American Chemical Society
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Reversible Switching between Nonporous and Porous Phases of a New SIFSIX Coordination Network Induced by a Flexible Linker Ligand

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journal contribution
posted on 2020-04-03, 14:06 authored by Bai-Qiao Song, Qing-Yuan Yang, Shi-Qiang Wang, Matthias Vandichel, Amrit Kumar, Clare Crowley, Naveen Kumar, Cheng-Hua Deng, Victoria GasconPerez, Matteo Lusi, Hui Wu, Wei Zhou, Michael J. Zaworotko
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.