Reversible transformations between the non-porous phases of a flexible coordination network enabled by transient porosity
Varvara I. Nikolayenko, Dominic C. Castell, Debobroto Sensharma, Mohana Shivanna, Leigh Loots, Katherine A. Forrest, Carlos J. Solanilla‐Salinas, Ken‐ichi Otake, Susumu Kitagawa, Leonard J. Barbour, Brian Space, Michael J. Zaworotko
Abstract
Flexible metal-organic materials that exhibit stimulus-responsive switching between closed (non-porous) and open (porous) structures induced by gas molecules are of potential utility in gas storage and separation. Such behaviour is currently limited to a few dozen physisorbents that typically switch through a breathing mechanism requiring structural contortions. Here we show a clathrate (non-porous) coordination network that undergoes gas-induced switching between multiple non-porous phases through transient porosity, which involves the diffusion of guests between discrete voids through intra-network distortions. This material is synthesized as a clathrate phase with solvent-filled cavities; evacuation affords a single-crystal to single-crystal transformation to a phase with smaller cavities. At 298 K, carbon dioxide, acetylene, ethylene and ethane induce reversible switching between guest-free and gas-loaded clathrate phases. For carbon dioxide and acetylene at cryogenic temperatures, phases showing progressively higher loadings were observed and characterized using in situ X-ray diffraction, and the mechanism of diffusion was computationally elucidated.