan Yang, Shi‐Qiang Wang, Matthias Vandichel, Amrit Kumar, Clare M. Crowley, Naveen Kumar, Chenghua Deng, Victoria Gascón, Matteo Lusi, Hui Wu, Wei Zhou, Michael J. Zaworotko
Abstract
Closed-to-open structural transformations in flexible coordination networks are of potential utility in gas storage and separation. Herein, we report the first example of a flexible SiF62–-pillared square grid material, [Cu(SiF6)(L)2]n (L = 1,4-bis(1-imidazolyl)benzene), SIFSIX-23-Cu. SIFSIX-23-Cu exhibits reversible switching between nonporous (β1) and several porous (α, γ1, γ2, and γ3) phases triggered by exposure to N2, CO2, or H2O. In addition, heating β1 to 433 K resulted in irreversible transformation to a closed polymorph, β2. Single-crystal X-ray diffraction studies revealed that the phase transformations are enabled by rotation and geometrical contortion of L. Density functional theory calculations indicated that L exhibits a low barrier to rotation (as low as 8 kJmol–1) and a rather flat energy surface. In situ neutron powder diffraction studies provided further insight into these sorbate-induced phase changes. SIFSIX-23-Cu combines stability in water for over a year, high CO2 uptake (ca. 216 cm3/g at 195 K), and good thermal stability.