Crystallographic visualization of C3-hydrocarbon-induced structural transformation and guest encapsulation within a flexible coordination network.

Flexible coordination polymers that can self-adjust, via closed (nonporous) to open (porous) switching, to match the size/shape of guest molecules are of particular interest. Herein, we report that C3 hydrocarbons can trigger a flexible SIFSIX network, [Cu(SiF6)(L)2] n (L = 1,4-bis(1-imidazolyl)benzene), SIFSIX-23-Cu, to switch from nonporous to partially open phases at 298 K with different gate opening pressures (propyne < propylene < propane). The single-crystal X-ray diffraction (SCXRD) measurements have succeeded in the crystallographic visualization of the C3-induced closed-to-open switching and the binding sites of gas molecules confined in the open phases. The results unambiguously showed that the closed phase can undergo adaptive structural expansion upon sorption of different C3 molecules, and the conformational changes of Lvia rotation and contortion under gas loading are responsible for the structural transformation. The host-gas interactions are dominated by C-H⋯F hydrogen bonds between gas molecules and SiF6 2- anions and the size-matched chelation of linear propyne by SiF6 2- pairs results in the stronger binding strength of propyne over propylene (propane), leading to the selective sorption of propyne from binary and ternary C3 gas mixtures, as confirmed by breakthrough experiments. This work highlights the vital role of host-gas interactions in governing the structural transitions and affords an efficient strategy to design high-performance flexible sorbents for challenging gas recognition and sorption.